Patent Grant
9066827
1. Field of the Inventions
The present inventions relate generally to expandable medical implants for maintaining support of a body lumen, and more specifically, to a uniform stent having improved mechanical and post-deployment dynamic capabilities.
2. Description of the Related Art
Various embodiments of vascular implants; such as stents, thrombus filters, and heart valves, are used in their various embodiments for medical applications. Of these vascular devices, one of the leading candidates as a stent device and structural component is the radially expandable and slidably engaged stent as disclosed in commonly owned U.S. Pat. No. 6,033,436; U.S. Pat. No. 6,224,626; and U.S. Pat. No. 6,623,521; the disclosures of which are hereby incorporated by reference. These radially expandable and slidably engaged stents offer the strength of prior expandable stents with the added improvements of low cross-section deliverability, less bulk material thickness, high resolution fitting, and shape customization such as hourglass-shape configurations.
Other radially expandable and slidably engaged stents; such as those disclosed in U.S. Pat. No. 5,797,951; U.S. Pat. No. 5,549,662; and U.S. Pat. No. 5,733,328; further describe the state of the art and their disclosures are hereby incorporated by reference.
Although promising candidates for use as implantable devices and device components, these known radially expandable and slidably engaged stents have mechanical and vasodynamic limitations of which the inventors of the present application set out to address. These limitations can be characterized as deployment related limitations, and limitations related to vasodynamic capabilities.
Deployment related limitations of prior art stents are herein described. Intravascular space; especially that of a patient in need of a vascular implant, is generally inconsistent and varies upon the individual with respect to curvature, plaque buildup and other luminary obstructions.
Procedures are available to physicians such as balloon angioplasty, which aid in the reduction of plaque prior to stenting. However, even after such procedures, vascular characteristics remain patient delineated and largely inconsistent. Inconsistencies in vascular characteristics; such as the interference due to a luminary occlusion, require flexibility, distribution of material strength, and vascular adaptability of devices to be implanted.
In accordance with at least one of the embodiments disclosed herein is the realization that a vascular implant may experience a number of mechanical limitations related to delivery. For example, some portions of the vasculature are curved or substantially non-cylindrical. These portions of the vasculature have proven difficult to deploy stent devices. Sometimes, the curvature of the vessel can cause a deployed stent to fold, especially in stents with insufficient flexibility in the design. Curved vessels further increase the potential for hinging and denting as described in further detail below.
A vascular implant may also experience a number of countering forces post-deployment. Some of these countering forces are a result of what is herein referred to as vasodynamics; the resulting movements, constrictions and contortions of the vasculature. Of these countering forces is crush force, caused by post-expansion elastic recoil of the vessel.
Additionally, some stents experience an occlusion-derived impaction force; a point force derived from the impact of a luminary occlusion directly onto the device; such a luminary occlusion can be plaque or a thrombus. Other countering forces such as dilation, and contortion, are to be discussed in further detail below.
The inventors of the present application have recognized a problem with known radially expandable and slidably engaged stents, the problem herein referred to as “hinging.” Many slidably-engaged expandable stents possess a common limitation where the engagements are generally longitudinally aligned, thereby inherently creating an alignment of failure points. A failure point is a weakness in a stent design, usually a point where two parts are joined together in a less than permanent fashion such as an engagement between slidably-engaged radial modules. When an amount of radial pressure is exerted on the expanded stent, the stent tends to buckle or fold at the failure point. A series of failure points that are longitudinally aligned can act as a perforation in the material and cause a substantial weakness and propensity for hinging.
Another plaque-related problem is herein referred to as “denting.” Denting is caused by an inherent device pattern weakness where a vaso-occlusion can drive a portion of at least one stent module into the luminary space, thereby substantially enhancing the effect of the vaso-occlusion. Such an occlusion or dent can lead to collection of thrombus or flow distortions which are problematic and can increase stenosis.
Vascular plaque is typically non-uniform and often forms in a bulky occlusion, such an occlusion can place added stress on the stent via a point force, and increase the risk of hinging or denting.
The inventors of the present application have recognized that denting can significantly dampen or interfere with vasodynamics, and therefore may cause an increase in realized stenosis. Furthermore, denting may not be immediately apparent to the implanting physician where a polymer stent is adapted for increased ductility over time.
Many devices are fabricated from a biodegradable polymer which may become substantially more ductile and flexible with the progression of time up to a point of water absorption equilibrium. As water is absorbed, the polymer material becomes bendable or ductile. Differing polymer compositions will have a varied rate of moisture absorption. The inventors of the present application recognized the benefits of controlled water absorption into the polymer material such as a reduced propensity for microfissures. Furthermore, the inventors of the present application recognized detriments such as a propensity for denting where the design pattern provides unsupported adjacent components. The likelihood of denting occurrences is increased for stent patterns lacking the support of a structural backbone, especially when there are unsecured corners or other points having a propensity for weakness. Often, the extent to which denting occurs cannot be determined until several hours after the deployment procedure, hence the importance to minimize the potential for denting and improving the design pattern of the target device.
In accordance with at least one of the embodiments disclosed herein, the inventors of the present application have recognized that a mechanically-improved stent design will overcome these limitations set out above, and will further set out to increase adaptability to the dynamics of the vasculature.
Many prior art stent embodiments are designed around crush force and maintaining patency of a luminary space. Although patency of the lumen is of primary concern, there are other factors which must be addressed in an effort to go beyond functionality, but rather to move toward the successful treatment and healing of a vessel.
The vasculature is a dynamic system. Although it is difficult to quantify, the vasculature may experience a number of dynamic movements at any given moment in time. Of these is a wave-like dilation, which presents variability in the interior diameter of the vessel at a given location. Dilation can occur from a change in blood pressure or other change in the circulation. Additionally, portions of the vasculature can experience a contortion or twist like motion in addition to dilation. Where there is plaque or a luminary occlusion, the vasculature can experience a resistance to these natural movements. Such a resistance can cause the adjacent tissue to undergo a cytotic response, such as the division of cells, or intravascular cell growth known as neointimal growth. Neointimal growth is a new or thickened layer of arterial intima formed especially on a prosthesis or in atherosclerosis by migration and proliferation of cells.
Clinical data generally shows that stent implants stimulate neointimal growth in the vessel immediately subsequent to implantation. Neointimal growth is acceptable up to a point where blood pressure is substantially increased or where the lumen is obstructed and blood can no longer efficiently pass.
It is thought that resistance to vasodynamics, among other things, can dramatically increase stenosis surrounding an implanted vascular device. Therefore, it is critical to understand the dynamics of the vasculature and to design a stent capable of maintaining patency of the lumen while promoting the motions associated with vasodynamics such as periodic dilation and contortion. A stent designed to incorporate the dynamics of the vasculature can better serve to treat and ultimately heal the vessel.
Generally, neointimal growth surrounds and encompasses the implanted stent, leaving the stent to reside substantially within the new vessel wall. It is in this state that stent mechanics are critical in minimizing further stenosis.
Although stents can be made of generally any biocompatible material, there is a movement toward the use of stents fabricated from a biodegradable and bioresorbable polymer. Biodegradation is the structural decomposition of a polymer, often occurring as bulk erosion, surface erosion, or a combination thereof. Bioresorption includes the cellular metabolism of the degraded polymer. The inventors of the present application have set out to design a stent capable of utilizing the degradation and resorption properties of the polymer to enhance the healing and treatment of the vessel.
In some embodiments, there is provided a stent having a uniform distribution of failure points. This uniform distribution can minimize, if not eliminate the potential for hinging and denting.
In other embodiments, there is provided a stent having a rotationally flexible backbone capable of adaption to vasodynamic movements, thereby minimizing stenosis of the vasculature.
In yet other embodiments, there is provided a stent design capable of being efficiently encapsulated with neointimal growth, such that initial degradation of the stent material will transform the stent into a rotationally flexible and vaso-adaptive support within the new vessel wall.
In summary, there remains a need for an improved radially expandable and slidably engaged luminary support structure: one that uniformly distributes failure points about the device so as to prevent hinging, one that provides adequate support to components so as to prevent denting, one that embraces the effects of water absorption so as to prevent micro fissures while providing effective stenting to the vasculature, one that is capable of restoring vaso-motion to the treated vessel upon neo-intima containment, and one that embraces known properties of radially expandable and slidably engaged support structures such as low cross-section deliverability, less bulk material thickness, high resolution fitting, and shape customization such as hourglass-shape configurations.
An expandable stent is disclosed in accordance with an embodiment of the present inventions. The stent can provide radial support to maintain patency of a lumen, a flexible vaso-adaptive backbone structure, and a uniform circumferential distribution of slidable engagements.
Aside from radial expansion and an ability to maintain patency of the body lumen, the present disclosure provides solutions to the aforementioned problems of hinging, denting and restriction of vasodynamic movements.
In accordance with at least one of the embodiments disclosed herein is the realization that a propensity for hinging is increased in stent designs having an alignment of engagement means that are substantially parallel with respect to the longitudinal axis of the stent. Further, in accordance with at least one of the embodiments disclosed herein is the realization that a potential for denting can be minimized by incorporating a support backbone to secure the extremities and corners of those members or features associated with maintaining patency of the lumen, herein elongate members.
Additionally, in accordance with at least one of the embodiments disclosed herein is the realization of the importance of providing a stent having flexibility sufficient to promote and adapt to natural vasodynamic movements while maintaining patency of the lumen. Further, stenosis can be minimized by improving the flexibility of the stent so as to provide adaption to vasodynamic movements such as wave-like dilation and contortion movements.
In an embodiment, the stent can comprise a tubular member having a circumference which is expandable between at least a first collapsed diameter and at least a second expanded diameter. The expandable stent can provide minimally invasive delivery capabilities, and can be adapted for delivery and deployment via a catheter, especially a balloon expandable catheter.
The tubular member can be generally configured from at least two slidably engaged radial elements. The slidably engaged radial elements can be configured to collectively define the circumference of the tubular member.
In an embodiment, an expandable slide and lock polymer stent is provided that can comprise first and second helical backbones, first and second sets of elongate members, and first and second crossbars. The first and second helical backbones can each comprise a plurality of slots. In this regard, each slot can have an axis extending in a circumferential direction, and the first and second helical backbones can extend in a helical path along an axis of the stent.
The first set of elongate members can define proximal and distal ends. The proximal ends of the first set of elongate members can be coupled to the first helical backbone with the first set of elongate members extending in a circumferential direction from the first helical backbone through the slots of the second helical backbone. The first set of elongate members can be axially offset from each other. The first crossbar can couple the distal ends of the first set of elongate members.
The second set of elongate members can define proximal and distal ends. The proximal ends of the second set of elongate members can be coupled to the second helical backbone and extending in a circumferential direction from the second helical backbone through the slots of the first helical backbone. The second set of elongate members can be axially offset from each other and from the first set of elongate members. Further, the second crossbar can couple the distal ends of the second set of elongate members.
In some embodiments, the first and second helical backbones and the first and second sets of elongate members and the first and second crossbars can form first and second radial elements that can be interconnected to collectively form a tubular member having a circumference which is expandable between a collapsed diameter and an expanded diameter. The first and second radial elements can be configured to provide one-way expansion from the collapsed diameter to the expanded diameter.
In some optional implementations, the first crossbar can have a recessed portion and the second crossbar can have a recessed portion. The recessed portion of the first crossbar can be configured such that one of the elongate members of the second set can be at least partially disposed in the recessed portion of the first crossbar. The recessed portion of the second crossbar can be configured to at least partially receive one of the elongate members of the first set therein. Further, the recessed portions of the first and second crossbars can be recessed radially inwardly relative to the respective ones of the elongate members of the second and first sets. Additionally, it is contemplated the recessed portions of the first and second crossbars can be configured to be recessed radially outwardly relative to the respective ones of the elongate members of the second and first sets.
In optional embodiments, the stent can be configured such that the first set of elongate members is monolithically formed with the first helical backbone such that the coupling of the first crossbar to the distal ends of the first set of elongate members forms a tail-bond. Further, the second set of elongate members can be monolithically formed with the second helical backbone such that the coupling of the second crossbar to the distal ends of the second set of elongate members forms a tail-bond.
Alternatively, the first set of elongate members can be formed separately from the first helical backbone such that the coupling of the first set of elongate members with the first helical backbone forms one of a core-bond and a mid-rail bond. Further, the second set of elongate members can be formed separately from the second helical backbone such that the coupling of the second set of elongate members with the second helical backbone forms one of a core-bond and a mid-rail bond. Accordingly, in such embodiments, the first crossbar can be monolithically formed with the first set of elongate members. Furthermore, the second crossbar can be monolithically formed with the second set of elongate members.
In addition, in some embodiments, the elongate members can comprise one or more teeth for engaging respective slots to provide one-way expansion of the stent. Further, the stent can be configured such that each slot comprises a central passage and at least one internal recess for engaging the teeth of the elongate member. In this regard, it is contemplated that a method can be provided for forming such an embodiment. The method can comprise forming the central passage as a first through hole in the backbone in a circumferential direction of stent, and forming the at least one internal recess as a second through hole in the backbone in a direction transverse to the circumferential direction of the central passage such that the first and second through holes partially overlap.
