Stretch resistant vaso-occlusive coils

Abstract: This is an implantable vaso-occlusive device. It is typically a vaso-occlusive coil comprised of a primary helically wound coil which may then be wound into a secondary shape. Central to the invention is the use of a stretch-resisting member fixedly attached within at least a portion of the primary coil. The stretch-resisting member may be formed into coil tips at the ends of the coil by melting the polymeric fibers or alloys or by attaching the fibers with a glue. This stretch-resisting member is for the primary purpose of preventing stretching of the coil during movement of that coil, e.g., by retrieval or repositioning after deployment. The device typically has a self-forming secondary shape made from a pre-formed primary linear helically wound coil, although it need not have the secondary form. External fibers may be attached to the device and affixed to the pre-formed linear member to increase. The vaso-occlusive member may be also be covered with a fibrous braid. The device is typically introduced into the body through a catheter. The device is passed axially through the catheter sheath and assumes its secondary form upon exiting the catheter.

Description: This invention is an implantable vaso-occlusive device. It is typically a vaso-occlusive coil comprised of a primary helically wound coil which may then be wound into a secondary shape. Central to the invention is the use of a stretch-resisting member extending through the lumen formed by the coil. The stretch-resisting member is fixedly attached to the coil in at least two locations, at least one of those locations being between the ends of the coil. The stretch-resisting member may be formed into coil tips at the ends of the coil using simple equipment such as soldering irons or the like. The tips are typically of the same diameter as is the coil body itself. This stretch-resisting member is for the primary purpose of preventing stretching of the coil during movement of that coil, e.g., by retrieval or repositioning after deployment. The device typically has a self-forming secondary shape made from a pre-formed primary linear helically wound coil, although it need not have the secondary form. External fibers may be attached to the device and affixed to the pre-formed linear member to increase thrombogenicity. The vaso-occlusive member may also be covered with a fibrous braid. The device is typically introduced into the body through a catheter. The device is passed axially through the catheter sheath and assumes its secondary form upon exiting the catheter. Vaso-occlusion devices are surgical implements or implants that are placed within the vasculature of the human body, typically via a catheter, either to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus or to form such an embolus within an aneurysm stemming from the vessel. One widely used vaso-occlusive device is a helical wire coil having windings which may be dimensioned to engage the walls of the vessels. Other less stiff, helically coiled devices have been described, as well as those involving woven braids. For instance, US Patent No. 4,994,069, to Ritchart et al., describes a vaso-occlusive coil that assumes a linear helical configuration when stretched and a folded, convoluted configuration when relaxed. The stretched condition is used in placing the coil at the desired site (by its passage through the catheter) and the coil assumes a relaxed configuration -- which is better suited to occlude the vessel -- once the device is so placed. Ritchart et al. describes a variety of shapes. The secondary shapes of the disclosed coils include "flower" shapes and double vortices. A random secondary shape is described, as well. Vaso-occlusive coils having attached fibrous elements in a variety of secondary shapes are shown in US Patent No. 5,304,194, to Chee et al. Chee et al. describes a helically wound device having a secondary shape in which the fibrous elements extend in a sinusoidal fashion down the length of the coil. These coils, as with Ritchart et al., are produced in such a way that they will pass through the lumen of a catheter in a generally straight configuration and, when released from the catheter, form a relaxed or folded shape in the lumen or cavity chosen within the human body. The fibrous elements shown in Chee et al. enhance the ability of the coil to fill space within the vasculature and to facilitate formation of embolus and subsequent allied tissue. There are a variety of ways of discharging shaped coils and linear coils into the human vasculature. In addition to those patents which apparently describe only the physical pushing of a coil out into the vasculature (e.g., Ritchart et al.), there are a number of other ways to release the coil at a specifically chosen time and site. US Patent No. 5,354,295 and its parent, 5,122,136, both to Guglielmi et al., describe an electrolytically detachable embolic device. A variety of mechanically detachable devices are also known. For instance, US Patent No. 5,234,437, to Sepetka, shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces. US Patent No. 5,250,071, to Palermo, shows an embolic coil assembly using interlocking clasps mounted both on the pusher and on the embolic coil. US Patent No. 5,261,916, to Engelson, shows a detachable pusher-vaso-occlusive coil assembly having an interlocking ball and keyway-type coupling. US Patent No. 5,304,195, to Twyford et al., shows a pusher-vaso-occlusive coil assembly having an affixed, proximally extending wire carrying a ball on its proximal end and a pusher having a similar end. The two ends are interlocked and disengage when expelled from the distal tip of the catheter. US Patent No. 5,312,415, to Palermo, also shows a method for discharging numerous coils from a single pusher by use of a guidewire which has a section capable of interconnecting with the interior of the helically wound coil. US Patent No. 5,350,397, to Palermo et al., shows a pusher having a throat at its distal end and a pusher through its axis. The pusher sheath will hold onto the end of an embolic coil and will then be released upon pushing the axially placed pusher wire against the member found on the proximal end of the vaso-occlusive coil. Vaso-occlusive coils having little or no inherent secondary shape have also been described. For instance, in US Patent Application 07/978,320, filed November 18, 1992, entitled "Ultrasoft Embolization Coils with Fluid-Like Properties" by Berenstein et al., (also published as WO-A-94/10936) is found a coil having little or no shape after introduction into the vascular space. None of these devices is a helical coil which has a stretch-resisting member contained therein. US Patent No. 5,217,484 discloses a vaso-occlusive device in accordance with the pre-characterising section of claim 1. In said device the stretch-resisting member is attached to the opposite ends of the outer stretchable member. According to the present invention there is provided a stretch-resisting vaso-occlusive device, wherein the device is of a size and shape which can be introduced into an aneurysm and comprises: i. an outer stretchable member having a first end and a second end and defining a lumen between said first and second ends; and ii. a stretch-resisting member attached to said outer stretchable member in at least two attachment locations so as to resist stretching of said outer stretchable member, said stretch-resisting member extending between said attachment locations within the lumen; characterised in that at least one of said attachment locations is between the first and second ends of said outer stretchable member said at least one attachment location not being as an end. A deployment tip may be attached to at least one of said first and second ends, this deployment tip preferably comprising an electrolytically detachable end adapted to detach from a pusher by imposition of a current on said pusher. The outer stretchable member may comprise a polymer containing a radio-opaque filler. Furthermore, external filamentary material may be attached to the outer stretchable member. The stretch-resisting member advantageously comprises a polymer. When the stretch-resisting member comprises a thermoplastic it is advantageously made of polyethylene terephthalate. The present invention will be more clearly understood from the following description, given by way of example only, with reference to the accompanying drawings. None of the drawings shows a device which, in the exact form illustrated, is in accordance with the present invention in that none employs a stretch-resisting member attached to the outer stretchable member in at least two locations, at least one of which locations is between the first and second ends of the outer stretchable member. Nevertheless, when modified to include stretch-resisting members which are attached to their outer stretchable member in at least two locations, at least one of which is between the opposite ends of the outer stretchable member, these devices may be brought into accordance with the present invention. Figure 1A shows a side view; partial cutaway of a vaso-occlusive coil having a generally linear fibrous stretch-resisting member. Figure 1B shows a side view, partial cutaway of a vaso-occlusive coil having a generally linear wire stretch-resisting member. Figure 1C shows a side view, partial