Patent Application
20120253381
1. Field of the Invention
The invention relates to implants within body vessels and more particularly to occlusive devices including embolic coils having resistance to stretching.
2. Description of the Related Art
Vascular disorders and defects such as aneurysms and other arterio-venous malformations are especially difficult to treat when located near critical tissues or where ready access to a malformation is not available. Both difficulty factors apply especially to cranial aneurysms. Due to the sensitive brain tissue surrounding cranial blood vessels and the restricted access, it is very challenging and often risky to surgically treat defects of the cranial vasculature.
Alternative treatments include vascular occlusion devices such as embolic coils deployed using catheter delivery systems. In a currently preferred procedure to treat a cranial aneurysm, the distal end of an embolic coil delivery catheter is inserted into non-cranial vasculature of a patient, typically through a femoral artery in the groin, and guided to a predetermined delivery site within the cranium. A number of delivery techniques for vaso-occlusive devices, including use of fluid pressure to release an embolic coil once it is properly positioned, are described by Diaz et al. in U.S. Pat. Nos. 6,063,100 and 6,179,857, for example.
Multiple embolic coils of various lengths, commonly 1 to 30 centimetres, and preselected stiffness often are packed sequentially within a cranial aneurysm to limit blood flow therein and to encourage embolism formation. Typically, physicians first utilize stiffer coils to establish a framework within the aneurysm and then select more flexible coils to fill spaces within the framework. Ideally, each coil conforms both to the aneurysm and to previously implanted coils. Each successive coil is selected individually based on factors including stiffness, length, and preformed shape which the coil will tend to assume after delivery.
During implantation, the physician manipulates each embolic coil until it is in a satisfactory position, as seen by an imaging technique such as fluoroscopic visualization, before detaching the coil from the delivery system. It is highly desired for both ends of each coil to remain positioned within the aneurysm after delivery, because a length of coil protruding into the main lumen of the blood vessel invites undesired clotting external to the aneurysm. After each successive coil is detached, the next coil is at an increasing risk of becoming entangled in the growing mass of coils, thereby restricting the depth of insertion for that coil into the aneurysm.
Difficulties may arise due to stretching of the embolic coils during repositioning or attempted retrieval of the coils, especially if the coil becomes entangled and complete insertion of the coil into the aneurysm is not accomplished. If pulling forces applied to a coil exceed its elastic limit, the coil will not return to its original shape. A stretched coil exhibits diminished pushability or retractability, and becomes more difficult to manipulate into an optimal position or to be removed. Moreover, a stretched coil occupies less volume than an unstretched coil, which increases the number of coils needed to sufficiently pack the aneurysm to encourage formation of a robust embolus positioned wholly within the aneurysm.
There have been a number of attempts to address stretch-related problems in embolic coils. Several stretch-resistant devices are disclosed in U.S. Pat. No. 5,853,418 to Ken et al., having a primary coil and an elongated stretch-resisting member fixedly attached to the primary coil in at least two locations. While Ken et al. mention possible hydraulic delivery of their coils through a lumen of a catheter, they teach that it is desirable to controllably release each coil using a severable or mechanical joint such as an electrolytically detachable joint. Such joints are not compatible with certain delivery systems, and some physicians prefer not to use electrical currents to detach embolic coils from a delivery catheter.
Another embolic device, described in U.S. Pat. No. 6,183,491 by Lulo, has a support wire attached at one end to a proximal end of the coil and attached at its other end to an attachment point located in an intermediate portion of the coil. The embolic device has a closed proximal end and is suitable for hydraulic release from a delivery system after the device is properly positioned. However, only the proximal portion of the coil resists stretching; any length of coil distal to the intermediate attachment point is unprotected from excessive elongation forces.
A vaso-occlusive device described by Schaefer et al. in U.S. Patent Publication No. 2004/0006362 has a number of elongate filars conjointly wound into respective helical coils having respective windings arranged in an alternating fashion to define a hollow axial lumen. It is mentioned that a flexible hollow tube or porous sponge may be inserted within the axial lumen to serve a reservoir to deliver therapeutic agents. Schaefer et al. note that the bending resistance of the occlusive device may be increased by the inserted tube or sponge.
