Cross-linking characteristics and mechanical properties of an injectable biomaterial composed of polypropylene fumarate and polycaprolactone co-polymer

In this work, a series of co-polymers of polypropylene fumarate-co- polycaprolactone (PPF-co-PCL) were synthesized via a three-step polycondensation reaction of oligomeric polypropylene fumarate (PPF) with polycaprolactone (PCL). The effects of PPF precursor molecular weight, PCL precursor molecular weight and PCL fraction in the co-polymer (PCL feed ratio) on the maximum cross-linking temperature, gelation time and mechanical properties of the cross-linked co-polymers were investigated. The maximum cross-linking temperature fell between 38.2 ± 0.3 and 47.2 ± 0.4°C, which increased with increasing PCL precursor molecular weight. The gelation time was between 4.2 ± 0.2 and 8.5 ± 0.7 min, and decreased with increasing PCL precursor molecular weight. The compressive moduli ranged from 44 ± 1.8 to 142 ± 7.4 MPa, with enhanced moduli at higher PPF precursor molecular weight and lower PCL feed ratio. The compressive toughness was in the range of 4.1 ± 0.3 and 17.1 ± 1.3 kJ/m³. Our data suggest that the cross-linking and mechanical properties of PPF-co-PCL can be modulated by varying the composition. Therefore, the PPF-co-PCL co-polymers may offer increased versatility as an injectable, in situ polymerizable biomaterial than the individual polymers of PPF and PCL.