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 = 1) and two (m = 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 = 1) polymer networks increased from 11.2 ± 1.8 to 66.2 ± 5.5 MPa as the double bond ratio of PPF/PPF-DA (m = 1) decreased from 4 to 0.5. An increase in compressive modulus was also observed from 19.4 ± 1.8 to 340.2 ± 30.7 MPa for the same range of the double bond ratio of PPF/PPF-DA. Increasing the molecular weight of PPF-DA (m = 2) caused both the compressive strength at fracture and modulus of the corresponding polymer networks to increase to the ranges of 14.4 ± 4.2 to 88.2 ± 6.1 MPa and 28.0 ± 2.4 to 480.4 ± 35.9 MPa, respectively. Similarly, both were increased as the PPF/PPF-DA (m = 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.