Plasma Electrolytic Oxidation (PEO) Coated CP-Ti: Wear Performance on Reciprocating Mode and Chondrogenic–Osteogenic Differentiation

Biocompatible oxide coatings obtained by plasma electrolyte oxidation (PEO) have been used to improve the surface properties of bone grafts made of titanium. However, few studies explore the occurrence of wear in reciprocating mode. The chondrogenic differentiation over coatings obtained by PEO has not been explored either. These coatings tend to induce the osseointegration by contributing to the osteogenic differentiation behaviour, however, there is no evidence of their influence on the formation of cartilaginous matrix. Thus, this work aimed to investigate the behaviour of cell viability and differentiation (osteogenic and chondrogenic) and the tribological properties of coatings obtained by PEO at different voltages on the CP-Ti substrate for future applications in tissue engineering field. The morphology and structure of the coatings were characterised by scanning electron microscopy, profilometry and X-ray diffraction, respectively. The chemical composition of the coatings was analysed by energy dispersive spectroscopy and Rutherford Backscattering Spectrometry. Wear resistance was evaluated in a tribometer, in ball-on-plate configuration and in reciprocating mode. The biological behaviour was characterised by cell viability, adhesion and differentiation of mesenchymal stem cells assays. The results showed that the formation of the rutile phase in Ti-PEO 250V and Ti-PEO 300V coatings influenced the superior wear resistance behaviour, in relation to Ti-PEO 200V . Furthermore, it was found that the increase in the applied voltage caused an increase in the incorporation of Ca and P elements in the coatings. Besides this, biological results indicated that all obtained coatings were not cytotoxic, allowing adhesion and consequently cell differentiation in osteogenic and chondrogenic lineages.