Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Having pores
Reexamination Certificate
1999-10-08
2003-11-25
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Having pores
C623S001380, C623S001200, C623S001220, C623S001530, C623S023700, C623S023750, C606S191000
Reexamination Certificate
active
06652582
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a bioabsorbable implantable endoprosthesis having one or more reservoir portions including hollow, cavity, or porous portions to accumulate by-products of degradation.
Self-expanding medical prostheses frequently referred to as stents are well known and commercially available. They are, for example, disclosed generally in the Wallsten U.S. Pat. No. 4,655,771, the Wallsten et al. U.S. Pat. No. 5,061,275 and in Hachtmann et al., U.S. Pat. No. 5,645,559. 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, and renal tracts, and vena cava filters.
A delivery device which retains the stent in its compressed state is used to deliver the stent to a treatment site through vessels in the body. The flexible nature and reduced radius of the compressed stent enables it to be delivered through relatively small and curved vessels. In percutaneous transluminal angioplasty, an implantable endoprosthesis is introduced through a small percutaneous puncture site, airway, or port and is passed through various body vessels to the treatment site. After the stent is positioned at the treatment site, the delivery device is actuated to release the stent, thereby allowing the stent to self-expand within the body vessel. The delivery device is then detached from the stent and removed from the patent The stent remains in the vessel at the treatment site as an implant.
Stents must exhibit a relatively high degree of biocompatibility since they are implanted in the body. An endoprosthesis may be delivered into a body lumen on or within a surgical delivery system such as preferred delivery devices shown in U.S. Pat. Nos. 4,954,126 and 5,026,377. Suitable materials for use in such delivery devices are described in U.S. patent application Ser. No. 08/833,639, filed Apr. 8, 1997. The stents of the present invention may be delivered by alternative methods or by using alternative devices.
Commonly used materials for known stent filaments include Elgiloy® and Phynox® metal spring alloys. Other metallic materials than can be used for self-expanding stent filaments are 316 stainless steel, MP35N alloy, and superelastic Nitinol nickel-titanium. Another self-expanding stent, available from Schneider (USA) Inc. of Minneapolis, Minn., has a radiopaque clad composite structure such as shown in U.S. Pat. No. 5,630,840 to Mayer. Self-expanding stents can be made of a Titanium Alloy as described in U.S. patent application Ser. No. 08/598,751, filed Feb. 8, 1996.
The strength and modulus of elasticity of the filaments forming the stents are also important characteristics. Elgiloy®, Phynox®, MP35N and stainless steel are all high strength and high modulus metals. Nitinol has relatively lower strength and modulus.
The implantation of an intraluminal stent will preferably cause a generally reduced amount of acute and chronic trauma to the luminal wall while performing its function. A stent that applies a gentle radial force against the wall and that is compliant and flexible with lumen movements is preferred for use in diseased, weakened, or brittle lumens. The stent will preferably be capable of withstanding radially occlusive pressure from tumors, plaque, and luminal recoil and remodeling.
There remains a continuing need for self-expanding stents with particular characteristics for use in various medical indications. Stents are needed for implantation in an ever growing list of vessels in the body. Different physiological environments are encountered and it is recognized that there is no universally acceptable set of stent characteristics. The strength and modulus of elasticity of the filaments forming the stents are important characteristics.
A need exists for a stent which has self expanding characteristics, but which is bioabsorbable. A surgical implant such as a stent endoprosthesis must be made of a non-toxic, biocompatible material in order to minimize the foreign-body response of the host tissue. The implant must also have sufficient structural strength, biostability, size, and durability to withstand the conditions and confinement in a body lumen.
All documents cited herein, including the foregoing, are incorporated herein by reference in their entireties for all purposes.
SUMMARY OF THE INVENTION
The present invention is an improved implantable medical device comprised of a tubular, radially compressible, axially flexible and radially self-expandable structure including elongate filaments having reservoir portion. The filaments are formed in a braid-like configuration. The filaments consist of a bioabsorbable polymer which exhibits a relatively high degree of biocompatibility.
Briefly, self-expanding stents of the present invention are formed from a number of resilient filaments which are helically wound and interwoven in a braided configuration. The stents assume a substantially tubular form in their unloaded or expanded state when they are not subjected to external forces. When subjected to inwardly directed radial forces the stents are forced into a reduced-radius and extended-length loaded or compressed state. The stents are generally characterized by a longitudinal shortening upon radial expansion.
In one preferred embodiment, the device 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.
There is a need for a bioabsorbable implantable endoprosthesis that has a high rate of degradation and may be tailored to degrade over predetermined periods of time. One way to avoid long-term complications from an implant is to make the implant bioabsorbable so that the device is naturally eliminated from the treatment site after it has served its intended function.
Such a bioabsorbable implantable endoprosthesis would be especially advantageous for medical procedures requiring an endoprosthesis for short term or temporary use. For example, it would be advantageous to implant an implantable endoprosthesis that functions for a specific period of time and does not require a surgical procedure for removal at the end of its functional lifetime. With such an endoprosthesis, there is no need to remove the endoprosthesis because the bioabsorbable material therein decomposes over a period of time into non-toxic biological substances (e.g. lactic acid and glycolic acid) which are easily metabolized or excreted by the body. Such a bioabsorbable implantable endoprosthesis would be advantageous in urological, biliary, vascular, and airway applications where use is desired for only weeks, months, or a few years while a benign stricture is cured or healed, or for use in pre-operative palliation. Such a device may also offer an advantage in that shorter resorption times may reduce the time of inflammatory response and may reduce scarring.
Bioabsorbable implantable endoprostheses of the present invention include stents, stent-grafts, grafts, filters, occlusive devices, and valves which may be made of poly(alpha-hydroxy acid) such as polylactide [poly-L-lactide (PLLA), poly-D-lactide (PDLA)], polyglycolide (PGA), polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylene oxide copolymers, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), or related copolymers materials, each of which have 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 material (months to years).
An implantable endoprosthesis constructed of a bioabsorbable polymer provides certain advantages relative to metal stents such as natural decomposition into non-toxic chemical species over a period of time. Also, bioabsorbable polymeric stents may be manufactured at relatively low manufacturing costs sinc
Boston Scientific SciMed, Inc.
Chattopadhyay Urmi
Larkin Hoffman Daly & Lindgren Ltd.
Niebuhr, Esq. Frederick W.
Willse David H.
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