In Vitro Biocompatibility of Surface Corrosion Films upon Magnesium

Biocompatibility is an essential requirement for implantable biomaterials, particularly for magnesium (Mg) and its alloys which are being pursued as biodegradable implants. In this study, the influence of corrosion-products layers upon the surface of pure Mg specimens was evaluated through direct contact with simulated body fluid. The immersion of pure Mg specimens was conducted in Dulbecco’s modified Eagle’s medium (DMEM) at physiological conditions over defined time durations (from 24 h to 14 d). Surface morphology, chemical composition, and cross-sectional structure of corrosion layers were examined by means of focused ion beam, scanning electron microscopy, and x-ray diffraction. Results reveal a duplex Mg(OH)₂/CaPO₄ corrosion layer was produced upon pure Mg as a result of immersion in DMEM, similar to the in vivo surface corrosion films observed on pure Mg in the murine artery. The concentration of Mg in the surface corrosion film decreased with immersion time, from approximately 64 wt% (1 d) to approximately 22 wt% (14 d). Conversely, Ca and P, representing the key constituents in DMEM, were incorporated in corrosion products, resulting in unique surfaces being presented to cells as a function of Mg dissolution. MG63 osteoblast proliferation assay demonstrates comparative cell viability on all corroded surfaces obtained through immersion in DMEM for 1 d, 3 d, 7 d, and 14 d, varying from 90% to 100%. Cell viability on all corroded surfaces was higher than that of bare metal surface (82%), signifying enhanced biocompatibility of corroded surfaces related to the bare metal surface.