Patent Application
20100125326
The technical field of this disclosure is medical implant devices, particularly, braided stents.
Stents are generally cylindrical shaped devices that are radially expandable to hold open a segment of a blood vessel or other anatomical lumen after implantation into the body lumen. Stents have been developed with coatings to deliver drugs or other therapeutic agents.
Stents are used in conjunction with balloon catheters in a variety of medical therapeutic applications including intravascular angioplasty. For example, a balloon catheter device is inflated during PTCA (percutaneous transluminal coronary angioplasty) to dilate a stenotic blood vessel. The stenosis may be the result of a lesion such as a plaque or thrombus. After inflation, the pressurized balloon exerts a compressive force on the lesion thereby increasing the inner diameter of the affected vessel. The increased interior vessel diameter facilitates improved blood flow. Soon after the procedure, however, a significant proportion of treated vessels re-narrow.
To prevent restenosis, short flexible cylinders, or stents, constructed of metal or various polymers are implanted within the vessel to maintain lumen size. The stents acts as a scaffold to support the lumen in an open position. Various configurations of stents include a cylindrical tube defined by a mesh, interconnected stents or like segments. Some exemplary stents are disclosed in U.S. Pat. No. 5,292,331 to Boneau, U.S. Pat. No. 6,090,127 to Globerman, U.S. Pat. No. 5,133,732 to Wiktor, U.S. Pat. No. 4,739,762 to Palmaz and U.S. Pat. No. 5,421,955 to Lau. Balloon-expandable stents are mounted on a collapsed balloon at a diameter smaller than when the stents are deployed. Stents can also be self-expanding, growing to a final diameter when deployed without mechanical assistance from a balloon or like device.
One approach has been to fabricate stents from braided fibers, such as polymer fibers, for making a braided stent with little or no metal. Concern over the long-term effects of stents in the body has led to experimentation with bioabsorbable stents, i.e., stents that are absorbed by the body after deployment. Unfortunately, braided polymer stents often undergo plastic relaxation in the delivery system, leading to a smaller deployment diameter. They also often lack the radial strength to prop open the vessel and maintain a fixed position in the vessel lumen. One approach to alleviate this problem has been to increase the diameter of the fibers forming the braided stent to increase the radial strength. Unfortunately, this increases the crossing profile of the compressed stent, reducing maneuverability and the ability to deploy the stent in smaller vessels. An increased fiber diameter may also increase the time for a bioabsorbable stent to be absorbed and interrupt blood flow dynamics.
Another approach to this problem has been to attach elastomeric axial runners to the braided fiber body. Unfortunately, the elastomeric runners can cause problems during storage and deployment. During storage, the elastomeric runners constantly exert force on the braided fiber body, which can permanently distort the braided fiber body. The elastomeric runners can also lose their elasticity with age and the constant loading and become ineffective. During deployment, the elastomeric runners exert force on the braided fiber body as the braided stent leaves the compressing sheath, so placement of the expanding braided stent is difficult. Due to the high degree of foreshortening of braided stents during deployment, an elastomeric material which has sufficient strength to open a stent would likely deform the undeployed stent when stretched to its full length in the delivery system.
It would be desirable to have a braided stent that would overcome the above disadvantages.
One aspect of the present invention provides a stent delivery system including a catheter; and a stent disposed on the catheter. The stent includes a braided stent framework having a first framework end and a second framework end; and a plurality of shortenable tethers, each of the plurality of shortenable tethers having a first tether end and a second tether end, the plurality of shortenable tethers being disposed along a length of the braided stent framework and fixed to the braided stent framework at the first tether end and the second tether end. The plurality of shortenable tethers shorten in response to vessel conditions to urge the first framework end and the second framework end toward each other when the stent is deployed in a vessel to urge a circumference of the braided stent framework toward a vessel wall.
Another aspect of the present invention provides a stent for use in a vessel having a vessel wall including a braided stent framework having a first framework end and a second framework end; and a plurality of shortenable tethers, each of the plurality of shortenable tethers having a first tether end and a second tether end, the plurality of shortenable tethers being disposed along a length of the braided stent framework and fixed to the braided stent framework at the first tether end and the second tether end. The plurality of shortenable tethers shorten in response to vessel conditions to urge the first framework end and the second framework end toward each other when the stent is deployed in the vessel to urge a circumference of the braided stent framework toward the vessel wall.