There are several patents by Greene, Jr. et al., including U.S. Pat. No. 7,491,214, disclosing one or more expansile embolizing elements to assist occlusion. These elements may be made of a hydrophilic, macroporous hydrogel foam material. Several types of occlusive devices having a coating material such as a porous, non-absorbable foam, preferably made of polyvinylidene fluoride-co-hexafluropropylene (PVDF/HFP), are disclosed by Yang et al. in U.S. Patent Publication No. 2007/0239205.
It is therefore desirable to have an improved stretch-resistant occlusive device which retains flexibility and conformability during insertion into a vascular malformation yet resists stretching along its entire length when pulling forces are applied to it. It is also desirable to have such a device which enhances thrombus formation and cellular proliferation, especially to treat cerebral aneurysms.
An object of the present invention is to maintain high flexibility and conformability in an occlusive device while providing resistance to stretching.
Another object of the present invention is to provide stretch resistance without impairing the ability of an embolic coil to assume a pre-formed shape after delivery to an arterio-venous malformation.
It is yet another object of the invention to provide novel stretch-resistant embolic devices which promote thrombus formation and encourage cellular proliferation to accelerate vessel remodelling within an aneurysm.
This invention results from the realization that stretch resistance can be added to occlusive devices such as embolic coils by utilizing at least one of a stretch-resistant tube and/or one or more filaments together with an elongated porous elastomeric structure which enhances thrombus formation and cellular proliferation.
This invention features an occlusive device having an elongated, substantially cylindrical porous elastomeric structure and at least one of an elongated stretch-resistant tube and at least one stretch-resistant filament. The elongated porous structure lies within an elongated outer embolic structure such as a helically-wound embolic coil.
In some embodiments, the elongated porous structure includes open-cell foam material, having an average pore diameter of one micron to 100 microns, and a plurality of stretch resistant filaments are embedded within the elongated porous structure. In certain embodiments, the elongated porous structure includes a biodegradable material. In one embodiment, a gap separates the elongated porous structure from the outer embolic structure and, in another embodiment, the elongated porous structure includes a low-friction layer separating it from the outer embolic structure. In yet another embodiment, the elongated porous structure includes a layer of dissolvable material separating it from the outer embolic structure.
In certain embodiments, the outer embolic structure is a helically wound coil and, in some embodiments, the helically wound coil is substantially cylindrical and defines the coil lumen to have a lumen diameter at its proximal end. In one embodiment, the porous elastomeric structure is decoupled from the helically wound coil to enhance flexibility.
In what follows, preferred embodiments of the invention are explained in more detail with reference to the drawings, in which:
Stretch resistance and the ability to enhance thrombus formation is provided to occlusive devices such as embolic coils according to the present invention by utilizing an elongated, substantially cylindrical porous elastomeric structure and a stretch resistant member comprising at least one of an elongated stretch-resistant tube and/or at least one stretch-resistant filament. The elongated porous structure lies within an elongated outer embolic structure, which in some constructions is a helically wound embolic coil.
Occlusive device 200,
Preferably, porous structure 202 serves as a three-dimensional elastomeric scaffold for cellular proliferation to accelerate vessel remodelling at the site of an aneurysm into which device 200 is implanted. The average pore size and number of pores affects the overall porosity of structure 202. In some constructions, acceptable parameters include average pore diameters ranging between one micron to 100 microns, more preferably three microns to 50 microns, as measured from scanning electron microscope images along a plane substantially parallel to the surface of the porous structure. In some constructions, the pore sizes are distributed over a wide size range. It is preferred to have a number of pores larger than three microns to easily accommodate platelets to enhance thrombus formation. Suitable biodegradable materials for structure 202 include polycaprolactone-co-glycolyde (Cap-Gly), polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyglycolic acid (PGA), and polyglycolic lactic acid (PGLA), also known as poly(lactic-co-glycolic acid) (PLGA). Suitable biocompatible but non-biodegradable materials include urethane, nylon and other polyamides, and expanded polytetrafluoroethylene (EPTFE).
