Regulation/modification of stent contact surface for polymer free drug coating

Abstract

There is disclosed a method of improving the reliability of coating an implantable medical device, such as a stent, with bioactive material in the absence of a carrier material such as a matrix or polymer layer. The method involves cleaning volatile components from the exposed surfaces of the medical device, removing carbon deposits and then applying a uniform carbon layer in a controlled environment. The deliberately applied carbon layer masks impurities of the underlying native oxide layer and leads to more uniform bioactive material coating not only a over the surfaces of a single medical device but also from device to device within a batch and between batches of devices. This improves production as well as optimising the amount and release of drug on the medical device without the need for a carrier material.

We claim: 
     
         1 . A method of forming a coated implantable medical device including the steps of:
 removing non-volatile carbon deposits from at least one surface of the medical device;   applying a layer of carbon over the at least one surface by a carbon deposition process; and   applying a layer of therapeutic or bioactive material over the layer of carbon.   
     
     
         2 . A method according to  claim 1 , wherein the step of applying a layer of carbon over the at least one surface applies a layer of pure carbon or of at least 90% pure carbon. 
     
     
         3 . A method according to  claim 1 , wherein the step of applying a layer of carbon over the at least one surface applies a layer of substantially uniform thickness over the at least one surface. 
     
     
         4 . A method according to  claim 1 , wherein the layer of carbon over the at least one surface is one of impervious and substantially non-porous. 
     
     
         5 . A method according to  claim 1 , wherein the layer of carbon over the at least one surface is amorphous. 
     
     
         6 . A method according to  claim 1 , including the step of removing volatile deposits from the at least one surface before the step of removing non-volatile carbon deposits. 
     
     
         7 . A method according to  claim 1 , wherein the step of removing non-volatile carbon deposits exposes native oxides of the at least one surface. 
     
     
         8 . A method according to  claim 1 , wherein the step of removing non-volatile carbon deposits includes one of: plasma cleaning and UV zone cleaning. 
     
     
         9 . A method according to  claim 1 , wherein the step of removing non-volatile carbon deposits includes one of: plasma cleaning by an H 2 O 2  plasma, an H 2 O plasma, an H 2  and O 2  plasma, an O 2 +H 2 O plasma, an evaporated ethanol plasma and a helium argon or argon/hydrogen plasma. 
     
     
         10 . A method according to  claim 1 , wherein the layer of carbon over the at least one surface is applied by one of an ethanol plasma, an IPA plasma and by sputtering. 
     
     
         11 . A method according to  claim 1 , wherein the medical device is made of a metal or metal alloy and the at least one surface is a surface of said metal or metal alloy. 
     
     
         12 . A method according to  claim 1 , wherein the therapeutic or bioactive material is or includes an anti-proliferative bioactive substance. 
     
     
         13 . A method according to  claim 12 , wherein the therapeutic or bioactive material is or includes paclitaxel. 
     
     
         14 . A method according to  claim 1 , wherein the layer of therapeutic or bioactive material is free of containment elements and/or binding agents and/or of polymer or other matrix material. 
     
     
         15 . A coated implantable medical device including:
 a base structure including at least one coating surface;   a uniform layer of carbon posited over the at least one surface; and   a layer of therapeutic or bioactive material posited over the layer of carbon.   
     
     
         16 . A coated implantable medical device according to  claim 15 , wherein the at least one surface comprises native oxides. 
     
     
         17 . A coated implantable medical device according to  claim 15 , wherein the layer of carbon over the at least one surface is a layer of pure carbon or at least 90% pure carbon. 
     
     
         18 . A coated implantable medical device according to  claim 15 , wherein the layer of carbon has a substantially uniform thickness over the at least one surface. 
     
     
         19 . A coated implantable medical device according to  claim 15 , wherein the therapeutic or bioactive material is or includes paclitaxel. 
     
     
         20 . A coated implantable medical device according to  claim 15 , wherein the layer of therapeutic or bioactive material is free of containment elements and/or free of binding agents.