CA2543840A1

CA2543840A1 - Vaso-occlusive devices with in-situ stiffening elements

Info

Publication number: CA2543840A1
Application number: CA002543840A
Authority: CA
Inventors: Stephen C. Porter
Original assignee: Individual
Current assignee: Boston Scientific Ltd Barbados
Priority date: 2003-10-27
Filing date: 2004-10-08
Publication date: 2005-05-19
Also published as: EP1680030A1; US7645292B2; US20050090861A1; EP1680030B1; ATE496582T1; WO2005044113A1; DE602004031248D1; JP2007509650A

Abstract

Vaso-occlusive devices for occluding a body cavity include an internal element located within a lumen of the device. The internal element may include an active element (214) configured to stiffen the coil in-situ made from a material that can expand to a desired size, thereby inducing a radial stress to the coil to stiffen the occlusive device. Alternatively, the active element is secured to two points on the occlusive device, and is made from a material that contracts, thereby inducing a compression to stiffen the device.

Description

VASO-OCCLUSIVE DEVICES WITH IN-SITU STIFFENING ELEMENTS
FIELD OF INVENTION
The invention pertains to medical devices, and more particularly to vaso-occlusive devices with in-situ stiffening elements to assist the devices to retain their deployed shape.
BACKGROUND
In many clinical situations, blood vessels are occluded for a variety of purposes, such as to control bleeding, to prevent blood supply to tumors, and to block blood flow within an aneurysm, arteriovenous malformation, or arteriovenous fistula. Vaso-occlusive devices are surgical implants placed within blood vessels or vascular cavities, typically by using a catheter as a conduit, to arrest blood flow, form a thrombus and occlude the site. For instance, a stroke or other such vascular occurrence may be treated by placing a vaso-occlusive device proximal of the site to block the flow of blood to the site and alleviate the leakage. An aneurysm may similarly be treated by introducing one or more vaso-occlusive devices through the neck of the aneurysm. The placement of the vaso-occlusive devices) helps cause a mass to form in the aneurismal sac and alleviate the potential for growth of the aneurysm and its subsequent rupture.
There are a variety of known vaso-occlusive devices suitable for creating an embolic obstruction for therapeutic purposes. One such device is found in U.S. Patent No. 4,994,069, to Ritchart et al.. That patent describes a vaso-occlusive coil that assumes a linear helical configuration when stretched and a folded convoluted configuration when relaxed. The coil has a stretched configuration when placed in a catheter, which is used in placement of the coil at the desired site, and assumes the convoluted configuration when the coil is ejected from the catheter and the coil relaxes. Ritchart et al. describes a variety of shapes, including "flower" shapes and double vortices. A random shape is described as well.
Vaso-occlusive coils having complex, three-dimensional structures in a relaxed configuration are described in U.S. Patent No. 6,322,57681 to Wallace et al. The coils may be deployed in the approximate shape of a sphere, an ovoid;
a clover, a box-like structure or other distorted spherical shape. The patent also describes methods of winding the anatomically shaped vaso-occlusive device into appropriately shaped forms and annealing them to form various devices.
One problem associated with existing vaso-occlusive. devices is that they may not have a sufficient strength or stiffness to retain their shape after they are delivered into an aneurysm. When the above-mentioned vaso-occlusive devices are placed within an aneurysm, they tend to induce a formation of a thrombi for occlusion of the aneurysm. However, with time and the influence of hemodynamic forces and thrombolytic processes, the delivered vaso-occlusive devices may move or change shape due to their relatively low stiffness or through the process of seeking a minimally energetic morphology. As a result, the delivered vaso-occlusive devices may move out of the position or shape in which they were originally placed. In some cases, the delivered vaso-occlusive devices may even dislodge out of the sack of an aneurysm.

