Enhancement of Hydrophilicity of Nano-Pitted TiO₂ Surface Using Phosphoric Acid Etching

Our research group developed a novel nano-pitted (NP) TiO₂ surface on grade 2 titanium that showed good mechanical, osteogenic, and antibacterial properties; however, it showed weak hydrophilicity. Our objective was to develop a surface treatment method to enhance the hydrophilicity of the NP TiO₂ surface without the destruction of the nano-topography. The effects of dilute and concentrated orthophosphoric (H₃PO₄) and nitric acids were investigated on wettability using contact angle measurement. Optical profilometry and atomic force microscopy were used for surface roughness measurement. The chemical composition of the TiO₂ surface and the oxidation state of Ti was investigated using X-ray photoelectron spectroscopy. The ccH₃PO₄ treatment significantly increased the wettability of the NP TiO₂ surfaces (30°) compared to the untreated control (88°). The quantity of the absorbed phosphorus significantly increased following ccH₃PO₄ treatment compared to the control and caused the oxidation state of titanium to decrease (Ti⁴⁺ → Ti³⁺). Owing to its simplicity and robustness the presented surface treatment method may be utilized in the industrial-scale manufacturing of titanium implants.