Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent in combination with graft
Reexamination Certificate
2001-01-16
2003-04-15
Truong, Kevin T. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent in combination with graft
C606S198000
Reexamination Certificate
active
06547814
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to endoluminal stent-graft devices suitable for percutaneous delivery into a body through anatomical passageways to treat injured or diseased areas of the body. More particularly, the present invention relates to a method of bonding microporous polytetrafluoroethylene (“PTFE”) coverings over a stent scaffold in a manner which maintains unbonded regions to act as slip planes or pockets to accommodate planar movement of stent elements. In one embodiment of the present invention bonded and unbonded regions are formed by means of a mandrel which has a pattern of either raised projections or recesses in its surface which are either synchronous or asynchronous, respectively, with stent elements.
The use of implantable vascular grafts comprised of PTFE is well known in the art. These grafts are typically used to replace or repair damaged or occluded blood vessels within the body. However, if such grafts are radially expanded within a blood vessel, they will exhibit some subsequent retraction. Further, such grafts usually require additional means for anchoring the graft within the blood vessel, such as sutures, clamps, or similarly functioning elements. To minimize the retraction and eliminate the requirement for additional attachment means, those skilled in the art have used stents, such as those presented by Palmaz in U.S. Pat. No. 4,733,665 and Gianturco in U.S. Pat. No. 4,580,568 which patents are herein incorporated by reference, either alone or in combination with PTFE grafts.
For example, the stent described by Palmaz in U.S. Pat. No. 4,733,665 can be used to repair an occluded blood vessel. The stent is introduced into the blood vessel via a balloon catheter, which is then positioned at the occluded site of the blood vessel. The balloon is then expanded thereby expanding the overlying stent to a diameter comparable to the diameter of an unoccluded blood vessel. The balloon catheter is then deflated and removed with the stent remaining seated within the blood vessel because the stent shows little or no radial retraction. Use of radially expandable stents in combination with a PTFE graft is disclosed in U.S. Pat. No. 5,078,726 to Kreamer. This reference teaches placing a pair of expandable stents within the interior ends of a prosthetic graft having a length that is sufficient to span the damaged section of a blood vessel. The stents are then expanded to secure the graft to the blood vessel wall via a friction fit.
Although stents and stent/graft combinations have been used to provide endovascular prostheses that are capable of maintaining their fit against blood vessel walls, other desirable features are lacking. For instance, features such as increased strength and durability of the prosthesis, as well as an inert, smooth, biocompatible blood flow surface on the luminal surface of the prosthesis and an inert, smooth biocompatible surface on the abluminal surface of the prosthesis, are advantageous characteristics of an implantable vascular graft. Some of those skilled in the art have recently addressed these desirable characteristics by producing strengthened and reinforced prostheses composed entirely of biocompatible grafts and graft layers.
For example, U.S. Pat. No. 5,048,065, issued to Weldon, et al. discloses a reinforced graft assembly comprising a biologic or biosynthetic graft component having a porous surface and a biologic or biosynthetic reinforcing sleeve which is concentrically fitted over the graft component. The reinforcing sleeve includes an internal layer, an intermediate layer, and an external layer, all of which comprise biocompatible fibers. The sleeve component functions to provide compliant reinforcement to the graft component. Further, U.S. Pat. No. 5,163,951, issued to Pinchuk, et al. describes a composite vascular graft having an inner component, an intermediate component, and an outer component. The inner and outer components are preferably formed of expanded PTFE while the intermediate component is formed of strands of biocompatible synthetic material having a melting point lower than the material which comprises the inner and outer components.
Another reinforced vascular prosthesis having enhanced compatibility and compliance is disclosed in U.S. Pat. No. 5,354,329, issued to Whalen. This patent discloses a non-pyrogenic vascular prosthesis comprising a multilamellar tubular member having an interior stratum, a unitary medial stratum, and an exterior stratum. The medial stratum forms an exclusionary boundary between the interior and exterior strata One embodiment of this prosthesis is formed entirely of silicone rubber that comprises different characteristics for the different strata contained within the graft.
The prior art also includes grafts having increased strength and durability, which have been reinforced with stent-like members. For example, U.S. Pat. No. 4,731,073, issued to Robinson discloses an arterial graft prosthesis comprising a multi-layer graft having a helical reinforcement embedded within the wall of the graft. U.S. Pat. No. 4,969,896, issued to Shors describes an inner elastomeric biocompatible tube having a plurality of rib members spaced about the exterior surface of the inner tube, and a perforate flexible biocompatible wrap circumferentially disposed about, and attached to, the rib members.
Another example of a graft having reinforcing stent-like members is disclosed in U.S. Pat. No. 5,123,917, issued to Lee which describes an expandable intraluminal vascular graft having an inner flexible cylindrical tube, an outer flexible cylindrical tube concentrically enclosing the inner tube, and a plurality of separate scaffold members positioned between the inner and outer tubes. Further, U.S. Pat. No. 5,282,860, issued to Matsuno et al. discloses a multi-layer stent comprising an outer resin tube having at least one flap to provide an anchoring means, an inner fluorine-based resin tube and a mechanical reinforcing layer positioned between the inner and outer tubes.
Still another stent containing graft is described in U.S. Pat. No. 5,389,106 issued to Tower which discloses an impermeable expandable intravascular stent including a dispensable frame and an impermeable deformable membrane interconnecting portions of the frame to form an impermeable exterior wall. The membrane comprises a synthetic non-latex, non-vinyl polymer while the frame is comprised of a fine platinum wire. The membrane is attached to the frame by placing the frame on a mandrel, dipping the frame and the mandrel into a polymer and organic solvent solution, withdrawing the frame and mandrel from the solution, drying the frame and mandrel, and removing the mandrel from the polymer-coated frame.
Microporous expanded polytetrafluoroethylene (“ePTFE”) tubes may made by any of a number of well-known methods. Expanded PTFE is frequently produced by admixing particulate dry polytetrafluoroethylene resin with a liquid lubricant to form a viscous slurry. The mixture is poured into a mold, typically a cylindrical mold, and compressed to form a cylindrical billet. The billet is then ram extruded through an extrusion die into either tubular or sheet structures, termed extrudates in the art. The extrudates consist of extruded PTFE-lubricant mixture called “wet PTFE.” Wet PTFE has a microstructure of coalesced, coherent PTFE resin particles in a highly crystalline state. Following extrusion, the wet PTFE is heated to a temperature below the flash point of the lubricant to volatilize a major fraction of the lubricant from the PTFE extrudate. The resulting PTFE extrudate without a major fraction of lubricant is known in the art as dried PTFE. The dried PTFE is then either uniaxially, biaxially or radially expanded using appropriate mechanical apparatus known in the art. Expansion is typically carried out at an elevated temperature, eg., above room temperature but below 327° C., the crystalline melt point of PTFE. Uniaxial, biaxial or radial expansion of the dried PTFE causes the coalesced, coherent PTFE resin to
Banas Christopher E.
Edwin Tarun J.
McCrea Brendan J.
Randall Scott L.
IMPRA, Inc.
Morrison & Foerster
Truong Kevin T.
LandOfFree
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