Metal working – Method of mechanical manufacture – Combined manufacture including applying or shaping of fluent...
Reexamination Certificate
1997-04-15
2001-06-05
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Combined manufacture including applying or shaping of fluent...
C623S001420, C623S001460, C623S001440, C623S001390, C419S002000
Reexamination Certificate
active
06240616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a medicated prosthesis or implant. More particularly, the invention relates to a medicated intra-vascular prosthesis, such as a stent, that is radially expandable in the vasculature of a patient and delivers a therapeutic agent to the site of the implantation.
2. Description of Related Art
Stents are generally cylindrically shaped prosthetic implants which function to hold open and sometimes expand a segment of a blood vessel or other anatomical lumen. They are particularly suitable for supporting and preventing a torn or injured arterial lining from occluding a fluid passageway. Intravascular stents are increasingly useful for treatment of coronary artery stenoses, and for reducing the likelihood of the development of restenosis or closure after balloon angioplasty.
The success of a stent can be assessed by evaluating a number of factors, such as thrombosis; neointimal hyperplasia, smooth muscle cell migration and proliferation following implantation of the stent; injury to the artery wall; overall loss of luminal patency; stent diameter in vivo; thickness of the stent; and leukocyte adhesion to the luminal lining of stented arteries. However, the chief areas of concern are early subacute thrombosis, and eventual restenosis of the blood vessel due to intimal hyperplasia.
Therapeutic pharmacological agents have been developed to improve successful placement of the stent and are delivered to the site of stent implantation. Stents that are of a common metallic structure were previously unable to deliver localized therapeutic pharmacological agents to a blood vessel at the location being treated with the stent. There are polymeric materials that can be loaded with and release therapeutic agents including drugs or other pharmacological treatments which can be used for drug delivery. However, these polymeric materials may not fulfill the structural and mechanical requirements of a stent, especially when the polymeric materials are loaded with a drug, since drug loading of a polymeric material can significantly reduce the structural and mechanical properties of the polymeric material.
It has been known in the art to coat a metallic stent with a polymeric material and load the polymeric material with a drug. Alternatively stents of polymeric materials have been reinforced with metal structure. These stent designs have the strength necessary to hold open the lumen of the vessel because of the reinforced strength of the metal. Stents made of both polymeric material and metal have a larger radial profile because the volume occupied by the metal portion of the stent cannot absorb and retain drugs. Reducing the profile of a stent is preferable because it increases the in vivo diameter of the lumen created by the stent. Thus it is desirable to configure a metallic stent to deliver drugs to the blood vessel walls without substantially increasing the profile of the stent. The present invention meets these needs.
SUMMARY OF THE INVENTION
Briefly and in general terms, the present invention is a method of manufacturing a medicated prosthesis. The method comprises providing a porous metal material having a plurality of porous cavities, forming the material into a prosthesis having a plurality of porous cavities, and loading therapeutic agents into the pores of the prosthesis. In one embodiment, the prosthesis is a stent for implantation into a blood vessel, biliary duct, esophagus or other body lumen. In one embodiment, the method comprises sintering metal particles including spherical particles, filaments or fibers into a wire, a sheet or tube. Then, the wire, sheet, or tube is further manufactured by forming the stent from the same. Sheets or tubes can be formed into stents by chemical etching or laser cutting the same according to a stent pattern. In another embodiment, the sheet is formed by weaving metallic fibers and sintering the metallic fibers in a metal wire or a sheet.
In yet another embodiment, a sheet of stent material is formed in a plurality of layers. A layer of large diameter particles are arranged in a first horizontal plane. Two layers of small diameter particles are arranged on both sides of the plane. The particles are sintered into a sheet of particles that has a large core formed of large diameter particles sandwiched between two layers of small diameter particles. Similarly, a sintered stent wire can be formed by arranging large diameter particles along a first axis and then arranging small diameter particles radially outward from and coaxial to the large diameter particles. Then, the particles are sintered to form a stent wire that has a substantially porous central cavity and an outer layer that has smaller pore diameter.
In yet another embodiment, the method of forming a stent comprises arranging a sheet of solid metal between two layers of particles. The particles are then sintered to both sides of the sheet. Similarly, the particles can be sintered to one side of the metal sheet. Alternatively, particles can be oriented radially outward from a solid metal wire and sintered into a partially porous wire. The partially porous wire and the stent with a sheet metal core are believed to improve the strength of the overall stent.
According to one embodiment of the present invention, a therapeutic agent can be loaded into the pores of the stent by immersing the stent in a liquid solution containing the therapeutic agent. The stent is emersed for a period of time sufficient to permit therapeutic agent to be absorbed into the porous cavities of the stent. The therapeutic agent may be any number of drugs or chemical agents that treat arterial diseases and stent implantation side effects.
In yet another embodiment of the invention the method includes coating the stent with a polymer. The polymer may itself be loaded with one or more therapeutic agents or may be applied to delay the release of medicine or otherwise control the rate that the therapeutic agent diffuses into the body.
These and other features of the present invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the present invention.
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Lambert, Thomas L., M.D., et al., Localized Arterial Wall Drug Delivery From a Polymer-Coated Removable Metallic Stent,Circulation,Eol. 90, No. 2 (Aug. 1994) pp. 1003-1011.
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Advanced Cardiovascular Systems Inc.
Fulwider Patton Lee & Utecht LLP
Hughes S. Thomas
Jimenez Marc
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