Synthesis of biodegradable poly(propylene fumarate) networks with poly(propylene fumarate)-diacrylate macromers as crosslinking agents and characterization of their degradation products

New biodegradable poly(propylene fumarate)-based polymer networks have been prepared by radical polymerization using poly(propylene fumarate) (PPF) and poly(propylene fumarate)-diacrylate (PPF-DA) macromers. Two PPF-DAs were synthesized incorporating one (m identical with 1) and two (m identical with 2) fumarate units, and were employed in the synthesis of the polymer networks. The PPF/PPF-DA double bond ratio and the molecular weight of PPF-DA were varied to assess their effects on the mechanical properties of the resulting polymer networks as well as on their equilibrium water content. The compressive strength at fracture of PPF/PPF-DA (m identical with 1) polymer networks increased from 11.2 plus or minus 1.8 to 66.2 plus or minus 5.5 MPa as the double bond ratio of PPF/PPF-DA (m identical with 1) decreased from 4 to 0.5. An increase in compressive modulus was also observed from 19.4 plus or minus 1.8 to 340.2 plus or minus 30.7 MPa for the same range of the double bond ratio of PPF/PPF-DA. Increasing the molecular weight of PPF-DA (m identical with 2) caused both the compressive strength at fracture and modulus of the corresponding polymer networks to increase to the ranges of 14.4 plus or minus 4.2 to 88.2 plus or minus 6.1 MPa and 28.0 plus or minus 2.4 to 480.4 plus or minus 35.9 MPa, respectively. Similarly, both were increased as the PPF/PPF-DA (m identical with 2) double bond ratio decreased from 4 to 0.5. The PPF/PPF-DA crosslinked polymer networks showed negligible equilibrium water content for all 10 formulations tested in this study. The degradation reaction of the PPF/PPF-DA polymer networks under basic conditions was investigated. The degradation products were isolated and characterized by NMR and GC/MS as fumaric acid, propylene glycol, and poly(acrylic acid-co-fumaric acid) of weight average molecular weight of 5080. These data demonstrate that biodegradable PPF /PPF-DA polymer networks should have great potential as polymer scaffolds for orthopedic applications in tissue engineering.