Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent in combination with graft
Reexamination Certificate
1999-01-22
2003-02-11
Milano, Michael J. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent in combination with graft
Reexamination Certificate
active
06517571
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of vascular grafts typically used to replace, line or otherwise repair living blood vessels or other body conduits.
BACKGROUND
The first effective vascular surgery reported in the literature was the work of T. Gluck who described in 1898 his placement of a vein graft in the carotid artery of a patient in 1894. Carrel and Guthrie reported in 1908 that they had successfully grafted a segment of a dog's vena cava, previously preserved in formalin, into a carotid artery. Guthrie prophetically concluded that these graft segments did not maintain the viability of living tissue but simply served as a conduit for blood and provided a possible scaffold for the ingrowth of cells. Carrel subsequently and unsuccessfully attempted to use tubes of glass and metal as vascular grafts.
Following the discovery by Voorhees that a loose silk thread lying within the right ventricle of a dog's heart became coated with an endothelial-like substance, it was proposed that a vascular substitute might be made of such threads. Vorhees et al. described in 1952 the use of short lengths of tubes made from Vinyon “N” cloth as replacements for aortic segments in dogs. In 1954, Voorhees and Blakemore described the replacement of 17 abdominal aneurysms and a popliteal aneurysm with synthetic tubes. Years of additional work by vascular surgeons building on this beginning led to the understanding that while conventional synthetic grafts of materials such as polyethylene terephthalate (PET) worked well in large diameter applications (for example, those involving repair of aortic aneurysms), their patency decreased with decreasing diameters. Darling and Linton in 1972 reported that eight-year PET implants in the leg had patency rates of about 10% in comparison to reversed saphenous vein patency rates of about 65-70%.
R. W. Gore invented porous expanded polytetrafluoroethylene (ePTFE) in 1969. He taught in U.S. Pat. Nos. 3,953,566 and 4,187,390 that polytetrafluoroethylene (PTFE) paste extrudate, following removal of the extrusion lubricant, could be rapidly stretched at a temperature below the crystalline melt point of PTFE to create the resulting porous microstructure of nodes interconnected by fibrils. During 1972, Soyer et al. reported using ePTFE tubes as venous replacements in pigs. Matsumoto et al. in 1973 described the use of ePTFE tubes as femoral artery replacements in dogs. In 1976, Campbell et al. first reported the use of ePTFE as a vascular substitute in humans. With further development to ensure adequate mechanical strength, these grafts soon became the standard for small diameter synthetic grafts. Even so, it was recognized that these improved synthetics sometimes did not perform equally as well as autologous saphenous vein grafts. It was noted that synthetic grafts, both PET and ePTFE, generally did not endothelialize beyond 1 or 2 cm from each anastomosis. The primary focus of further work on improved synthetic grafts since then has involved attempts to improve endothelialization of graft luminal surfaces. With regard to ePTFE grafts, this work frequently entailed methods of modifying the surface energy of the graft luminal surfaces to render the hydrophobic PTFE material much more hydrophilic. Conversely, woven PET grafts have been provided with luminal surface coatings of plasma-applied tetrafluoroethylene (TFE) monomer gas as taught by U.S. Pat. No. 4,718,907 to Karwoski et al.
Porosity has long been recognized to be a fundamental characteristic which affects the patency of synthetic vascular grafts; see, for example, the pioneering paper by Wesolowski et al., entitled “Porosity: primary determinant of ultimate fate of synthetic vascular grafts” (Suraerv, Vol. 50, No. 1 (July, 1961)). Accordingly, a great deal of the research into ePTFE grafts focused on efforts to optimize the mean fibril length of such grafts. While it has generally been concluded that these grafts were required to have a mean fibril length of at least 5-6 microns and no more than about 90 microns, the data reported in the literature remain inconsistent. See, e.g., Golden et al., “Healing of polytetrafluoroethylene arterial grafts is influenced by graft porosity,”
J. Vasc. Surg
., pp. 838-845 (June, 1990); also, Branson et al., “Expanded Polytetrafluoroethylene as a Microvascular Graft: A Study of Four Fibril Lengths,”
Plastic and Reconstructive Surgery
, Vol. 76, No. 5, pp. 754-763 (November 1985). Commercially available ePTFE grafts typically have a mean fibril length at the luminal surface in the range of about 15-30 microns.
Various ePTFE tubes are described in the patent literature which have different mean fibril lengths on the luminal surface than elsewhere on the tube or which otherwise have at least two differing microstructures within the structure of the tube. They may differ in mean fibril length, directional orientation of the fibrils, or both.
U.S. Pat. Nos. 4,082,893 and 4,208,745 to Okita and 4,332,035 to Mano describe ePTFE tubes, intended for use as vascular grafts, which have been exposed to heat above the crystalline melt temperature of PTFE at their outer surface for a period of time adequate to cause modification of the exterior surface with the result that the microstructure at the exterior surface of the tube becomes coarser as a result of coalescing together of the components of the microstructure, and oriented radially rather than longitudinally. U.S. Pat. No. 4,822,361 to Okita et al. describes that this same type of tube may be optionally impregnated with various resorbable materials including collagen, albumin, chitosan and heparin.
U.S. Pat. No. 4,225,547 to Okita and U.S. Pat. No. 4,743,480 to Campbell et al. describe different methods of orienting the microstructure of ePTFE tubes in different directions at the inner and outer surfaces of the tubes. The tubes are also intended to be used as vascular grafts.
U.S. Pat. No. 4,550,447 to Seiler et al. teaches modification of tubular PTFE extrudate by scoring through a portion of the exterior wall prior to removal of the extrusion lubricant and stretching below the melt temperature, with the result being the creation of a denser, exterior ribbed structure integrally formed with the remainder of the tube. The tube is described as an exteriorly reinforced vascular graft.
Various patents teach coextrusion methods whereby different microstructures may be created in different, concentrically-arranged parts of the wall of ePTFE tubes. Different PTFE or other fluoropolymer resins may be concentrically coextruded to result in the differing microstructures. Likewise other materials such as siloxanes may be included in one or more of the coextruded layers. These patents include U.S. Pat. No. 4,816,339 to Tu et al., U.S. Pat. No. 4,973,609 to Browne, U.S. Pat. No. 5,064,593 to Tamaru et al., and U.S. Pat. No. 5,453,235 to Calcote et al. All of these teach the construction of ePTFE vascular grafts.
Still other patents teach the construction of ePTFE tubes having changing or alternating regions of different porosity along the length of the tube made by making radially oriented segments which differ in porosity between adjacent segments. U.S. Pat. No. 5,433,909 to Martakos et al. teaches a tubular ePTFE vascular graft made having narrow, alternating ring-shaped segments of porous ePTFE and non-porous PTFE. U.S. Pat. No. 5,747128 to Campbell et al. describes an ePTFE vascular graft having alternating ring-shaped segments of more and less dense ePTFE. This graft may be made to be circumferentially distensible to larger diameters, in which form it is useful as an intraluminal graft.
Various patents describe the modification of the luminal surfaces of ePTFE vascular grafts. For example, U.S. Pat. No. 5,246,451 to Trescony et al. teaches modification of ePTFE vascular graft luminal surfaces by gas plasma deposition of fluoropolymer coatings followed by binding of a protein to the modified luminal surface. Optionally, the resulting luminal surface is seeded with endothelial cells. European Pa
Brauker James Howard
Butters Leslie Charles
Davidson Daniel Francis
Ulm Mark Joseph
Bui Vy Q.
Gore Enterprise Holdings Inc.
House Wayne
Milano Michael J.
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