Fungistatic and bacteriostatic Mg-enriched oxide coatings on titanium formed via plasma electrolytic oxidation

This paper reports the surface modification of titanium via a plasma electrolytic oxidation (PEO) process in baths based on 0.1 M Ca(H₂PO₂)₂ with Mg-containing additives: insoluble MgO or MgHPO₄ or highly-soluble Mg(CH₃COO)₂. The surface morphology and roughness were investigated using scanning electron microscopy (SEM), which showed that porous oxide layers were formed and the roughness increased. To determine the presence of bioactive Ca and P and bacteriostatic Mg, energy-dispersive X-ray spectroscopy (EDX) analysis was performed, as well as XPS analysis and Raman spectroscopy, which proved their successful incorporation into the oxide layer. All investigated oxide coatings were continuous and the thickest one was observed on Ti-PEO-MgP surface (5.2 µm–7.5 µm). The bacteriostatic and fungistatic properties of the investigated surfaces were determined via Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Candida albicans ATCC 2091 adhesion tests. The concentration of Mg and Ti released from the PEO-modified Ti surfaces after immersion up to 14 days in Ringer's solution was evaluated via ICP-OES technique. All studied Mg-containing PEO coatings exhibited bacteriostatic and fungistatic properties, which suggests the possible application of Mg-doped titanium PEO coatings as long-term implant materials dedicated to bone tissue.