Injectable and biodegradable nanohybrid polymers with simultaneously enhanced stiffness and toughness for bone repair

A series of novel injectable and photo-crosslinkable poly(propylene fumarate) (PPF)-co-polyhedral oligomeric silsesquioxane (POSS) copolymers are synthesized via two-step polycondensation to improve both stiffness and toughness and to promote biological performance of bone tissue engineering scaffolds. The viscoelastic behavior of uncrosslinked PPF-co-POSS and the thermal, mechanical, and surface characteristics of photo-crosslinked PPF-co-POSS are investigated as well as the degradation behavior and microscopic POSS domain structures at various weight compositions of POSS (φ _POSS). Tensile and compressive moduli and facture toughness are enhanced for crosslinked PPF-co-POSS when POSS nanocages are well distributed and their crystallinity is completely confined in the networks. Decreases in these mechanical properties are observed at higher φ _POSS because of decreased crosslinking density and larger POSS aggregates. The mechanical properties are correlated with in vitro mouse pre-osteoblastic MC3T3-E1 cell functions including cell attachment, spreading, proliferation, differentiation, and gene expression, which all maximize at φ _POSS of 10%.