Injectable biodegradable polymer composites based on poly(propylene fumarate) crosslinked with poly(ethylene glycol)-dimethacrylate

New injectable, in situ crosslinkable biodegradable polymer composites were investigated consisting of poly(propylene fumarate) (PPF), poly(ethylene g lycol)-dimethacrylate (PEG-DMA), and beta-tricalcium phosphate (beta-TCP). We examined the effects of the PEG-DMA/PPF double-bond ratio and beta-TCP c ontent on the crosslinking characteristics of the composites including the maximum crosslinking temperature and the gel point, as well as the properti es of the crosslinked composites such as the compressive strength and modul us, and the water-holding capacity. The maximum crosslinking temperature wa s constant averaging 39.7 degrees C for the composite formulations tested. The gel points varied from 8.0 +/- 1.0 to 12.6 +/- 2.5 min and were not aff ected by the relative amounts of PEG-DMA. The compressive strength at yield of PEG-DMA/PPF composites without beta-TCP increased from 5.9 +/- 1.0 to 1 1.2 +/- 2.2 MPa as the double-bond ratio of PEG-DMA/PPF increased from 0.38 to 1.88. An increase in compressive modulus was also observed from 30.2 +/ - 3.5 to 58.4 +/- 6.2 MPa for the same range of the PEG-DMA/PPF double-bond ratio. Also, the addition of beta-TCP (33 wt%) enhanced the mechanical pro perties of all composites. The equilibrium water content of networks withou t beta-TCP increased from 21.7 +/- 0.2 to 30.6 +/- 0.2% for a double-bond r atio of PEG-DMA/PPF ranging from 0.38 to 1.88. However, the mechanical prop erties of the swollen composites under compression were smaller than the dr y ones. These data demonstrate the feasibility of fabricating injectable bi odegradle polymer composites with engineered mechanical properties for orth opedic tissue engineering. (C) 2000 Elsevier Science Ltd. All rights reserv ed.