Improved biocompatibility of Ti-based bulk metallic glasses by electrochemical formation of nanoporous oxide layers

Ti-based bulk metallic glasses (BMGs) with excellent strength-to-stiffness ratio have great potential as new bone implant material. But alloy design criteria for high glass-forming ability pose challenges for biocompatibility, like corrosion and release of cytotoxic species. For Ti₄₇Cu₃₈Zr_7.5Fe_2.5Sn₂Si₁Ag₂ BMG, we developed an electrochemical pseudo-dealloying treatment to generate nanoporous Ti/Zr oxide layers related with near-surface Cu depletion. The anodic treatment in 5 M HNO₃ at 333 K is applicable to BMG ribbons and bulk specimens. It enhances the wear resistance and does not deteriorate the mechanical compressibility. Linear anodic polarization measurements and metal release studies (ICP-OES) in PBS solution (pH 7.4) and DMEM cell culture medium (pH 7.6) revealed low free corrosion rates with initial burst of Cu release, i.e. after 1 h in DMEM: 8.65 × 10^-6 mmol/cm² and in PBS: 4.10 × 10^-6 mmol/cm² for non-treated metallic glass surfaces. The pseudo-dealloying treatment reduces effectively the Cu release rates and suppresses pitting corrosion upon anodic polarization. The influence of these strongly hydrophilic surfaces on cell morphology, metabolic activity and osteogenic differentiation potential was examined on the basis of in vitro studies with human bone marrow stromal cells (hBMSC). The formation of pro-inflammatory mediators in response to different material surfaces was evaluated in conditioned cell culture medium. Compared to non-treated surfaces and CP-Ti, hBMSC on treated nanoporous metallic glass surfaces exhibited higher metabolic activity and TNAP activity. The moderate formation of pro-inflammatory mediators indicate that the materials can contribute to and support the bone healing process.