Bioabsorbable stent with time dependent structure and properties and regio-selective degradation

Abstract

A bioabsorbable polymeric stent with time dependent structure and properties and methods of treating a diseased blood vessel with the bioabsorable polymeric stent are disclosed. The structure and properties of the stent change with time and allow the vessel to be restored to a natural unstented state. The bioabsorbable stent loses mechanical integrity in a controlled manner due to modification of selected structural elements.

What is claimed is: 
     
         1 . A stent for treating a diseased section of a blood vessel, comprising:
 a bioabsorbable polymeric scaffolding composed of a pattern of struts, the pattern comprising a first axial section and a second axial section, wherein the first axial section comprises a first set of cylindrical rings each connected by a set of linking struts and the second axial section comprises a second set of cylindrical rings each connected by a set of linking struts,   wherein the first axial section and the second axial section are connected by a set of modified linking struts,   wherein each of the modified linking struts comprises a structural feature different from the linking struts in the first and second axial sections, and   wherein the structural feature induces failure of the modified linking struts before the linking struts in the first and second axial sections after deployment in a living body resulting in disconnecting of the first and second axial sections.   
     
     
         2 . The stent of  claim 1 , wherein the structural feature comprises a notch in each of the modified linking struts, wherein the notch concentrates stress and accelerates degradation which facilitates failure of the modified linking struts. 
     
     
         3 . The stent of  claim 1 , wherein the structural feature comprises a section along the length of the modified linking struts having a reduced cross-section, wherein the section concentrates stress and accelerates degradation which facilitates failure of the modified linking struts. 
     
     
         4 . The stent of  claim 1 , wherein the structural feature comprises a smaller cross-section along a whole length of the modified linking strut than a cross-section of the linking struts of the first and second sections. 
     
     
         5 . The stent of  claim 4 , wherein a thickness of the modified linking struts is between 0.1 and ⅔ a thickness of the linking struts of the first and second axial sections. 
     
     
         6 . The stent of  claim 1 , wherein the structural feature comprises a hole at or near a connection region of the modified linking struts to the first axial section, second axial section or both. 
     
     
         7 . The stent of  claim 1 , wherein the structural feature comprises a hole in the modified linking strut along a length of the linking strut. 
     
     
         8 . The stent of  claim 1 , wherein the structural feature comprises two opposing half-circle cavities in the side walls of the modified linking strut that reduce the moment of inertia of the modified linking strut. 
     
     
         9 . A method of treating a diseased section of a blood vessel, comprising:
 deploying a bioabsorbable polymeric stent to a deployment diameter at a diseased section of a blood vessel to form a stented segment of the vessel comprising the stent and the vessel wall, the stent comprising a scaffolding composed of a pattern of struts, the pattern comprising a plurality of cylindrical rings connected by linking struts,   wherein selected linking struts break resulting in at least one ring or at least one group of consecutive rings being disconnected from adjacent rings, and   wherein the at least one ring or the group of rings remain structurally intact after the selected linking struts break.   
     
     
         10 . The method of  claim 9 , wherein the disconnected rings support the vessel wall at or near the deployment diameter. 
     
     
         11 . The method of  claim 9 , wherein all of the rings are disconnected from adjacent rings due to the breaking of the selected linking struts. 
     
     
         12 . The method of  claim 9 , wherein each of the selected linking struts has a region with a reduced cross-section as compared to outside the region, the reduced cross-section inducing breaking of the selected linking struts. 
     
     
         13 . The method of  claim 12 , wherein the reduced cross-section region comprises a notch. 
     
     
         14 . The method of  claim 9 , wherein the blood vessel is a superficial femoral artery. 
     
     
         15 . The method of  claim 9 , wherein the disconnected rings support the vessel section between 1 to 4 months, after which the radial strength declines and the disconnected rings can no longer support the vessel at or near the deployment diameter.