Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Stent structure
Reexamination Certificate
2000-01-11
2002-07-02
Milano, Michael J. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Stent structure
C623S001440, C623S001460
Reexamination Certificate
active
06413271
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of preparing an implantable radioactive metallic medical device. More particularly, the present invention relates to a method of preparing a radioactive metallic stent for use in preventing restenosis in atherosclerotic coronary arteries that have been subjected to percutaneous transluminal coronary angioplasty, hereinafter referred to as “balloon angioplasty”.
Atherosclerosis is a disease in which vascular lesions or plaques consisting of cholesterol crystals, necrotic cells, excess fiber elements and calcium deposits accumulate on the interior walls of an individual's arteries. The presence of such plaques in the artery leads to thickening and retraction of the artery. Eventually the enlargement of such plaques can lead to an occlusion of the lumen of the artery at the site of the lesion. One of the most successful procedures for treating the narrowing of the arteries caused by atherosclerosis is balloon angioplasty. Balloon angioplasty consists of introducing a deflated balloon into the atherosclerotic artery, placing the balloon adjacent the site of the plaque or atherosclerotic lesion, inflating the balloon to a pressure of approximately 6 to 20 atmospheres thereby “cracking” the plaque and increasing the cross-sectional area of the lumen of the artery.
Unfortunately, the pressure that is exerted on the plaque during balloon angioplasty also traumatizes the artery. Accordingly, in 30-40% of the cases the vessel either gradually renarrows or recloses at the locus of the original stenotic lesion. This gradual renarrowing or reclosure is referred to as restenosis. Studies of the mechanism of restenosis have shown that it is due in part to a proliferation of smooth muscle cells and in part to retraction or recoil of the blood vessels.
A number of approaches for preventing restenosis are currently being used or tested. One approach employs a metallic stent which is deployed at the site of the stenotic lesion following balloon angioplasty. Typically, metallic stents are made in the form of a mesh-like network of linked wires and open spaces. Metallic stents have the mechanical strength necessary to prevent recoil or retraction of the barotraumatized vessel. However, the metallic stents that are presently used do not prevent proliferation of the smooth muscle cells.
Animal studies have shown that the rate of restenosis can be further reduced by implanting radioactive metallic stents at the site of the atherosclerotic lesion following balloon angioplasty. The local irradiation supplied by such stents prevents smooth muscle cell proliferation. The use of such radioactive stents is currently being tested in a clinical phase I trial. The stents that are being used in these trials are loaded with
32
P by ion implantation. This process involves the bombardment of rotating stents with
32
P ions. The
32
P ions become embedded in the metal surface to a depth of a few &mgr;m.
Typically,
32
P stents cannot be activated within the hospital.
32
P stents must be activated in advance and then shipped to the hospital. Because of constant decay of the radioisotope,
32
P stents may not be able to deliver the required dose to the site of the stenotic lesion if stored for any length of time at the hospital. Therefore, unless a hospital receives a fresh supply of
32
P stents of various types, lengths and doses on a daily basis, a
32
P stent that matches the individual lesion characteristics of the patient may not be available at the time of insertion. In addition,
32
P stents deliver radiation to the area near the stent for more than 30 days after implantation. Radiobiological concerns make delivering the radiation over this length of time undesirable. Previous studies have shown that irradiation of the vessel within a few hours prior to and 3 days post angioplasty is the most desirable range of time for treatment. Thus, the length of time the patient is exposed to radiation from the
32
P stents is excessive. Moreover, it is likely that
32
P stents will deliver radioactivity to the target tissue at a dose rate of less than 10 cGy per hour during most of the time the
32
P stent delivers radioactivity. Concerns have been raised that subjecting the cells in the vicinity of the
32
P stent to such low dose rates of radiation following implantation may not only be ineffective for restenosis prevention, but may even activate cellular proliferation.
Accordingly, it is desirable to have a new radioactive metallic stent and methods of preparing the same that overcome the disadvantages of the
32
P stent. A stent that is loaded with a radioisotope that delivers radiation for a shorter period of time is desirable. A stent that is capable of delivering radioactivity at a dose rate of at least 10 cGy per hour during the first twelve hours to twelve days after the stent is implanted is also desirable. A method which is relatively simple and rapid and allows a predictable amount of radioactivity to be incorporated into stents of various lengths and types on the same day the stenting procedure is being performed is especially desirable.
SUMMARY OF THE INVENTION
The present invention provides a simple and rapid method for preparing an implantable medical device having at least one radioactive metallic surface. The method comprises the steps of depositing a radioactive metal layer onto the surface of the device. The metal layer comprises a radioactive metal that emits beta particles and that has a half-life of between 2 hours and 7 days and a maximum beta energy of between 0.6 and 2.3 MeV. In one embodiment, the radioactive layer is deposited by electroplating the radioactive metal and a carrier metal onto the metallic surface. The carrier metal has the ability to adhere to the metal surface and to co-deposit with the radioactive metal. In another embodiment, the method further comprises the step of electroplating a second metallic layer comprising a barrier metal onto the radioactive metal layer. The barrier metal is biocompatible and has the ability to adhere to the radioactive layer.
The present invention also provides an implantable, radioactive metallic medical device comprising a surface having a radioactive metallic coating thereon. The coating comprises a radioactive layer comprising a radioactive metal that emits beta-particles having a half-life of between 2 hours and 7 days and an energy level of from about 0.6 MeV to 2.3 MeV. In one embodiment the radioactive layer further comprises a carrier metal. In another embodiment, the coating further comprises a second layer deposited on the radioactive layer. The second layer comprises a biocompatible metal. In a preferred embodiment the medical device is a stent.
The present invention also relates to a system for applying the radioactive coating to the implantable medical device. The system comprises a package and a sterile electroplating cell contained within the package. The electroplating cell comprises a wall defining a chamber and an electrode attached to the inside wall of the cell or embedded in the inside wall of the cell, so that at least a portion of the electrode is in communication with the chamber. The system further comprises a conductive fastener for electrically connecting the metallic medical device to the power supply and positioning the device within the chamber. In a preferred embodiment, the cell further comprises an inlet port in fluid communication with the chamber for delivering solutions to the chamber, and an outlet port in communication with the chamber of the cell for removing solutions from the chamber.
DETAILED DESCRIPTION OF THE INVENTION
Method for Making a Radioactive Metallic Medical Device
In one aspect, the present invention provides a method for making radioactive any medical device that comprises at least one surface made from a metal, preferably from a biocompatible metal such as, for example, stainless steel, tantalum, cobalt-based alloys or nitinol. The method comprises depositing a coating which comprises a radioactive metal onto the
Hafeli Urs
Landau Uziel
Warburton Matt C.
Bui Vy Q.
Calfee Halter & Griswold LLP
Milano Michael J.
The Cleveland Clinic Foundation
LandOfFree
Method of making a radioactive stent does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of making a radioactive stent, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making a radioactive stent will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2904498