In accordance with another embodiment, the stent can optionally be configured such that the stent can provide structural properties comparable to a metal stent while providing bioresorbability. For example, the stent can comprise a plurality of radial elements interconnected to collectively form a tubular member. Each radial element can comprising a continuously-slotted helical backbone and a plurality of elongate rails that is offset from slots of the continuously-slotted helical backbone. The rails can extend from the helical backbone in a circumferential direction at an angle that is greater than or less than 90°. For example, the helix angle can be between about 30° to about 80°. However, the helix angle can be between about 40° to about 60°. Further, a first radial element can be interconnected with a second radial element with the elongate rails of the first radial element being received into the slots of the continuously slotted backbone of the second radial element.
Moreover, embodiments of the stent can be formed using one or more radial elements. In this regard, an embodiment of such a radial element can be formed to comprise a helical backbone and a plurality of rib elements.
In some embodiments, the backbone can be a continuously-slotted helical backbone member having a plurality of engagement slots and a plurality of connection slots. For example, the engagement slots can be spaced between consecutive connection slots along the backbone. Further, each helical backbone member can generally define a longitudinal axis.
The elongate rib elements can be configured to have having proximal and distal portions. The proximal portion can be interconnectable with one or more connections slots of the continuously slotted backbone member. Further, each rib element can be positionable generally circumferentially about the longitudinal axis and have a fixed engagement at a non-perpendicular angle with respect to the helical backbone member.
Accordingly, in such embodiments, the plurality of elongate rib elements can be arranged to interconnect with at least one other helical backbone member of another radial element so as to form an expandable tubular skeleton. The elongate rib elements can provide a one-way slidable engagement with the engagement slots of the helical backbone member of the other radial element. Further, the tubular skeleton can be configured to expand radially between a collapsed diameter and an expanded diameter upon circumferential motion of the slidable engagement of the rib elements to the helical backbone members. Furthermore, the slidable engagement can include a mechanism that is operative to restrain collapse of the tubular skeleton from the expanded diameter towards the collapsed diameter.
In some optional embodiments of the radial element, the helical backbone can comprise portions of reduced thickness for allowing at least partial nesting of an elongate rib element thereagainst. Further, the radial element can be configured such that a pair of elongate rib elements are interconnected at their distal portions by a crossbar. Furthermore, the crossbar can comprise an offset portion configured to at least partially receive an elongate rib of an adjacent radial element for reducing a passing profile of a stent formed using a plurality of radial elements.
According to yet other optional embodiments, the radial element can be configured such that the helical backbone extends helically at a generally fixed radius and helix angle relative to the longitudinal axis. In this regard, the engagement slot can comprises a through slot that defines a central axis extending in a generally circumferential direction and within a plane that is perpendicular to the longitudinal axis of the radial element, and the central axis of the engagement slot can extend at a non-perpendicular angle relative to the helical backbone.
In one further embodiment, an expandable stent is disclosed, comprising a plurality of radial elements interconnected to form a tubular member, each radial element comprising a helical support member comprising a plurality of slots and a plurality of circumferential rails, wherein a first radial element is interconnected with a second radial element, such that the circumferential rails of the first radial element are received into the slots of the helical support member of the second radial element, wherein the expandable stent is made from a bioresorbable polymer and exhibits structural properties comparable to a metal stent.
The abovementioned and other features of the inventions disclosed herein are described below with reference to the drawings of the embodiments. The illustrated embodiments are intended to illustrate, but not to limit the inventions. The drawings contain the following figures:
As will be discussed herein, embodiments of the stent summarized above and defined by the enumerated claims may be better understood by referring to the following detailed description, which should be read in conjunction with the accompanying drawings. This detailed description of embodiments, set out below to enable one having skill in the art to build and use one particular implementation, is not intended to limit the enumerated claims, but to serve as a particular example thereof.
While the description sets forth various embodiments in specific detail, it will be appreciated that the description is illustrative only and should not be construed in any way as limiting the same. Furthermore, various applications of the embodiments, and modifications thereto, which can occur to those who are skilled in the art, are also encompassed by the general concepts described herein.
The term “stent” is used herein to designate embodiments for placement in (1) vascular body lumens (i.e., arteries and/or veins) such as coronary vessels, neurovascular vessels and peripheral vessels for instance renal, iliac, femoral, popliteal, subclavian and carotid; and in (2) nonvascular body lumens such as those treated currently i.e., digestive lumens (e.g., gastrointestinal, duodenum and esophagus, biliary ducts), respiratory lumens (e.g., tracheal and bronchial), and urinary lumens (e.g., urethra); (3) additionally such embodiments can be useful in lumens of other body systems such as the reproductive, endocrine, hematopoietic and/or the integumentary, musculoskeletal/orthopedic and nervous systems (including auditory and ophthalmic applications); and, (4) finally, stent embodiments can be useful for expanding an obstructed lumen and for inducing an obstruction (e.g., as in the case of aneurysms).
The term “stent” is further used herein to designate embodiments such as; support structures for maintaining patency of a body lumen; support structures for anchoring thrombus filters and heart valves; as well as support structures for the distribution and delivery of therapeutic agents as well as other devices.
In the following description of embodiments, the term “stent” can be used interchangeably with the term “prosthesis” and should be interpreted broadly to include a wide variety of devices configured for supporting a segment of a body passageway. Furthermore, it should be understood that the term “body passageway” encompasses any lumen or duct within a body, such as those described herein.
Still further, it should be understood that the term “shape-memory material” is a broad term that can include a variety of known shape memory alloys, such as nickel-titanium alloys, as well as any other materials that return to a previously defined shape after undergoing substantial plastic deformation.
The term “radial strength,” as used herein, describes the external pressure that a stent is able to withstand without incurring clinically significant damage. Due to their high radial strength, balloon expandable stents are commonly used in the coronary arteries to ensure patency of the vessel. During deployment in a body lumen, the inflation of the balloon can be regulated for expanding the stent to a particular desired diameter. Accordingly, balloon expandable stents can be used in applications wherein precise placement and sizing are important. Balloon expandable stents can be used for direct stenting applications, where there is no pre-dilation of the vessel before stent deployment, or in prosthetic applications, following a pre-dilation procedure (e.g., balloon angioplasty). During direct stenting, the expansion of the inflatable balloon dilates the vessel while also expanding the stent.
The stent can be fabricated from at least one or more materials. These materials include metals, polymers, composites, and shape-memory materials. In another optional embodiment, the stent further can comprise a tubular member formed from a biocompatible and preferably, bioresorbable polymer, such as those disclosed in co-pending U.S. application Ser. No. 10/952,202, the disclosure of which is incorporated herein in its entirety by reference. It is also understood that the various polymer formulae employed can include homopolymers and heteropolymers, which can include stereoisomerism, composites, filled materials, etc. Homopolymer is used herein to designate a polymer comprised of all the same type of monomers. Heteropolymer is used herein to designate a polymer comprised of two or more different types of monomer which is also called a co-polymer. A heteropolymer or co-polymer can be of a kind known as block, random and alternating. Further with respect to the presentation of the various polymer formulae, products according to embodiments can be comprised of a homopolymer, heteropolymer and/or a blend of such polymers.
The term “bioresorbable” is used herein to designate polymers that undergo biodegradation (through the action of water and/or enzymes to be chemically degraded) and at least some of the degradation products can be eliminated and/or absorbed by the body. The term “radiopaque” is used herein to designate an object or material comprising the object visible by in vivo analysis techniques for imaging such as, but not limited to, methods such as x-ray radiography, fluoroscopy, other forms of radiation, MRI, electromagnetic energy, structural imaging (such as computed or computerized tomography), and functional imaging (such as ultrasonography). The term “inherently radiopaque” is used herein to designate polymer that is intrinsically radiopaque due to the covalent bonding of halogen species to the polymer. Accordingly, the term does encompass a polymer which is simply blended with a halogenated species or other radiopacifying agents such as metals and their complexes.
In another optional variation, the stent further can comprise an amount of a therapeutic agent (for example, a pharmaceutical agent and/or a biologic agent) sufficient to exert a selected therapeutic effect. The term “pharmaceutical agent”, as used herein, encompasses a substance intended for mitigation, treatment, or prevention of disease that stimulates a specific physiologic (metabolic) response. The term “biological agent”, as used herein, encompasses any substance that possesses structural and/or functional activity in a biological system, including without limitation, organ, tissue or cell based derivatives, cells, viruses, vectors, nucleic acids (animal, plant, microbial, and viral) that can be natural and recombinant and synthetic in origin and of any sequence and size, antibodies, polynucleotides, oligonucleotides, cDNA's, oncogenes, proteins, peptides, amino acids, lipoproteins, glycoproteins, lipids, carbohydrates, polysaccharides, lipids, liposomes, or other cellular components or organelles for instance receptors and ligands. Further the term “biological agent”, as used herein, can include virus, serum, toxin, antitoxin, vaccine, blood, blood component or derivative, allergenic product, or analogous product, or arsphenamine or its derivatives (or any trivalent organic arsenic compound) applicable to the prevention, treatment, or cure of diseases or injuries of man (per Section 351(a) of the Public Health Service Act (42 U.S.C. 262(a)). Further the term “biological agent” can include 1) “biomolecule”, as used herein, encompassing a biologically active peptide, protein, carbohydrate, vitamin, lipid, or nucleic acid produced by and purified from naturally occurring or recombinant organisms, tissues or cell lines or synthetic analogs of such molecules, including antibodies, growth factors, interleukins and interferons; 2) “genetic material” as used herein, encompassing nucleic acid (either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), genetic element, gene, factor, allele, operon, structural gene, regulator gene, operator gene, gene complement, genome, genetic code, codon, anticodon, messenger RNA (mRNA), transfer RNA (tRNA), ribosomal extrachromosomal genetic element, plasmagene, plasmid, transposon, gene mutation, gene sequence, exon, intron, and, 3) “processed biologics”, as used herein, such as cells, tissues or organs that have undergone manipulation. The therapeutic agent can also include vitamin or mineral substances or other natural elements.
In some embodiments, the design features of the axially or circumferentially offset elements can be varied to customize the functional features of strength, compliance, radius of curvature at deployment and expansion ratio. In some embodiments, the stent can comprise a resorbable material and vanishes when its job is done. In some embodiments, the stent serves as a therapeutic delivery platform.
Some aspects are also disclosed in co-pending U.S. patent application Ser. Nos. 11/016,269, 60/601,526, 10/655,338, 10/773,756, and 10/897,235, the disclosures of each of which are incorporated herein in their entirety by reference thereto.
Some features and arrangements of embodiments of stents are disclosed in U.S. Pat. Nos. 6,033,436, 6,224,626, and 6,623,521, each issued to Steinke, the disclosures of each of which are hereby incorporated in their entirety by reference thereto.
Advantageously, the stent design elements and interlocks can be varied to customize the functional features of strength, compliance, radius of curvature at deployment and expansion ratio. In some embodiments, the stent can comprise a resorbable material and vanishes when its job is done. In some embodiments, the stent serves as a delivery platform for therapeutic agents such as pharmaceutical compounds or biological materials.
Some embodiments relate to a radially expandable stent used to open, or to expand a targeted area in a body lumen. Some embodiments relate to a radially expandable stent used as a drug delivery platform to treat vascular conditions. In some embodiments, the assembled stent can comprise a tubular member having a length in the longitudinal axis and a diameter in the radial axis, of appropriate size to be inserted into the body lumen. The length and diameter of the tubular member can vary considerably for deployment in different selected target lumens depending on the number and configuration of the structural components, described below.
The tubular member in accordance with some embodiments can have a “clear through-lumen,” which can be defined as having no structural elements protruding into the lumen in either the collapsed or expanded diameters. Further, the tubular member can have smooth marginal edges to minimize the trauma of edge effects. The tubular member can be preferably thin-walled and flexible (e.g., less than about 0.01 Newtons force/millimeter deflection) to facilitate delivery to small vessels and through tortuous vasculature.
In optional embodiments, the wall thickness can be about 0.0001 inches to about 0.0250 inches, and more preferably about 0.0010 to about 0.0100 inches. However, the wall thickness depends, at least in part, on the selected material. For example, the thickness can be less than about 0.0080 inches for plastic and degradable materials and can be less than about 0.0020 inches for metal materials. More particularly, for a 3.00 mm stent application, when a plastic material is used, the thickness can be preferably in the range of about 0.0020 inches to about 0.0100 inches. The thin walled design can also minimize blood turbulence and thus risk of thrombosis. The thin profile of the deployed tubular member in accordance with some embodiments also facilitates more rapid endothelialization of the stent. The above thickness ranges have been found to provide superior characteristics through all aspects of the device including assembly and deployment. However, it will be appreciated that the above thickness ranges should not be limiting with respect to the scope of the embodiments and that the present teachings can be applied to devices having dimensions not discussed herein.
In accordance with the principles of the inventions disclosed herein, the geometry of the stent may be generally described as a tubular member. In accordance with these various features, the slidably engaged expandable stent can include at least two slidably engaged radial elements defining a circumference of the tubular member.
