Development and characterization of biodegradable nanocomposite injectables for orthopaedic applications based on polyphosphazenes

Self-setting hydroxyapatite-biodegradable injectable composites are excellent candidates for applications in orthopaedics. We have previously demonstrated the feasibility of development of self-setting calcium-deficient nanocrystalline hydroxyapatite-polymer composites using different calcium phosphate precursors and biodegradable polyphosphazenes. This study aimed to evaluate these novel injectable composites as suitable materials for orthopaedic applications through evaluating their biomechanical properties, osteoblast cellular attachment and gene expression over time. Our studies demonstrated that the morphology of the composite groups (PNEA-CDHA, PNEA-CDSHA, PNEA ₅₀mPh₅₀-CDHA, PNEA₅₀mPh₅₀-CDSHA, PNEA₅₀PhPh₅₀-CDHA, and PNEA₅₀PhPh ₅₀-CDSHA) formed was similar and found to have micro- and nanoporous structures resembling trabecular bone. The osteoblast phenotypic marker of bone, alkaline phosphatase, was expressed by the cells on the surface of the composites throughout the study and was comparable to tissue-culture polystyrene (control). Furthermore, the cells seeded on the composites expressed the characteristic osteoblastic genes, such as type-I collagen, alkaline phosphatase, osteocalcin, osteopontin and bone sialoprotein, indicating osteoblast differentiation, maturation and mineralization. Within our injectable composite groups, significant gene expression levels were displayed (P < 0.05). These novel injectable biodegradable polyphosphazenes-calcium-deficient hydroxyapatites materials are promising candidates for orthopaedic applications.