Evaluation of thermal‐ and photo‐crosslinked biodegradable poly(propylene fumarate)‐based networks

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Abstract
Biodegradable networks of poly(propylene fumarate) (PPF) and the crosslinking reagent poly(propylene fumarate)‐diacrylate (PPF‐DA) were prepared with thermal‐ and photo‐initiator systems. Thermal‐crosslinking was performed with benzoyl peroxide (BP), which is accelerated by N,N‐dimethyl‐p‐toluidine (DMT) and enables injection and in situ polymerization. Photo‐crosslinking was accomplished with bis(2,4,6‐trimethylbenzoyl) phenylphosphine oxide (BAPO), which is activated by long‐wavelength UV light and facilitates material processing with rapid manufacturing techniques, such as stereolithography. Networks were evaluated to assess the effects of the initiators and the PPF/PPF‐DA double bond ratio on the mechanical properties. Regardless of the initiator system, the compressive properties of the PPF/PPF‐DA networks increased as the double bond ratio decreased from 2 to 0.5. BAPO/UV‐initiated networks were significantly stronger than those formed with BP/DMT. The compressive modulus of the photo‐ and thermal‐crosslinked PPF/PPF‐DA networks ranged from 310 ± 25 to 1270 ± 286 MPa and 75 ± 8 to 332 ± 89 MPa, respectively. The corresponding fracture strengths varied from 58 ± 7 to 129 ± 17 MPa and 31 ± 13 to 105 ± 12 MPa. The mechanical properties were not affected by the initiator concentration. Characterization of the network structures indicated that BAPO was a more efficient initiator for the crosslinking of PPF/PPF‐DA, achieving a higher double bond conversion and crosslinking density than its BP counterpart. Estimated average molecular weights between crosslinks (Mc) confirmed the effects of the initiators and PPF/PPF‐DA double bond ratio on the mechanical properties. This work demonstrates the capability to control the properties of PPF/PPF‐DA networks as well as their versatility to be used as an injectable material or a prefabricated implant. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 66A: 811–818, 2003

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