In some embodiments, the stent can comprise one or more helical backbone assemblies. The helical backbone assembly of the embodiments described herein provides a high degree of longitudinal structural integrity combined with longitudinal and rotational flexibility, both in the compacted and deployed configurations. The array of elongate members, elongate rails, or rail elements that extend from the backbones can interlock with other backbones to form an interwoven circumferential surface that provides crush strength and radial stiffness without unduly inhibiting longitudinal or rotational flexibility. The generally circumferential alignment of the elongate members allows the elongate members to engage each other and the backbone in a configuration which provides “hoop-strength” without direct coupling, thus providing a substantial increase overall longitudinal “beam” stiffness. In certain embodiments, the stent structure may be described as expandable tubular “skeleton” assembly defined by the systematic movable interconnection of a plurality helical “backbone members” via a plurality of circumferentially arranged rail or “rib” elements.
Further, the backbones of many of the backbone assemblies disclosed herein provide a continuously-slotted backbone. In other words, embodiments of the backbone can be configured to comprise a series of slots formed along the backbone for facilitating interconnection of the backbone assembly with another backbone assembly. The continuous slotting of the backbone can be advantageous by reducing the tendency for hinging, kinking, and buckling of the stent. Further, due to the unique helical backbone structure and slide-and-lock expansion mechanism of embodiments disclosed herein, a continuously-slotted backbone can also contribute to superior flexion and crush strength of the stent.
Accordingly, various embodiments described herein can provide for a polymeric stent that exhibits advantageous structural properties that are comparable to those of a metal stent. For example, research has illustrated that the helical backbone construction, paired with the slide-and-lock interconnection of radial elements, can be used in a polymer stent such that the advantages of bioresorbability and superior structural stiffness and strength (similar to that of a metal stent) can be realized. This significant advance in stent technology allows other preferable materials—not just metals—to be used in a stent to achieve desirable material properties, while ensuring that the necessary structural properties of the stent are also achieved.
The slidably engaged radial elements can be configured for unidirectional slidable movement so as to permit the radial expansion of the tubular member. In an embodiment, the stent can define a first collapsed diameter, and a second expanded diameter. The slidably engaged expandable stent is adapted to be expandable between at least the first collapsed diameter and at least the second expanded diameter.
In some embodiments, the slidably engaged expandable stent is configured with two radial modules, each radial module being slidably engaged and configured for unidirectional expansive movement. Each radial module can include a backbone, a first elongate member and a second elongate member. In some embodiments, the elongate members are annular elongate members; ring-like members elongated from the backbone. The elongate members are slidably engaged with slots and configured for unidirectional slidable movement.
The slidably engaged expandable stent in some embodiments has a plurality of annular elongate members, including a first elongate member and a second elongate member. These annular elongate members are substantially commonly oriented with respect to the backbone. Additionally, the second elongate member is axially or circumferentially offset with respect to the first elongate member.
The axially or circumferential offsetting of elongate members allows a distribution of slidable engagements. Such a distribution of slidable engagements is said to render the stent uniform with respect to mechanical failure points; as the slidable engagements are the weakest mechanical points in the design. Slidable engagements are herein defined as the engagement means between two slidably engaged radial modules. In some embodiments, the slidable engagements are defined by the interlocking of slots and contained rails of the slidably engaged elongate members.
The slots can further comprise a locking member. A locking member can be a tooth, a deflectable tooth, or a stop. In some embodiments, the slots comprise a number of stops inside the surface or cavity of the slot. In another embodiment, the slots comprise at least one tooth adjacent to the entry side of the slot.
Additionally, the elongate members can be configured to comprise at least one conjugate locking member. A conjugate locking member is essentially a component designed to engage with the locking member. In some embodiments, a conjugate locking member is adapted to fit be engaged by the locking member. In one embodiment, the conjugate locking member is one of a tooth, a deflectable tooth, or a stop. A locking member and a conjugate locking member define an engagement means whereby the radial modules are slidably engaged.
A conjugate locking member can be located on any part of the stent; however in some embodiments, the conjugate locking member is located on the rail of an elongate member. Each elongate member has at least one radial surface and at least two axial sides. Axial sides are substantially perpendicular to the longitudinal axis of the elongate member. In some embodiments, a plurality of conjugate locking members can be distributed on both axial sides of the rail. In one embodiment, the conjugate locking members on both axial sides of the elongate member can be substantially aligned in a mirrored distribution. In another embodiment, the conjugate locking members can be substantially mirrored but offset by a vertical distance with respect to the opposite axial side. Axial locking members can be axially nested and substantially prevented from protruding into the vessel wall, thereby preventing undesired agitation which can cause stenosis.
Further, conjugate locking members can be spaced apart by a defined distance. The conjugate locking members on one axial side can be offset with respect to the conjugate locking members of the second axial side. Such an offsetting of conjugate locking members can provide a higher resolution for stent diameter customization.
In another embodiment, the stent comprises a backbone adapted to substantially coil about the tubular member. A substantially coiled backbone; or otherwise herein referred to as a helical backbone or a flexible backbone, gives rotational flexibility to the stent design. Rotational flexibility is an important improvement which will allow the stent to adapt to vasodynamic movements. A substantially coiled backbone can be an elongate backbone configured to coil about the tubular member, or alternatively can be a stair-step pattern, a wave-like pattern, or any other pattern which is substantially configured in a helical orientation about the tubular member.
In an embodiment, a plurality of radial elements each comprising a backbone can be configured into a tubular member having a plurality of substantially coiled backbones. A flexible backbone is herein defined as any backbone of a radial element which is configured to substantially coil about the tubular member.
Additionally, a flexible backbone can comprise a flexible link in the backbone, such as a spring link. Or alternatively, the flexible backbone can be made of an elastomeric polymer material sufficient to promote adaption to vasodynamic movements. Elastomeric polymers are defined in the art, however for illustrative purposes examples can include polycaprolactone, polydioxanone, and polyhexamethylcarbonate.
Referring to
As will be described herein, various embodiments of the stent component or radial element can comprise a slot. The slot can be configured as a completely or fully captive slot or as a substantially or semi-captive slot. It is contemplated that when referring to a completely or fully captive slot, the completely or fully captive slot can be an opening, cut, slit, incision, etc. in a material such that an element disposed through the slot is captured on the lateral, upper, and lower sides thereof, thus only allowing one degree of motion, such as movement or translation in a posterior-anterior direction through the slot. In other words, a completely or fully captive slot can restrict motion of the element in all directions except for anterior (forward) and posterior (rearward) sliding or translating motion (permitting only one degree of motion) into and out of the slot.
A substantially or semi-captive slot can be configured to allow two or more degrees of motion. When compared to a completely or fully captive slot, a semi-captive slot can provide at least one additional degree of freedom of movement of the element disposed therethrough. For example, as noted above, a fully captive slot can capture an element on the lateral, upper, and lower sides thereof, thus only allowing the element to move or slide in a posterior-anterior direction through the slot. In contrast, a semi-captive slot may provide movement in a posterior-anterior direction, as well as a rotational motion or translational movement in a lateral or upper or lower direction (in other words, two or more degrees of movement). For example, a semi-captive slot can surround an element on three sides and allow the element to be move in a posterior-anterior direction and to be slide or translate in a lateral or upper or lower direction relative to the slot.
It is also noted that the embodiments shown in
In accordance with some embodiments, the stent 10 can be formed from a sheet of material that is formed to create one or more stent components, such as the radial elements 20, 22, that can be wound or curled upon itself to create a cylindrical or tubular member. While a single radial element may be used to form the stent in some embodiments, greater radial expansion is possible using two or more radial elements.
As illustrated in the
Additionally, it is contemplated that at least a portion of a stent component can comprise one or more thicknesses and/or comprise one or more radially offset portions. In this regard, the radial elements can comprise one or more sections that overlap or nest with each other. Such a configuration can provide for a more compact stent with a reduced profile in either or both of an expanded and/or collapsed diameter.
For example, at least one of the radial elements 20, 22 can comprise one or more thicknesses and/or comprise one or more crossbars, bridge portions, or radially offset portions 36, 46. The crossbars, bridge portions, or offset portions 36, 46 can be formed between distal ends of the elongate members 32, 42 and thereby interconnect distal ends of a pair of elongate members 32, 42. Further, the crossbars 36, 46 can define a thickness that is different from the thickness of the elongate members 32, 42. For example, an outer surface of the elongate members 32, 42 can be in a common plane with an outer surface of the crossbars 36, 46 with an inner surface of the elongate members 32, 42 being in a plane that is offset from a plane of an inner surface of the crossbars 36, 46. However, the crossbars 36, 46 can also define inner and outer surfaces that are both generally radially offset from inner and outer surfaces of the elongate members 32, 42.
As shown in
In some embodiments having a plurality of radially overlapping stent components or radial elements, the stent components or radial elements can comprise reduced thicknesses or offset portions that are configured to at least partially receive a plurality of stent components or radial elements. For example, a backbone of a first radial element can be configured with a slot for accommodating at least a portion of a second radial element and a reduced thickness or offset portion for accommodating at least a portion of a third radial element.
In such embodiments, the passing or outer profile of the stent can be minimized in order to facilitate placement and deployment of the stent, as well as to maximize the interior cross-sectional area of the stent relative to the passing or outer profile.
As noted, it is contemplated that other overlapping sections of the stent can have one or more offset portions. The offset portions can be offset in a radial direction such that when overlapping with another stent component, the passing profile of the stent is generally reduced. An example of a crossbar 36 is illustrated in
In this regard, in accordance with some embodiments, an offset portion or bridge portion formed intermediate one or more elongate members can be referred to as a “semi-captive” slot.
Further, it is contemplated that in some embodiments, the offset portion of a stent component can comprise an engagement means. The engagement means can be configured to contact and to interact with a portion of a corresponding stent component. Thus, when a corresponding stent component is received against the offset portion, the offset portion can function to restrict the articulation or movement of the portion of the corresponding stent component relative to the offset portion. Thus, in some embodiments, a stent component or radial element can comprise a semi-captive slot having an engagement means that interconnects the semi-captive slot (and therefore indirectly interconnects the distal ends of the elongate members) with the overlapped portion of the stent component or radial element. However, the semi-captive slot need not comprise an engagement means, but can comprise three or more surfaces or boundaries that restrict movement of the portion of the corresponding stent component in three or more respective directions. In some embodiments, a direction in which the movement is restricted can be in a circumferential direction which allows the offset portion to participate in restricting expansion or contraction of the stent.
It is also noted that in
Referring again to
With respect to
Additionally, one having skill will recognize that the slots 34, 44 located along the backbones 30, 40 can have an increased thickness with respect to the flexible backbone. Further, the slots 34, 44 along the elongate members 32, 42 can variable thickness or be formed from an offset portion with respect to the elongate members 32, 42, as discussed above. It may be advantageous to minimize the thickness of the flexible backbones 30, 40 in order to increase flexibility of the stent 10; however thickness around the captive slots 34, 44 can serve an alternate function, to provide strength and support to the engaged rails. Thus, in this embodiment, the thickness of the flexible backbone linking two captive slots can be minimized to allow for greater flexibility as seen in
Additionally, as illustrated in the embodiment of
The radial element 60 shown in
For example, in some embodiments, the radial elements 60, 62 can each comprise offset portions 76, 86. The offset portions 76, 86 can be configured such that they are disposed on a radially interior portion of the stent component or radial elements 60, 62. In such embodiments, as shown in
Thus, the elongate members 72, 82 of the radial elements 60, 62 can be radially nested while preventing protrusion of the elongate members 72, 82 of the radial elements 60, 62 toward the lumen or vessel of the patient. In other words, if the offset portions 76, 86 are configured to underlay a portion of the corresponding stent components or radial elements 60, 62, any resilience of the stent component itself (which may cause the stent component to straighten and protrude outwardly toward the vessel wall) can be counteracted due to the interweaving and underlayment of the offset portion with a section or portion of the corresponding stent component. Additionally, in some embodiments, the flexible backbones 70, 80 can be configured with variable thickness to provide the desired flexibility for an intended use.
Additionally, one having skill will recognize that the captive slots located along the backbone and on the annular elongate members have an increased thickness with respect to the flexible backbone. It is important to minimize the thickness of the flexible backbone in order to increase flexibility; however thickness around the captive slots serves an alternate function, to provide strength and support to the engaged rails. Thus, in this embodiment, the thickness of the flexible backbone linking two captive slots can be minimized to allow for greater flexibility as seen in
As noted,
The embodiments illustrated in
Additionally, the disclosures of Applicant's patents and copending patent applications are hereby incorporated by reference in their entireties and include U.S. patent application Ser. Nos. 11/016,269, 11/455,986, 11/196,800, 12/193,673, 11/399,136, 11/627,898, 11/897,235, 11/950,351, 11/580,645, 11/680,532, and U.S. Pat. No. 6,951,053.
In the embodiment illustrated in
In the embodiment shown in
An embodiment shown in
Additionally, it is contemplated that the embodiment of
The embodiments of
Additionally, the embodiments in these figures introduce a deflectable tooth 194, 204 at the distal end of elongate members 196, 206 of the radial elements 190, 200, respectively. It would be understood by one having skill in the art that a plurality of deflectable teeth can be added to provide for customization of the diameter of the stent. Further, the flexible teeth 194, 204 can be configured on either axial side in a mirrored alignment, or a mirrored and offset alignment as described above. Furthermore, the elongate members 196, 206 can be radially spaced at approximately between one to two times the width of a slot.
