Stent fabrication via tubular casting processes

Abstract

Tubular casting processes, such as dip-coating, may be used to form substrates from polymeric solutions which may be used to fabricate implantable devices such as stents. The polymeric substrates may have multiple layers which retain the inherent properties of their starting materials and which are sufficiently ductile to prevent brittle fracture. Parameters such as the number of times the mandrel is immersed, the duration of time of each immersion within the solution, as well as the delay time between each immersion or the drying or curing time between dips and withdrawal rates of the mandrel from the solution may each be controlled to result in the desired mechanical characteristics. Additional post-processing may also be utilized to further increase strength of the substrate or to alter its shape.

What is claimed is: 
     
         1 . A polymeric substrate characterized by a length, an inner diameter, an outer diameter and a thickness, comprising a bioresorbable polymer characterized by a molecular weight from 259,000 g/mol to 2,120,000 g/mol and a crystallinity from 20% to 40%. 
     
     
         2 . The polymeric substrate of  claim 1 , wherein the substrate is characterized by a crystallinity from 27% to 35%. 
     
     
         3 . The polymeric substrate of  claim 1 , wherein the substrate is characterized by crystalline regions and amorphous regions. 
     
     
         4 . The polymeric substrate of  claim 3 , wherein the crystalline regions are isotropic. 
     
     
         5 . The polymeric substrate of  claim 3 , wherein the crystalline regions are oriented. 
     
     
         6 . The polymeric substrate of  claim 3 , wherein the crystalline regions are longitudinally oriented. 
     
     
         7 . The polymeric substrate of  claim 3  wherein the crystalline regions are circumferentially oriented. 
     
     
         8 . The polymeric substrate of  claim 1 , wherein physical properties of the substrate are isotropic. 
     
     
         9 . The polymeric substrate of  claim 1 , wherein the substrate is characterized by a solvent content less than 100 ppm. 
     
     
         10 . The polymeric substrate of  claim 1 , wherein the outer diameter is from 1.5 mm to 10 mm. 
     
     
         11 . The polymeric substrate of  claim 1 , wherein the bioresorbable polymer is characterized by an intrinsic viscosity from 4.3 dL/g to 8.4 dL/g. 
     
     
         12 . The polymeric substrate of  claim 1 , wherein the bioresorbable polymer is characterized by an intrinsic viscosity from 8.28 to 8.4 dL/g 
     
     
         13 . The polymeric substrate of  claim 1 , wherein the bioresorbable polymer is characterized by an elastic modulus from 1000 MPa to 3000 MPa. 
     
     
         14 . The polymeric substrate of  claim 1 , wherein the thickness comprises a plurality of polymer layers. 
     
     
         15 . The polymeric substrate of  claim 14 , wherein the plurality of polymer layers is from 2 layers to 20 layers. 
     
     
         16 . The polymeric substrate of  claim 1 , wherein each of the plurality of polymer layers comprises the same polymer. 
     
     
         17 . The polymeric substrate of  claim 14 , wherein the plurality polymer layers comprises a first polymer layer and a second polymer layer, wherein the first polymer layer comprises a first polymer and the second polymer layer comprises a second polymer, wherein the first polymer and the second polymer are the same. 
     
     
         18 . The polymeric substrate of  claim 14 , wherein the plurality of polymer layers comprises a first polymer layer and a second polymer layer, wherein the first polymer layer comprises a first polymer and the second polymer layer comprises a second polymer, wherein the first polymer and the second polymer are different. 
     
     
         19 . The polymeric substrate of  claim 14 , wherein the plurality of polymer layers comprises a first polymer layer and a second polymer layer, wherein the first polymer layer comprises a first polymer and the second polymer layer comprises a second polymer, wherein the first polymer and the second polymer are characterized by a different physical property. 
     
     
         20 . The polymeric substrate of  claim 19 , wherein the physical property is selected from bioresorption rate, degradation rate, molecular weight, glass transition temperature, crystallinity, intrinsic viscosity, and a combination of any of the foregoing. 
     
     
         21 . The polymeric substrate of  claim 14 , wherein at least one of the plurality of polymer layers comprises a pharmaceutical agent. 
     
     
         22 . The polymeric substrate of  claim 1 , configured as a solid tube. 
     
     
         23 . The polymeric substrate of  claim 22 , wherein the solid tube exhibits ductile failure under an applied load. 
     
     
         24 . The polymeric substrate of  claim 23 , wherein the applied load at failure is from 100 N to 300 N. 
     
     
         25 . The polymeric substrate of  claim 22 , wherein the solid tube is configured to curve up to 180° about a 1 cm curvature radius without fracture formation or failure. 
     
     
         26 . The polymeric substrate of  claim 1 , wherein the substrate is configured as a stent. 
     
     
         27 . The polymeric substrate of  claim 26 , wherein the stent is characterized by a radial strength of at least about 10N per 1 cm length at about 20% compression. 
     
     
         28 . The polymeric substrate of  claim 26 , wherein the stent is characterized by a radial strength of 0.1 N to 5 N per 1 cm at 20% compression. 
     
     
         29 . The polymeric substrate of  claim 26 , wherein the stent is configured to withstand a strain of at least 150% without failure. 
     
     
         30 . The polymeric substrate of  claim 26 , wherein the stent exhibits ductile failure under an applied load. 
     
     
         31 . The polymeric substrate of  claim 30 , wherein the applied load at failure is from 100 N to 300 N. 
     
     
         32 . The polymeric substrate of  claim 30 , wherein the stent is configured to curve up to 180° about a 1 cm curvature radius without fracture formation or failure. 
     
     
         33 . The polymeric substrate of  claim 30 , wherein the stent is configured such that the inner diameter can be expanded from 5% to 80% without fracture formation or failure. 
     
     
         34 . The polymeric substrate of  claim 30 , wherein the sent is configured such that the outer diameter may be reduced by 5% to 70% when placed under and external load without plastic deformation.