SUMMARY OF THE INVENTION
Avaso-occlusive device having an internal active element with in-situ stiffening capability is provided. In one embodiment, the vaso-occlusive device includes a coil, with the active element disposed within a lumen of the coil.
The active element can have any of a number of shapes, such as, by way of non-limiting examples, an elongate shape, a form of a sphere, a cone, a plate, a mesh, or some other customized shape. By way of a further non-limiting example, the active element can be made from an expansive material, such as a hydrogel, that causes the active element to expand when placed in a body. In such an embodiment, the expanded active element imparts a radial stress within the coil to thereby stiffen and stabilize the shape of at least a portion of the coil in-situ.
Alternatively, the active element can be made from a material that causes the active element to contract when placed in a body. In such an embodiment, the active element may be anchored or secured to the coil at two points along a length of the coil. When the active element contracts, it compresses the coil between the two points of attachment, to thereby stiffen and stabilize the shape of at least a portion of the coil in-situ.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings illustrate the design and utility of embodiments of the invention, in which similar elements are referred to by common reference numerals, and in which:

FIG. 1 is a side view of a vaso-occlusive device in accordance with another embodiment, including an active element disposed within a lumen of a coil;
FIG. 2 is a side view of the vaso-occlusive device of FIG. 1, showing the active element having an expanded configuration;
FIGS. 3-5 are side views of embodiments of vaso-occlusive devices; and FIGS. 6-12 show embodiments of vaso-occlusive devices having secondary shapes.
DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS
The vaso-occlusive device 200 of FIG. 1 is provided with an active element 214 configured to provide in-situ stiffening of the coil 200. The coil is made from a linear element 216, such as a wire, which preferably has a circular cross-sectional shape. Alternatively, the linear element 216 of the coil 212 may have a rectangular, triangular, other geometric cross-section, or an irregular shaped cross-section.
The coil 212 includes one or more loops or windings 218 formed by the linear element 216. The loops 218 define a central lumen 220 in which the active element 214 is placed. Any of the materials described previously with reference to the coil 12 is also suitable for construction of the coil 212. In the illustrated embodiment, the vaso-occlusive device 200 has an overall diameter or cross-section which is preferably in the range of 0.010 to 0.023 inches. However, the vaso-occlusive device 200 may have other diameters and/or cross-sections, as well. The vaso-occlusive device 200 may optionally include one or more end caps 222 secured to a first end 224 and/or a second end 226 of the coil 212.
As shown in FIG. 1, the active element 214 includes an axially oriented element 230 having a substantially rectilinear or a curvilinear (less than 360°) configuration along a length of the vaso-occlusive device 200. Again, in the case of more complex coil shapes, the active element could mirror the shape of the coil. The axially oriented element 30 is located within the lumen 220 of the coil 212 and is secured to the ends 224 and 226 or the end caps 222 of the coil 212.
The securing may be accomplished by any of the methods described previously.
In alternative embodiments, instead of securing to both ends 224 and 226 of the coil 212, the axially oriented element 230 can be secured to the coil 212 at one of the ends 224 and 226 of the coil 212 or at one or more points along a length of the coil 212 by a suitable adhesive or by wrapping around one or more windings 218 of the coil 212. Furthermore, in another embodiment, the axially oriented element 230 is not secured to the coil 212. In this case, the axially oriented element 230 is simply disposed within the lumen 220 of the coil 212, or is coupled to the coil 210 by a surface friction, in which case, the surface of the axially oriented element 230 may be textured to improve the coupling force between the axially oriented element 230 and the coil 212.
The active element 214 is configured to undergo a reaction that changes a structural characteristic of the vaso-occlusive device 200 when placed in a body cavity. In one embodiment, the active element 214 includes an expansible material, which will expand in size when placed in an aqueous environment within a living mammal. In this case, the cross-section of the active element is configured such that it can expand to a size which is slightly larger than the internal diameter (or the lumen 220) of the coil 212 (FIG. 2). In one embodiment, the cross-sectional dimension of the active member 214 is configured such that its swollen cross-sectional dimension is at least equal to 100% - 500%, and more particularly, between 110% - 200%, of the internal diameter of the coil 212.
The expanded material imparts a radial stress within the coil 212 to thereby stiffen and stabilize the coil 212 in-situ.
An example of the expansible material that can be used for construction of the active element 214 is a hydrogel, which is capable of absorbing a desired amount of aqueous fluid. Examples of hydrogels include gels formed from homopolymers, copolymers, and/or network polymers containing: polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylates, polymethacrXlates, polyacrylamides, polyethyloxazoline, polysaccharides, mucopolysaccharides, polyaminoacids, carboxy alkyl celluloses, partially oxidized cellulose, hyaluronic acid, dextran, heparin sulfate, chondroitin sulfate, heparin, agar, starch, alginate, fibronectin, gelatin, collagen, fibrin, pectins, albumin, polyesters of .alpha.-hydroxy acids including polyglycolic acid, poly-DL-lactic, poly-L-lactic acid, polylactones, polyanhydrides, polyorthoesters, polydioxanone, polycaprolactones, poly(delta-valerolactone), poly(gamma-butyrolactone), and combinations thereof. The gel may further comprise a chemical cross-linking agent having two or more reactive groups in order to form chemical bridges between two or more polymeric molecules.