cutaway of a vaso-occlusive coil having a generally helical stretch-resisting member. Figures 2A, 2B, and 2C show side view, partial cutaways of typical ends of vaso-occlusive coils. Figures 3A and 3B show a side view, partial cutaway of electrolytically severable joints suitable for use with vaso-occlusive coils made according to the invention. Figures 4A and 4B show a side view, partial cutaway of a typical mechanically detachable joint suitable for use with vaso-occlusive coils made according to the invention. Figure 5 shows a "C" shaped secondary shape for a vaso-occlusive device. Figure 6 shows a clover-leaf secondary shape for a vaso-occlusive device. Figure 7 shows a double-looped secondary shape for a vaso-occlusive device. Figure 8 shows attachment of external fibrous material to a vaso-occlusive device. Figure 9 shows attachment of external braided fibrous material to a vaso-occlusive device. Figures 10A-10D show a procedure for introducing a vaso-occlusive coil such as found in the other Figures into an aneurysm. Figures 1A, 1B, and 1C show side-view partial cross-sections (or cutaways) of vaso-occlusive devices (100, 200, 210). The devices shown in Figures 1A and 1B are made up of a helically wound outer coil (102, 202) having a first end (104, 204) and a second end (106, 206). We refer to this form as the "primary" winding or shape. These devices include a stretch-resisting member (108, 208, 214) which is shown to be fixedly attached both to the first end (104, 204) and to the second end (106, 206). In Figures 1A and 1B the stretch-resisting member (108, 208) is attached to both ends. The devices of Figures 1A and 1B are not in accordance with the present invention. To be in accordance with the present invention the stretch resisting member must be attached to the coil in at least two locations, with one of those locations being between the first and second ends (104, 204; 106, 206) at the coil (102, 202). The stretch-resisting member (108) of the device shown in Figure 1A is fibrous and desirably polymeric. It may be a thermoplastic or thermosetting and comprise a bundle of threads or a single filament melted onto, glued, or otherwise fixedly attached to the vaso-occlusive coil (100). In some instances, it may also be desirable to include one or more metallic strands in the stretch-resisting member (108) to provide stiffness or electrical conductance for specific applications. The stretch-resisting member (208) of the variation shown in Figure 1 B is a simple wire or "ribbon" which is soldered, brazed, glued, or otherwise fixedly attached to the first end (204), second end (206), or to the coil at one or more locations intermediate to those the ends. The variation shown in Figure 1C includes a stretch-resisting member (214) which is comprised of a helically wound coil which is soldered, brazed, glued, or otherwise fixedly attached to the first end (204) or second end (206) or in one or more intermediate locations. The stretch-resisting member (214) in this configuration provides a greater measure of lateral flexibility than the wire variation (208 in Figure 1B). It may be wound in either the same direction as is the outer coil (202) or in the alternate direction. A modest drawback to this variation is that it will stretch more than the Figure 1B variation when axially stressed. The materials used in constructing the vaso-occlusive coil (102, 202) and the stretch resisting member (108, 208, 214) may be any of a wide variety of materials; preferably, a radio-opaque material such as a metal or a polymer is used. Suitable metals and alloys for the wire making up the primary coil (102, 202) and the stretch-resisting member (108, 208, 214) include the Platinum Group metals, especially platinum, rhodium, palladium, rhenium, as well as tungsten, gold, silver, tantalum, and alloys of these metals. These metals have significant radio-opacity and in their alloys may be tailored to accomplish an appropriate blend of flexibility and stiffness. They are also largely biologically inert. Highly preferred is a platinum/tungsten alloy, e.g., 8% tungsten and the remainder platinum. The ribbon or coil stretch-resisting members (208, 214) may also be of any of a wide variety of stainless steels if some sacrifice of radio-opacity and flexibility may be tolerated. Very desirable materials of construction, from a mechanical point of view, are materials which maintain their shape despite being subjected to high stress. Certain "super-elastic alloys" include various nickel/titanium alloys (48-58 atomic % nickel and optionally containing modest amounts of iron); copper/zinc alloys (38-42 weight % zinc); copper/zinc alloys containing 1-10 weight % of