Surface engineering of Ti6Al4V alloys by bioactive coatings

Surface engineering plays a key role in enhancing the performance of next-generation titanium-based implantable medical devices. Incorporating bioactive agents into protective coating offers a promising strategy to tailor surface properties to improve biological responses after implantation. This study aims to develop PMMA–silica coatings containing calcium and silver phosphates in the surface layer, acting simultaneously as an anticorrosion barrier and a bioactive layer. PMMA–silica coatings were synthesized by combining the sol–gel process of tetraethylorthosilicate (TEOS) with the radical polymerization of methyl methacrylate (MMA) and 3-methacryloxypropyl trimethoxysilane (MPTS). Bioactive agents, including hydroxyapatite (HA), β-tricalcium phosphate (β-TCP), and silver phosphate (Ag₃PO₄), were dispersed in the PMMA–silica solution. The coatings were deposited onto Ti6Al4V substrates by immersion, resulting in uniform layers with thicknesses of up to 17 µm, free of cracks and exhibiting excellent adhesion strength (>14 MPa). The influence of the additives on the structural properties of the nanocomposites was analyzed using infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermal analysis, and contact angle measurements. Electrochemical impedance spectroscopy conducted in simulated body fluid (SBF, ISO 23317) confirmed the excellent anticorrosion performance of the modified coatings, showing an impedance modulus of up to 70 GΩ cm² after 100 days in SBF, which is four orders of magnitude higher than that of uncoated Ti6Al4V. Additionally, apatite crystal deposits observed after 28 days of immersion in SBF are an indicator of the in vivo bone bioactivity of the coatings. Biological evaluations revealed enhanced proliferation of SaOS-2 osteoblasts after 7 days of culture on coatings containing β-TCP or HA combined with Ag₃PO₄. These results highlight the potential of modified PMMA–silica coatings as highly promising materials for improving the bioactive and anticorrosive properties of Ti-based implants.

Acknowledgments: This research received financial support from the Brazilian funding agencies CNPq and CAPES.