Patent Application
20230071512
Interventional devices such as guidewires and catheters are frequently utilized in the medical field to perform delicate procedures deep within the human body. Typically, a catheter is inserted into a patient’s femoral, radial, carotid, or jugular vessel and navigated through the patient’s vasculature to the heart, brain, or other targeted anatomy over a guidewire. Once in place, the catheter can be used to deliver drugs, stents, embolic devices, radiopaque dyes, or other devices or substances for treating the patient in a desired manner.
In many applications, such an interventional device must be navigated through the tortuous bends and curves of a vasculature passageway to arrive at the targeted anatomy. Such an interventional device requires sufficient flexibility, particularly closer to its distal end, to navigate such tortuous pathways. However, other design aspects must also be considered. For example, the interventional device must also be able to provide sufficient torquability (i.e., the ability to transmit torque applied at the proximal end all the way to the distal end), pushability (i.e., the ability to transmit axial push to the distal end rather than bending and binding intermediate portions), and structural integrity for performing intended medical functions.
It is desirable for catheter devices to have good axial response. In other words, when the user moves the proximal end of the device, he/she expects the distal end to move the same distance. Often, however, as the device is positioned within the bends and curves of the vasculature, much of the axial movement is used to push intermediate portions of the device into the walls of the curved portions of the vasculature rather than actually advancing the distal end forward. This lack of correspondence between the amount of axial push provided by the user at the proximal end and the resulting forward movement of the distal end makes navigation more difficult and less tactilely intuitive.
In addition, conventional catheter devices utilize multiple different materials to provide a gradient in bending stiffness from proximal end to distal end. However, whenever there is a transition between materials of differing stiffness, the bending, axial, and torsional stiffness profiles of the device includes an abrupt step change. Such abrupt changes in bending stiffness are undesirable because they can concentrate mechanical stresses at particular locations, cause kink points, disrupt the smooth movement and bending of the device, and complicate navigation in tortuous vasculature.
Accordingly, there exist several limitations in the field of catheter devices, and there is an ongoing need, for example, for devices that improve axial and/or torsional response, the distribution of bending forces, and/or are capable of providing a smooth bending stiffness profile.
Various objects, features, characteristics, and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings and the appended claims, all of which form a part of this specification. In the Drawings, like reference numerals may be utilized to designate corresponding or similar parts in the various Figures, and the various elements depicted are not necessarily drawn to scale, wherein:
The catheter device 100 includes a catheter 102 connected to a hub 104 at a proximal end and extending therefrom to a distal end 103. The catheter 102 may be coupled to the hub 104 using adhesive, a friction fit, through insertion molding, and/or other appropriate attachment means. A strain-relief member 106 is also disposed over the proximal section of the catheter 102 near the hub 104. The strain-relief member 106 has an outer diameter that substantially matches the adjacent section of the hub 104. The strain-relief member 106 extends for a distance from the hub 104 with a substantially constant outer diameter before tapering distally to the end where the catheter 102 emerges and extends farther distally. The strain-relief member 106 may include a groove pattern 108, disposed at the section of substantially constant outer diameter, that functions to provide additional flexibility to the strain-relief member 106 and/or to provide surface features for enhancing user grip and tactile engagement.
The working length of the catheter 102 (i.e., the distance between the distal end of the strain-relief (106) and the catheter (102) distal end (103) may vary according to particular application needs. As an example, the catheter 102 may have a working length of about 50 cm to about 200 cm, though shorter or longer lengths may be utilized where appropriate. The catheter size (typically referring to the inner diameter/lumen size) may also vary according to particular application needs. Examples include 0.010 inches, 0.013 inches, 0.017 inches, 0.021 inches, 0.027 inches, 0.030 inches, 0.035 inches, 0.038 inches, 0.045 inches, 0.065 inches, 0.085 inches, 0.100 inches, or a range including any two of the foregoing values as endpoints. The inside diameter of the catheter can taper from a smaller distal portion to a larger proximal portion. Smaller or larger sizes may be utilized in some applications as appropriate.