beryllium, silicon, tin, aluminum, or gallium; or nickel/aluminum alloys (36-38 atomic % aluminum). Particularly preferred are the alloys described in US Patent Nos. 3,174,851; 3,351,463; and 3,753,700. Especially preferred is the titanium/nickel alloy known as "nitinol". These are very sturdy alloys which will tolerate significant flexing without deformation even when used as very small diameter wire. If a superelastic alloy such as nitinol is used in the device, the diameter of the coil wire may be significantly smaller than that used when the relatively more ductile platinum or platinum/tungsten alloy is used as the material of construction. The coils may be made of radiolucent fibers or polymers (or metallic threads coated with radiolucent or radio-opaque fibers) such as Dacron (polyester), polyglycolic acid, polylactic acid, fluoropoly mers (polytetrafluoro-ethylene), Nylon (polyamide), or even silk. Should a polymer be used as the major component of the vaso-occlusive coil member, it is desirably filled with some amount of a radio-opaque material such as powdered tantalum, powdered tungsten, bismuth oxide, barium sulfate, and the like. The coil material is first wound into a primary coil (102, 202). The primary coil is typically linear after it has been wound. Generally speaking, when the coil (102, 202) is a metallic coil and that coil is a platinum alloy or a superelastic alloy such as nitinol, the diameter of the wire used in the production of the coil (102, 202) will be in the range of 0.0064 and 0.152 mm (0.00025 and 0.006 inches). The wire is wound into a primary coil (102, 202) having a primary diameter of between 0.076 and 0.635 mm (0.003 and 0.025 inches). For most neurovascular indications, the preferable primary coil (102, 202) diameter is 0.2 to 0.46 mm (0.008 to 0.018 inches). We have generally found that the coil wire may be of sufficient diameter to provide a hoop strength to the resulting device sufficient to hold the device in place within the chosen body site, lumen or cavity, without substantially distending the wall of the site and without moving from the site as a result of the repetitive fluid pulsing found in the vascular system. The axial length of the primary coil will usually fall in the range of 0.5 to 100 cm, more usually 2.0 to 40 cm. Depending upon usage, the coil may well have 10-75 turns per centimeter, preferably 10-40 turns per centimeter. All of the dimensions here are provided only as guidelines and are not critical to the invention. However, only dimensions suitable for use in occluding sites within the human body are included in the scope of this invention. Once the primary coil (102, 202) is wound, the stretch-resisting member (108, 208) is inserted into the lumen of the primary coil (102, 202) and secured to the coil as desired. Ends (104, 204, 106, 206) are preferably of the same diameter as is the primary coil (102, 202). Suitable polymeric materials for the polymeric stretch-resisting member (108) can be either thermosetting or thermoplastic. Thermoplastics are preferred because they allow simplification of the procedure for constructing the device (100) since they may be melted and formed into the end or ends (104, 106). Simple devices such as soldering irons may be used to form the ends. Thermosetting plastics would typically be held in place by an adhesive. Suitable polymers include most biocompatible materials which may be made into fibers but include polyester such as polyethylene terephthalate (especially Dacron) and polyamides including the Nylons, polyglycolic acid, polylactic acid, fluoropolymers (polytetrafluoro-ethylene), or even silk. Especially preferred because of the long history of safe and effective usage in the human body is fibrous polyethylene terephthalate (PET) sold as Dacron. Figure 2A shows a side-view partial cross-section of one end of a coil (100). Figure 2A also shows the helically wound outer coil (102) having an end (106) which is formed from a formerly molten fiber which also makes up the stretch-resisting member (114). An end of this type may be considered to have modestly higher vaso-occluding properties than a metallic end. Other functional euqivalents to this structure include ends (106) formed of glues such as epoxies and their equivalents, and which are mechanical in nature. Figure 2B shows an external knot (112) which fixes the length of the coil member (102) and keeps it from stretching; Figure 2C shows a reformed mass of formerly molten polymer or of glue which is of a diameter larger than the inner diameter of coil (102) and prevents the coil from stretching. The knot (112) and block (114) are not shown to be attached to the coil (102) but may be. To be