Stretch resistant member 208 has filaments mechanically attached at the terminal ends of embolic coil 204. The cumulative cross-sections of all of the filaments comprising stretch resistant member 208 is sufficient to sustain a desired tensile load, while maintaining overall desired flexibility of device 200. Stretch resistant member 208 can be formed from biocompatible metallic or polymeric materials capable of being manufactured to sustain the desired tensile load. Suitable materials include platinum-tungsten (PtW), stainless steel, gold (Au), platinum-iridium (PtIr), nylon, Cap-Gly, PGLA, polylactic acid (PLA), EPTFE, polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), polypropylene, polyester, and nitinol (NiTi). In some constructions, the diameters of stretch-resistant filaments formed from these materials range from 0.0005 inch to 0.003 inch.
One technique for forming device 200 includes selecting five filaments more than twice as long as the desired final length of device 200 and folding them in half to form proximal bights with ten filament segments running the desired length of device 200. The proximal bights may be slidably engaged with an anchor filament or other proximal retaining element as described below in more detail. Foam is cast about the filaments to form a three-dimensional, open-cell scaffold structure. The distal ends of the filament segments can be melted to form a distal bead as described in more detail below.
In another manufacturing technique, the porous structure is formed as a solidified foam, with internal stretch resistant filaments distributed therein, in an extended length which is then cut to multiple desired lengths, one length for each device according to the present invention. The ends of each foam length is then dissolved to expose the filaments for attachment at one or both ends of a device 200.
In yet another technique, foam material is injected in liquid form into the lumen of a coil containing one or more stretch resistant members, such as coils disclosed by Wilson et al. in U.S. Pat. No. 7,572,246, which is incorporated herein in its entirety. The proximal bight of the stretch resistant member is held by a connector fiber which detachably mounts the stretch resistant member to a pusher member during implantation. Alternatively, foam material is cast around one or more stretch resistant members before the assembly is inserted into the coil lumen.
An alternative occlusive device 300,
In some constructions, helically wound wire or other materials are wrapped or otherwise placed around tube 304. Although no stretch resistant filaments are illustrated in
In certain constructions, the occlusive device utilizes a novel proximal headpiece portion as described by Lorenzo et al. in U.S. patent application Ser. No. 12/816,694 filed Jun. 16, 2010, entitled “Occlusive Device with Stretch Resistant Member and Anchor Filament” and incorporated herein by reference. The headpiece defines a headpiece lumen, and a novel proximal anchor filament is passed distally through the headpiece lumen and joined with a flexible distal stretch resistant member. Together, the anchor filament and the stretch resistant member may be referred to as a stretch-resistant assembly which extends along the entire axial interior of the helically wound coil to minimize undue coil elongation without impairing coil flexibility and conformability during and after implantation.
The occlusive device 100, which is an embolic coil in this construction, and the distal end 12 of catheter 16 are shown in more detail in
As shown in
Referring particularly to
A stretch resistant member 130 passes through eye 126 and extends distally as a loop with two legs 132 and 134 that terminate in distal bead 136 having atraumatic distal surface 138. A cross-sectional view through proximal coil portion 108 showing headpiece distal end 107, and anchor bight 124 distal to headpiece lumen 122, as seen within coil lumen 109 is illustrated in
A procedure for manufacturing stretch-resistant occlusive devices such as embolic coils according to one embodiment of the present invention includes some or all of the following steps. A distal end of a headpiece is attached to a proximal end portion of a helically wound coil defining a coil lumen extending along the entire axial length of the coil and having a coil distal end portion. The headpiece also has a proximal end and defines a headpiece lumen extending between the proximal and distal ends of the headpiece. Next, a distal portion of an anchor filament, defining an eye, is advanced distally through the headpiece lumen and through the coil lumen to expose the eye beyond the coil distal end portion. A stretch resistant member is passed through the eye to join the member with the filament to create a stretch-resistant assembly extending through the coil lumen and the headpiece lumen, and the anchor filament is retracted to bring the eye in proximity to the distal end of the headpiece. The anchor filament is secured to the proximal end of the headpiece so that the eye is positioned distal to the distal end of the headpiece, and the stretch resistant member is secured to the distal end of the coil, with an atraumatic distal surface, so that proximal and distal ends of the stretch-resistant assembly are secured to resist pulling forces which may be applied to the helically wound coil during implantation in a patient.