The slidable engagement between radial elements allows for a reduced cross sectional area which greatly improves deliverability by allowing a minimally invasive delivery of the stent.
The embodiment of
The embodiment of
Another embodiment illustrated in
In order to assemble the stent assembly, with reference to
In yet another alternative, the conjugate locking members or ratcheting teeth 304 on the rail or radial element 310 may be configured to permit them to be deflected into a non-engaging position by means of one or more shims or enclosing covers (not shown) during assembly, permitting the element 310 to be moved through captive slot 312 (of a companion, adjacent radial element 300) toward an assembled collapsed stent configuration. Removal of the shims or enclosing covers then permits the members 304 to return to an engaging or locking configuration following assembly.
Note that there does not necessarily need to be a conjugate paring of locking mechanisms on the radial or rail elements 310 and on the backbone 302. For example, as shown the embodiments of
Subsequently, during expansion, the teeth 314 can engage the conjugate locking members 304 to provide a ratcheting-type movement of the elongate member 306 relative to the slot 312. As the rail 306 moves through the slot 312 from the bottom portion to the top portion, the deflectable tooth is deflected out. However, a rail 306 attempting to move in a direction from the top portion 320 to the bottom portion 322 of the slot 312 will engage the deflectable tooth 314 and deflect that tooth 314 in order to prevent further movement in the undesired direction. As illustrated, because in this embodiment, the teeth 314 extend from an outer rim 320 of the slot 312, movement of the stent from an expanded to a collapsed state creates compressive stress against the teeth 314. As such, the locking mechanism 314 resists collapse of the stent and can exhibit superior strength and structural properties in maintaining the stent in an expanded configuration.
One having skill in the art can recognize that the features of the previous embodiments can be incorporated to adjust flexibility, strength, and size as illustrated in
Added radial support can be provided by the embodiment illustrated in
The fully captive slots 366 shown in
The fully captive slots described above are further illustrated in
Referring now to
Subsequently, distal ends 614 of the elongate members 610 of the first radial element 600 can be interconnected. For example, in some embodiments, as shown in
As also shown in
Subsequently, the method can comprise interconnecting crossbars with distal ends of elongate members of other radial elements in a manner as described above. Depending on the size and configuration of the stent, various radial elements can be used. As shown in
Further, in embodiments using three or more radial elements, it is contemplated that the elongate members 610 and the crossbar 620 can also be disposed or layered above a backbone 630 and elongate members 632 of a third radial element 604 and the elongate members 634 of the second radial element 602. Alternatively, the elongate members 610 and the crossbar 620 can also be disposed or layered beneath the backbone 630 of the third radial element 604 and the elongate members of the second radial element 602. In this manner, expansion of the stent can be unhindered as the elongate members 610 and crossbar 620 pass over or under the backbone 630 and the elongate members 632, 634.
Another feature of at least one embodiment disclosed herein is a slot having improved locking resolution, as disclosed in
Therefore, in some embodiments, a slot configuration is provided that can enhance the resolution of the slot. Resolution can refer to the number of teeth or engagement members that participate in the engagement. In other words, resolution can define the manner and distribution of the stresses of the engagement. In this regard, it is contemplated that improvements in locking resolution can also permit improved customization of the diameter and configuration of the stent. Further, by improving the resolution of the slot, in some embodiments, a captive slot can be fabricated from a biodegradable polymer while maintaining the same advantageous structural properties as a slot formed in a metal stent. For example, a polymeric slot can be formed to comprise teeth and stops inside the captive slot that can experience slow degradation of the material with respect to the polymer surface which is exposed to the tissue and surrounding water.
One of the advantages of embodiments disclosed herein is that relatively slow degradation allows for long lasting mechanical lockouts relative to the life of the stent and prevents premature lockout failures. This is because most biodegradable polymers degrade by a process known as hydrolysis, the breakdown of ester bonds in the polymer. Based on the material properties of the biodegradable polymer, the polymer may absorb an amount of water. The degree to which water is absorbed, among other properties, will determine how the polymer degrades over time. A relatively higher rate of water absorption will likely result in bulk erosion of the polymer material, the polymer more or less degrades from the inside out. Alternatively a polymer designed to have a relatively lower water absorption rate will tend to degrade by surface erosion, or from the outside surface.
Therefore, in accordance with an embodiment,
Thus, as shown in
Accordingly, in some embodiments, a method is provided for making a slot with improved resolution. One method of making stops is to etch, drill, or otherwise cut into the radial element so as to pass at least partially through the slot, creating a through space or aperture and one or more stops within the interior of the slot. For example, the through space or aperture can pass through the entire width of the radial element. In such an embodiment, the etching, drilling, or cutting is done in a direction that is transverse to the direction of the slot. In some embodiments, the direction of the etching, drilling, or cutting can be perpendicular to the direction of the slot. Another method is to bond a stack of sheets wherein the contained sheets are pre-etched. An advantageous method of etching is laser etching. In this manner, a series of interior stops can be formed within the slot for engaging a plurality of engagement members, such as teeth, of a corresponding stent component.
The embodiment disclosed in
As noted above, the various embodiments described herein can comprise a helical backbone assembly that provides a high degree of longitudinal structural integrity combined with longitudinal and rotational flexibility, both in the compacted and deployed configurations. The array of elongate members of the described embodiments engage to form an interwoven circumferential surface that provides crush strength and radial stiffness without unduly inhibiting longitudinal or rotational flexibility. The generally circumferential alignment of the rails allow the elongate members to engage each other and the backbone in a configuration which provides “hoop-strength” without coupling, thus providing a substantial increase overall longitudinal “beam” stiffness. In certain embodiments, the stent structure may be described as expandable flexible tubular multiple-spine “skeleton” assembly defined by the systematic movable interconnection of a plurality helical “backbone members” via a plurality of circumferentially arranged rail or “rib” elements.
With reference to
Advantageous structural properties of the embodiments disclosed herein—including the avoidance of plastic deformation, radial stiffness/strength without recoil, compact wall configuration, and longitudinal/rotational flexibility can allow the structural members comprising bioresorbable materials (such as polymers) to be sized so as to provide a selectably high ratio of wall opening area to overall stent circumferential surface (e.g., see
The stent structure may advantageously comprise a fracture-toughened polymer composition. For many treatment applications, it is desirable to have a bioresorbable stent structure, and it is also often desirable to have a radio-opaque structure facilitating medical imagery. For such applications, the backbone members and/or other elements of the stent may comprise a polymeric composition with is both bioresorbable and radio-opaque. See further description of such polymers above, and also U.S. Pat. Nos. 5,099,060; 6,120,491; and 6,475,477; and Patent Application Nos. 2005-0106,119 and 2006-0034,769, each of which is incorporated by reference. In various alternative embodiments, radio-opaque markers may be included which are distinct from the primary stent structural elements; certain structural elements may be radio-opaque; or a non-uniform material may be used have radio-opaque regions and radio-transmissive regions. Not all stent structural elements need comprise of the same material composition. Likewise, materials used may be isotropic or anisotropic, uniform or non-uniform, layered, and/or composite. Further, as discussed further below, various elements can comprise composite materials.
The described embodiments are readily manufacturable, as further described above. For example, members and elements of the stent structure may be cut from a sheet comprising one or more suitable biocompatible polymeric materials. The shaping of the structural members, and various slots and other details may be performed by known methods such as numerically-controlled laser cutting, or the like. The structural elements may comprise pharmaceutical agents or constituents which elute, upon stent deployment, into adjacent body fluids or tissues. Alternatively such pharmaceutical agents and compositions may be coated onto all or a portion of the stent assembly. In yet other alternatives, the stent assembly may include reservoir or storage elements containing pharmaceutical agents.
The example shown includes three such backbone members 760, 762, 764, although the stent or stent assembly 750 may include fewer or more than three backbone members. The array of backbone members 760, 762, 764 are interconnected by a plurality of elongate members 770, 772, 774 which extend generally circumferentially so as to integrate the stent assembly 750, as is described further below.
Although the backbone members 760, 762, 764 may be substantially parallel to the stent longitudinal axis, advantageously each backbone 760, 762, 764 may be disposed at an angle α to the longitudinal axis of the stent, so that when the backbones 760, 762, 764 are formed into a tubular member, the backbones 760, 762, 764 form a helical arrangement (see also
In
Note, when describing stent lumen expansion, the terms “radial expansion” and “circumferential expansion” are generally used interchangeably herein, as would be true for expansion having a consistently circular cross-sectional shape, or another constant cross-sectional shape. Where a stent is expanded with a change of general cross-sectional shape (e.g., from a circular compacted shape to an expanded irregular or flattened lumen profile; or other non-regular expansion) there may not be a linear relation between mean stent radius to stent circumference during expansion. Likewise, when a stent is deployed to conform to a flared, hour-glass, tapered or bulged lumen, the expanded cross-sectional shape may vary considerably along the longitudinal axis. Although not illustrated in the figures, the inventive principles of the embodiments may be applied to bifurcated stents or other complex configurations.
In
The crossbar can have any variety of configurations and cross-sections. For example, the crossbar can be shaped as a generally cylindrical member, a flat plate, or a combination of one or more shapes extending between the distal ends of the elongate members or rails. Further, the rails of the elongate members 770, 772, 774 can be configured to comprise a narrowed proximal portion that can attach to connection slots of a respective backbone for fixing the elongate member to the respective backbone. Furthermore, the rails of the elongate members 770, 772, 774 can also each comprise a distal or engagement section having one or more engagement members, such as teeth.
In use, the proximal narrow portion of the rail of each elongate member can be passed through a pass-through or engagement slot of a first backbone and then connected with connection slots of a second backbone. Thus, relative to the elongate member, the first backbone is slidably received onto the proximal portion of the rails of the elongate member. However, as the first backbone advances toward the distal or engagement portion of the rails of the elongate member, it is contemplated that the engagement members of the rail can engage with the pass-through or engagement slot of the first backbone.
Accordingly, the slot of the first backbone can be termed a pass-through slot insofar as it serves to permit passage of the rail of the elongate member therethrough; however, the slot of the first backbone can also be termed an engagement slot insofar as it engages with the engagement members of the rail of the elongate member. Further, the elongate members 770, 772, 774 may include a single rail, or more than two rails (e.g. three or more), and different elongate member configurations may be included in a single stent assembly.
As assembled, the proximal ends of the rails of a given elongate member 770, 772, 774 are connected to a single backbone member 760, 762, 764. In this manner, the elongate members 770, 772, 774 form a core-bonded stent assembly. For example, a given backbone member may include a connection slot to receive the proximal end of a given elongate member. The proximal end of the elongate member may be fixed to the backbone by a latching mechanism, an adhesive bond, a fastener or the like, or by a combination of these.
For example, as illustrated in
As shown in
In an alternative example illustrated in
In the compacted configuration of
One may see that alternative partially-restraining engagement mechanisms between elongate member 770 and backbone 762 may be included in substitution for the sliding pass-through or engagement slot shown, for example, by including a mechanism having an alignment pin engaged in a longitudinal slot. However, it has been demonstrated that the partially-restraining engagement mechanism shown (a rail sliding portion passing through a simple transverse backbone slot with a selectable clearance) functions well for this purpose; is structurally simple, compact and robust; and may be produced and assembled by known manufacturing methods.
In reference to the configurations of
In the example shown, the teeth can be configured to extend axially within the stent circumferential surface sufficiently to fill the lateral clearance between rail and slot (an advantageously compact arrangement), but the teeth or barbs may alternatively or additional be disposed to extend in a radial direction.
One may see that alternative ratcheting and/or locking engagement mechanisms between the ratchet rail portion of element 770 and backbone 760 may be included in substitution for the sliding pass-through or engagement slot shown. For example, a ratcheting mechanism structurally independent of the pass-through or engagement slot may be included. However, it has been demonstrated that the ratcheting engagement mechanism shown (a series of laterally disposed teeth or barbs in the rail extending to engage the inner surface and openings of the pass-through or engagement slot) functions well for this purpose, and is simple and compact, permitting convenient manufacturing and assembly.
In the example shown in
As shown in
Additionally, embodiments of the stent, such as that shown in
Moreover, it is also contemplated that in some embodiments, one or more of the helical backbones can be oriented at a given helix angle α relative to the longitudinal axis of the stent. For example, the helix angle α can be between about 20° and about 80°. More specifically, the helix angle α can be between about 30° to about 60°. In some embodiments, the helix angle α is about 45°. As such, the elongate members or rails can extend from the helical backbone in a circumferential direction at a coupling angle (the acute angle formed between the backbone and the elongate member or rail) that is less than 90°. In other words, the elongate members or rails of some embodiments are not oriented perpendicularly relative to the backbone. For example, the coupling angle can be between about 30° to about 80°. However, the coupling angle can be between about 40° to about 70°. In some embodiments, the coupling angle is about 45°.
In this regard, it is contemplated that by adjusting the helix angle and the coupling angle, embodiments can be optimized to provide a desirable stiffness and other structural properties.