Examples of such cross-linking agents include diacrylates, oligoacrylates, dimethacrylates, oligomethacrylates, divinyl ethers, certain cations, and combinations thereof.
The active element 214 can also include a radiopaque material mixed or coated with the hydrogel, or alternatively, include a radiopaque marker secured to the active element 214.
Other expansive materials that respond to changes in moisture, ionic strength, temperature, pH, or materials that selectively absorb blood borne substances (e.g. silicones or other polymers which absorb lipids) may also be used. The rate at which the active element 214 expands may be customized, such as by changing a composition of the active element 214, so that placement and repositioning of the coil 212 may be performed within a period after it has been delivered to a site. The rate at which the active element 214 expands may also be customized or by varying a spacing between the pitch of the coil 212, thereby controlling the amount of bodily fluid that flows into the lumen 220 of the coil 212. The rate may also be controlled by a coating that may be soluble or insoluble which, in either case, limits diffusion of water into the active element.
In another embodiment, the active element 214 can be made from a material that undergoes contraction due to an environmental stimuli, such as moisture, , ionic strength, pH temperature. In this case, the active element 214 is secured to the coil 212 at two points along a length of the coil 212. For example, the active element 214 can be secured to the ends 224 and 226 of the coil 212 using any of the methods described previously. Alternatively, the active element 214 can also be secured to the coil 212 along its length by an adhesive or by wrapping around the loops 218 of the coil 212. When the active element 214 is placed inside a body, it reacts with a stimuli, such as blood or other bodily fluids, and undergoes contraction. Contraction of the active element 214 induces a compressive load on the coil 212 (i.e., the active element 214 compresses the coil 212 between the two points of attachment), which in turn stiffens and stabilizes the coil 212 in-situ.
Contraction of the active element may be achieved, by way of example, by localized injection of a warm fluid or an ionic solution, provided that the material transition is irreversible. Alternatively, the active element may be pre-tensioned, wherein prior to use, the device is conditioned with a solvent (e.g., an aqueous ionic solution or polar organic solvent) to cause initial expansion of the element prior to placement inside a body. Once placed in the body, contact with blood causes the solvent to diffuse out of the active element, further causing it to contract.
Examples of materials that undergoes contraction due to an environmental stimuli includes shape memory alloys and polymers, such as NitinoITM or polyurethanes and poly(norbornene), which contract (or expand) with changes in temperature. Other, temperature-sensitive contracting materials include protein fibers that undergo thermally induced phase transitions or denaturation at or near body temperature, and thermoresponsive hydrogels, which include polymer gels swollen by aqueous solutions which change volume in response to thermally induced molecular motions that alter the balance of hydrophilic/hydrophobic interactions between the polymer chains and the surrounding aqueous environment. Examples of such hydrogels include ones containing n-isopropyl, acrylamide, chitosan, hyaluronic acid, or polyethylene oxide-co-propylene oxide). Examples of materials that contract in response to changes in pH
and/or ionic strength include polyelectrolyte hydrogels, which are polymer gels swollen by aqueous solutions which change volume in response to electrostatic interactions between polymer chains and ions in the surrounding aqueous environment. Examples of such hydrogels include ones containing acrylic acid, n-isopropyl acrylamide, amino acids, carboxyl methacrylate, chitosan or xanthan.
Protein fibers that undergo pH induced phase transitions or denaturation at or near body pH may also be suitable for use as a contracting agent, as would polymer gels comprising a biocompatible polymer swollen with a non-aqueous solvent that will diffuse out of the gel upon contact with water (or blood), such as silicones, urethanes, acrylics and polyesters.
It should be noted that although the vaso-occlusive device 10 has been described as having an agent delivery capability, and the vaso-occlusive device 200 has been described as having an in-situ stifFening capability, the scope of the invention should not be so limited. In an alternative embodiment, a vaso-occlusive device can be configured both to be stiffened in-situ and to deliver a bioactive agent. For example, the vaso-occlusive device 200 configured to be stifFened in-situ can also carry a bioactive agent that causes a tissue reaction when delivered in a body.