Another aspect of the present invention provides a stent for use in a vessel having a vessel wall including a braided stent framework having a first framework end and a second framework end; and means for urging the first framework end and the second framework end toward each other in response to vessel conditions when the stent is deployed in the vessel to urge a circumference of the braided stent framework toward the vessel wall.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention, rather than limiting the scope of the invention being defined by the appended claims and equivalents thereof.
The stent 120 can be any variety of braided implantable prosthetic devices known in the art. In one embodiment, the stent 120 can be capable of carrying a coating, such as a polymer coating carrying one or more therapeutic agents, such as anti-inflammatory agents or anti-proliferative agents. In another embodiment, the stent 120 can include one or more therapeutic agents within the stent material. The stent 120 can be bioabsorbable.
Referring to
The shortenable tethers 130 are shortenable, which is defined herein as having a first length when not deployed in a vessel and having a second length shorter than the first length in response to vessel conditions when deployed in a vessel. The shortenable tethers 130 can shorten in the vessel due to vessel conditions of temperature, exposure to liquid, a combination thereof, or any other vessel condition that causes the material of the shortenable tether 130 to shorten. Each of the shortenable tethers 130 has a first tether end 132 and a second tether end 134. The shortenable tethers 130 are disposed along the length of the braided stent framework 122, and are fixed to the braided stent framework 122 at the first tether end 132 and the second tether end 134. In operation, the shortenable tethers 130 shorten to urge the first framework end 124 and the second framework end 126 toward each other when the stent 120 is deployed in the vessel to urge the circumference of the braided stent framework 122 toward the vessel wall.
The fibers 128 of the braided stent framework 122 are sufficiently flexible and braided in pattern such that urging the framework ends toward each other increases the circumference of the braided stent framework 122. The fibers 128 of the braided stent framework 122 can be made of a wide variety of medical implantable materials, such as stainless steel (particularly 316-L or 316LS stainless steel), MP35 alloy, nitinol, tantalum, ceramic, nickel, titanium, aluminum, degradable and/or nondegradable polymeric materials, tantalum, MP35N, titanium ASTM F63-83 Grade 1, niobium, high carat gold K 19-22, and combinations thereof. The fibers 128 can be single fibers or can be braided. In one example, the fibers 128 can be made of a nondegradable polymer such as polyethylene naphathalate. In another example, the fibers 128 can be made of a bioabsorbable polymer such as poly(lactide-co-glycolide), poly(L-lactide), poly(L,DL,-lactide), poly(lactide-co-lactide-co-trimethylene carbonate), poly(lactide-co-carprolactone), poly(ε-arprolactone), or blends thereof. Those skilled in the art will appreciate that the fibers 128 at the first framework end 124 and second framework end 126 can be free of each other or connected together as desired for a particular application.
The shortenable tethers 130 can be made of any material having a first length when not deployed in a vessel and shortening to a second length shorter than the first length in response to vessel conditions when deployed in a vessel. Exemplary materials include homopolymers and copolymers (including random and block polymers) of D-lactide, L-lactide, DL-lactide, carprolactone, trimethylenecarbonate, glycolide, carprolactone derivatives, P-Dioxanone, and combinations thereof. Polyethylene oxide can be part of the polymer chain. Another exemplary material is degradable polyurethane. In one embodiment, the shortenable tethers 130 can be made of a shape memory polymer that shortens due to temperature change when released from a constraining sheath into physiologic conditions. Exemplary shape memory polymers include block polymers of poly(lactide-b-carprolactone), copolymers of oligo(ε-caprolactone)diol and crystallisable oligo(ρ-dioxanone)diol, and the like. In another embodiment, the shortenable tethers 130 can be made of a shrinkable polymer that shortens when exposed to liquid, heat, or a combination thereof. Exemplary shrinkable polymers include degradable polyurethane, and the like. The shortenable tethers 130 can attain shortenable properties in an initial extrusion or can be subject to a secondary extrusion that softens and draws down the material. The cross section of the shortenable tethers 130 can be circular, rectangular, ellipsoid, or any other cross section as desired for a particular application.
The body of the shortenable tether 130 between the first tether end 132 and the second tether end 134 is sufficiently free to move to be able to urge the first framework end 124 and the second framework end 126 toward each other. In one embodiment, intermediate points on the body of the shortenable tether 130 between the first tether end 132 and the second tether end 134 can also the attached to the inside or the outside of the braided stent framework 122. The shortenable tethers 130 can be attached at the very end of the braided stent framework 122, i.e., at the edge of the first framework end 124 and the second framework end 126, or can be attached a few fiber crossings in from the very end.
