Plastic and nonmetallic article shaping or treating: processes – With severing – removing material from preform mechanically,...
Reexamination Certificate
1998-08-27
2001-02-20
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With severing, removing material from preform mechanically,...
C264S151000, C264S159000, C264S296000, C264S314000, C264S320000, C264S523000, C264S540000, C264S573000, C264S536000, C264S138000, C425S182000, C425S185000, C425S195000, C425S389000, C425S392000, C425S393000, C425S527000, C425S531000, C623S001210, C623S011110, C623S017120
Reexamination Certificate
active
06190590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to vascular grafts, and more particularly to a method and apparatus for forming the flanged polytetrafluoroethylene (PTFE) cuffed section from a tubular PTFE graft to form a flanged vascular graft for end-to-side anastomosis useful for purposes of bypassing an occluded or diseased section of a blood vessel or as an access graft for hemodialysis. The PTFE graft has an integral terminal PTFE flanged cuff section which permits an end-to-side anastomosis with a blood vessel in which the terminal PTFE flanged cuff section is sutured to the blood vessel and provides a PTFE-tissue interface between the graft and the blood vessel. The flanged PTFE graft is the subject of U.S. Ser. No. 09/125,907, which is hereby expressly incorporated by reference as being illustrative of types of flanged grafts useful for distal bypass or hemodialysis access grafts which may be made using the apparatus and method of the present invention.
2. Description of the Prior Art
The uses of cuff grafts for bypassing peripheral vascular occlusive conditions, particularly femoro-crural patch prostheses, or for hemodialysis access grafts are well known in the art. To date, however, either autologous grafts or synthetic grafts with a terminal cuff fashioned from venous tissue at the anastomotic site have been used. Examples of conventional cuffed grafts are the Miller collar described in J. H. Miller,
The Use of the Vein Cuff and PTFE
, in VASCULAR SURGICAL TECHNIQUES 2 ed., 276-286 (W. B. Saunders 1989), and the Taylor patch described in Taylor, R. S., et al, Improved technique for polytetrafluoroethylene bypass grafting: long-term results using anastomotic vein patches,
Br. J. Surg.,
79:348-354 (1992). Both the Miller graft and the Taylor graft are cuff grafts and each employs a PTFE graft with an autologous venous cuff at the anastomotic site. The Miller collar and the Taylor patch each use venous tissue at the anastomotic site to avoid a compliance mismatch at the PTFE-tissue interface.
The flanged PTFE graft in U.S. Ser. No. 09/125,907, hereby incorporated by reference, offers a new type of anastomosis for femoro-crural bypass or access grafting in which the graft is fabricated in a flared, double-bulb configuration. The inventive graft configuration offers an optimal geometry for the anastomosis as a function of hemodynamic properties. By optimizing blood flow from the bypass prosthesis to the artery, formation of intimal hyperplasia may be reduced with a concomitant increase in graft patency and decreased morbidity.
The apparatus of the present invention consists of an annular mold having a radially extending annular slot, forming an expansion port. The flanged cuff graft is made by first forming an unsintered tubular PTFE vascular graft by extruding a PTFE lubricant mixture into a billet to form a tubular extrudate, placing the extrudate in the annular mold, and forming an annular cuff by either: 1) application of a negative pressure to the expansion port, or 2) application of positive pressure, as by a highly compliant angioplasty balloon, through the tubular extrudate lumen, to radially displace a section of the tubular extrudate, thereby forming a cuffed graft.
Various different approaches have been taken to fabricate branched grafts. As early as 1938, U.S. Pat. No. 2,127,903 to Bowen disclosed a bioabsorbable surgically implantable graft made of animal tissue and a binder formed by wrapping strips of the treated animal tissue about a structural form. U.S. Pat. No. 4,909,979, issued Mar. 20, 1990 to Possis, discloses a method of shaping a human umbilical cord for use as a vascular graft. The method employs a mandrel to support and shape the umbilical cord during forming and curing of the cord. The forming and curing process provides a cord with a blood flow restrictor section. PTFE coatings are provided on the mandrel to facilitate mounting the umbilical cord onto the mandrel. A shaping section of the mandrel is provided with a plurality of vacuum openings in the mandrel. The umbilical cord is treated with ethanol and a vacuum applied until the cord is dehydrated. The cord is then exposed to a curative and fixative solution and a vacuum applied until the umbilical cord is cured substantially airtight and circumferentially compressed and compacted around the mandrel forming section.
