Nitrogen plasma immersion ion implantation treatment to enhance corrosion resistance, bone cell growth, and antibacterial adhesion of Ti-6Al-4V alloy in dental applications

Ti-6Al-4V is a biocompatible alloy widely used for dental prostheses. Unfortunately, the oxide film that forms spontaneously on the surface is bioinert and sometimes prone to the release of metal ions. In this study, we applied nitrogen plasma immersion ion implantation (N-PIII) treatment to Ti-6Al-4V in order to improve corrosion resistance and biological responses, including cell growth and antibacterial adhesion, for dental applications. We then analyzed the surface characteristics, such as topography, chemical composition, hardness, and hydrophilicity. Resistance to corrosion was examined using potentiodynamic polarization curves obtained in artificial saliva, simulated body fluid, and simulated blood plasma solutions. Human bone marrow mesenchymal stem cells were used to test cell responses, including adhesion, proliferation, and mineralization. The oral bacteria, Streptococcus salivarius, was used to evaluate antibacterial adhesion, including bacterial attachment and morphology. Our results demonstrate that N-PIII treatment did not significantly affect surface roughness at the macroscopic (micrometer) scale or hydrophilicity. During N-PIII treatment, a thin film of TiN (< 1 mu m in thickness) formed on the surface of the Ti-6Al-4V. The presence of TiN positively affected the surface hardness, corrosion resistance (i.e., decreased corrosion rate and passive current), cell responses (i.e., enhanced cell adhesion, proliferation, and mineralization), and antibacterial adhesion. These effects were particularly evident when N-PIII treatment was applied at higher voltage. Our results demonstrate that the proposed N-PIII treatment increases the corrosion resistance of Ti-6Al-4V alloy, while promoting cell responses and antibacterial adhesion for dental applications.