Injectable calcium-phosphate-based composites for skeletal bone treatments

Alpha-tricalcium-phosphate-based bone cements hydrolyze and set, producing calcium-deficient hydroxyapatite. They can result in an effective solution for bone defect reconstruction due to their biocompatibility, bioactivity and adaptation to shape and bone defect sizes, together with an excellent contact between bone and graft. Moreover, the integration of hydrogel phase based on poly(vinyl alcohol) (PVA) to H-cem-composed of α-tricalcium phosphate (98% wt) and hydroxyapatite (2% wt)-allows improving the mechanical and biological properties of the cement. The aim of this work was to evaluate the influence of the PVA on relevant properties for the final use of the injectable bone substitute, such as setting, hardening, injectability and in vivo behaviour. It was shown that by using PVA it is possible to modulate the setting and hardening properties: large increase in injectability time (1 h) in relation with the plain cement (few minutes) was achieved. Moreover, in vivo tests confirmed the ability of the composite to enhance bone healing in trabecular tissue. Histological results from critical size defects produced in rabbit distal femoral condyles showed after 12 weeks implantation a greater deposition of new tissue on bone-composite interfaces in comparison to bone-cement interfaces. The quality of bone growth was confirmed through histomorphometric and microhardness analysis. Bone formation in the composite implantation sites was significantly higher than in H-cem implants at both times of evaluation.