With reference again to
Similarly, with reference again to
Thus, in accordance with an embodiment, a stent is provided that can comprise at least first and second radial elements. The radial elements can each comprise a helical backbone member and at least one elongate member. Further, the elongate member of the first radial element can be disposed through a pass-through or engagement slot of a helical backbone member of a second radial element such that the first and second radial elements form a tubular stent. Further, the elongate member can comprise a sliding rail portion and a ratchet rail portion. The sliding rail portion is configured to allow the helical backbone member of the second radial element to slide freely relative to the elongate member. Additionally, the ratchet rail portion is configured to promote engagement between the helical backbone member of the second radial element and the elongate member for maintaining the stent in at least one expanded position or diameter. In some embodiments, the lengths of the sliding rail portion and the ratchet rail portion can be configured to allow for various ranges of flexibility and/or expansion. Further, in other embodiments, a proximal portion of the elongate member can be attached to the helical backbone at a connection slot thereof.
Note with respect to the expanded configuration of
As discussed above,
As shown in
The embodiment of
A elongate member 920, in this example, comprising a parallel spaced-apart pair of rails 922, 924, is shown as it is inserted to engage the backbone array. Each proximal end of the rails 922, 924 of the elongate member 920 has been passed through a corresponding pass-through or engagement slot 930 in backbone member 912 and extends through to an adjacent receiving (fixation or connection) slot 932 in backbone member 910. The rails 922, 924 of the elongate member 920 are offset in length from one another so that both proximal rail ends contact the helical form of backbone 910 while the distal portion of the elongate member 920 extends generally perpendicularly to the helix axis. A second elongate member pair is shown in the right-hand portion of the photograph showing this offset.
In
Note that as assembled on the mandrel 902, the rail “teeth” or other ratcheting elements 938 of each rail are outside the pass-through or engagement slot 930 of the backbone 912. Subsequently, additional elongate members may be mounted in other longitudinal locations along the stent 900 to pass through pass-through or engagement slots in the backbone 912 and affix to connection slots of the backbone 910, in the manner of a row of shingles. A plurality of elongate members may be similarly mounted so as to pass through pass-through or engagement slots in backbone 910 and affix to connection slots of the backbone 914. A plurality of elongate members may be similarly mounted so as to pass through pass-through or engagement slots in backbone 914 and affix to connection slots of the backbone 912, so as to complete a circumferential network of elongate members integrating the backbone array.
FIGS. 46 and 47A-B are perspective and side view drawings showing the manner of mounting the assembled stent 960 on a delivery device 962, such as a rapid-exchange balloon catheter assembly.
In some embodiments, the compacted stent 960 and balloon can be covered by a retractable flexible polymer sheath to secure the stent and assist passage and advancement of the catheter-stent assembly though a body lumen to an intended treatment target within the lumen.
In these diagrams,
Beginning with
According to some embodiments, the elongate members and their rails and crossbars are represented collectively by a rectangular series of light dashed lines interconnecting the backbone members 1, 2, 3. In the top portion of
Note in the series of cross-sections of the top view, the position of backbone member #1, moving with the view from left to right, describes a counter-clockwise circular motion representing the helical change of circumferential position of the member.
The bottom portion or view of
It should be noted that notwithstanding the longitudinal flexibility of the overall stent assembly and the overall spring-like configuration of the backbone members, each backbone member is locally rigid and structurally continuous. Thus, the helical backbone members serve well to longitudinally integrate the circumferential radial strength of the hoop-like elongate members, so as to provide a smooth longitudinal bending behavior with minimal stress concentration. This provides a high resistance to kinking, hinging, and buckling. This forms a structure which is resistant to radial crush forces and denting, while still having a high degree of overall longitudinal flexibility. It can be understood that the helical backbone array likewise provides rotational (torsional) flexibility. These advantageous structural properties of the inventive stent assembly embodiments facilitate luminal insertion of the stent in the compacted state, flexible expansion and deployment of the stent in complexly curved lumen contours, and provide an expanded stent that is resistant to vasodynamic and dilative stresses and structural fatigue.
Furthermore, another advantage of some embodiments disclosed herein is that in contrast to prior art stents that may incorporate a helical design element, embodiments disclosed in the present application do not exhibit foreshortening when expanding from the collapsed diameter to the expanded diameter. In other words, the inventors of the present application have discovered that the various unique helical backbone structures disclosed herein can be used in combination with the slide-and-lock expansion mechanism disclosed herein in order to create a stent that has excellent flexibility, stiffness, and that also does not foreshorten, or decrease in axial or longitudinal length when expanded from the collapsed diameter to the expanded diameter. Foreshortening is a significant problem in other prior art stents, such as coil stents. Furthermore, the unique incorporation of the slide-and-lock expansion mechanism allows the helix angle of the helical backbone members to be maintained regardless of the diameter of the stent. Moreover, the inventors have also found that the unique alignment and orientation of the helical backbones, slots, and rail members in some embodiments provides a surprisingly efficient and effective expansion device exhibiting structural properties that are superior to prior art polymer stents and that rival structural properties of metal stents. As such, embodiments disclosed herein provide solutions to significant medical challenges and allow a patient to receive a stent that not only has structural properties that are optimized for the application, but that also is able to be resorbed into the body lumen upon completion of the goal.
Turning now to
The central portion or view of
In contrast, as discussed above, embodiments of the present application provide a uniquely-configured stent having a slide-and-lock helical backbone structure that provides essentially identical structural strength in any given bending direction. Once again, this unique feature of embodiments disclosed herein provides significant advantages over the prior art. Further, as shown in
Further, as discussed above with respect to other embodiments, the illustrated embodiment of
One of the many advantages of such an embodiment of a core-bonded stent is realized in the assembly of the stent. In particular, it is noted that during assembly, the distal ends 1122 of the elongate members 1106 are attached to the connection slots 1120 of the first helical backbone 1102 with the narrowed or non-engaging portions 1142 of the elongate members 1106, 1108 passing through the pass-through or engagement slots 1130 of the second helical backbone 1104. In this initial state of expansion, the stent assembly 1100 is in a compacted configuration. Accordingly, when the stent assembly 1100 expands for the first time, teeth 1144 of the elongate members 1106, 1108 will interact for the first time with the pass-through or engagement slots 1130 of the second helical backbone 1104. Because this is the first interaction between the teeth 1144 and the engagement slot 1130, the mechanical integrity will have been preserved and the slide-and-lock functionality of the stent 1100 will be maximized. Further, as discussed above, some embodiments can be configured to vary the length of the sliding rail portion and the ratcheting rail portion (see
These beneficial results of the disclosed embodiments of the core-bonded stents can be contrasted to situations in which the teeth of an elongate member are forced through an engagement slot during assembly in order to obtain an initial, collapsed configuration or where the engagement mechanism must otherwise be defeated to allow the elongate members and the helical backbone to assume an initial collapsed orientation.
Referring now to
For example, the expanded view of the stent assembly 1200 shown in
Finally, the stent assembly 1200 also illustrates that the backbone members 1202, 1204, 1206 can be configured to include portions of reduced thickness or offsets in areas of overlap with the elongate members 1210, 1212, 1214. For example, as shown in
The cross-sectional view of
Further,
Referring now to
In addition, it is noted that one of the advantages of mid-rail bonded stents can be realized in the assembly of the stent 1370. In particular, it is noted that a backbone member 1390 of an additional radial element is positioned such that pass-through or engagement slots 1392 of the backbone member 1390 receive the elongate member 1372 therethrough. As noted above, once the elongate member 1372 is attached and received within the slots 1380 in the collapsed state, the expansion of the stent to the expanded state will be the first time that the engagement mechanism is activated. As such, it is contemplated that the engagement between the teeth of the elongate member 1372 and the slots 1380 will be optimal.
For example, the structural properties of a given polymer, metal, or composite can be targeted in a given combination. The chemical (including medicinal) properties of a given polymer, metal, or composite can be targeted in another combination. Further, the degradation rate of a metal, polymer, or composite can be targeted in yet another combination. Accordingly, in some embodiments, it is contemplated that polymer, metal, and/or composite materials can be used in combinations that provide stents having one or more types of a polymer, metal, and/or composite. In particular, it is contemplated that composite polymer stents can be provided that have structural properties that mimic structural properties of metal stents.
Testing Data of Stent Embodiments Compared to Prior Art Stents
As discussed herein, embodiments of the helical slide-and-lock stents can provide superior flexibility and stiffness compared to prior polymer stents. In this regard, various tests have shown that the stiffness of embodiments disclosed herein is greater than that of prior art polymer stents. Indeed, the structural properties, such as the stiffness, of embodiments disclosed herein more closely mimics the structural properties of metal stents.
Accordingly, embodiments of the stents disclosed herein represent a significant advance in stent technology which allows a polymer and/or composite material to be used in a configuration that provides structural properties that can approach and/or replicate the structural properties of a metal stent. Metal stents have the disadvantage of not being as bioresorbable as polymer stents; however, metal stents have long provided superior structural properties that may be needed for severe lesions, such as rigidity, stiffness, and crush strength. In contrast, prior polymer stents could provide resorbability and other benefits not available with metal stents; however, prior polymer stent were not as stiff, rigid, or strong as the metal counterparts. One of the solutions and advances made by embodiments of the stent of the present application is the provision of a manner of achieving bioresorbability and the other benefits of polymers while exhibiting superior structural properties similar to metal stents. Indeed, the unique features and configurations of the helical slide-and-lock polymer stents disclosed herein enable one of skill to obtain the benefits of polymer and metal stents. Further, the present disclosure also provides for a variety of stents having a composite material structure which can incorporate advantages of various materials.
Lamination Manufacturing Process Embodiments
Stents in accordance with embodiments can be fabricated or created using a wide variety of manufacturing methods, techniques and procedures. These include, but are not limited to, laser processing, milling, stamping, forming, casting, molding, bonding, welding, adhesively fixing, and the like, among others.
In some embodiments, stent features and mechanisms can be created in a generally two dimensional geometry and further processed, for example by utilizing, but not limited to, bonding, lamination and the like, into three dimensional designs and features. In other embodiments, stent features and mechanisms can be directly created into three dimensional shapes, for example by utilizing, but not limited to, processes such as injection molding and the like.
In certain embodiments, stents can be fabricated by using an injection molding process, technique or method. For example, an injection molding process or the like, among others, can be used to form stent rows as integral units. The axially extending rows can then be connected and rolled into a tubular form in the collapsed state.
In some embodiments, a lamination stack can used to fabricate the stent rows by a lamination process in accordance with one embodiment. The axially extending rows can then be connected and rolled into a tubular form in the collapsed state.
The lamination stack, in some embodiments, generally can comprise three sheets or pallets which can have the desired features formed thereon, for example, by laser cutting, etching and the like. The pallets can be aligned and joined, for example, by bonding, welding and the like to form a unit. The excess material (e.g., side and end rails) can be removed to form the stent rows. The pallets can include various circumferentially nesting features such as male and female articulating and/or ratcheting designs to control and limit the diameter in collapsed and fully deployed states.
Metal Stents and Methods of Manufacturing
Possible materials for making the stents in accordance with some embodiments include cobalt chrome, 316 stainless steel, tantalum, titanium, tungsten, gold, platinum, iridium, rhodium and alloys thereof or pyrolytic carbon. In still other alternative embodiments, the stents can be formed of a corrodible material, for instance, a magnesium alloy. Although various stent embodiments have been described as being conventional balloon expandable stents, those skilled in the art will appreciate that stent constructions according to embodiments can also be formed from a variety of other materials to make a stent crush-recoverable. For example, in alternative embodiments, such as self expandable stents, shape memory alloys that allow for such, such as Nitinol and Elastinite®, can be used in accordance with embodiments.
Various methods of forming the individual elements from metal sheets can comprise laser cutting, laser ablation, die-cutting, chemical etching, plasma etching and stamping and water jet cutting of either tube or flat sheet material or other methods known in the art which are capable of producing high-resolution components. The method of manufacture, in some embodiments, depends on the material used to form the stent. Chemical etching provides high-resolution components at relatively low price, particularly in comparison to high cost of competitive product laser cutting. Some methods allow for different front and back etch artwork, which could result in chamfered edges, which can be desirable to help improve engagements of lockouts. Further one can use plasma etching or other methods known in the art which are capable of producing high-resolution and polished components. The embodiments disclosed herein are not limited to the means by which stent or stent elements can be fabricated.
Once the base geometry is achieved, the elements can be assembled numerous ways. Tack-welding, adhesives, mechanical attachment (snap-together and/or weave together), and other art-recognized methods of attachment, can be used to fasten the individual elements. Some methods allow for different front and back etch artwork, which could result in chamfered edges, which can be desirable to help improve engagements of lockouts. In an advantageous method of manufacture, the components of the stent can be heat set at various desired curvatures. For example, the stent can be set to have a diameter equal to that of the deflated balloon, as deployed, at a maximum diameter, or greater than the maximum diameter. In yet another example, elements can be electropolished and then assembled, or electropolished, coated, and then assembled, or assembled and then electropolished.
Polymeric Stents
While metal stents possess certain desirable characteristics, the useful lifespan of a stent is estimated to be in the range of about 6 to 9 months, the time at which in-stent restenosis stabilizes and healing plateaus. In contrast to a metal stent, a bioresorbable stent cannot outlive its usefulness within the vessel. Moreover, a bioresorbable stent could potentially be used to deliver a greater dose of a therapeutic agent, deliver multiple therapeutic agents at the same time or at various times of its life cycle, to treat specific aspects or events of vascular disease. Additionally, a bioresorbable stent can also allow for repeat treatment of the same approximate region of the blood vessel. Accordingly, there remains an important unmet need to develop temporary (i.e., bioresorbable and/or radiopaque) stents, wherein the polymeric materials used to fabricate these stents can have the desirable qualities of metal (e.g., sufficient radial strength and radiopacity, etc.), while circumventing or alleviating the many disadvantages or limitations associated with the use of permanent metal stents.
