Production of Bioactive Coatings on Titanium Implants Using a Micro-Arc Oxidation Process Assisted with Ultrasound

Introduction
Various factors such as aging, inactivity, and accidents can cause musculoskeletal disorders, often requiring surgical intervention for severe damage. The increasing number of implant surgeries has sparked interest in bone tissue engineering. Commercially pure titanium (CP-Ti) is highly favored in medicine for its biocompatibility, stability in body fluids, and tensile strength. However, a drawback is its lack of bioactivity. Bioactive coatings can address this issue by improving bone cell interaction with the material.

Materials and Methods
CP-Ti surfaces were modified using micro-arc oxidation (MAO) and ultrasound micro-arc oxidation (UMAO) in an electrolyte with calcium and phosphorus ions. This study assessed various process parameters, including voltage (400 V), duration (450 or 600 s), current density (120 or 60 mA/cm²), and two ultrasound operating modes (sinusoidal and unipolar rectangular). The coatings were analyzed through the assessment of morphology, chemical composition, topography, wettability, nanomechanical properties, corrosion behavior, coating thickness and adhesion, cytocompatibility, as well as cell adhesion and proliferation of the hFOB 1.19 cell line.

Results
Porous calcium phosphate coatings produced on CP-Ti samples exhibited hydrophilicity, an isotropic structure, and strong adhesion to the substrate. They also had a corrosion rate suitable for biomaterial applications. Further, this study showed that various MAO process parameters and ultrasound types significantly influenced the chemical composition as well as the physicochemical and mechanical properties of the coatings. Incorporating ultrasound during the MAO process enhanced coating thickness, porosity, roughness, isotropy, skewness, and calcium integration. Overall, they were characterized by favorable cytocompatibility.

Conclusions
The findings highlight the importance of surface treatment for the biomedical use of titanium. Optimal coating characteristics were achieved at a current of 136 mA, a duration of 450 s, and using unipolar rectangular ultrasound. Combining micro-arc oxidation with ultrasound improves CP-Ti properties concerning biomedical applications, such as customizing implants for knee joint resurfacing or craniofacial reconstruction.