Channeled biomedical foams and method for producing same

Abstract

The present invention provides a biomedical, biocompatible, polymeric foam scaffold suitable for use in the repair and regeneration of tissue and which contains located therein a network of, branched channels that are effective to encourage and facilitate vascularization and tissue growth within the scaffold and to methods for making such biomedical scaffolds.

We claim:  
     
         1 . A biomedical, biocompatible scaffold suitable for use in the repair and regeneration of tissue, comprising a polymeric foam, said foam comprising a network of branched channels effective to encourage and facilitate vascularization and tissue growth in said scaffold.  
     
     
         2 . The biomedical scaffold of  claim 1  wherein said scaffold is bioabsorbable.  
     
     
         3 . The biomedical scaffold of  claim 1  wherein said scaffold comprises a bioabsorbable polymer selected from the group consisting of aliphatic polyesters, poly(amino acids), polyalkylenes oxalates, polyamides, tyrosine derived polycarbonates, polyorthoesters, polyoxaesters, and poly(anhydrides).  
     
     
         4 . The biomedical scaffold of  claim 3  wherein said polymer comprises an aliphatic polyester selected from the group consisting of homopolymers and copolymers of lactide, lactic acid, glycolide, glycolic acid, ε-caprolactone, p-dioxanone, trimethylene carbonate, alkyl derivatives of trimethylene carbonate, δ-valerolactone, β-butyrolactone, γ-butyrolactone, ε-decalactone, hydroxybutyrate, hydroxyvalerate, 1,4-dioxepan-2-one, 1,5,8,12-tetraoxacyclotetradecane-7,14-dione, 1,5-dioxepan-2-one, and 6,6-dimethyl-1,4-dioxan-2-one.  
     
     
         5 . The biomedical scaffold of  claim 4  wherein said aliphatic polyester comprises an elastomer selected from the group consisting of copolymers of lactide and ε-caprolactone, and lactide and glycolide.  
     
     
         6 . The biomedical scaffold of  claim 5  wherein said elastomer has an inherent viscosity in the range of about 1 to 2 deciliters per gram as determined at 25° C. in a 0.1 gram per deciliter solution of polymer in hexafluoroisopropanol.  
     
     
         7 . The biomedical scaffold of  claim 6  wherein said copolymer of lactide and ε-caprolactone comprises a mole ratio of lactide to ε-caprolactone from about 30/70 to about 50/50.  
     
     
         8 . The biomedical scaffold of  claim 6  wherein said copolymer of lactide and glycolide comprises a mole ratio of lactide to glycolide from about 75/25 to about 95/5.  
     
     
         9 . The biomedical scaffold of  claim 1  comprising a continuous polymer phase comprising interconnected pores of between about 50 and about 500 microns in diameter.  
     
     
         10 . The biomedical scaffold of  claim 1  further comprising cells.  
     
     
         11 . The biomedical scaffold of  claim 1  further comprising a bioactive substance.  
     
     
         12 . A process for making biomedical, biocompatible scaffolds suitable for use in the repair and regeneration of tissue, comprising: 
 preparing a homogenous mixture comprising a synthetic, biocompatible polymer, a solvent in which said polymer is soluble, and a non-solvent in which said polymer is not soluble, wherein said solvent and said non-solvent are miscible, and wherein the freezing point of said non-solvent is higher than the freezing point of said solvent,    placing said homogenous mixture in a mold or other device suitable for preparing foam scaffolds suit-able for use in repair and regeneration of tissue,    cooling said homogenous mixture to a first temperature effective to freeze said non-solvent, maintaining said first temperature for a time effective to allow phase separation of said non-solvent from said homogenous mixture,    cooling said homogenous mixture to a second temperature sufficient to form a solid, and    removing said solvent and said non-solvent from said solid to provide a biocompatible, porous foam scaffold which comprises a network of branched channels.    
     
     
         13 . The process of  claim 12  wherein said polymer is bioabsorbable.  
     
     
         14 . The process of  claim 13  wherein said bioabsorbable polymer is selected from the group consisting of aliphatic polyesters, poly(amino acids), polyalkylenes oxalates, polyamides, tyrosine derived polycarbonates, polyorthoesters, polyoxaesters and poly(anhydrides).  
     
     
         15 . The process of  claim 14  wherein said polymer comprises an aliphatic polyester selected from the group consisting of homopolymers and copolymers of lactide, lactic acid, glycolide, glycolic acid, ε-caprolactone, p-dioxanone, trimethylene carbonate, alkyl derivatives of trimethylene carbonate, δ-valerolactone, β-butyrolactone, δ-butyrolactone, ε-decalactone, hydroxybutyrate, hydroxyvalerate, 1,4-dioxepan-2-one, 1,5,8,12-tetraoxacyclotetradecane-7,14-dione, 1,5-dioxepan-2-one, and 6,6-dimethyl-1,4-dioxan-2-one.  
     
     
         16 . The process of  claim 15  wherein said aliphatic polyester comprises an elastomer selected from the group consisting of copolymers of lactide and ε-caprolactone, lactide and glycolide, and blends thereof.  
     
     
         17 . The process of  claim 16  wherein said copolymer of lactide and ε-caprolactone comprises a mole ratio of lactide to ε-caprolactone from about 30/70 to about 50/50.  
     
     
         18 . The process of  claim 16  wherein said copolymer of lactide and glycolide comprises a mole ratio of lactide to glycolide from about 75/25 to about 95/5.  
     
     
         19 . The process of  claim 14  wherein said solvent is selected from the group consisting of dimethyl carbonate, 1,4-dioxane and diethyl carbonate.  
     
     
         20 . The process of  claim 19  wherein said non-solvent is selected from the group consisting of t-butanol, tert-amyl alcohol, 3,3 dimethyl-2 butanol, octanol, nonanol, decanol, n-decanol and dodecanol.