Nano‐Hydroxyapatite/Fluoridated and Unfluoridated Bioactive Glass Composites: Structural Analysis and Bioactivity Evaluation

Biphasic bioceramic composites containing nano‐hydroxyapatite (HAP) and nanosized bioactive glasses have been prepared in the form of pellets and have been examined for the effects of bioglass concentrations and sintering temperature on the structural transformations and bioactivity behavior. Pure stoichiometric nano‐HAP was synthesized using sol‐gel technique. Two bioglasses synthesized in this work—fluoridated bioglass $(Cao‐P2O5‐Na2O3‐CaF2)$ and unfluoridated bioglass $(Cao‐P2O5‐Na2O3)$ designated as FBG and UFBG respectively, were added to nano‐HAP with concentrations of 5, 10, 12 and 15%. The average particle sizes of synthesized HAP and bioglasses were 23 nm and 35 nm, respectively. The pellets were sintered at four different temperatures i.e. $1000 °C,$ $1150 °C,$ $1250 °C$ and $1350 °C.$ The investigations involved study of structural and bioactivity behavior of green and sintered pellets and their deviations from original materials i.e. HAP, FBG and UFBG, using X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The phase composition of the sintered pellets was found to be non‐stoichiometric HAP with α‐TCP (tricalcium phosphate) and β‐TCP. It was revealed from SEM images that bonding mechanism was mainly solid state sintering for all pellets sintered at $1000 °C$ and $1150 °C$ and also for pellets with lower concentrations of bioglass i.e. 5% and 10% sintered at $1250 °C.$ Partly liquid phase sintering was observed for pellets with higher bioglass concentrations of 12% and 15% sintered at $1250 °C$ and same behaviour was noted for pellets at all concentrations of bioglasses at $1350 °C.$ The sintered density, hardness and compression strength of pellets have been influenced both by the concentration of the bioglasses and sintering temperature. It was observed that the biological HAP layer formation was faster on the green pellets surface than on pure HAP and sintered pellets, showing higher bioactivity in the green pellets.