Biodegradable endoprostheses and methods for their fabrication

Abstract

Biodegradable endoprostheses are formed from amorphous polymers having desirable biodegradation characteristics. The strength of such amorphous polymers is enhanced by annealing to increase crystallinity without substantially increasing the biodegradation time.

1 . A method of making a stent prosthesis, comprising:
 a. providing a tubular member comprising a biodegradable polymeric material;   b. subjecting the tubular member to a treatment to control the crystallinity so the biodegradable polymeric material has a Tg greater than 37° C.; and   c. patterning the tubular member to form the stent prosthesis;   wherein the stent prosthesis at 37° C. is expandable to a deployed configuration and has sufficient strength to support a blood vessel in the deployed configuration.   
     
     
         2 . The method of  claim 1  wherein the patterned tubular member is crimped to a deliverable configuration. 
     
     
         3 . The method of  claim 2  wherein the patterned tubular member is expandable from a deliverable configuration to a deployed configuration at 37° C. 
     
     
         4 . The method of  claim 1  wherein the tubular member is subjected to the treatment before patterning. 
     
     
         5 . The method of  claim 1  wherein the tubular member is subjected to the treatment after patterning. 
     
     
         6 . The method of  claim 1  wherein the treatment comprises at least one of heating, cooling, pressurizing, cross-linking, exposure to radiation, drawing and addition of additives. 
     
     
         7 . The method of  claim 1  wherein the treatment includes heating the tubular member above Tg and below a melting point of the polymeric material. 
     
     
         8 . The method of  claim 7  wherein the treatment includes at least one cycle of heating and cooling the tubular member. 
     
     
         9 . The method of  claim 1  wherein the tubular member has a crystallinity below 10% prior to treatment. 
     
     
         10 . The method of  claim 1  wherein the tubular member has an initial crystallinity prior to treatment and has an increase in crystallinity of at least 20% of the initial crystallinity after treatment. 
     
     
         11 . The method of  claim 10  wherein the tubular member has an increase in crystallinity of at least 100% of the initial crystallinity. 
     
     
         12 . The method of  claim 1  wherein the tubular member is formed by a process selected from the group consisting of extruding, molding, dipping and spraying. 
     
     
         13 . The method of  claim 12  wherein the tubular member is formed by spraying the polymeric material onto a cylindrical surface. 
     
     
         14 . The method of  claim 13  wherein the polymeric material is dissolved in a solvent. 
     
     
         15 . The method of  claim 13  wherein solvent also contains an additive. 
     
     
         16 . The method of  claim 15  wherein the polymeric material is selected from at least one copolymer or blend selected from the group consisting of polylactide and polycaprolactone and polylactide and polyglycolide. 
     
     
         17 . The method of  claim 1  wherein the polymeric material after treatment has one or more properties selected from the group consisting of a yield strength of at least 50% of ultimate strength, an elastic modulus of at least 0.5 GPa, a yield strain of at most 10% and a plastic strain of at least 20%. 
     
     
         18 . The method of  claim 1  wherein the tubular member has a diameter of about 1 to 1.5 times a deployed diameter. 
     
     
         19 . The method of  claim 1  wherein the tubular member has a diameter of about 1 to 1.3 times a deployed diameter. 
     
     
         20 . The method of  claim 1  wherein the prosthesis has a recoil of less than 10% in the deployed configuration. 
     
     
         21 . The method of  claim 1  wherein the tubular member is substantially amorphous after treatment. 
     
     
         22 . The method of  claim 1  wherein the tubular member has a crystallinity of about 10-30% after treatment. 
     
     
         23 . The method of  claim 1  wherein the tubular body comprises a drug. 
     
     
         24 . The method of  claim 1  wherein the biodegradable polymeric material is amorphous prior to treatment.