Post deployment radial force recovery of biodegradable scaffolds

Abstract

Post deployment radial force recovery of biodegradable scaffolds are described where a high molecular weight polymer may be formed into a high molecular weight scaffold by solution casting into a tubular substrate such that the scaffold retains its mechanical properties through processing. The tubular substrate is laser cut and subsequently crimped onto a catheter for deployment into a body lumen. The polymeric scaffold may retain its mechanical properties and result in increased radial strength post-deployment in a saline environment, e.g., within a body lumen. This scaffold enhancement may be attributable at least in part to entanglement of high molecular weight polymer chains as one factor that effects radial force recovery and also to the design or geometry of the scaffold as another factor that effects radial force recovery after deployment.

What is claimed is: 
     
         1 . A scaffold comprising a first radial strength prior to being crimped at a first temperature and a second radial strength when expanded and exposed to an elevated second temperature of at least 37° C. and less than T g  of a polymer making up the scaffold and within a saline environment, wherein the scaffold regains at least 30% of the first radial strength of the scaffold. 
     
     
         2 . The scaffold of  claim 1 , wherein the scaffold is formed by:
 dissolving a raw polymeric resin in a solvent to form at least a first polymeric solution, wherein the resin has a relatively high molecular weight;   forming at least a first layer of a biocompatible polymer tube comprising a first diameter with the first polymeric solution;   curing the tube;   processing the tube to form the scaffold comprising the first diameter; and   reducing the first diameter of the scaffold to a second smaller diameter, wherein the scaffold retains at least 90% of the molecular weight of the resin and at least a portion a crystallinity of the resin such that the scaffold exhibits ductility upon application of a load.   
     
     
         3 . The scaffold of  claim 1 , wherein the scaffold is configured to increase a second radial strength of the scaffold when over expanded beyond an original intended diameter. 
     
     
         4 . The scaffold of  claim 1 , wherein the scaffold comprises a plurality of circumferential support elements and a plurality of coupling elements, wherein at least one of the coupling elements extends between a first trough of a first circumferential support element and a second trough of a second circumferential support element, wherein the second trough is connected to the at least one of the coupling elements and is defined by a trough undulation. 
     
     
         5 . The scaffold of  claim 4 , wherein the trough undulation comprises a distal curved radius along a distal side of the trough undulation, wherein the distal curved radius is between 0.0001 in. to 0.75 in. 
     
     
         6 . The scaffold of  claim 5 , wherein the first trough forms a radiused extension portion where the at least one of the coupling elements joins a distal side of the first circumferential support element, wherein the radiused extension portion has a radius between 0.0001 in. and 0.75 in. 
     
     
         7 . The scaffold of  claim 1 , wherein the scaffold defines a surface area of 3 mm 2  to 3000 mm 2  over an outer surface of the scaffold which contacts a vessel wall, and wherein the scaffold further defines a total surface area of the scaffold of 20 mm 2  to 12,000 mm 2 . 
     
     
         8 . The scaffold of  claim 4 , wherein the circumferential support elements of the scaffold comprise a sinusoidal ring design configured to control a tensile strain upon expansion such that failure of the scaffold is inhibited. 
     
     
         9 . The scaffold of  claim 8 , wherein the sinusoidal ring design is further configured to capture stress and strain of the scaffold in isolated regions of peaks and troughs of the scaffold. 
     
     
         10 . The scaffold of  claim 4 , wherein the scaffold is configured to translate diametric expansion of the scaffold to relative angular changes of the coupling elements. 
     
     
         11 . The scaffold of  claim 1 , wherein a fatigue level of the scaffold is reduced for at least 6 months after expansion. 
     
     
         12 . The scaffold of  claim 4 , wherein the scaffold is configured to minimize diametric recoil when an imparted strain remains above a tensile strain at yield and below a strain causing elongation of at least one of the coupling elements. 
     
     
         13 . The scaffold of  claim 4 , wherein at least one mechanical property of the scaffold is increased for at least 6 months after expansion. 
     
     
         14 . The scaffold of  claim 13 , wherein the at least one mechanical property comprises an increased second radial strength. 
     
     
         15 . The scaffold of  claim 13 , wherein the coupling elements are configured to reorient radially upon expansion such that elongation of the coupling elements is inhibited and the second radial strength is increased. 
     
     
         16 . The scaffold of  claim 14 , wherein the second radial strength does not decrease for at least 6 months after expansion. 
     
     
         17 . The scaffold of  claim 1 , wherein the scaffold is coated with sirolimus. 
     
     
         18 . The scaffold of  claim 1 , wherein the scaffold has a diameter between 3.80 mm and 3.94 mm. 
     
     
         19 . A scaffold comprising a tensile strain at yield within a range of 3% to 4% in one or more of the following conditions:
 crimping to onset of contact, crimping to a catheter diameter ID, no crimping, axial 6% extension, no crimping, axial 6% contraction, crimping to implantation diameter and axial 6% extension, crimping to implantation diameter and axial 6% contraction, crimping to fixed lumen diameter and axial 6% extension, and crimping to fixed lumen diameter and axial 6% contraction.   
     
     
         20 . A scaffold comprising a tensile strain at yield within a range of 3% to 4% in one or more of the following conditions:
 crimping to a diameter just prior to onset of self-contact, crimping to an outside diameter of 1.1 mm, crimping to an outside diameter of 1.2 mm, no crimping and simultaneous axial contraction 6%, no crimping and simultaneous axial extension 6%, 15% crimping and simultaneous axial contraction 6%, 15% crimping and simultaneous axial extension 6%, 11% crimping and simultaneous axial contraction 6%, and 11% crimping and simultaneous axial extension 6%.