Although the distal section of the catheter 102 is shown in this example as having a straight shape, other embodiments may include a shaped distal tip. For example, the distal section of the catheter 102 may have an angled shape, a curved shape (e.g., 45 degree angle, 90 degree angle, J shape, etc.), a compound curved shape, or other appropriate angled or bent shape as known in the art.
The catheter device 100 described herein may be utilized for a variety of interventional applications, most commonly in cardiovascular, peripheral vascular, and neurovascular interventional procedures. Examples include accessing distal anatomy, crossing vessel lesions or blood clots, ischemic treatments, delivering therapeutic agents (e.g., embolic coils or other embolic agents), injecting diagnostic agents (e.g., contrast media or saline), retrieval applications, aspiration applications, or other applications where microcatheter use is beneficial.
Internal features of the catheter 102 are described in greater detail below. The outer surface of the catheter 102 may be coated with an appropriate coating material, such as a hydrophilic coating, to make the surface more lubricious. The coating material may cover substantially all of the working length of the catheter 102, or a portion thereof. For example, the coating material may be applied to the distal-most 30% to 80% of the working length of the catheter 102.
In one embodiment, the coil 114 is formed from stainless steel and the shaft 112 is formed from nitinol. These materials, when used in combination with other features described herein, have been found to provide effective axial response, effective distribution of bending forces, and a smooth bending stiffness profile. Other embodiments may utilize one or more different materials for the coil 114, the shaft 112, or both. In some embodiments, for example, the shaft 112 may include other superelastic alloys and/or one or more polymers such as a polyether ether ketone (PEEK) or other polyaryl ether ketone (PAEK). In some embodiments, the coil 114 may include a superelastic alloy such as nitinol, one or more other metals, alloys, or polymers.
The catheter 102 is configured so that the overall bending stiffness profile transitions from higher stiffness (and less bending flexibility) at the proximal sections to lower stiffness (and greater bending flexibility) at the distal sections. In most applications, it is desirable to give the proximal sections of the device relatively high axial, torsional, and bending stiffness so they can provide good combination of flexibility, pushability, and torquability. Distal sections, however, are often navigated through tortuous vasculature and are thus preferably relatively more flexible in bending. This stiffness profile gradient can be created by adjusting certain features of the microfabricated shaft 112 and/or by utilizing different polymer materials to coat and embed the shaft 112 in the outer member 115. As explained in more detail below, in some embodiments, the microcatheter 112 and the outer member 115 are configured to work together to provide an overall stiffness profile that minimizes abrupt changes in stiffness and provides smooth stiffness transitions.
The illustrated embodiment includes a distal section 120, an intermediate section 122, and a proximal section 124. In the distal section 120, the outer member 115 is formed from a first polymer material 116a. In the intermediate section 122, the outer member 115 is formed from a second polymer material 116b. In the proximal section 124, the outer member 115 is formed from a third polymer material 116c. The polymer materials 116a, 116b, and 116c have different hardness and thus affect the stiffness of their respective sections differently. The second polymer material 116b has a higher hardness than the first polymer material 116a, and the third polymer material 116c has a higher hardness than the second polymer material 116b. Some embodiments may include more than three polymer materials. In such embodiments, as with the illustrated embodiment, the polymer materials may have progressively higher hardness moving from one polymer material to the next in the proximal direction.
As one example of a set of polymer materials found to be effective when utilized together, the first polymer material 116a may have a Shore D hardness of about 20 to about 30, the second polymer material 116b may have a Shore D hardness of about 30 to about 50, and the third polymer material 116c may have a Shore D hardness of about 50 to about 80. Other embodiments may vary these values as desired such as softer in the distal portion, but the foregoing values have been found to be particularly effective. The polymer materials 116a, 116b, and 116c may be formed from independently from appropriate polymers such as polyether block amide (PEBA) polymers and can range in polymer durometers from Shore A hardness of about 10 to Shore D hardness of about 100.