Those skilled in the art will appreciate that the shortenable tethers 130 can be attached to the inside or the outside of the braided stent framework 122, i.e., along the vessel wall or within the stent lumen. In another embodiment, the shortenable tethers 130 can be woven through the braided stent framework 122 so that the shortenable tether 130 passes back and forth through the braided stent framework 122.
The number and placement of the shortenable tethers 130 can be selected to balance the tension about the circumference of each of the first framework end 124 and the second framework end 126. In one example, two shortenable tethers 130 can be located 180 degrees apart on the circumference of the braided stent framework 122. In another example, three shortenable tethers 130 can be located 120 degrees apart on the circumference of the braided stent framework 122. In yet another example, a number of shortenable tethers 130 wrap around the braided stent framework 122 in a helical shape to form a crossed or net pattern.
The first tether end 132 and the second tether end 134 can be attached to the braided stent framework 122 with an adhesive or weld. In one example, the adhesive is an ultraviolet curable adhesive. When the stent 120 is bioabsorbable, the adhesive can also be bioabsorbable. Welding processes include heat welding, laser welding, thermal welding, ultrasonic welding, or the like.
The stent 220 includes a braided stent framework 222 having a first framework end 224 and a second framework end 226, and shortenable tethers 230, 231. In this example, the shortenable tethers 230, 231 wrap around the outside of the braided stent framework 222 in a generally helical arc. Only a single pair of shortenable tethers is shown for clarity of illustration. Typically, another pair of shortenable tethers would be disposed on the opposite side of the braided stent framework 222 to balance the tension about the circumference of framework ends when the stent 220 is deployed. The braided stent framework 222 is formed of a number of fibers 228 braided together to form a generally tubular body.
The shortenable tether 230 has a first tether end 232 and a second tether end 234, and the shortenable tether 231 has a first tether end 233 and a second tether end 235. The shortenable tethers 230, 231 cross at a crossing point 236. The shortenable tethers 230, 231 are disposed along the length of the braided stent framework 222, and are fixed to the braided stent framework 222 at the tether ends. In operation, the shortenable tethers 230, 231 shorten to urge the first framework end 224 and the second framework end 226 toward each other when the stent 220 is deployed in the vessel to urge the circumference of the braided stent framework 222 toward the vessel wall.
In one embodiment, the crossed pattern can be extended into a net pattern encircling the braided stent framework 222. Adjacent tether ends at one framework end can be joined or affixed to the braided stent framework 222 so that the shortenable tethers form a continuous mesh. In one embodiment, a particular shortenable tether can cross more than one other shortenable tether in forming the net pattern, which is defined herein as a crossed pattern that passes around the circumference of the braided stent framework 222. The crossed pattern can be symmetric and at a lower braid angle with respect to the longitudinal axis than fibers making up the braid. Shortenable tethers that arc around the stent framework are subject to less strain during crimping than axial aligned shortenable tethers, and as such, are less likely to plastically deform the stent framework during crimping and storage.
The stent 320 includes a braided stent framework 322 having a first framework end 324 and a second framework end 326, first shortenable tethers 330, second shortenable tethers 331, and third shortenable tethers 336. The braided stent framework 322 is formed of a number of fibers 328 braided together to form a generally tubular body.
The first shortenable tethers 330 have a first tether end 332 and a second tether end 334, the second shortenable tethers 331 have a first tether end 333 and a second tether end 335, and the third shortenable tethers 336 have a first tether end 337 and a second tether end 338. The shortenable tethers 330, 331, 336 are disposed along the length of the braided stent framework 322, and are fixed to the braided stent framework 322 at the tether ends.
The shortenable tethers 330, 331, 336 are staggered, i.e., the axial position of the second tether ends 334 of the first shortenable tethers 330 overlaps the axial position of the first tether ends 333 of the second shortenable tethers 331 and the axial position of the second tether end 335 overlaps the axial position of the first tether ends 337 of the third shortenable tethers 336. In operation, the shortenable tethers 330, 331, 336 shorten to shorten the axial portion of the braided stent framework 322 adjacent the shortenable tethers, urging the circumference of the braided stent framework 322 in that axial portion toward the vessel wall. Those skilled in the art will appreciate that the shortenable tethers can be provided over a single axial portion of the braided stent framework to expand the circumference of just that single axial portion, or can be provided over a number of axial portions of the braided stent framework to expand the circumference of a number of axial portions.
It is important to note that
While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.
