Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Drug delivery
Reexamination Certificate
1998-10-23
2001-06-19
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Drug delivery
Reexamination Certificate
active
06248129
ABSTRACT:
This invention relates to an expandable polymeric stent with built-in elastic memory and delivery apparatus and method for use therewith.
Many different types of stents have heretofore been provided. For example, stents have been provided to attempt to prevent post-angioplasty vessel reclosure. Typically, such intravascular stents have been utilized in the region of the stenosis to maintain the passageway through the stenosis. Such stents usually have been formed of metal. Such metal stents have been found to be intrinsically thrombogenic because of their net surface charge and surface irregularities. In addition, expandable metal stents have created vessel wall thinning as well as intimal hyperplasia within the stent and at the borders of the stent. These can be caused by uneven circumferential contact of the stent with the vessel endoluminal surface, compliance mismatch between the stent and the vessel wall and excessive stent stiffness. A stent formed of plastic is disclosed in U.S. Pat. No. 4,820,298. As disclosed therein, a thermoplastic polyester polycarbonate copolymer is formed into a helical coil by providing a linear extrusion and winding the same on a mandril and reheating to form a helical spring coil. Strand material is secured to the helical coil. The stent is inserted with a stylet. When the stylet is removed, the stent expands under its recovery memory to assume a helical configuration. This recovery memory is based upon the fact that it was formed from a linear strip and wound onto a mandril which resulted in stored energy, causing it to expand into a helix when released from the stylet. The adjacent loops of the helical stent are constrained by the strand material which has been secured thereto. It is believed that even though such a stent is formed of plastic, it has a number of disadvantages making it unsuitable for use in many applications. It is necessary to mechanically restrain the stent to prevent it from expanding prior to insertion into the vessel. Also it is believed that it is hard to predict the expansion forces exerted when it is released.
In addition to mechanical stenting, pharmacological treatment is necessary to prevent restenosis. Conventional systemic drug delivery, however, is often ineffective in comparison to drug delivery that is localized to the specific site where therapy is needed. Systemic administration too often results in a drug's elimination in the blood or liver before it reaches its target site. Localized delivery, directly to the cells that need the drug, is more potent and reliable. U.S. Pat. No. 5,019,096 discloses the use of antimicrobial containing polymer solutions on surfaces of infection-resistant medical devices to effect a slow, localized release of said antimicrobial agents. Similarly, U.S. Pat. No. 4,979,959 discloses attaching growth hormones or an antithrombogenic agent to the surface of synthetic blood vessels in order to make them more biocompatible. Surface adsorption of drugs, however, can only provide small amounts for delivery. In addition, the literature describes controlled drug release implants for localized drug delivery wherein said implants are prepared by dispersing drugs in polymeric matrices. There is, however, no teaching of a medical device which incorporates the dual functions of vascular stenting and localized drug delivery wherein a drug is contained in other than a surface coating of said device and wherein the drug is for a purpose other than that of enhancing biocompatability of the device. There is therefore a need for an improved stent that carries and delivers drugs locally while it simultaneously functions mechanically.
In general it is an object of the present invention to provide a plastic stent which carries and delivers drugs locally while it functions as a stent, a delivery apparatus and method for use with the same.
In general it is another object of the present invention to provide a plastic stent which has a built-in elastic memory, a delivery apparatus and method for use with the same.
Another object of the invention is to provide a stent of the above character which is self-restrained permitting it to be readily inserted into a vessel of a patient.
Another object of the invention is to provide a stent of the above character which has low protein adsorption and is biocompatible.
Another object of the invention is to provide a stent of the above character which need not be physically constrained from expansion prior to placement in the vessel of a patient.
Another object of the invention is to provide a stent of the above character which can be provided with a predetermined stiffness to match the compliance of the vessel.
Another object of the invention is to provide a stent of the above character which can be provided with a surface which facilitates intimal and endothelial cell growth to enhance the biocompatibility of the stent.
Another object of the invention is to provide a stent of the above character which can carry medical agents such as thrombolytic agents, growth factors, and slow release medications.
Another object of the invention is to provide a stent of the above character which will expand to a greater diameter upon being subjected to an external factor.
Another object of the invention is to provide a stent of the above character which has a thermal transition incorporated therein.
Another object of the invention is to provide a stent of the above character which has been crosslinked.
Another object of the invention is to provide a stent of the above character which can be readily and economically manufactured.
Another object of the invention is to provide a stent of the above character which can be readily positioned in the desired location in the vessel of the patient.
Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in conjunction with the accompanying drawings.
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Flehr Hohbach Test Albritton & Herbert LLP
Jackson Suzette J.
Quanam Medical Corporation
Willse David H.
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