The shaft 112 also includes features that provide variable bending stiffness. As shown, the shaft 112 is a tube structure that includes a series of microfabricated cuts. The cuts form axially extending “beams” that connect successive circumferentially extending “rings”. These cut patterns can be varied to adjust the bending stiffness of the shaft 112. For example, the bending stiffness can be attuned by adjusting the number of beams that reside between each pair of adjacent rings. A “two-beam section”, such as shown in the distal section 120, includes two beams between each pair of adjacent rings. A “three-beam section”, such as shown in the intermediate section 122 and proximal section 124, includes three beams between each pair of adjacent rings. All else being equal (shaft material, cut depth, cut width, cut spacing), a three-beam section has greater bending stiffness than a two-beam section. A “one-beam section” with a single beam connecting adjacent rings may also be utilized, and will have even less bending stiffness than a two-beam section, all else being equal. A “four-beam section” and/or section having greater than four beams may also be utilized, and will accordingly provide greater bending stiffness as the number of beams between each pair of adjacent rings is increased.
In addition to adjusting the number of beams disposed between rings, the bending flexibility of the shaft 112 may be controlled by adjusting the depth of cuts, the width of cuts, and/or the spacing of cuts. Typically, the width of cuts is set at a given value (e.g., corresponding to a cutting blade size), and it is easier to adjust cut depth and/or cut spacing during manufacture in order to provide the desired control over the bending stiffness profile. All else being equal, as ring width is reduced (i.e., cut spacing is reduced), cut width is increased, and/or beam width is reduced (i.e., cut depth is increased), the resulting bending stiffness is reduced. In the illustrated embodiment, the spacing between cuts in the three-beam section (which is coincident with the intermediate section 122 and proximal section 124) is progressively reduced as it gets closer to the distal section 120. Similarly, the two-beam section (which is coincident with the distal section 120) begins with larger spaces between cuts and progresses to less space between cuts as it gets closer to the coil 114 and the distal end 103. Preferably, transitions between different geometries (e.g., three-beam to two-beam) are configured so that bending stiffness is the same or similar across the transition of these sections. The shaft 112 thus provides a stiffness gradient by way of transitioning from a three-beam section to a two-beam section, and also within the respective sections by way of transitioning from cuts that are more spaced apart to cuts that are relatively less spaced apart.
At the distal end of the two-beam section, the cut pattern is configured with relatively high flexibility in order to provide a smooth transition to the high flexibility of the coil 114. In some embodiments, the coil 114 is omitted and replaced by more of the two-beam section (or alternatively, a one-beam section) that extends to a position at or near the distal end 103.
The lengths of the sections 120, 122, and 124 may be varied according to particular application needs or preferences. In one embodiment, the distal section 120 may have a length of about 5 cm to about 40 cm, and the intermediate section 122 may have a length of about 10 cm to about 50 cm, with the proximal section 124 taking up the remainder of the working length of the catheter 102. The illustrated embodiment shows that the shaft 112 transitions from a three-beam configuration to a two-beam configuration at the transition of the intermediate section 122 to the distal section 120. However, the transitions of the shaft 112 need not necessarily correspond to the transitions of polymer material that define the separate sections 120, 122, and 124. As explained in more detail below, the shaft 112 and outer member 115 are configured together to compensate for and minimize abrupt stiffness changes, and in some instances, this may involve shaft transition zones that do not overlap completely with polymer transitions of the outer member 115.
The shaft 112 may include a circumferential groove at the position where the proximal marker band 142 is placed. This groove can receive the marker band 142 such that the outer surface of the marker band 142 does not extend excessively beyond the outer diameter of the shaft 112. Once covered by the outer member 115, the outer diameter of the device over the proximal marker band 142 remains substantially flush.
In the illustrated embodiment, the coil 114 is variably pitched. Each end of the coil 114 includes a region of narrowed pitch that provides more improved transitions in bending stiffness from one geometry to another such as where the coil transitions to a microfabricated tube. As an example, the coil 114 may have a length of about 1 cm to about 3 cm. As shown, a portion of the liner 110 may extend a distance distally from the coil 114 and distal marker coil 140. This distance may vary from about 0.2 mm to about 2 mm, for example.
The catheter devices described herein include features that effectively distribute bending forces and thereby provide improved axial response in use.
