The effect of different coatings on bone response and degradation behavior of porous magnesium-strontium devices in segmental defect regeneration

Regeneration of long-bone segmental defects remains a challenge for orthopedic surgery. Current treatment options often require several revision procedures to maintain acceptable alignment and achieve osseous healing. A novel hollow tubular system utilizing magnesium-strontium (Mg–Sr) alloy with autogenous morselized bone filled inside to repair segmental defects was developed. To improve the corrosion and biocompatible properties, two coatings, Ca–P and Sr–P coatings, were prepared on surface of the implants. Feasibility of applying these coated implants was systematically evaluated in vitro and in vivo, and simultaneously to have a better understanding on the relationship of degradation and bone regeneration on the healing process. According to the in vitro corrosion study by electrochemical measurements, greater corrosion resistance was obtained for Ca–P coated sample, and attributed to the double-layer protective structure. The cytotoxicity and alkaline phosphatase (ALP) assays demonstrated enhanced bioactivity for Sr–P coated group because of the long-lasting release of beneficial Sr(2+). At 12 weeks post-implantation with Mg–Sr alloy porous device, the segmental defects were effectively repaired with respect to both integrity and continuity. In addition, compared with the Ca–P coated implant, the Sr–P coated implant was more proficient at promoting bone formation and mineralization. In summary, the Sr–P coated implants have bioactive properties and exceptional durability, and promote bone healing that is close to the natural rate, implying their potential application for the regeneration of segmental defects.