A method is provided for synthesizing PLA/apatite composites with improved mechanical strength. In one aspect, a calcium-phosphate/phosphonate hybrid shell is developed to incorporate more reactive hydroxyl groups onto hydroxyapatite (HA) particles. PLA is covalently bonded to HA calcium phosphate hybrid shell, creating a strong interphase between HA and PLA, thus significantly improve the mechanical strength in comparison to that of non-modified HA.