Molybdenum as a biodegradable bone implant material assessed by ISO 10993-5/-12-compliant cytocompatibility testing...

Molybdenum is increasingly explored as a metallic implant material for bone regeneration owing to its high mechanical strength, controlled degradation behavior, and corrosion resistance. This study evaluated the cytocompatibility of metallic molybdenum using the osteoblast cell line hFOB 1.19 in both extract-based and direct-contact viability assays, conducted in strict accordance with ISO 10993-5/-12 to obtain valuable high-quality preclinical data. Molybdenum extracts demonstrated high cytocompatibility across all tested dilutions, with cell viability falling below the 70% ISO threshold only for the undiluted extract, indicating a mild concentration-dependent effect. In direct-contact assays, molybdenum preserved normal cell morphology and monolayer integrity comparable to titanium. In contrast, magnesium induced pronounced cytotoxic effects in both assay formats. All reference materials elicited the expected responses; however, gamma irradiation abolished the cytotoxicity of polyurethane containing zinc diethyldithiocarbamate, highlighting the critical importance of accounting for sterilization-induced material changes. Complementary transcriptomic analysis revealed upregulation of gene sets associated with immunostimulatory signaling, aerobic energy metabolism, and protein biosynthesis, while expression of osteogenic differentiation markers remained unimpaired. Together, these results demonstrate that cytotoxic effects of metallic molybdenum occur only at extract concentrations in the millimolar range, thereby establishing a sound preclinical basis for the further development of molybdenum-based biomaterials.