In contrast to the response of conventional catheters as in
During bending of the shaft 112, the shaft structure locally resists more bending stresses and distributes this stress to adjacent portions of the structure more effectively as compared to a coil or braid which are less likely to distribute bending stresses and more likely to kink. Additionally, the polymer material 116 effectively functions as a series of dampers each positioned between adjacent rings of the shaft 112. On the inner side of the bend, the polymer material 116 is compressed, and therefore provides a counteracting force that pushes outward against the rings and resists further bending. Similarly, on the outer side of the bend, the polymer material 116 is placed in tension, and therefore provides a counteracting force that pulls the rings inward and resists further bending. The bending stiffness of the catheter 102 is non-linear because it becomes increasingly resistant to bending, in a non-linear manner, as the bend angle is increased.
During bending, a conventional catheter will begin to bend at the apex and the cross-sectional shape of the catheter may tend to “ovalize”. Once ovalization begins, resistance to bending decreases and it therefore becomes increasingly easier to bend with continued application of bending forces. In contrast, in the disclosed catheter 102, the bending resistance provided by the action of the microfabricated structure and polymer material 116 against the shaft 112 tends to distribute bending forces along the axial length of the catheter 102 and avoid ovalization and concentration of bending forces at a particular kink point. For example, the bending resistance will tend to spread a bend out to a larger radius of curvature rather than concentrating the bend at specific point thereby creating a kink location. The bending resistance provided by the catheter structure can therefore provide enhanced axial responsiveness (as illustrated by
To compensate for this step change, the shaft is configured such that the bending stiffness changes complement and compensate for the abrupt change in bending stiffness of the polymer outer member. As a result, the overall bending stiffness of the catheter remains relatively smooth across the transition from the first polymer 116a to the second polymer 116b. Similar configurations can be utilized at other polymer transition zones to minimize and smooth out abrupt step changes in bending stiffness. The shaft 112 can be configured to compensate for the step change in a variety of ways. In the example of
Configuring the shaft 112 to compensate for abrupt bending stiffness changes of the polymer outer member 115 beneficially avoids the complications of other conventional approaches to smoothing out such transitions. Prior approaches rely on complicated splicing arrangements or polymer co-extrusion and mixing techniques. These add layers of extra complication to the manufacturing process and may still only marginally resolve the abruptness of the transition. Other approaches utilize different diameters of polymer tubing and diameter gradients to compensate for transitions between polymer types. However, these approaches result in an uneven outer diameter or add the requirement to somehow manage this by overlaying even more material.
The smoothing features described herein enable the manufacture of microcatheters having improved bending stiffness profiles as compared to conventional microcatheters.
Table 1 presents the data of
As shown, the Plato 17 has the lowest measured slope across the distal 15 cm section, across the distal 35 cm section, and across the distal 50 cm section. Based on the data of
In some embodiments, at least a portion of the distal 35 cm of the catheter device has a bending stiffness of 5 x 10-6 N·m2 or greater. In some embodiments, in addition to the foregoing stiffness minimum, a catheter device as described herein has a bending stiffness slope ((N·m2)/cm)) of no more than about 4.0 x 10-6 for a distal 35 cm section and/or no more than about 4.5 x 10-6 for a distal 50 cm section. As shown in
In some embodiments, a catheter device as described herein has (1) a bending stiffness of 5 x 10-6 N·m2 or greater in at least a portion of the distal 35 cm of the catheter device, (2) a change in outer diameter of no more than 0.002 inches across the distal 15 cm and/or distal 35 cm section, and (3) a bending stiffness slope ((N·m2)/cm)) of no more than about 1.3 x 10-6 for a distal 15 cm section, no more than about 4.2 x 10-6 for a distal 35 cm section, and/or no more than about 1.1 x 10-5 for a distal 50 cm section. While the Plato 17 device configured according to the present disclosure achieved each of the foregoing features, none of the other prior catheter devices tested were able to do so. That is, the Headway-17 catheter does not meet the minimum bending stiffness requirement, the Echelon-10 does meet the diameter change requirement, and none of the other tested catheters meet the slope requirements.
