Process of manufacturing a radially expandable PTFE...

Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor

Reexamination Certificate

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C156S086000, C156S242000, C264S127000, C264S230000, C264S294000, C264S3420RE, C623S001100, C623S001250, C623S901000, C606S194000, C600S036000

Reexamination Certificate

active

06267834

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to bioprosthetic vascular grafts, and more particularly to a method of manufacturing radially enlargeable, tubular, tape-reinforced polytetrafluoroethylene (PTFE) vascular grafts.
BACKGROUND OF THE INVENTION
Polytetrafluoroethylene (PTFE) has been used for the manufacture of various types of bioprosthetic vascular grafts, including tape-reinforced, tubular grafts of the type frequently utilized to replace or bypass a diseased or injured segment of blood vessel.
The expanded sintered PTFE from which the tubular base graft and the surrounding reinforcement tape are formed typically has a microstructure characterized by the presence of dense areas known as “nodes” interconnected by elongate strands known as “fibrils”. The directional orientation of fibrils is largely determined by the direction(s) in which the material was expanded prior to sintering thereof. The diameter and spacing of the fibrils is largely determined by the dynamics (i.e., rate frequency and amount) of the expansion. The porosity of the expanded sintered PTFE material is determined by the size of the spaces which exist between the fibrils, after the expansion step has been completed.
The sintering of the expanded PTFE is accomplished by heating the expanded workpiece to a temperature above the melting point of crystalline PTFE. Typically, this is effected by heating the workpiece to a temperature of 350°-370° C. This sintering process is characterized by a transition of the PTFE polymer from a highly crystalline form to a more amorphus form. Thus, the sintering process is sometimes referred to as “amorphous locking” of the PTFE polymer. The sintering process imparts significantly improved strength to the PTFE polymer matrix, while also causing the polymer matrix to become harder and less stretchable.
In the tape-reinforced PTFE vascular grafts of the prior art, it has been typical for the PTFE reinforcement tape to be wound spirally about the outer surface of the base graft. Such orientation and positioning of the relatively thin, sintered, PTFE reinforcement tape about the outer surface of the base graft substantially precludes or severely limits the amount of radial stretching or radial expansion that the base graft may undergo. Thus, the typical tape-reinforced tubular PTFE vascular graft of the prior art is incapable of undergoing more than a minimal amount (e.g., <5%) of radial stretching or radial expansion without tearing of the surrounding reinforcement tape.
The inability of tape-reinforced PTFE vascular grafts to undergo radial stretching or radial expansion has not interfered with the usual surgical implantation of such grafts because, in the usual surgical graft implantation procedure, the graft is sized-matched to the host blood vessel and is subsequently anastomosed into or onto the host blood vessel. Thus, in traditional surgical implantation procedures, there has been little or no need to effect radial stretching or radial expansion of the graft at the time of implantation.
Recently developed endovascular grafting procedures have, however, created a need for tape-reinforced tubular PTFE vascular grafts which are capable of undergoing significant amounts of radial enlargement (i.e., radial expansion with resultant enlargement of the radial dimension of the graft). In these endovascular grafting procedures, the tubular vascular graft is typically passed through a catheter into the lumen of a deceased blood vessel and, thereafter, is deployed to an open or extended configuration within the lumen of the host blood vessel. The graft is then anchored to the surrounding blood vessel wall, thereby effecting the desired endovascular placement of the graft within the lumen of the existing blood vessel. Thus, because it is necessary to initially compact the graft and pass it through the lumen of a relatively small catheter, and to subsequently radially enlarge the graft to its desired size and configuration, there exists a present need for the development of a tape-reinforced tubular vascular graft which is capable of undergoing in situ radial enlargement within the lumen of an existing blood vessel.
SUMMARY OF THE INVENTION
The present invention comprises a method for increasing or improving the ability of a tape-reinforced tubular graft (e.g., a graft comprising a tubular base graft formed of expanded sintered PTFE and a quantity of expanded sintered PTFE reinforcement tape wrapped about the outer surface of the base graft) to undergo radial enlargement without tearing or breaking.
In accordance with the present invention, a radially enlargeable tape-reinforced tubular vascular graft may be formed by initially manufacturing the tape-reinforced graft in accordance with any suitable manufacturing methodology, and subsequently radially shrinking the tape-reinforced graft to a decreased radial size. Such radial shrinkage of the tape-reinforced graft may be accomplished gradually, or in incremental steps, to minimize the likelihood of puckering of the tubular base graft as the surrounding reinforcement tape shrinks. Also, such radial shrinkage of the graft may be accomplished by any suitable polymer shrinkage technique, including heat-induced shrinkage or chemical-induced shrinkage.
Further in accordance with the present invention, one or more rigid mandrel(s) may be inserted into the lumen of the tubular base graft during the shrinkage process. In embodiments of the invention wherein the shrinkage process is accomplished in incremental or step wise manner, a single mandrel of adjustable diameter, or multiple mandrels of incrementally smaller diameter, may be utilized to effect the desired gradual, incremental or step-wise shrinkage of the graft.
Further in accordance with the invention, the desired shrinkage of the tape-reinforced graft may be accomplished by passing the tape-reinforced graft through a sizing dye to accomplish the desired radial shrinkage thereof.
Still further in accordance with the invention, the radially enlargeable tape-reinforced PTFE vascular graft may be alternatively formed by initially wrapping the expanded sintered PTFE reinforcement tape about the rigid mandrel to create a tape-tube which is devoid of any tubular base graft. The tape-tube is then radially shrunken, in accordance with the present invention, and the radially shrunken tape tube is subsequently applied to the outer surface of a relatively small-diameter tubular base graft. The tubular base graft and the surrounding shrunken tape-reinforcement may then be radially enlarged in accordance with the present invention, without tearing or breaking of the reinforcement tape.
Still further in accordance with the present invention, any embodiment of the radially enlargeable tape-reinforced tubular PTFE grafts of the present invention may be provided with external support filaments or beading to provide structural support to the graft, and to prevent indentation or kinking of the graft lumen when implanted. Such support filaments or beading may be formed of PTFE or any other suitable material.
Further objects and advantages of the invention will become apparent to those skilled in the art upon reading and understanding of the following detailed description, and consideration of the accompanying figures.


REFERENCES:
patent: 3225129 (1965-12-01), Taylor et al.
patent: 3939243 (1976-02-01), Dawson
patent: 4909979 (1990-03-01), Possis et al.
patent: 4955899 (1990-09-01), Della Corna et al.
patent: 4957669 (1990-09-01), Primm
patent: 5026513 (1991-06-01), House et al.
patent: 5128092 (1992-07-01), Asaumi et al.

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