EX-VIVO DEGRADATION OF A POLY(PROPYLENE GLYCOL-FUMARATE) BIODEGRADABLE PARTICULATE COMPOSITE BONE-CEMENT

We have developed a biodegradable particulate composite bone cement co nsisting of a poly(propylene glycol-fumarate)-(methylmethacrylate) mat rix mixed with calcium carbonate and tricalcium phosphate particulates . Previous ex vivo studies suggest that this system provides sufficien t strength for a number of potential clinical applications including s tructural reinforcement of osseous defects, internal fixation devices for age-related fractures, and delivery of antibiotics to treat osteom yelitis. As a first step toward investigating in vivo responses to thi s material, we studied the influence of varied concentrations of cross linker, accelerator, and free radical on the mechanical properties of the cement. We then developed an ex vivo degradation assay and correla ted the mechanical properties of degrading cement with the temporal ch anges in chemical properties of both the cement and the bathing medium . The optimal cement formulation was composed of one-third poly(propyl ene glycol-fumarate)-(methylmethacrylate), one-third calcium carbonate , and one-third tricalcium phosphate, and provided initial compressive strengths of up to 30 MPa and compressive moduli of up to 300 MPa. De gradation rates, measured by a decline in mechanical properties, disso lution of calcium from the cement, and change in pH of the bathing med ium, could be controlled by changing the concentration of reactants in the matrix. Specifically, an increase in methylmethacrylate or increa se in both methylmethacrylate and benzoyl peroxide was inversely propo rtional to the rate of degradation and directly proportional to the in itial mechanical properties. The degradation products and environmenta l changes appear to be compatible with physiologic remodeling and ther efore justify examination of the In vivo response to implantation of t his material. (C) 1997 John Wiley & Sons, Inc.