in accordance with the present invention a device must have its stretch-resisting member attached to the coil in at least two locations, at least one of these locations being between the opposite ends of the coil. The devices shown in Figures 1A, 1B, 1C and 2A, 2B, and 2C are designed to be deployed by use of a pusher and a catheter in the manner discussed in Ritchart et al, discussed above. Other methods (and concomitant fixtures or joints to accomplish those methods) may also be used. For instance, the end ofthe device may be adapted to accept an electrolytically severable joint of the type discussed in US Patent No. 5,354,295 and its parent, 5,122,136, both to Guglielmi and Sepetka, described above. Figures 3A and 3B depict, in partial cross section, such variations. The vaso-occlusive coil (130, 230) is attached to a fill member (132, 232). The fill member (132, 232) preferably comprises a thermoplastic formed into place or an epoxy or the like and adheres, in turn, both to the stretch resistant member (134, 234) and the core wire (136, 236). The core wire (136, 236) in this variation has an enlarged member which is embedded in the fill member (132, 232). The core wire (136, 236) is insulated, typically with a combination of polytetrafluoroethylene and parylene (polyparaxyxylene), except for a small sacrificial joint (138, 238) which is intended to be the site of the electrolysis as the joint (138, 238) is eroded or severed and the coil deployed into the body site. The details of this variation (sans stretch-resistant member (136, 236)) are discussed in Gia et al, US Patent application Serial No. 08/367,061, filed December 30, 1994. Figure 4A shows still another variation of a joint for releasing the inventive coil into a site within the human body. In this instance, the joint is mechanically deployed. The primary coil (140) incorporates interlocking clasps, one (142) located on an end of the coil (140) and one (144) located on the end of a pusher (146). The stretch-resisting member (148) is attached to the interlocking clasp (142) via a filler block (154). Again, the filler block (154) comprises a material (e.g., a thermoplastic or adhesive material) which may be placed in the coil and will adhere to the stretch-resistant member (148). The coil assembly (150), made up of the primary coil (140), interlocking clasp (142), and stretch-resisting member (148) is deployed by retracting catheter body (or sheath) (152). Figure 4B shows a variation of the device depicted in Figure 4A which does not employ special filler block material (154) for adhering to the stretch-resistant member. Other mechanically deployable joints suitable for use with the inventive coil are described in: US Patent No. 5,234,437, to Sepetka, (shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces). US Patent No. 5,250,071, to Palermo, (shows an embolic coil assembly using interlocking clasps mounted both on the pusher and on the embolic coil) US Patent No. 5,261,916, to Engelson, (shows a detachable pusher/vaso-occlusive coil assembly having an interlocking ball and keyway-type coupling) US Patent No. 5,304,195, to Twyford et al. (shows a pusher-vaso-occlusive coil assembly having an affixed, proximally extending wire carrying a ball on its proximal end and a pusher having a similar end, which two ends are interlocked and disengage when expelled from the distal tip of the catheter) US Patent No. 5,312,415, to Palermo (also shows a method for discharging numerous coils from a single pusher by use of a guidewire which has a section capable of interconnecting with the interior of the helically wound coil). US Patent No. 5,350,397, to Palermo et al. (shows a pusher having a throat at its distal end and a pusher through its axis. The pusher sheath will hold onto the end of an embolic coil and will then be released upon pushing the axially placed pusher wire against the member found on the proximal end of the vaso-occlusive coil). As was noted above, the devices of this invention may have the simple linear shape shown in Figures 1 and 2 or may have shapes which are not so simple. Figures 5, 6, and 7 show what are termed "secondary" shapes in that they are formed from the primary coil by the simple act of winding the primary coil on a form of a desired shape and then heat treating the so-formed shape. Figure 5 shows a "C" shaped coil assembly (160) having a stretch-resistant member (162). Figure 6 shows a clover-leaf shaped coil assembly (164) also having a stretch-resistant member (162). Figure 7 shows a double-loop coil assembly (166). These are indicative of the various secondary shapes suitable for this invention. Additionally, these inventive devices may also. be used