Polymer coating for medical devices

Abstract

Coatings are provided in which surfaces may be activated by covalently bonding a silane derivative to the metal surface, covalently bonding a lactone polymer to the silane derivative by in situ ring opening polymerization, and depositing at least one layer of a polyester on the bonded lactone. Biologically active agents may be deposited with the polyester layers. Such coated surfaces may be useful in medical devices, in particular stents.

1 . A method for coating a medical device comprising:
 (a) reacting the surface of a medical device with a silane-based activating reagent to form a polymerized silane derivative covalently bonded to the surface of the medical device, said polymerized silane derivative containing hydroxyl or other functional groups that can be transformed into hydroxyl groups;   (b) reacting the device of step (a) with at least one lactone monomer in the presence of a metal catalyst to form a lactone polymer chain covalently bonded to the polymerized silane derivative, said chains grown on the hydroxyl or amino functional groups of the silane derivative through in-situ ring opening graft polymerization of lactone monomers, said polymerization initiated by said hydroxyl or amino functional groups of the silane derivative covalently bonded to the surface of the medical device, said lactone polymer chains and said silane derivative together forming a grafted lactone polymer layer; and   (c) treating the device of step (b) with at least one polyester polymer layer deposited on the grafted lactone polymer layer, wherein at least the first of the deposited polyester polymer layers is chemically compatible with the grafted lactone polymer layer to allow for entanglement of said deposited polyester polymer chains with the chains of said grafted lactone polymer chains for strong adhesion, and wherein the deposited polyester polymer layer is a lactone homopolymer or a lactone copolymer.   
     
     
         2 . The method of  claim 1  wherein the polyester component of the deposited polymer comprises a lactone homopolymer or a lactone copolymer, wherein the lactone homopolymer comprises polyglycolide, poly(L-lactide), poly(D-lactide), poly(ε-caprolactone), poly(p-dioxanone), poly(dioxepanone), or poly(D,L-lactide), or wherein the lactone copolymer comprises statistical or block copolymers, wherein the statistical or block copolymers comprise poly(L-lactide-co-D-lactide), poly(L-lactide-co-glycolide), poly(D-lactide-co-glycolide), poly(D,L-lactide-co-glycolide), poly(lactide-co-caprolactone), poly(lactide-co-dioxanone), or poly(lactide-co-dioxepanone). 
     
     
         3 . The method of  claim 2  wherein the lactone copolymer comprises a block copolymer wherein at least one polylactone block comprises polyglycolide, poly(L-lactide), poly(D-lactide), poly(ε-caprolactone), poly(p-dioxanone), poly(dioxepanone), poly(D,L-lactide), poly(L-lactide-co-D-lactide), poly(L-lactide-co-glycolide), poly(D-lactide-co-glycolide), poly(D,L-lactide-co-glycolide), poly(lactide-co-caprolactone), poly(lactide-co-dioxanone), or poly(lactide-co-dioxepanone) and, wherein the other block copolymer comprises polyalkyleneoxide, poly(amino acid), poly(acrylate), poly(methacrylate), or a polybutadiene. 
     
     
         4 . The method of  claim 1  wherein step (c) is repeated two or more times to provide multiple layers of polyester polymer deposited on the covalently grafted lactone polymer layer. 
     
     
         5 . The method of  claim 1  wherein the at least one deposited polyester polymer layer comprises from about 0.5% to about 60% by weight of one or more biologically active agents. 
     
     
         6 . The method of  claim 5  wherein the concentration of biologically active agent in the layers of the coating may be the same for each layer or the concentration may vary from layer to layer of the coating.