Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Having pores
Reexamination Certificate
2001-11-30
2004-02-10
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Having pores
C623S001440
Reexamination Certificate
active
06689160
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a prosthesis for a blood vessel, which is composed of an expanded porous polytetrafluoroethylene (i.e., a stretched polytetrafluoroethylene) tube manufactured by stretching process using a polytetrafluoroethylene (PTFE) as a raw material. And more particularly to a prosthesis for a blood vessel which is excellent in mechanical properties and histocompatibility and exhibits good patency even when its inner diameter is as small as less than 6 mm, particularly at most 5 mm, more particularly at most 4 mm. The prosthesis for a blood vessel includes a vascular prosthesis, a covering material of a covered stent, etc. and may hereinafter be referred to as “vascular prosthesis” which is representative thereof.
BACKGROUND ART
Prostheses for blood vessels typified by vascular prostheses are used as a substitute for a lesion part of a vital blood vessel, a prosthesis for a defective part, a bypass for going around the lesion part to maintain blood flow, a conduit for shunting an artery to a vein, etc. As materials for the vascular prostheses, are used, for example, porous PTFE tubes manufactured by a stretching process, woven fabrics and knitted webs of polyester fibers, etc. The vascular prostheses are required to have antithrombogenicity and histocompatibility, since blood flows through their lumina, and they are often implanted in vivo for use by substitution implantation, bypass implantation or the like.
Among the vascular prostheses, a vascular prosthesis composed of an expanded porous PTFE tube (hereinafter referred to as “a porous PTFE vascular prosthesis”) is excellent in antithrombogenicity and histocompatibility and hence used widely. The features of the porous PTFE vascular prosthesis reside in that first of all the PTFE itself of a material is excellent in antithrombogenicity. Therefore, the porous PTFE vascular prosthesis is excellent in antithrombogenicity.
Second, the porous PTFE vascular prosthesis has a fine fibrous structure comprising a number of fine fibers (i.e., fibrils) and nodes interconnected with one another by said fibrils. This fine fibrous structure forms a porous structure composed of communicable pores. The porous structure composed of such a fine fibrous structure itself is excellent in affinity for the vital tissue, and the vital tissue penetrates into the porous structure, whereby healing by organization is easy to facilitate.
Third, in the porous PTFE vascular prosthesis, the porous structures such as average fibril length, average pore diameter and porosity, and the forms such as inner diameter and wall thickness may be easily changed by controlling production conditions such as draw ratio upon stretching. Therefore, the porous PTFE vascular prosthesis can cope with various requirements.
As described above, the porous PTFE vascular prosthesis is excellent in antithrombogenicity and histocompatibility and exhibits excellent properties compared with a polyester fiber-made vascular prosthesis. However, although the expanded porous PTFE vascular prosthesis has such excellent properties, when it is provided as a vascular prosthesis having an inner diameter as small as less than 6 mm, particularly at most 5 mm, it occludes in a relatively short period of time after implantation into the vital body so that any good patency cannot be achieved. When occlusion is repeated, the vascular prosthesis must be replaced on that occasion. Therefore, the porous PTFE vascular prosthesis is only put to practical use in a region of the inner diameter of at least 6 mm.
Various techniques have heretofore been proposed in order to improve the patency of the porous PTFE vascular prosthesis. These techniques are roughly divided into (1) a method in which the surface of the porous PTFE vascular prosthesis is modified by, for example, coating the surface with an antithrombogenic substance, thereby improving the antithrombogenicity and histocompatibility thereof, and (2) a method in which the fine fibrous structure constituting the porous structure is modified or optimized, thereby improving the physical properties and/or the histocompatibility thereof. Among these techniques, the method of modifying the surface of the porous PTFE vascular prosthesis is not sufficient in the improving effect by itself, and it is hence desirable to practice it in combination with the method of modifying or optimizing the fine fibrous structure.
The method of modifying or optimizing the fine fibrous structure includes a method in which the average fibril length (distance between nodes) in the fine fibrous structure is lengthened to enlarge the pore diameter of the vascular prosthesis for the purpose of enhancing the penetrability of the vital tissues into the porous structure after implantation of the porous PTFE vascular prosthesis for facilitating healing by organization. Specifically, in Journal of VASCULAR SURGERY, Vol. 11, No. 6, p. 838-845, June (1990), it is reported that a porous PTFE vascular prosthesis, the average fibril length of which has been enlarged to 30 to 60 &mgr;m, particularly about 60 &mgr;m, exhibits a marked healing effect compared with a generally marketed porous PTFE vascular prosthesis the average fibril length of which is about 10 to 30 &mgr;m.
Japanese Patent Application Laid-Open No. 135894/1975 has proposed a porous PTFE vascular prosthesis in which the length of fibrils has been controlled to longer than 5 &mgr;m, preferably longer than 5 &mgr;m, but not longer than 1000 &mgr;m, more preferably 20 to 100 &mgr;m.
According to the result of an implantation experiment by the present inventors, however, it has been found that no sufficient patency is achieved only by enlarging the average fibril length in a small diameter porous PTFE vascular prosthesis having an inner diameter as small as less than 6 mm. The analysis of the reason for it has revealed the following fact.
First, in an expanded porous PTFE tube, the fibrils are strongly oriented in the axial direction of the tube by stretching. Therefore, the rigidity against compression in axial and radial directions of the tube is low though the tensile strength in the axial direction of the tube is high. When the draw ratio upon stretching is made high to enlarge the average fibril length, the rigidity against compression in the axial and radial directions of the tube is further lowered.
When the porous PTFE vascular prosthesis is implanted at a site to which a bending load is applied, a site pressured from surroundings, a site low in blood pressure such as a vein or the like, mechanical pressure is given to the prosthesis, and the prosthesis to become easy constricted. In addition, when the surrounding vital tissue adhered to the outer surface of the porous PTFE vascular prosthesis, or the vital tissue penetrated into the porous wall thereof contracts, the porous PTFE vascular prosthesis tends to be shortened correspondingly. When the porous PTFE vascular prosthesis undergoes deformation such as constriction or shortening, the patency after the implantation into the vital body markedly drops. Such a problem becomes particularly marked when the average fibril length is lengthened, the wall thickness is thinned, or the inner diameter is made small. More specifically, when it is intended to increase the draw ratio upon stretching to enlarge the pore diameter (fibril length) for the purpose of enhancing the affinity for the vital tissue, there arises a problem that the rigidity of the expanded porous PTFE tube is further lowered to fail to apply it to a vascular prosthesis.
In order to solve the problem that the rigidity of the porous PTFE vascular prosthesis against compression in the axial and radial directions thereof is low, there has heretofore been proposed, for example, a method in which reinforcing filaments are wound in the form of a coil or ring around the outer surface of an expanded porous PTFE tube (Japanese Patent Publication Nos. 37734/1985 and 56619/1985). In the method in which the reinforcing filaments are wound around the outer surface of the expanded porou
Hayashi Fumihiro
Kumada Toshihiko
Miura Hidehiko
Natori Koichiro
Nishibe Toshiya
McDermott Corrine
McDermott & Will & Emery
Phan Hieu
Sumitomo Electric Industries Ltd.
LandOfFree
Prosthesis for blood vessel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Prosthesis for blood vessel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Prosthesis for blood vessel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3342216