In some embodiments, the stent can be formed from biocompatible polymers that are bio-resorbable (e.g., bio-erodible or bio-degradable). Bio-resorbable materials can be preferably selected from the group consisting of any hydrolytically degradable and/or enzymatically degradable biomaterial. Examples of suitable degradable polymers include, but are not limited to, polyhydroxybutyrate/polyhydroxyvalerate copolymers (PHV/PHB), polyesteramides, polylactic acid, polyglycolic acid, lactone based polymers, polycaprolactone, poly(propylene fumarate-co-ethylene glycol) copolymer (aka fumarate anhydrides), polyamides, polyanhydride esters, polyanhydrides, polylactic acid/polyglycolic acid with a calcium phosphate glass, polyorthesters, silk-elastin polymers, polyphosphazenes, copolymers of polylactic acid and polyglycolic acid and polycaprolactone, aliphatic polyurethanes, polyhydroxy acids, polyether esters, polyesters, polydepsidpetides, polysaccharides, polyhydroxyalkanoates, and copolymers thereof. For additional information, see U.S. Pat. Nos. 4,980,449, 5,140,094, and 5,264,537, the disclosures of each of which are incorporated by reference herein.
In one mode, the degradable materials can be selected from the group consisting of poly(glycolide-trimethylene carbonate), poly(alkylene oxalates), polyaspartimic acid, polyglutarunic acid polymer, poly-p-dioxanone, poly-.beta.-dioxanone, asymmetrically 3,6-substituted poly-1,4-dioxane-2,5-diones, polyalkyl-2-cyanoacrylates, polydepsipeptides (glycine-DL-lactide copolymer), polydihydropyranes, polyalkyl-2-cyanoacrylates, poly-.beta.-maleic acid (PMLA), polyalkanotes and poly-.beta.-alkanoic acids. There are many other degradable materials known in the art. (See e.g., Biomaterials Science: An Introduction to Materials in Medicine (29 Jul., 2004) Ratner, Hoffman, Schoen, and Lemons; and Atala, A., Mooney, D. Synthetic Biodegradable Polymer Scaffolds. 1997 Birkhauser, Boston; each of which are incorporated herein by reference).
Further still, in another embodiment, the stents can be formed of a polycarbonate material, such as, for example, tyrosine-derived polycarbonates, tyrosine-derived polyarylates, tyrosine-derived diphenol monomers, iodinated and/or brominated tyrosine-derived polycarbonates, iodinated and/or brominated tyrosine-derived polyarylates. For additional information, see U.S. Pat. Nos. 5,099,060, 5,198,507, 5,587,507, which was resiussed in U.S. Pat. Nos. RE37,160, 5,670,602, which was resiussed in U.S. Pat. Nos. RE37,795, 5,658,995, 6,048,521, 6,120,491, 6,319,492, 6,475,477, 5,317,077, and 5,216,115, and U.S. application Ser. No. 09/350,423, the disclosures of each of which are incorporated by reference herein. In yet another embodiment, the polymer can be any of the biocompatible, bioabsorbable, radiopaque polymers disclosed in: U.S. Patent Application Nos. 60/852,513, 60/852,471, 60/601,526, 60/586,796, 60/866,281, 60/885,600, Ser. Nos. 10/952,202, 11/176,638, 11/335,771, 11/200,656, 11/024,355, 10/691,749, 11/418,943, and 11/873,362; U.S. Patent Publication No. US26115449A1; U.S. Pat. Nos. 6,852,308 and 7,056,493; and PCT Application Nos. PCT/US2005/024289, PCT/US2005/028228, PCT/US07/01011, and PCT/US07/81571, the disclosures of each of which are incorporated herein by reference thereto.
Natural polymers (biopolymers) include any protein or peptide. Biopolymers can be selected from the group consisting of alginate, cellulose and ester, chitosan, collagen, dextran, elastin, fibrin, gelatin, hyaluronic acid, hydroxyapatite, spider silk, cotton, other polypeptides and proteins, and any combinations thereof.
In yet another alternative embodiment, shape-shifting polymers can be used to fabricate stents constructed according to embodiments. Suitable shape-shifting polymers can be selected from the group consisting of polyhydroxy acids, polyorthoesters, polyether esters, polyesters, polyamides, polyesteramides, polydepsidpetides, aliphatic polyurethanes, polysaccharides, polyhydroxyalkanoates, and copolymers thereof. For addition disclosure on bio-degradable shape-shifting polymers, see U.S. Pat. Nos. 6,160,084 and 6,284,862, the disclosures of each of which are incorporated by reference herein. For additional disclosure on shape memory polymers, see U.S. Pat. Nos. 6,388,043 and 6,720,402, the disclosures of each of which are incorporated by reference herein. Further the transition temperature can be set such that the stent can be in a collapsed condition at a normal body temperature. However, with the application of heat during stent placement and delivery, such as via a hot balloon catheter or a hot liquid (e.g., saline) perfusion system, the stent can expand to assume its final diameter in the body lumen. When a thermal memory material is used, it can provide a crush-recoverable structure.
Further still, stents can be formed from biocompatible polymers that are biostable (e.g., non-degrading and non-erodible). Examples of suitable non-degrading materials include, but are not limited to, polyurethane, Delrin, high density polyethylene, polypropylene, and poly(dimethyl siloxane).
In some embodiments, the layers can comprise or contain any example of thermoplastics, such as the following, among others: fluorinated ethylene-propylene, poly(2-hydroxyethyl methacrylate) (aka pHEMA), poly(ethylene terephthalate) fiber (aka Dacron®) or film (Mylar®), poly(methyl methacrylate) (aka PMMA), Poly(tetrafluoroethylene) (aka PTFE and ePTFE and Gore-Tex®), poly(vinyl chloride), polyacrylates and polyacrylonitrile (PAN), polyamides (aka Nylon), polycarbonates and polycarbonate urethanes, polyethylene and poly(ethylene-co-vinyl acetate), polypropylene, polystyrene, polysulphone, polyurethane and polyetherurethane elastomers such as Pellethane® and Estane®, Silicone rubbers, Siloxane, polydimethylsiloxane (aka PDMS), Silastic®, Siliconized Polyurethane.
Finally, the polymer(s) utilized in embodiments of the stent can be fabricated according to any variety of processes, such as those discussed in U.S. Patent Application Nos. 60/852,471 and 60/852,513, and U.S. Pat. Nos. 5,194,570, 5,242,997, 6,359,102, 6,620,356, and 6,916,868, the disclosures of each of which are incorporated by reference herein.
Methods of Manufacturing and Assembling Polymeric Stents
Where plastic and/or degradable materials are used, the elements can be made using laser ablation with a screen, stencil or mask; solvent casting; forming by stamping, embossing, compression molding, centripetal spin casting and molding; extrusion and cutting, three-dimensional rapid prototyping using solid free-form fabrication technology, stereolithography, selective laser sintering, or the like; etching techniques comprising plasma etching; textile manufacturing methods comprising felting, knitting, or weaving; molding techniques comprising fused deposition modeling, injection molding, room temperature vulcanized molding, or silicone rubber molding; casting techniques comprising casting with solvents, direct shell production casting, investment casting, pressure die casting, resin injection, resin processing electroforming, or injection molding or reaction injection molding. Certain embodiments with the disclosed polymers can be shaped into stents via combinations of two or more thereof, and the like.
Such processes can further include two-dimensional methods of fabrication such as cutting extruded sheets of polymer, via laser cutting, etching, mechanical cutting, or other methods, and assembling the resulting cut portions into stents, or similar methods of three-dimensional fabrication of devices from solid forms. For additional information, see U.S. patent application Ser. No. 10/655,338, the disclosure of which is incorporated by reference herein.
Stents of some of the embodiments can be manufactured with elements prepared in full stent lengths or in partial lengths of which two or more are then connected or attached. If using partial lengths, two or more can be connected or attached to comprise a full length stent. In this arrangement the parts can be assembled to give rise to a central opening. The assembled full or partial length parts and/or modules can be assembled by inter-weaving them in various states, from a collapsed state, to a partially expanded state, to an expanded state.
Further, elements can be connected or attached by solvent or thermal bonding, or by mechanical attachment. If bonding, advantageous methods of bonding comprise the use of ultrasonic radiofrequency or other thermal methods, and by solvents or adhesives or ultraviolet curing processes or photoreactive processes. The elements can be rolled by thermal forming, cold forming, solvent weakening forming and evaporation, or by preforming parts before linking.
Rolling of the flat series of module(s) to form a tubular member can be accomplished by any means known in the art, including rolling between two plates, which can be each padded on the side in contact with the stent elements. One plate can be held immobile and the other can move laterally with respect to the other. Thus, the stent elements sandwiched between the plates can be rolled about a mandrel by the movement of the plates relative to one another. Alternatively, 3-way spindle methods known in the art can also be used to roll the tubular member. Other rolling methods that can be used in accordance with certain embodiments include those used for “jelly-roll” designs, as disclosed for example, in U.S. Pat. Nos. 5,421,955, 5,441,515, 5,618,299, 5,443,500, 5,649,977, 5,643,314 and 5,735,872, the disclosures of each of which are incorporated herein in their entireties by reference thereto.
The construction of the slide-and-lock stents in these fashions can provide a great deal of benefit over the prior art. The construction of the locking mechanism can be largely material-independent. This allows the structure of the stent to comprise high strength materials, not possible with designs that require deformation of the material to complete the locking mechanism. The incorporation of these materials will allow the thickness required of the material to decrease, while retaining the strength characteristics of thicker stents. In some embodiments, the frequency of catches, stops or teeth present on selected circumferential elements can prevent unnecessary recoil of the stent subsequent to expansion.
Radiopacity
Traditional methods for adding radiopacity to a medical product include the use of metal bands, inserts and/or markers, electrochemical deposition (i.e., electroplating), or coatings. The addition of radiopacifiers (i.e., radiopaque materials) to facilitate tracking and positioning of the stent could be accommodated by adding such an element in any fabrication method, by absorbing into or spraying onto the surface of part or all of the device. The degree of radiopacity contrast can be altered by element content.
For plastics and coatings, radiopacity can be imparted by use of monomers or polymers comprising iodine or other radiopaque elements, i.e., inherently radiopaque materials. Common radiopaque materials include barium sulfate, bismuth subcarbonate, and zirconium dioxide. Other radiopaque elements include: cadmium, tungsten, gold, tantalum, bismuth, platinum, iridium, and rhodium. In some embodiments, a halogen such as iodine and/or bromine can be employed for its radiopacity and antimicrobial properties.
Multi-Material Vascular Prosthesis
In still other alternative embodiments, various materials (e.g., metals, polymers, ceramics, and therapeutic agents) can be used to fabricate stent embodiments. The embodiments can comprise: 1) differentially layered materials (through stacking in the vertical or radial axis) to create a stack of materials (materials can be stacked in any configuration, e.g., parallel, staggered, etc.); 2) spatially localized materials which can vary along the long axis and/or thickness of the stent body; 3) materials that are mixed or fused to create a composite stent body (e.g., whereby a therapeutic agent(s) is within the stent body with a polymer); 4) embodiments whereby a material can be laminated (or coated) on the surface of the stent body (see Stent Surface Coatings with Functional Properties as well as see Therapeutic Agents Delivered by Stents); and, 5) stents comprised of 2 or more parts where at least one part can be materially distinct from a second part, or any combination thereof.
The fashioning of a slide-and-lock multi-material stent can have between two or more materials. Thickness of each material can vary relative to other materials. This approach as needed or desired allows an overall structural member to be built with each material having one or more functions contributing towards enabling prosthesis function which can include, but is not limited to: 1) enabling mechanical properties for stent performance as defined by ultimate tensile strength, yield strength, Young's modulus, elongation at yield, elongation at break, and Poisson's ratio; 2) enabling the thickness of the substrate, geometrical shape (e.g., bifurcated, variable surface coverage); 3) enabling chemical properties of the material that bear relevance to the materials performance and physical state such as rate of degradation and resorption (which can impact therapeutic delivery), glass transition temperature, melting temperature, molecular weight; 4) enabling radiopacity or other forms of visibility and detection; 5) enabling radiation emission; 6) enabling delivery of a therapeutic agent (see Therapeutic Agents Delivered by Stents); and 7) enabling stent retention and/or other functional properties (see Stent Surface Coatings with Functional Properties).
In some embodiments, the materials can comprise load-bearing properties, elastomeric properties, mechanical strength that can be specific to a direction or orientation e.g., parallel to another material and/or to the long axis of the stent, or perpendicular or uniform strength to another material and/or stent. The materials can comprise stiffeners, such as the following, boron or carbon fibers, pyrolytic carbon. Further, stents can be comprised of at least one re-enforcement such a fibers, nanoparticles or the like.
