Biological Effects of Titanium Surface Charge with a Focus on Protein Adsorption

The effect of changes in surface charge on the biological properties of implants is not clear. The objective of this study was to evaluate the biological properties of the surface of titanium sheets with different charges due to different treatment methods. Titanium sheets were sandblasted with large grit and underwent acid etching before being subsequently divided into the following groups: SLA, no further treatment; SLA-Ca²⁺, immersed in 1% CaCl₂ solution; SLA-NaCl, immersed in saline; and SLA-Ca²⁺-NaCl, immersed in 1% CaCl₂ solution followed by saline. Surface characteristics were evaluated using field-emission scanning electron microscopy with energy-dispersive spectrometry, surface profilometry, and contact angle assays. Additionally, we used a ζ-potential analyzer to directly measure the electrostatic charge on the different group surfaces. The effect of changes in the Ti surface on biological processes after different treatments was determined by analyzing fibronectin adsorption, osteoblast-like MG63 cell adhesion and proliferation, and the expression of osteogenesis-related genes. Compared to the SLA surface, the other three groups contained corresponding trace elements because they were soaked in different liquids; the contact angles of the three groups were not significantly different, but they were significantly smaller than that of the SLA group; and there was no change in the surface topography or roughness. Furthermore, the SLA-Ca²⁺ group had a significantly reduced negative charge compared to that of the other three groups. There were no differences between the SLA-NaCl and SLA-Ca²⁺-NaCl groups in terms of negative charge, and the SLA group surface carried the most negative charge. Fibronectin adsorption capacity and cytological performance testing further showed that the SLA-Ca²⁺ group had the most significant change, followed by the SLA-NaCl and SLA-Ca²⁺-NaCl groups; the SLA group had significantly lower capacity and performance than the other three groups. These results suggest that the surface charge of the titanium sheet changed when immersed in different liquids and that this treatment enhanced biocompatibility by reducing the electrostatic repulsion between biomaterials and biomolecules.