Crosslinking characteristics of an injectable poly(propylene fumarate)/beta-tricalcium phosphate paste and mechanical properties of the crosslinked composite for use as a biodegradable bone cement

We investigated the crosslinking characteristics of an injectable composite paste of poly(propylene fumarate) (PPF), N-vinyl pyrrolidinone (N-VP), ben zoyl peroxide (BP), sodium chloride (NaCl), and beta-tricalcium phosphate ( beta-TCP). We examined the effects of PPF molecular weight, N-VP/PPF ratio, BP/PPF ratio, and NaCl weight percent on the crosslinking temperature, hea t release upon crosslinking, gel point, and the composite compressive stren gth and modulus. The maximum crosslinking temperature did not vary widely a mong formulations, with the absolute values falling between 38 degrees and 48 degrees C, which was much lower than that of 94 degrees C for poly(methy l methacrylate) bone cement controls tested under the same conditions. The total heat released upon crosslinking was decreased by an increase in PPF m olecular weight and a decrease in N-VP/PPF ratio. The gel point was affecte d strongly by the PPF molecular weight, with a decrease in PPF molecular we ight more rapidly leading to a gel point. An increase in initiator concentr ation had the same effect to a lesser degree. The time frame for curing was varied from 1-121 min, allowing the composite to be tailored to specific a pplications. The compressive strength and compressive modulus values increa sed with decreasing N-VP/PPF, increasing NaCl content, and increasing BP/PP F ratio. For all formulations, the compressive strength values fell between I and 12 MPa, and the compressive modulus values fell between 23 and 265 M Pa. These data suggest that injectable PPF/beta-TCP pastes can be prepared with handling characteristics appropriate for clinical orthopedic applicati ons and that the mechanical properties of the cured composites are suitable for trabecular bone replacement. (C) 1999 John Wiley & Sons, Inc.