U.S. Pat. No. 4,354,495, issued Oct.19, 1982 to Bodicky, discloses a method of connecting a PTFE tube to a hub made of a moldable plastic, e.g., polyurethane, acrylics, polyethylene, polycarbonates, etc. The method involves selectively heating a portion of the PTFE tube to form a bulge or protrusion, then inserting the bulge into a mold and molding the moldable plastic hub about the bulge in the mold. U.S. Pat. No. 4,957,508, issued Sep.18, 1990 to Kaneko et al., discloses an elastomeric medical tube having proximal and distal ends, outwardly flared. The outward flare of the ends is achieved by forming the inner and outer surfaces of the tube to exhibit inverse elastomeric properties, i.e., the inner surface exhibits a dilating force, while the outer surface exhibits a shrinking force. The tube is made of high molecular weight polymers, particularly, polyvinyl halide, polystyrene, polyolefin series polymers, polyester series condensates, cellulose series high polymers, polyurethane series high polymers, polysulfone series resins, polyamides, etc. along with copolymers or mixtures of these.
U.S. Pat. No. 5,387,236 to Noshiki et al., issued Feb. 7, 1995, discloses a vascular prosthesis and method of making a vascular prosthesis by providing a vascular prosthesis substrate made of PTFE or other microporous material, and depositing and capturing within the wall of the prosthesis substrate fragments of biological tissue. The biological tissue fragments may be vascular tissues, connective tissues, fat tissues and muscular tissues and/or vascular endothelial cells, smooth muscle cells and fibroblast cells. The impregnation process is conducted by depositing the cellular material on the inner wall of the graft and applying a pressure differential between the lumenal and ablumenal wall surfaces to drive the tissue fragments into the microporous matrix of the vascular prosthesis. U.S. Pat. No. 4,883,453 to Berry et al., issued Nov. 28, 1989, discloses an aorto-coronary bypass graft and a method of making the graft. The graft consists of a plate portion and at least one tube portion extending from the plate portion. The graft and plate are disclosed as being made of an electrostatically-spun fibrous structure. The graft is adhered to the plate by mounting the graft onto a mandrel, applying adhesive to the surface of the plate surrounding an opening in the plate, and passing the mandrel through an opening in the plate until the graft contacts the adhesive. The adhesive is any suitable adhesive for the materials forming the plate and the graft. According to the preferred embodiment described in this reference, the graft preferably has a tapered wall thickness, such that the graft wall thickness adjacent the plate is greater than that distant the plate.
U.S. Pat. No. 5,110,526 to Hayashi et al., issued May 5, 1992, discloses a process for producing molded PTFE articles. According to this process, unsintered PTFE extrudates are inserted into a sintering mold. The sintering mold has a diameter slightly larger than the outside diameter of the unsintered PTFE extrudate. Clearance between the outside diameter of the unsintered PTFE extrudate and the inside surface of the sintering mold is on the order of 2% of the diameter of the sintering mold. The extrudate is drawn into the sintering mold via a plug, inserted into the terminal lumen of the extrudate and a wire and take-up reel. The PTFE extrudate is cut to match the length of the sintering mold, and the sintering mold is sealed on the cut extrudate end. The assembly is transferred to a sintering oven and sintered. During sintering, the extrudate expands in contact with the sintering mold and co
Lamay Albert L.
Randall Scott
Tang Roy H.
Impra, Inc.
Morrison & Foerster / LLP
Poe Michael I.
Silbaugh Jan H.
Wight Todd W.
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