In another implementation of some embodiments, the stent can be made, at least in part, from a polymeric material, which can be degradable. The motivation for using a degradable stent can be that the mechanical support of a stent can only be necessary for several weeks. In some embodiments, bioresorbable materials with varying rates of resorption can be employed. For additional information, see U.S. patent application Ser. Nos. 10/952,202 and 60/601,526, the disclosures of each of which are incorporated by reference herein. Degradable polymeric stent materials can be particularly useful if it also controls restenosis and thrombosis by delivering pharmacologic agents. Degradable materials can be well suited for therapeutic delivery (see Therapeutic Agents Delivered by Stents).
In some embodiments, the materials can comprise or contain any class of degradable polymer as previously defined. Along with variation in the time of degradation and/or resorption the degradable polymer can have other qualities that are desirable. For example, in some embodiments the materials can comprise or contain any example of natural polymers (biopolymers) and/or those that degrade by hydrolytic and/or enzymatic action. In some embodiments, the material can comprise or contain any example of hydrogels that can or cannot be thermally reversible hydrogels, or any example of a light or energy curable material, or magnetically stimulateable (responding) material. Each of these responses can provide for a specific functionality.
In some embodiments, the materials can comprise or be made from or with constituents which can have some radiopaque material alternatively, a clinically visible material which can be visible by x-ray, fluoroscopy, ultrasound, MRI, or Imatron Electron Beam Tomography (EBT).
In some embodiments, one or more of the materials can emit predetermined or prescribed levels of therapeutic radiation. In an embodiment, the material can be charged with beta radiation. In another embodiment, the material can be charged with Gamma radiation. In yet another embodiment, the material can be charged with a combination of both Beta and Gamma radiation. Stent radioisotopes that can be used include, but are not limited to, 103Pd and 32P (phosphorus-32) and two neutron-activated examples, 65Cu and 87Rb2O, (90)Sr, tungsten-188 (188).
In some embodiments, one or more of the materials can comprise or contain a therapeutic agent. The therapeutic agents can have unique, delivery kinetics, mode of action, dose, half-life, purpose, et cetera. In some embodiments, one or more of the materials comprise an agent which provides a mode and site of action for therapy for example by a mode of action in the extracellular space, cell membrane, cytoplasm, nucleus and/or other intracellular organelle. Additionally an agent that serves as a chemoattractant for specific cell types to influence tissue formation and cellular responses for example host-biomaterial interactions, including anti-cancer effects. In some embodiments, one or more of the materials deliver cells in any form or state of development or origin. These could for example be encapsulated in a degradable microsphere, or mixed directly with polymer, or hydrogel and serve as vehicle for pharmaceutical delivery. Living cells could be used to continuously deliver pharmaceutical type molecules, for instance, cytokines and growth factors. Nonliving cells can serve as a limited release system. For additional concepts of therapeutic delivery, see the section entitled: Therapeutic Agents Delivered by Stents.
Therapeutic Agents Delivered by Stents
In another implementation, the stent further can comprise an amount of a therapeutic agent (as previously defined for a pharmaceutical agent and/or a biologic agent) sufficient to exert a selected therapeutic effect. The material of at least a portion of the stent itself can comprise at least one therapeutic agent, or at least one therapeutic agent can be added to the stent in a subsequent forming process or step. In some embodiments of the stent (e.g., polymer stents and multi-material stents), the therapeutic agent can be contained within the stent as the agent is blended with the polymer or admixed by other means known to those skilled in the art.
For example, one or more therapeutic agents can be delivered through a multi-material vascular prosthesis. In some embodiments, the entire stent can be formed from materials comprising one or more therapeutic agents. In other embodiments, portions of the stent, such as individual components thereof, can comprise materials comprising one or more therapeutic agents. In such embodiments, it is contemplated that the therapeutic agent(s) can be released as the stent material degrades.
For example, the therapeutic agent can be embedded or impregnated into the film by means of a combination of solvent casting and thermal pressing. In such a method, the film can be formed from a mixture of the polymer and the therapeutic agent (20% solids polymer, for example poly(90% DTE-co-10% DT carbonate), which can be made with 1% rapamycin in dichloromethane). Once this mixture is prepared, the film can be cast using a doctor blade. Alternatively, the film can be formed by using a mechanical reverse roll coater or other solvent-based film caster. Once the film is cast, the solvent can be evaporated off using a vacuum oven, e.g., for a period of time and at a temperature suitable for the polymer and drug, such as at 40° C. for at least 20 hours. Once the film is dried, it can be thermally pressed, e.g., at a temperature of 100° C. between two heated platens of a hydraulic press. This allows the potency of the drug to be retained.
In addition, the therapeutic agent can be embedded or impregnated into the film using only a solvent or by spin casting. Once a therapeutic agent is selected, one needs to determine if the solvent is compatible with the agent and the polymer chosen. The objective is to prepare a suitable sprayable suspension. Additionally, the stability of the drug can be measured such that the therapeutic agent can remain active while in the coating as well under physiological conditions once released from the film. This can be determined by those skilled in the art who conduct standard in vitro elution studies (see Dhanikula et al., Development and Characterization of Biodegradable Chitosan Films for Local Delivery of Paclitaxel, The AAPS Journal, 6 (3) Article 27 (2004), http://www.aapsj.org/view.asp?art=aapsj060327; and Kothwala et al., Paclitaxel Drug Delivery from Cardiovascular Stent, Trends in Biomaterials Artificial Organs, Vol. 19(2), 88-92 (2006), http://medind.nic.in/taa/t06/i1/taat06i1p88.pdf) of agent embedded films and through the use of analytical methods such as HPLC methods (see Dhanikula et al., Development and Characterization of Biodegradable Chitosan Films for Local Delivery of Paclitaxel; and Kothwala et al., Paclitaxel Drug Delivery from Cardiovascular Stent) to detect the purity of the drug.
In other embodiments, at least one therapeutic agent can be added to the stent and/or its components after the formation of the stent and/or its components. For example, at least one therapeutic agent can be added to individual stent components, through a coating process or otherwise. The addition of at least one therapeutic agent can occur before or after cutting or lasing of the stent components. In another example, at least one therapeutic agent can also be added to at least a portion of the stent after partial or full assembly thereof, through a coating process or otherwise. In some embodiments of the stent, the therapeutic agent can be delivered from a polymer coating on the stent surface. In other embodiments of the stent, a therapeutic agent can be localized in or around a specific structural aspect of the device.
For example, the therapeutic agent can be delivered from a polymer coating on the stent surface. Thus, the stent can be made by applying the therapeutic agent to a stent component before the stent is assembled or formed. In this regard, the stent component can be created from a polymer sheet, such as a flat polymer film. Thus, at least one stent component can be separated from a remainder or excess portion of the film either before or after the therapeutic agent has been applied to the stent component and/or film. After the therapeutic agent is applied and the stent component is separated from the film, the stent component can be assembled (and in some embodiments, with other stent components) to form a stent therefrom.
In an exemplary embodiment, the stent can be prepared with the following preparation method. The stent can be initially prepared by creating a pattern of a stent component on a flat polymer film. The creation of the pattern on the film can occur before or after application of a therapeutic agent thereto, as discussed below. The pattern of the stent component can be created on the film such that the stent component can be detached from the film when desired. In some embodiments, the pattern can be created using a laser to lase the pattern onto the film. Additionally, the lased pattern can be of any given stent component design, such as that used in a slide and lock stent design. After the pattern is created on the film, the entire film can be cleaned. For example, if the therapeutic agent has not yet been applied to the film, the entire lased film can be immersed into a cleaning solution that is compatible with the specific type of polymer from which the film is made. The cleaned film can then be dried, for example, by being blown and oven dried.
A coating formulation can be prepared by dissolving or dispersing the polymer and the therapeutic agent(s) of choice and solvent(s) or other compatible excipient(s) using a calculated amount of each component to achieve the desired concentration. The coating formulation can then be applied to the lased polymer film using one or more coating methods. For example, the film may be coated by means of spraying, dipping, or other coating methods. Additionally cross-linking reagents may also be used to prepare a coating.
In a spraying coating method, the lased polymer films can be coated with the coating formulation by first mounting the cleaned dried films into a spray apparatus. The coating formulation can then be sprayed onto the film, and the film can be rotated 180 degrees such that the other side can be coated if desired. This method can allow for coating of one or both sides of the stent component(s). This method can also allow one to apply different therapeutic agents per side of the lased film and/or stent component and to selectively coat regions thereof. The method can further allow one to coat multiple drugs per film and/or stent component. Alternative coating methods can allow for other similar benefits.
For example, a therapeutic agent can be coated onto a film or stent component as in the following illustration. First, the therapeutic agent in this example is a Polymer-Paclitaxel Formulation, such as a 0.5% [25% Paclitaxel/75% Poly(86.75% I2DTE-co-10% I2DT-co-3.25% PEG2000 carbonate)] in tetrahydrofuran (THF), which can be prepared using an analytical balance. In order to do so, one must first weigh 0.0150 g of Paclitaxel into a tared vial. Then weigh 0.0450 g of polymer into another vial. Next, weigh 11.940 g of THF into each vial. Shake the vials on a laboratory shaker, such as a Roto-genie, for at least one hour. In this example, coating can be achieved using a spray gun apparatus, such as an air brush (see Westedt, U., Biodegradable Paclitaxel-loaded Nanoparticles and Stent Coatings as Local Delivery Systems for the Prevention of Restenosis—Dissertation, Marburg/Lahn (2004), http://deposit.ddb.de/cgi-bin/dokserv?idn=972868100&dokvar=d1&dokext=pdf&filename=972868100.pdf; and Berger, H. L. Using Ultrasonic Spray Nozzles to Coat Drug-Eluting Stents, Medical Device Technology (2006), http://www.devicelink.com/mdt/archive/06/11/004.html). Typically, the spray gun apparatus should first be cleaned with THF. In order to do so, a syringe can be filled with at least 10 ml of THF. The syringe can then be attached to a spray line attached to the spray gun. Gradually, the 10 ml of THF can be pushed from the syringe into the spray gun without N2 pressure. This can be repeated as necessary to ensure that the line is washed clean. The syringe pump can then be set up with the syringe containing the Polymer-Paclitaxel Formulation.
Next, a film, which can be either lased or unlased, can be placed into a hooded environment and mounted or clipped into a holder. If necessary, the surfaces of the film can be cleaned of lint and dust using a pure air or gas source or equivalent. For consistent coating quality, the film can be programmed to move at a set rate (distance and speed) relative to a spray stream by integrating the film holder apparatus with a motion control system. Manual coating without the motion control can also be used to achieve a coating. The spray gun can also be set to direct the spray to only a given location to control coating distribution.
In some embodiments, to coat both sides of the film uniformly, the spray cycle can start with the spray hitting at the bottom corner of the film, and the motion control should move the film incrementally as it traverses back and forth in front of the spray nozzle. The system can then move the film back to the start position so the spray is directed at the bottom. The film holder can be turned 180 degrees and the cycle can be repeated to coat the second side. After coating, the film holder can be removed with the film and the film can be dried in a vacuum oven at a temperature suitable for the drug and polymer, e.g., 25°±5° C. for at least 20 hours.
Other methods and teachings related to impregnation or coating processes are found in the following references, the entirety of each of which is hereby incorporated by reference herein: Westedt, U., Biodegradable Paclitaxel-loaded Nanoparticles and Stent Coatings as Local Delivery Systems for the Prevention of Restenosis—Dissertation, Marburg/Lahn (2004), http://deposit.ddb.de/cgi-bin/dokserv?idn=972868100&dokvar=d1&dokext=pdf&filename=972868100.pdf; Berger, H. L. Using Ultrasonic Spray Nozzles to Coat Drug-Eluting Stents, Medical Device Technology (2006), http://www.devicelink.com/mdt/archive/06/11/004.html; Dhanikula et al., Development and Characterization of Biodegradable Chitosan Films for Local Delivery of Paclitaxel, The AAPS Journal, 6 (3) Article 27 (2004), http://www.aapsj.org/view.asp?art=aapsj060327; and Kothwala et al., Paclitaxel Drug Delivery from Cardiovascular Stent, Trends in Biomaterials & Artificial Organs, Vol. 19(2), 88-92 (2006), http://medind.nic.in/taa/t06/i1/taat06i1p88.pdf.
After the film is coated using a given coating method, the film can be given time to dry. Once dried, the lased, coated stent component(s) can be separated from the remainder of the film. Care should be taken to not disturb the surfaces of the coated stent component(s) when being detached from the film and assembled or knitted together to form a three-dimensional cylindrical stent.
In another variation the therapeutic agent can be delivered by means of a non-polymer coating. In other embodiments of the stent, the therapeutic agent can be delivered from at least one region or one surface of the stent. The therapeutic agent can be chemically bonded to the polymer or carrier used for delivery of the therapeutic from at least one portion of the stent and/or the therapeutic can be chemically bonded to the polymer that can comprise at least one portion of the stent body. In some embodiments, a polymer can be used as a component of the coating formulation. Accordingly, the coating can essentially bond directly to a clean lased film and/or stent component, which can also be comprised of a polymer. Such an embodiment of the method can provide for a seamless interface between the coating and the lased film and/or stent component. Further, in another embodiment, more than one therapeutic agent can be delivered.
