Biocompatibility and bio-corrosion behavior of medical grade titanium alloy developed through the direct energy deposition (DED) method

Additive manufacturing of titanium alloys has gained significant attention for biomedical applications due to its ability to fabricate complex geometries with controlled microstructures. In this study, a titanium alloy was fabricated using the direct energy deposition (DED) technique and evaluated in the as-built and double-aged conditionsfor biomedical suitability. Post-processing involved a two-stage aging treatment at 720°C and 620°Cto enhance microstructural stability and mechanical performance. Optical microscopy revealed a fine acicular lath structure in the as-built alloy resulting from rapid solidification, while the heat-treated alloy exhibited a coarser and thermodynamically stable α + βmicrostructure. The as-built DED Ti alloy showed a hardness of 360 Hv and density of 4.29 g/cc, which increased to 371 Hv and 4.49 g/cc after heat treatment due to martensite decomposition, secondary α precipitation, and porosity reduction. Cytocompatibility assessed using L929 fibroblast cellsfollowing ISO 10993-5 (MTT assay)confirmed cell viability above 70% for 72 hfor both conditions, with the as-built alloy exhibiting comparatively higher viability. Electrochemical corrosion studies conducted in simulated body fluid (SBF) demonstrated very low corrosion current densities (~10⁻³ mA/cm²) and corrosion rates (~0.009 mm/year), indicating excellent corrosion resistance. Notably, the as-built alloy exhibited superior passivation behavior due to the formation of a stable TiO₂-rich oxide layer. These results confirm the suitability of DED-fabricated titanium alloys for biomedical implant applications.