Investigation on the in vitro cytocompatibility of Mg-Zn-Y-Nd-Zr alloys as degradable orthopaedic implant materials.

Mg-Zn-Y-Nd-Zr alloy has been developed as a new type of biodegradable orthopaedic implant material by the authors' research group with its excellent mechanical properties and controllable degradation rate. In this study, the cytocompatibility of Mg-Zn-Y-Nd-Zr alloy was systematically evaluated through in vitro cell culture method. MTT assay was applied to evaluate the cytotoxicity of Mg-Zn-Y-Nd-Zr alloy and no toxic effect was observed on L929 and MC3T3-E1 cells followed the protocol of ISO 10993 standard. Considering the potential ion accumulation in the bony environment, this study further investigated the cytotoxic effect of accumulated metallic ions during the alloy degradation by extending the extract preparation time. When the extract preparation time was prolonged to 1440 h, the accumulated metallic ions leaded to severe cell apoptosis, of which the combined ion concentration was determined as 39.5-65.8 µM of Mg2+, 3.5-5.9 µM of Zn2+, 0.44-0.74 µM of Y3+, 0.3-0.52 µM of Nd3+ and 0.11-0.18 µM of Zr4+ for L929, and 65.8-92.2 µM of Mg2+, 5.9-8.3 µM of Zn2+, 0.74-1.04 µM of Y3+, 0.52-0.73 µM of Nd3+ and 0.18-0.25 µM of Zr4+ for MC3T3-E1 cells. Besides the cell viability assessment, high expression of ALP activity and calcified nodules implied that metal elements in Mg-Zn-Y-Nd-Zr alloys can promote the osteogenic differentiation. Hence, excellent cytocompatibility has equipped Mg-Zn-Y-Nd-Zr alloy as a promising candidate for orthopaedic implant application, which can remarkably guide the magnesium-based alloy design and provide scientific evidence for clinical practice in future.