The amount of the therapeutic agent can be preferably sufficient to inhibit restenosis or thrombosis or to affect some other state of the stented tissue, for instance, heal a vulnerable plaque, and/or prevent rupture or stimulate endothelialization or limit other cell types from proliferating and from producing and depositing extracellular matrix molecules. The agent(s) can be selected from the group consisting of antiproliferative agents, anti-inflammatory, anti-matrix metalloproteinase, and lipid lowering, cholesterol modifying, anti-thrombotic and antiplatelet agents, in accordance with some embodiments. For vascular stent applications, some anti-proliferative agents that improve vascular patency include without limitation paclitaxel, Rapamycin, ABT-578, Biolimus A9, everolimus, dexamethasone, nitric oxide modulating molecules for endothelial function, tacrolimus, estradiol, mycophenolic acid, C6-ceramide, actinomycin-D and epothilones, and derivatives and analogs of each.
Some agents act as an antiplatelet agent, antithrombin agent, compounds to address other pathologic events and/or vascular diseases. Various therapeutic agents can be classified in terms of their sites of action in the host: agents that exert their actions extracellularly or at specific membrane receptor sites, those that act on the plasma membrane, within the cytoplasm, and/or the nucleus.
In addition to the aforementioned, therapeutic agents can include other pharmaceutical and/or biologic agents intended for purposes of treating body lumens other than arteries and/or veins). Therapeutic agents can be specific for treating nonvascular body lumens such as digestive lumens (e.g., gastrointestinal, duodenum and esophagus, biliary ducts), respiratory lumens (e.g., tracheal and bronchial), and urinary lumens (e.g., urethra). Additionally such embodiments can be useful in lumens of other body systems such as the reproductive, endocrine, hematopoietic and/or the integumentary, musculoskeletal/orthopedic and nervous systems (including auditory and ophthalmic applications); and finally, stent embodiments with therapeutic agents can be useful for expanding an obstructed lumen and for inducing an obstruction (e.g., as in the case of aneurysms).
Therapeutic release can occur by controlled release mechanisms, diffusion, interaction with another agent(s) delivered by intravenous injection, aerosolization, or orally. Release can also occur by application of a magnetic field, an electrical field, or use of ultrasound.
Stent Surface Coatings with Functional Properties
In addition to stents that can deliver a therapeutic agent, for instance delivery of a biological polymer on the stent such as a repellant phosphorylcholine, the stent can be coated with other bioresorbable polymers predetermined to promote biological responses in the body lumen desired for certain clinical effectiveness. Further the coating can be used to mask (temporarily or permanently) the surface properties of the polymer used to comprise the stent embodiment. The coating can be selected from the broad class of any biocompatible bioresorbable polymer which can include any one or combination of halogenated and/or non-halogenated which can or cannot comprise any poly(alkylene glycol). These polymers can include compositional variations including homopolymers and heteropolymers, stereoisomers and/or a blend of such polymers. These polymers can include for example, but are not limited to, polycarbonates, polyarylates, poly(ester amides), poly(amide carbonates), trimethylene carbonate, polycaprolactone, polydioxane, polyhydroxybutyrate, poly-hydroxyvalerate, polyglycolide, polylactides and stereoisomers and copolymers thereof, such as glycolide/lactide copolymers. In an embodiment, the stent can be coated with a polymer that exhibits a negative charge that repels the negatively charged red blood cells' outer membranes thereby reducing the risk of clot formation. In another embodiment, the stent can be coated with a polymer that exhibits an affinity for cells, (e.g., endothelial cells) to promote healing. In yet another embodiment, the stent can be coated with a polymer that repels the attachment and/or proliferation of specific cells, for instance arterial fibroblasts and/or smooth muscle cells in order to lessen restenosis and/or inflammatory cells such as macrophages.
Described above are embodiments that can be modified with a coating to achieve functional properties that support biological responses. Such coatings or compositions of material with a therapeutic agent can be formed on stents or applied in the process of making a stent body via techniques such as dipping, spray coating, cross-linking combinations thereof, and the like, as mentioned and described above. Such coatings or compositions of material can also serve purpose other than delivering a therapeutic, such as to enhance stent retention on a balloon when the coating is placed intraluminally on the stent body and/or placed over the entire device after the stent is mounted on the balloon system to keep the stent in a collapsed formation. Other purposes can be envisioned by those skilled in the art when using any polymer material.
In accordance with an aspect of certain embodiments, a stent would have a coating applied that can alter the physical characteristics of the stent, such as to provide specific mechanical properties to the stent. The properties can include inter alia thickness, tensile strength, glass transition temperature, and surface finish. The coating can be preferably applied prior to final crimping or application of the stent to the catheter. The stent can then be applied to the catheter and the system can have either heat or pressure or both applied in a compressive manner. In the process, the coating can form frangible bonds with both the catheter and the other stent surfaces. The bonds would enable a reliable method of creating stent retention and of holding the stent crossing profile over time. The bonds would break upon the balloon deployment pressures. The coating would be a lower Tg than the substrate to ensure no changes in the substrate.
Stent Deployment
The distal sheath portion can be attached to the tip body of the catheter. A pressure or frictional fit may provide sufficient stability to the sheath distal portion during passage of the catheter/stent assembly to a deployment site through the lumen. For example, the distal end of the sheath 1810 is firmly heat shrunk to the tip body. In certain embodiments, the distal sheath tip may be fit to a tapered portion of the tip body so as to urge the sheath material to elastically expand as the sheath is initially retracted. Similarly, an elastic band may be included overlapping the distal end of the sheath. Further, the distal sheath portion can comprise a perforation line at a distal end thereof in order to allow the distal sheath portion to be separated from the tip body during deployment. Alternatively, the distal sheath portion can be attached to the tip body with a breakable bond. In this regard, as shown in
Finally,
As discussed above, embodiments disclosed herein can utilize a catheter having an expandable member, preferably an inflatable balloon, such as an angioplasty balloon, disposed along a distal end portion. An example of a balloon catheter for use with a stent is described in U.S. Pat. No. 4,733,665 to Palmaz, the disclosure of which is incorporated by reference herein. A stent on a catheter can be commonly collectively referred to as a stent system. Catheters include but are not limited to over-the-wire catheters, coaxial rapid-exchange designs and the Medtronic Zipper Technology that is a new delivery platform. Such catheters can include for instance those described in Bonzel U.S. Pat. Nos. 4,762,129 and 5,232,445 and by Yock U.S. Pat. Nos. 4,748,982, 5,496,346, 5,626,600, 5,040,548, 5,061,273, 5,350,395, 5,451,233 and 5,749,888. Additionally, catheters can include for instance those as described in U.S. Pat. Nos. 4,762,129, 5,092,877, 5,108,416, 5,197,978, 5,232,445, 5,300,085, 5,445,646, 5,496,275, 5,545,135, 5,545,138, 5,549,556, 5,755,708, 5,769,868, 5,800,393, 5,836,965, 5,989,280, 6,019,785, 6,036,715, 5,242,399, 5,158,548, and 6,007,545. The disclosures of each of the above-cited patents are incorporated herein in their entirety by reference thereto.
Catheters can be specialized with highly compliant polymers and for various purposes such as to produce an ultrasound effect, electric field, magnetic field, light and/or temperature effect. Heating catheters can include for example those described in U.S. Pat. Nos. 5,151,100, 5,230,349, 6,447,508, and 6,562,021 as well as WO9014046A1. Infrared light emitting catheters can include for example those described in U.S. Pat. Nos. 5,910,816 and 5,423,321. The disclosures of each of the above-cited patents and patent publications are incorporated herein in their entirety by reference thereto.
An expandable member, such as an inflatable balloon, can be preferably used to deploy the stent at the treatment site. As the balloon is expanded, the radial force of the balloon overcomes the initial resistance of the constraining mechanism, thereby allowing the stent to expand.
The stent of embodiments described herein can be adapted for deployment using conventional methods known in the art and employing percutaneous transluminal catheter devices. This can include deployment in a body lumen by means of a balloon expandable design whereby expansion can be driven by the balloon expanding. Alternatively, the stent can be mounted onto a catheter that holds the stent as it is delivered through the body lumen and then releases the stent and allows it to self-expand into contact with the body lumen. The restraining means can comprise a removable/retractable sheath, a sheath that remains with the stent, and/or a mechanical aspect of the stent design.
The use of a sheath can be beneficial for several reasons. The sheath can be used to control delivery and deployment of the stent. For example, the sheath can be used to reduce and/or eliminate “negative aspects” of certain configurations of the stent, such as certain “slide-and-lock” designs; however, the sheath can also be used to make other designs possible.
The stent is composed of a polymeric sheath, most likely made out of a biodegradable material, which has sufficient elasticity to stretch during deployment of the stent and not break. The polymer also may include radiopaque, biodegradable polymers. The sheath is tubular in nature, and may include cutouts patterns to provide lower deployment pressures, increase flexibility and allow access to side branches of the artery. Ideally the sheath is very thin, such as less than 0.002″, and ideality 0.0005″ thick. The material need not have a high yield strength, but should have an elongation at break of greater than 150%, and possibly as much as 300%.
The sheath can be made from a variety of materials, such as polymers, natural materials, etc., which can include biodegradable materials. Further, the polymer can be radiopaque, biocompatible, and/or biodegradable, as discussed herein. In some embodiments, the sheath can be made from a resorbable material, and the sheath and stent can degrade together, thus leaving a healed, unencumbered vessel. The sheath material can be selected such that during stent expansion, the sheath can deform and expand plastically with the stent. In some embodiments, the sheath can have sufficient elasticity to stretch during deployment of the stent without breaking. Although high yield strength may not be required, the material preferably provides the sheath with an elongation at break of greater than 150%, and possibly as much as 300%.
Further, the sheath can be very thin, such as less than about 0.002 inches thick, but can preferably be about 0.0005 inches thick; other thicknesses can also be used in accordance with the teachings herein. Thus, the sheath can be beneficially used to eliminate or reduce negative aspects of certain stent designs, such as may be encountered during stent deployment, as well as to make other stent designs possible.
From the foregoing description, it will be appreciated that a novel approach for expanding a lumen has been disclosed. While several components, techniques and aspects have been described with a certain degree of particularity, it is manifest that many changes can be made in the specific designs, constructions and methodology herein above described without departing from the spirit and scope of this disclosure.
The methods which are described and illustrated herein are not limited to the sequence of acts described, nor are they necessarily limited to the practice of all of the acts set forth. Other sequences of acts, or less than all of the acts, or simultaneous occurrence of the acts, can be utilized in practicing embodiments.
While a number of embodiments and variations thereof have been described in detail, other modifications and methods of using and medical applications for the same will be apparent to those of skill in the art. Accordingly, it should be understood that various applications, modifications, materials, and substitutions can be made of equivalents without departing from the spirit of the inventions or the scope of the claims.
Various modifications and applications of the embodiments can occur to those who are skilled in the art, without departing from the true spirit or scope of the embodiments and inventions disclosed herein. It should be understood that the present inventions are not limited to the embodiments set forth herein for purposes of exemplification, but is to be defined only by a fair reading of the claims, including the full range of equivalency to which each element thereof is entitled.
For example, a uniform expandable stent can be provided that comprises a tubular member having a circumference which is expandable between at least a first collapsed diameter and at least a second expanded diameter, said tubular member comprising; at least two slidably engaged radial elements collectively defining the circumference of said tubular member, said at least two slidably engaged radial elements individually comprising; a flexible backbone, a first elongate member and a second elongate member, wherein said first elongate member and said second elongate member are substantially commonly oriented with respect to said flexible backbone, wherein said second elongate member is at least partially axially or circumferentially-offset with respect to said first elongate member.
In some embodiments, at least one of said first elongate member and said second elongate member can be a paired elongate member. In other embodiments, at least one of said first elongate member or said second elongate member can be an annular elongate member. In yet other embodiments, said annular elongate member can further comprise a substantially captive slot. Further, said flexible backbone can be configured to substantially coil about said tubular member.
Moreover, said flexible backbone can be configured to stair-step in a helical orientation about said tubular member. In this regard, said flexible backbone can further comprise at least one substantially captive slot. Additionally, said substantially captive slot can further comprise a locking member. Furthermore, said locking member can further comprise at least one of a tooth, a deflectable tooth, or a stop. In yet other embodiments, at least one of said elongate members can comprise at least one conjugate locking member, wherein said locking member and said conjugate locking member define an engagement means, said engagement means being adapted to allow substantially unidirectional slidable movement. Additionally, at least one of said elongate members can further comprise a first axial side and a second axial side, wherein at least one of said first axial side and said second axial side comprises at least one conjugate locking member. Finally, said at least one conjugate locking member is one of a tooth, a deflectable tooth, or a stop.
Some of the references cited herein are listed below, the entirety of each one of which is hereby incorporated by reference herein:
This application is a continuation of U.S. application Ser. No. 13/113,894, filed on May 23, 2011, which is a continuation of U.S. application Ser. No. 12/577,018, filed on Oct. 9, 2009, which claims the benefit of U.S. Provisional Application Nos. 61/104,683, filed Oct. 10, 2008, and 61/231,972, filed Aug. 6, 2009, the entireties of which are incorporated herein by reference.
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| Number | Date | Country | |
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