While the agent carrier 14 and the active element 214 have been described as having a substantially rectilinear or curvilinear (less than 360°) shape, they are not limited to such shapes, but can have other shapes or configurations in alternative embodiments so long as they are located substantially within the central lumen of the coil.
FIGS. 4-6 each shows a vaso-occlusive device 300 having a coil 302 and an internal element 304 in accordance with alternative embodiments of the present invention. The coil 302 in these figures represents the coil 12 or the coil 212 described previously, and the internal element 304 represents the agent carrier 14 or the active element 214 described previously.
FIG. 3 shows a vaso-occlusive device 300(1 ) that includes a coil 302 and an internal element 304(1 ) having a shape of a coil. As similarly discussed previously, the internal element 304(1 ) may be secured to one or both ends of the coil 302, secured to the coil 302 at one or more points along a length of the coil 302, or coupled to the coil 302 by a surface friction.
FIG. 4 shows another vaso-occlusive device 300(2) that includes a coil 302 and one or more internal elements 304(2). In this case, the internal element 304(2) does not extend approximately from one end to the other end of the coil 302. Instead, the internal element 304(2) only extends along a portion of the length of the coil 302. In the illustrated embodiment, the internal element 304(2) has a shape of a cylinder. However, the internal element 304(2) can also have other shapes or configurations. For examples, the internal element 304(2) can be in a form of a sphere, a cone, a plate, a mesh, or other customized shapes.

FIG. 5 shows a vaso-occlusive device 300(3) that includes an internal element 304(3) having a random shape.
The vaso-occlusive devices shown in the above-described embodiments generally have a substantially rectilinear (straight) or a curvilinear (slightly curved, i.e. having less.than 360° spiral) relaxed configurations. Such devices may assume folded or bent configurations when they are subjected to an external force (e.g., compressive forces generated when they are pushed against an object, such as the wall of an aneurysm). The devices may also assume a variety of secondary shapes or relaxed configurations. The space-filling capacity of these vaso-occlusive devices is inherent~within the secondary relaxed shape of these devices.
FIGS. 7-13 illustrate various vaso-occlusive devices 400 that include a coil 402 having a primary shape and a secondary shape. These shapes are simply indicative of the various secondary shapes that may be used, and other shapes may be used as well. While not always shown, the devices 400 illustrated in FIGS. 7-13 are each provided with an internal element 304, which can be the agent carrier 14 or the active element 214, as discussed previously.
FIG. 6 depicts a device 400(1 ) having a secondary shape of a clover leaf.
FIG. 7 depicts a device 400(2) having a secondary shape of a twisted figure-8.
FIG. 8 depicts a device 400(3) having a flower-shaped secondary shape. FIG. 9 depicts a device 400(4) having a substantially spherical secondary shape. FIG.

10 illustrates a device 400(5) having a random secondary shape. FIG. 11 illustrates a device 400(6) having a secondary shape of a vortex. FIG. 12 illustrates a device 400(7) having a secondary shape of an ovoid. It should be noted that vaso-occlusive device 400 may also have other secondary shapes, and that it should not be limited to the examples illustrated previously. To make a secondary shaped vaso-occlusive device 400, a coil (i.e., the coil 402) having a primary shape that is substantially rectilinear or curvilinear may be wrapped around a mandrel or other shaping element to form a secondary shape. The coil 402 may be heat treated to shape the coil 402 into the secondary shape.

