Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Absorbable in natural tissue
Reexamination Certificate
1997-12-18
2003-09-30
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Absorbable in natural tissue
C623S001530
Reexamination Certificate
active
06626939
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to implantable, radially expandable medical prostheses which are frequently referred to as stent-grafts. In particular, the present invention is a self-expanding stent-graft having a bioabsorbable structural component and a permanent graft component.
Self-expanding stents and methods for fabricating a stent are known and are, for example, shown in the U.S. Pat. Nos. 4,655,771; 4,954,126; 5,061,275; and in 5,645,559. Such devices are used within body vessels of humans for a variety of medical applications. Examples include intravascular stents for treating stenoses, stents for maintaining openings in the urinary, biliary, tracheobronchial, esophageal, renal tracts, and vena cava filters. A stent-graft is described in U.S. patent application Ser. No. 08/640,253, entitled “Cobalt-Chromium-Molybdenum Alloy Stent and Stent Graft”, filed Apr. 30, 1996.
A delivery device is used to deliver the stent-graft through vessels in the body to a treatment site. The flexible nature and reduced radius of the compressed stent-graft enables it to be delivered through relatively small and curved vessels.
All references cited herein, including the foregoing, are incorporated herein in their entireties for all purposes.
SUMMARY OF THE INVENTION
The present invention relates to a self-expanding stent-graft having a bioabsorbable structure such as a stent and a permanent graft bonded together with an adhesive. The implantable stent-graft may include a tubular, radially compressible, axially flexible and radially self-expandable structure made from bioabsorbable elongate filaments formed in a braid-like configuration and a graft made from materials such as polyethylene terephthalate (PET), expanded polytetrafluoroethylene (ePTFE), polycarbonate urethane (PCU) or polyurethane (PU). The graft may be adhered to a surface of the bioabsorbable structure or interwoven or braided into the bioabsorbable structure. The preferred graft of the stent-graft is made of braided, woven, or spray-cast PET, PCU, or PU fibers. The raft may also be made of film, sheet, or tube such as an ePTFE or PCU material. The graft is designed to remain permanently implanted in the body, however, small amounts of degradation may occur to the graft over time in the body environment.
The stent-graft generally assumes a substantially tubular form in an unloaded or expanded state when not subjected to external forces and is generally characterized by a longitudinal shortening upon radial expansion and a longitudinal lengthening upon radial contraction.
In a preferred embodiment, the bioabsorbable structure of the stent-graft assembly is a stent which substantially consists of a plurality of elongate polylactide bioabsorbable polymer filaments, helically wound and interwoven in a braided configuration to form a tube. The filaments may also be made of poly(alpha-hydroxy acid) such as poly-L-lactide (PLLA), poly-D-lactide (PDLA), polyglycolide (PGA), polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), or related copolymer materials.
Each bioabsorbable material has a characteristic degradation rate in the body. For example, PGA and polydioxanone are relatively fast-bioabsorbing materials (weeks to months) and PLA and polycaprolactone are relatively slow-bioabsorbing materials (months to years).
PLA, PLLA, PDLA and PGA have a tensile strength of from about 276 millions of Pascals (MPa) to about 827 MPa (40 thousands of pounds per square inch (ksi) to about 120 ksi); a tensile strength of 552 MPa (80 ksi) is typical; and a preferred tensile strength of from about 414 MPa (60 ksi) to about 827 MPa (120 ksi). Polydioxanone, polycaprolactone, and polygluconate include tensile strengths of from about 103 MPa (15 ksi) to about 414 MPa (60 ksi); a tensile strength of 241 MPa (35 ksi) is typical; and a preferred tensile strength of from about 172 MPa (25 ksi) to about 310 MPa (45 ksi).
PLA, PLLA, PDLA and PGA have a tensile modulus of from about 2758 MPa to 13790 MPa (400,000 pounds per square inch (psi) to about 2,000,000 psi); a tensile modulus of 6206 MPa (900,000 psi) is typical; and a preferred tensile modulus of from about 4827 MPa (700,000 psi) to about 8274 MPa (1,200,000 psi). Polydioxanone, polycaprolactone, and polygluconate have a tensile modulus of from about 1379 MPa (200,000 psi) to about 4827 MPa (700,000 psi); a tensile modulus of 3103 MPa (450,000 psi) is typical; and a preferred tensile modulus of from about 2413 MPa (350,000 psi) to about 3792 MPa (550,000 psi).
The preferred design for the bioabsorbable structure of the stent-graft includes 10-36 filaments braided into a tubular mesh configuration. Alternative designs could be made using more than 36 bioabsorbable filament strands. Stent-grafts are envisioned having as many as 500 filaments and which are made with braiders having sufficient carrier capacity.
Stents for arterial indications typically require high radial strength to resist elastic recoil after PTA dilation of the muscular arterial wall tissue. The radial strength of a stent-graft can be increased by increasing the number of filament strands in the design. Also the amount of open space in the stent mesh of the stent-grafts can be reduced by using more filament strands. It may be desirable to utilize stents with less open space if there is concern that the endoprosthesis may become occluded due to the ingrowth of tumorous tissue from cancer. A stent with little open space could be used to purposely seal off branch vessels from the main artery. Larger diameter stent-grafts require more filament strands in the braid to build the structural network over the larger surface area. Large stent-grafts would be needed for the aorta and for the trachea and esophagus. Also, large stent-grafts could be used in the airway and esophagus to seal off fistulas or to prevent or limit tissue ingrowth into the stent.
The present invention advantageously provides an improved stent-graft and a methods for making and using such a stent-graft.
In sum, the invention relates to a stent-graft including a bioabsorbable structural support including a tubular body having open ends, a sidewall structure having openings therein, and an inside and an outside surface and a permanent graft having an inside and outside surface. One of the bioabsorbable structural support or the permanent graft cooperates with the other and provides a coextensive portion wherein at least a part of the coextensive portion has a length of the bioabsorbable structural support and a length of the permanent graft bonded or interbraided together. The coextensive portion may be part or all of the longitudinal length of the stent-graft. The stent-graft may be adjustable between a nominal state and a radially-reduced state. The tubular body may further include a plurality of bioabsorbable elements formed in a generally elongated shape which is generally radially compressible and self-expandable. The stent-graft may provide an initial radial force when implanted in a body lumen and the bioabsorbable structure portion bioabsorbs over time in-vivo with an eventual resulting decrease in radial force to the vessel wall, and the permanent graft portion substantially remains in the body lumen. The structural support and the permanent graft may be bonded by adhesive means and the adhesive means may be bioabsorbable. The adhesive means may occupy a proximal and a distal end portion but not a mid portion over the coextensive portion which the structural support and graft are coextensive one another. The bioabsorbable structural support may be made of at least one of poly (alpha-hydroxy acid), PGA, PLA, PLLA, PDLA, polycaprolactone, polydioxanone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), or combinations thereof and the graft may be made of at least one
Burnside Diane K.
Chouinard Paul F.
Stinson Jonathan S.
Boston Scientific SciMed, Inc.
Larkins, Hoffman, Daly & Lindgren, Ltd.
Niebuhr, Esq. Frederick W.
Snow Bruce
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