In some embodiments, the beneficial bending stiffness profile features described above are specifically applicable to a transition section where a first polymer of the outer member transitions to a second polymer of the outer member.
In some embodiments, the shaft 112 maintains substantially the same wall thickness along its length. Other catheter devices based on coils and/or braids will most often have adjusted wall thicknesses at transition points. Changes in wall thickness can introduce additional kink or stress points and/or require additional manufacturing steps to manage.
In some embodiments, there may be an acceptable bending stiffness change associated with the distal tip region because the shaft 112 transitions to the coil 114 and/or the coil 114 transitions to the distal-most section of liner 110. These stiffness changes may be acceptable because they are so near the distal end 103. Thus, in some embodiments, the distal-most 3 to 5 cm may be excepted from the foregoing bending stiffness change limits.
The catheter devices described herein also beneficially provide effective fatigue resistance. For example, in a bend and twist fatigue test method based on ASTM E2948, catheter devices as described herein are capable of achieving greater than 20 cycles before breaking. The bend and twist fatigue test method is described in more detail in document TM-00127, which is attached hereto as Appendix 1. In short, the test is adapted from ASTM E2948, which is a standard test method for measuring rotating bending fatigue of solid round fine wire.
The effective fatigue resistance of the disclosed catheter devices may be present along the entire length of the shaft portion of the device, or along one or more sub-sections of the device (e.g., along one or more sections having length of about 3 to 35 cm, or about 3 to 20 cm, or about 3 to 10 cm). The effective fatigue resistance is provided by one or more of the following parameters: (1) maintaining ring widths at less than or equal to about 30% of the corresponding outer diameter of the shaft 112; and/or (2) maintaining cut depths at greater than or equal to about 11% of the outer diameter of the shaft 112.
While certain embodiments of the present disclosure have been described in detail, with reference to specific configurations, parameters, components, elements, etcetera, the descriptions are illustrative and are not to be construed as limiting the scope of the claimed invention.
As used herein, the term “microfabricated” refers to any fabrication process capable of manipulating a stock material to form a catheter device having one or more of the features disclosed herein, including any fabrication process capable of forming gaps in an inner shaft as disclosed herein. Examples include, but are not limited to, laser cutting and blade cutting.
For any given element of component of a described embodiment, any of the possible alternatives listed for that element or component may generally be used individually or in combination with one another, unless implicitly or explicitly stated otherwise.
Unless otherwise indicated, numbers expressing quantities, constituents, distances, or other measurements used in the specification and claims are to be understood as optionally being modified by the term “about” or its synonyms. When the terms “about,” “approximately,” “substantially,” or the like are used in conjunction with a stated amount, value, or condition, it may be taken to mean an amount, value or condition that deviates by less than 20%, less than 10%, less than 5%, less than 1%, less than 0.1%, or less than 0.01% of the stated amount, value, or condition. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Any headings and subheadings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims.
It will also be noted that, as used in this specification and the appended claims, the singular forms “a,” “an” and “the” do not exclude plural referents unless the context clearly dictates otherwise. Thus, for example, an embodiment referencing a singular referent (e.g., “widget”) may also include two or more such referents.
It will also be appreciated that embodiments described herein may include properties, features (e.g., ingredients, components, members, elements, parts, and/or portions) described in other embodiments described herein. Accordingly, the various features of a given embodiment can be combined with and/or incorporated into other embodiments of the present disclosure. Thus, disclosure of certain features relative to a specific embodiment of the present disclosure should not be construed as limiting application or inclusion of said features to the specific embodiment. Rather, it will be appreciated that other embodiments can also include such features.
This application claims priority to and the benefit of U.S. Provisional Application No. 63/271,114, filed Oct. 22, 2021 and titled “Intravascular Guidewire and Microcatheter System,” and to U.S. Provisional Application No. 63/240,845, filed on Sep. 3, 2021 and titled “Microcatheter Device with Non-Linear Bending Stiffness,” each of which is incorporated herein by this reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63271114 | Oct 2021 | US | |
| 63240845 | Sep 2021 | US |