Claims

1. A vaso-occlusive device, comprising:
an occlusive member having a lumen; and an active element carried in the lumen, wherein the active element expands or contracts when placed in a body to thereby cause the occlusive member to substantially retain its shape when deployed in a body cavity.

2. The vaso-occlusive device of claim 1, wherein the active element is secured at one or more locations along a length of the occlusive member.

3. The vaso-occlusive device of claims 1 or 2, wherein the active element comprises a hydrogel.

4. The vaso-occlusive device of claim 3, wherein the hydrogel comprises a homopolymer, copolymer, network polymer, or some combination or sub-combination thereof.

5. The vaso-occlusive device of claim 4, wherein the hydrogel comprises one or more of polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylates, polymethacrylates, polyacrylamides and polyehyloxazoline.

6. The vaso-occlusive device of claim 5, wherein the hydrogel further comprises one or more chemical cross-linking agents.

7. The vaso-occlusive device of claim 3, wherein the hydrogel comprises one or more of polysaccharides, mucopolysaccharides, polyaminoacids, carboxy alkyl celluloses, partially oxidized cellulose, hyaluronic acid, dextran, heparin sulfate, chondroitin sulfate, heparin, agar, starch, alginate, fibronectin, gelatin, collagen, fibrin, pectins, albumin and ovalbumin.

8. The vaso-occlusive device of claim 7, wherein the hydrogel further comprises one or more chemical cross-linking agents.

9. The vaso-occlusive device of claim 3, wherein the hydrogel comprises one or more polyester of alpha-hydroxy acids including polyglycolic acid, poly-DL-lactic, poly-L-lactic acid, polylactones, polyanhydrides, polyorthoesters, polydioxanone, polycaprolactones, poly(delta-valerolactone), and poly(gamma-butyrolactone).

10. The vaso-occlusive device of claim 9, wherein the hydrogel further comprises one or more chemical cross-linking agents.

11. The vaso-occlusive device of claim 3, wherein the hydrogel is thermoresponsive.

12. The vaso-occlusive device of claim 3, wherein the hydrogel comprises a polyelectrolyte.

13. The vaso-occlusive device of claim 12, wherein the polyelectrolyte undergoes an ionic concentration induced shape change at or near the ionic concentration present in blood plasma.

14. The vaso-occlusive device of any of claims 1-13, wherein the occlusive member is a coil.

15. The vaso-occlusive device of claim 14, wherein the active element has a coil shape.

16. The vaso-occlusive device of any of claims 1-13, wherein the active element expands when placed in the body, and when in the body, may be expanded to have a cross-sectional dimension that is at least 100% of an internal diameter of the occlusive member.

17. The vaso-occlusive device of claim 16, wherein the active element, when in the body, may be expanded to have a cross-sectional dimension between 100% and 200% of the internal diameter of the occlusive member.

18. The vaso-occlusive device of claims 1 or 2, wherein the active element comprises a shape memory alloy.

19. The vaso-occlusive device of claims 1 or 2, wherein the active element comprises a shape memory polymer.

20. The vaso-occlusive device of claims 1 or 2, wherein the active element is a fiber comprising protein.

21. The vaso-occlusive device of claim 20, wherein the fiber comprising protein undergoes a thermally induced phase transition or denaturation at or near body temperature.

22. The vaso-occlusive device of claim 20, wherein the fiber comprising protein undergoes a pH induced phase transition or denaturation at or near body pH.

23. The vaso-occlusive device of claims 1 or 2,. wherein the active element is a polymer gel comprising a biocompatible polymer swollen with a non-aqueous solvent that will diffuse out of the gel upon contact with blood.

24. The vaso-occlusive device of claims 1 or 2, wherein the active element expands or contracts within about forty-eight hours after being placed in a body.

25. The vaso-occlusive device of claim 24, wherein the active element expands contracts within about ten to twenty minutes after being placed in a body.