BIOABSORBABLE COMPOSITES .2. NONTOXIC, L-LYSINE-BASED POLY(ESTER-URETHANE) MATRIX COMPOSITES

Bioabsorbable composites were fabricated from poly(D,L-lactide-urethane) matrix reinforced with poly(glycolic acid) (DEXON) surgical mesh. The crosslinked polyurethane matrix was formed from the reaction of ethyl-2,6-diisocyanatohexanoate and poly(D,L-lactide) triol, initiated from glycerol; the ultimate degradation products of this matrix, L-lysine, lactic acid, glycerol, and CO2, are all nontoxic, naturally occurring metabolites. The composites were fabricated by two processing methods, with the final composite structures displaying very different physical properties. Composites fabricated by vacuum bag molding displayed tensile strength and modulus of 66 MPa and 468 MPa, respectively, with total elongation of 39%. Composites fabricated by the same method, but whose final cure included 24 h at 5000 psi, displayed tensile strength and modulus of 86 MPa and 3.4 GPa, respectively, with total elongation of 18%, suggesting a more fully developed matrix/fiber interphase and a reduction in microvoids, which lead to lower force failures. As poly(D,L-lactide) prepolymer molecular weights decreased, tensile strengths and glass transition temperatures of the polyurethane networks increased. These trends were attributed to increased hydrogen bonding with an increased crosslink density. The composites were sensitive to cyclic loading, regardless of the processing technique, suggesting an inefficient transfer of energy from the matrix into the load-bearing fibers. This weakness was confirmed by SEM microscopy, which revealed a gap at the fiber/matrix interface of an unfatigued composite sample. Poly(D,L-lactide-urethane) matrix composites were found to be unique since they can be custom shaped when heated above the glass transition of the matrix. DSC revealed the glass transitions for the matrices of around 60-degrees-C. The composites were easily shaped above this temperature, yet remained rigid at biological temperature.