Bio-inspired immobilization of strontium substituted hydroxyapatite nanocrystals and alendronate on the surface of AZ31 magnesium alloy for osteoporotic fracture repair

Osteoporosis is a significant public health problem associated with increased fracture risk. Magnesium (Mg) alloys are promising biodegradable implant materials for osteoporotic bone fracture repair due to their mechanical compatibility and biological safety. However, the degradation rate of Mg alloy does not match the healing rate of the fracture and the growth rate of new bone tissues. In order to treat and prevent osteoporosis, enhance peri-implant bone formation, inhibit bone resorption and slow down the degradation of Mg alloy, herein, we developed a novel bio-inspired therapeutic coating strategy by co-immobilizing strontium (Sr) substituted hydroxyapatite (Sr-HA) nanocrystals and bisphosphonate (BP) alendronate on the surface of AZ31 Mg alloy with the aid of polydopamine and carboxymethyl chitosan (CMCS). Such novel functionalized coating can not only improve the corrosion resistance of Mg alloy but also stimulate the proliferation and differentiation of osteoblast cells due to the sustained release of ALN and Sr ions from Sr-HA nanocrystals. The present coating strategy provides deep insights into clinical repair of osteoporosis-associated fractures and can potentially be extended to design of many other orthopedic devices.