Shulin He

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 glycol)-dimethacrylate (PEG-DMA), and beta-tricalcium phosphate (beta-TCP). We examined the effects of the PEG-DMA/PPF double-bond ratio and beta-TCP content on the crosslinking characteristics of the composites including the maximum crosslinking temperature and the gel point, as well as the properties of the crosslinked composites such as the compressive strength and modulus, and the water-holding capacity. The maximum crosslinking temperature was 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 affected 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 11.2 +/- 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 properties of all composites. The equilibrium water content of networks without beta-TCP increased from 21.7 +/- 0.2 to 30.6 +/- 0.2% for a double-bond ratio of PEG-DMA/PPF ranging from 0.38 to 1.88. However, the mechanical properties of the swollen composites under compression were smaller than the dry ones. These data demonstrate the feasibility of fabricating injectable biodegradable polymer composites with engineered mechanical properties for orthopedic tissue engineering.

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

Abstract 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.