Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Autogenously or by activation of dry coated particles
Reexamination Certificate
1997-02-03
2001-03-20
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Autogenously or by activation of dry coated particles
C264S210200, C264S210500, C264S294000, C264S331140
Reexamination Certificate
active
06203735
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to methods of making shaped three-dimensional products from microporous expanded polytetrafluoroethylene. More particularly, the present invention relates to a method of shaping three-dimensional products by manipulating an expanded polytetrafluoroethylene tubular body into a desired three-dimensional conformation. The present invention entails radially expanding a longitudinally expanded polytetrafluoroethylene (ePTFE) tube to form a radially expanded ePTFE (rePTFE) tube, engaging the rePTFE tube circumferentially about a shaping mandrel, heating the assembly to a temperature below the crystalline melt point temperature, or sintering temperature, of polytetrafluoroethylene to radially shrink the diameter of the rePTFE tube into intimate contact with the shaping mandrel, and heating the assembly to a temperature above the crystalline melt point temperature of polytetrafluoroethylene to amorphously lock the microstructure of the shaped polytetrafluoroethylene body.
The three-dimensional shaped microporous expanded polytetrafluoroethylene products made in accordance with the method of the present invention are particularly well suited for use as medical implants, and are particularly useful as venous or arterial prostheses either as vein or artery replacements, as endovascular liners, arterio-venous shunts, or as venous access grafts. As arterial or venous prosthesis, shaped microporous expanded polytetrafluoroethylene grafts have been made which have a flanged cuff section contiguous with an elongate tubular section. The cuffed prosthesis are particularly well suited for use in end-to-side anastomoses such as that required in femoro-popliteal bypass procedures where the flanged cuff section is sutured about an open arteriotomy to form the end-to-side anastomosis. As endovascular liners, the shaped expanded polytetrafluoroethylene products may be configured to have a taper along its longitudinal axis, with a proximal end having either a larger or smaller inner diameter than the distal end, or may have a step taper, where there is a tapered transition zone between two different inner diameter sections, or the product may be configured to have an intermediate section of a larger diameter than proximal or distal ends of the product, or the product may be configured into a bifurcated or trifurcated graft where each of the legs is formed from appropriately sized appendage sections of a base tubular graft member.
BACKGROUND OF THE PRIOR ART
Conventional processes for making ePTFE products are typically limited to fabricating sheets, tubes, rods or filaments. Methods for making complex conformational shapes of ePTFE are unknown in the prior art. The prior art is limited in its teaching to methods of making heat shrinkable tubing of either fluoroethylene co-polymers (FEP) or of non-expanded polytetrafluoroethylene (nPTFE). However, the uses of FEP and nPTFE heat shrink tubes has been limited to tubular profiles. Conventional methodologies are represented, for example, by Ely, Jr., el aL U.S. Pat. No. 3,196,194 issued in 1965, which discloses a FEP-Fluorocarbon Heat Shrinkable Tubing which is first expanded 33 to 100 percent of the initial internal diameter and is then correspondingly heat shrinkable by a factor of 33 to 100 percent diameter at 250-400° F. This patent teaches that expansion of the FEP-Fluorocarbon tubing may be accomplished by introducing a positive gas pressure into the lumen of a closed-end tube of the FEP-fluorocarbon. Seiler, Jr. et al. U.S. Pat. No. 4,647,416 issued Mar. 3, 1987 discloses a polytetrafluoroethelyne (PTFE) tube and a method of making the tube by creating radial scores in the outer surface of unsintered PTFE tubing and either longitudinally stretching the tubing to separate the score lines into discrete ribs or subjecting the tubing to sintering temperatures to cause shrinkage of the PTFE intermediate the score lines to differentiate the score lines into ribs during the sintering process.
Tu, et al. disclosed a trilogy of references which disclose methods of fabricating ePTFE elastomer impregnated materials which are radially and/or longitudinally compliant. U.S. Pat. No. 4,816,339 issued Mar. 28, 1989 discloses a tubular vascular graft material made of a layer of expanded polytetrafluoroethelyne (ePTFE) laminated with an ePTFE / elastomer layer and a method of making the same by preforming the graft, longitudinally expanding the graft, sintering the graft, radial expanding the graft using the elastomer matrix to permit radial expansion and compliance of the resulting graft and then wrapping or retreating the outer surface with another layer of the elastomeric material. This patent expressly teaches that standard ePTFE grafts do not hold or resist radial dilatation unless they are wrapped and if wrapped, they are non-compliant. The addition of the elastomer encapsulates the PTFE nodes and fibrils and penetrates into the microporous network of the ePTFE material. Tu, et al. U.S. Pat. No. 5,061,276 issued Oct. 29, 1991 is similar to the '399 Tu, et al. patent but discloses a graft which is made entirely of a PTFE elastomer solution admixture having inner surface distances of 25 microns and outer surface internodal distances of approximately 90 microns. The Tu, et al. U.S. Pat. No. 5,071,609 issued Dec. 10, 1991 discloses a graft made by paste extrusion of a PTFE elastomer admixture, followed by expansion and contraction of the finished product either in the longitudinal or radial direction. This patent teaches that the incorporation of the elastomer is necessary to achieve the property of being expandable and contractible, i.e., compliant in either the radial or longitudinal axis of the graft.
Yamamoto, et al. U.S. Pat. No. 4,830,062 issued May 16, 1989 disclose radial expansion of tetrafluoroethylene tubes to impart porosity in the tube and the resulting heat shrinkability of the radial expanded tetrafluoroethylene tube. This patent does not disclose either the radial expandability of longitudinally expanded ePTFE or the heat shrinkable nature of radial expanded ePTFE.
Interestingly, the Primm U.S. Pat. No. 4,957,669 issued Sep. 18, 1990, discloses a method for radially expanding a tapered ribbed graft, made in accordance with the teachings of Seiler, Jr., et al., U.S. Pat. No. 4,647,416, by mounting the ribbed graft onto an ultrasonic horn having a generally frustroconical tapered shape, restraining the ends, and ultrasonically heating the tubing while stretching the tubing over the tapered shape of the ultrasonic horn. However, this method relies upon ultrasonic heating of the ePTFE material which increases its workability and upon the ultrasonic energy which urges the heated material into the regular tapered frustroconical shape. This method radially expands the PTFE material using the heat and ultrasonic energy as the motive force for expansion. Because the method heats the ePTFE material as it is being urged into conformation with the tapered shape of the ultrasonic horn, the ePTFE microstructure is compromised. Moreover, because of the need for the ultrasonic horn, the conformational shapes which may be formed are limited to simple regular shapes which are capable of easy removal from the ultrasonic horn without compromising the integrity of the ePTFE material.
SUMMARY OF THE INVENTION
The fabrication of irregular-shaped, conformationally complex, medical endoprostheses from biocompatible prosthetic materials, such as ePTFE, has been difficult. Heretofore, those skilled in the art of making endoprostheses suitable for use as vein or arterial grafts, shunts, or the like, have been limited to fashioning the prosthesis of a substantially tubular structure. The surgeon has been left to adapt the tubular structure to the particular application, e.g., end-to-side anastomosis of a distal bypass graft for treating peripheral arterial occlusive disease, such as by fashioning a vein cuff by, for example, making a Miller cuff or a Taylor cuff to minimize compliance mismatch between the
Edwin Tarun J.
Randall Scott
Eashoo Mark
Impra, Inc.
Morrison & Foerster / LLP
Silbaugh Jan H.
Wight Todd W.
LandOfFree
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