Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Having marker
Reexamination Certificate
1997-08-01
2001-01-16
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Having marker
C623S001150, C606S198000
Reexamination Certificate
active
06174330
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a bioabsorbable marker having radiopaque constituents “bioabsorbable-radiopaque marker” for use on an implantable endoprosthesis such as a stent. The bioabsorbable marker includes dispersable radiopaque constituents which are not bioabsorbable or degradable, but are excreted from the body or stored in the body.
Implantable endoprostheses including stents, stent-grafts, and grafts are used in percutaneous transluminal coronary angioplasty and in other medical procedures to repair and support diseased or damaged arteries and body lumens. Grafts are implanted to cover or bridge leaks or dissections in vessels. Stent-grafts are stents which generally have a porous coating attachment. Unsupported grafts are porous tubes which are typically implanted by surgical cut-down.
In order to visualize the passage and placement of the implantable endoprosthesis in arteries and body lumens, many surgical procedures are performed with the aid of fluoroscopic angiography. The surgical delivery device and implantable endoprosthesis may be visualized if they are radiopaque and offer radiographic contrast relative to the body. For example, X-ray radiation may be used to visualize surgical delivery devices and deployment of the implant in the body. Also, radiographic contrast solution may be injected into the body lumen so that the lumen may be seen in the fluoroscopic image.
In order for the Implantable endoprosthesis to be radiopaque, it must be made from a material possessing radiographic density higher than surrounding host tissue and have sufficient thickness to affect the transmission of x-rays to produce contrast in the image. Reference is made to the clad composite stent shown in U.S. Pat. No. 5,630,840. An implantable endoprosthesis may be made of metals including tantalum, or platinum having relatively high radiographic densities. Other metals such as stainless steel, superalloys, nitinol, and titanium having lower radiographic densities may also be used. Reference is made to implantable devices shown in U.S. Pat. Nos. 4,655,771; 4,954,126; and 5,061,275.
An implantable polymeric endoprosthesis is generally radiolucent and does not possess sufficient radiographic density to be easily imaged by fluoroscopy. To improve the imaging of such polymeric materials, polymers may be mixed with radiopaque filler materials prior to molding or extruding in order to enhance the radiographic density. However, a disadvantage of using fillers with polymers is that changes in the properties of the polymer may occur. For example, the additions of fillers may reduce the strength or ductility of the polymer.
There is a need for an improved bioabsorbable-radiopaque marker for use in medical devices, particularly in temporary medical devices having low radiopacity. The need to improve the radiopacity of a relatively low radiopaque implantable endoprosthesis or to improve imaging in low radiopaque conditions is particularly important for surgery, micro-surgery, neuro-surgery, and conventional angioplasty procedures performed under fluoroscopy. Physicians are constantly being challenged to place small implants at specific intraluminal locations. Various devices having radiopacity are known in the art such as shown in U.S. Pat. Nos. 4,447,239; 5,354,257; and 5,423,849.
All documents cited herein, including the foregoing, are incorporated herein by reference in their entireties for all purposes.
SUMMARY OF THE INVENTION
Accordingly, there is a need for bioabsorbable-radiopaque markers for use on implantable endoprostheses in order to improve radiopacity and the locatability of an endoprosthesis during various medical procedures. Providing temporary radiopacity is especially advantageous for implantable endoprostheses having little or no radiopacity. The bioabsorbable-radiopaque markers allow radiographic identification of one or more locations of interest on an implantable endoprosthesis. Bioabsorbable-radiopaque markers in the fabric or covering materials of an implantable endoprosthesis are advantageous for indicating the location of the fabric or covering during implantation.
Alternative uses include threading the markers: adjacent a helical strand in the implantable endoprosthesis; circumferentially around the implantable endoprosthesis; or in a straight line in the axial direction of the implantable endoprosthesis. One or more bioabsorbable-radiopaque markers may be used on the implantable endoprosthesis having little or no radiopacity. After implantation, the bioabsorbable-radiopaque marker may be absorbed, dissolved, or excreted from the body so as not to effect the function of the endoprosthesis.
A disadvantage of certain permanent radiopaque markers is that they may compromise structural integrity, may not be biocompatible or biostable, and may be more thrombogenic than the implantable endoprosthesis.
The bioabsorbable-radiopaque marker of the present invention advantageously allows most any implantable endoprosthesis to have temporary radiopacity over a predetermined portion of its structure, and advantageously assists with proper positioning and locatability of the implantable endoprosthesis in a body lumen.
Use of the bioabsorbable-radiopaque marker is advantageous because the radiopaque property may be present only for a desired time period on an implantable endoprosthesis. For instance, once the implantable endoprosthesis is implanted, it may be more desirable to image with techniques such as ultrasound, magnetic resonance, and endoscopy and to avoid further radiation exposure to the patient. As the bioabsorbable polymer degrades, radiopaque material simultaneously or subsequently disperses into the body. The dispersion of the radiopaque material from the marker results in a loss of radiopacity in the marker. A predetermined rate of release of the radiopaque material may be designed into the bioabsorbable marker based on degradation of the polymer in the body or the design of the marker structure.
The bioabsorbable material in the bioabsorbable-radiopaque markers may include polymers or copolymers such as polylactide [poly-L-lactide (PLLA), poly-D-lactide (PDLA)], polyglycolide, polydioxanone, polycaprolactone, polygluconate, polylactic acid-polyethylene oxide copolymers, modified cellulose, collagen, poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(amino acids), poly(alpha-hydroxy acid) or related copolymers materials, each of which have a characteristic degradation rate in the body. For example, polyglycolide and polydioaxanone are relatively fast-bioabsorbing materials (weeks to months) and PLA is a relatively slow-bioabsorbing material (months to years). For a PLA member, mass degradation is completed with total absorption of the polymer endoprosthesis in about 1.5 to 3 years after implantation.
Bioabsorbable resins such as PLLA, PDLA, PGA and others are commercially available from several sources including PURAC America, Inc. of Lincolnshire, Ill. Radiopaque materials such as barium sulfate and bismuth trioxide are commercially available and compounded with the bioabsorbable resin by New England Urethane, Inc. of North Haven, Conn. The bioabsorbable resin or bioabsorbable-radiopaque resin may be extruded into filament by Albany International Research Co. of Mansfield, Mass.
The bioabsorption rate of the marker may be designed to be fast for applications where acute radiopacity is desired such as during positioning and placement of the implant. Alternatively, the bioabsorption rate may be designed to be slower for applications where the implant must be radiographically imaged for at least a portion of its functional time, for example, in implants where healing may take months. Other bioabsorption rates are also possible. The bioabsorption rate of the marker may be tailored by controlling the type of bioabsorbable polymer; chemical composition of the bioabsorbable polymer; molecular weight of the bioabsorbable polymer; thickness and density of the bioabsorbable polymer; surface area of the marker, exit area for t
Larkin Hoffman Daly & Lindgren Ltd.
Prebilic Paul B.
Schneider ( USA ) Inc
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