Helically wound coil stock is formed initially by winding a platinum-tungsten alloy wire about an elongated, non-curved mandrel to generate tight uniform helical turns defining a central lumen occupied by the mandrel. It is currently preferred for tungsten to comprise approximately six percent to ten percent of the alloy wire. Stiffer framing coils are formed by using round wire having a diameter of approximately 0.003 inch. More flexible fill coils utilize round alloy wire having a diameter of approximately 0.002 inch while even softer coil wire is approximately 0.0015 inch in diameter. The softer wire typically is wound over a slightly larger mandrel to generate a slightly larger wound coil diameter defining a correspondingly larger coil lumen. In other constructions, different alloys or material, or a tapered mandrel geometry, could be utilized to alter flexibility of the resulting helically wound coil.
After the mandrel is removed, the initial linear coil stock is cut to desired lengths, typically 1.5 cm to 30 cm, and each length may be thermally “set” into a desired overall curved, non-linear configuration that it will tend to assume after implantation. Configurations having a curved longitudinal axis include a helical or spiral shape and even more complex shapes. Various detachable embolic coils, each having a solid proximal headpiece that is releasably held by a polymeric distal gripper portion of a hydraulic delivery tube during cranial implantation, are currently commercially available as part of the TRUFILL® DCS ORBIT® Detachable Coil System from Codman & Shurtleff, Inc. of Raynham, Mass.
Novel headpieces according to the present invention define a headpiece lumen through which novel anchor filament is passed after the headpiece is attached to the proximal end of the external coil by a solder joint, welding or other secure bond. Examples of compatible headpiece and anchor filament components prior to assemblage are shown in
Anchor filament 120a,
Sutures provide acceptable stretch resistant members. A preferred non-absorbable suture is PROLENE® polypropylene monofilament suture, especially size 10-0 which is thinner than a human hair, available from Ethicon, Inc. Preferred absorbable sutures include VICRYL® polyglycolic acid monofilament or multifilament sutures, also available from Ethicon, Inc. Other polymeric or metallic fibres or wires can be utilized as desired according to the present invention. Further, the material utilized for the stretch resistant member, or an additive to that material, may be selected to have thrombogenic properties to promote clotting.
Next, the anchor filament with joined stretch resistant member is pulled proximally until the bight is positioned to be spaced several coil wire diameters from the distal end of the headpiece such as shown in
After the bight is properly positioned relative to the distal end of the headpiece, excess anchor filament material is trimmed. Heat, such as a plasma flame if the anchor filament is metallic, is applied to the remaining proximal filament ends until they melt and a proximal bead is formed at the proximal end of the headpiece, extending into the headpiece lumen such as shown in
Excess stretch resistant member material extending beyond the distal end of the coil is then trimmed, and heat is applied to melt the ends of the remaining material to form a distal bead, preferably concentric and substantially hemispherical in shape with a substantially smooth, atraumatic, low-friction outer surface to facilitate entry and conformance of the occlusive device during its delivery into a malformation of a patient. The amount of stretching of the helically wound coil permitted by the stretch resistant member depends on factors including the composition and thickness of stretch resistant member material, including its tensile properties, as well as the overall length of the stretch resistant member. For example, any desired amount of slack relative to the length of the coil can be established during manufacture by elongating the coil by the desired amount using a fixture before melting the distal portion of the stretch resistant member to form the distal bead, which generates that amount of slack in the stretch resistant member when the coil is released from the fixture.
The anchor filament and stretch resistant member together form a stretch-resistant assembly extending through the coil lumen and the headpiece lumen to minimize coil elongation when pulling forces are applied to the occlusive device. It is desirable for the stretch-resistant assembly to have a pull strength of at least 0.02 pounds at its proximal and distal ends when the pull strength of the coil to headpiece solder joint is about 0.05 pounds.
Thus, while there have been shown, described, and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions, substitutions, and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. For example, it is expressly intended that all combinations of those elements and/or steps that perform substantially the same function, in substantially the same way, to achieve the same results be within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale, but that they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
Every issued patent, pending patent application, publication, journal article, book or any other reference cited herein is each incorporated by reference in their entirety.