in conjunction with various external fiber adjuncts. Figure 8 shows a partial side-view of a linear variation of the inventive device (170) having filamentary material (172) looping through the coil (174). This method of attachment is described in greater detail in US Pat. Nos. 5,226,911 and 5,304,194, to Chee et al. A further description of a desirable fiber attachment is shown in US Pat. application No. 08/265,188, to Mirigian et al, filed June 24, 1994. Figure 9 shows a partial cutaway of a device (180) having a braided covering (182) of a filamentary material and a stretch-resisting member (184). This method of enveloping a coil is described in greater detail in US Pat. Nos. 5,382,259, to Phelps et al. The fibrous woven or braided tubular materials may be made from a biocompatible materials such as Dacron (polyester), polyglycolic acid, polylactic acid, fluoropolymers (polytetrafluoroethylene), Nylon (polyamide), or silk. The strands forming the braid should be reasonably heavy, e.g., having tensile strength of greater than about 0.66 N (0.15 pounds). The materials mentioned, to the extent that they are thermoplastics, may be melted or fused to the coils. Alternatively, they may be glued or otherwise fastened to the coils. Preferred materials are Dacron. Figures 10A-10D depict a common deployment method for introduction of the vaso-occlusive devices of the present invention. It may be observed that these procedures are not significantly different than those described in the Ritchart et al. patent mentioned above. Specifically, Figure 10A shows the distal tip of a delivery catheter (310) which is within the opening (312) of an aneurysm (314) found in an artery (316). The distal or end section of the vaso-occlusive device (318) is shown within the catheter (310). In Figure 10B, the distal end portion of the vaso-occlusive device (318) has exited the distal end of the catheter (310) and has wound into a secondary shape within the aneurysm (314). Figure 10C shows the completion of the formation of the secondary shape within the aneurysm (314). Figure 10D shows the separation of the vaso-occlusive device (318) from the pusher, placement within the aneurysm (314), and the withdrawal of the catheter from the mouth of the aneurysm. Once the inventive coil is in place in an aneurysm or other site, there may be an occasion during which the coil must be moved or even withdrawn. For instance, in Figure 10D, the coil might extend through the mouth (312) of the aneurysm into the artery. Occlusion would not be desirable in the artery. A device such as the endovascular snare shown in US Pat. No. 5,387,219, to Rappe, may then be used to grasp the exposed coil and move it or retrieve it from the body. The stretch-resisting member of this invention prevents the coil from stretching into a single strand of wire and multiplying in length. Modification of the above-described variations of carrying out the invention that would be apparent to those of skill in the fields of medical device design generally, and vaso-occlusive devices specifically, are intended to be within the scope of the following claims.

Claims: A stretch-resisting vaso-occlusive device, wherein the device is of a size and shape which can be introduced into an aneurysm and comprises: i. an outer stretchable member (102) having a first end (104) and a second end (106) and defining a lumen between said first and second ends; and ii. a stretch-resisting member (108) attached to said outer stretchable member in at least two attachment locations so as to resist stretching of said outer stretchable member, said stretch-resisting member extending between said attachment locations within the lumen; characterised in that at least one of said attachment locations is between the first and second ends of said outer stretchable member said at least one attachment location not being at an end. The device of claim 1, wherein said outer stretchable member comprises a polymer containing a radio-opaque filler. The device of any one of the preceding claims, additionally comprising external filamentary material (172) attached to said outer stretchable member (174). The device of any one of the preceding claims, wherein the stretch-resisting member comprises a polymer. The device of any one of the preceding claims, wherein the stretch-resisting member comprises a thermoplastic. The device of claim 5, wherein said thermoplastic comprises polyethylene terephthalate.

Inventors: ENGELSON ERIK T, GIA SON M, KEN CHRISTOPHER G M, ENGELSON, ERIK T., GIA, SON M., KEN, CHRISTOPHER G.M.
Applicants: BOSTON SCIENT LTD, BOSTON SCIENTIFIC LIMITED
Application year: 1996
Main classification: A61B17
IPC codes: A61B17, A61F2, A61B19