Bioactivity Performance of Pure Mg after Plasma Electrolytic Oxidation in Silicate-Based Solutions

Abstract

The biodegradable metals, including magnesium (Mg), are a convenient alternative to permanent metals but fast uncontrolled corrosion limited wide clinical application. Formation of a barrier coating on Mg alloys could be a successful strategy for the production of a stable external layer that prevents fast corrosion. Our research was aimed to develop an Mg stable oxide coating using plasma electrolytic oxidation (PEO) in silicate-based solutions. 99.9% pure Mg alloy was anodized in electrolytes contained mixtures of sodium silicate and sodium fluoride, calcium hydroxide and sodium hydroxide. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), contact angle (CA), Photoluminescence analysis and immersion tests were performed to assess structural and long-term corrosion properties of the new coating. Biocompatibility and antibacterial potential of the new coating were evaluated using U2OS cell culture and the gram-positive Staphylococcus aureus (S. aureus, strain B 918). PEO provided the formation of a porous oxide layer with relatively high roughness. It was shown that Ca(OH)2 was a crucial compound for oxidation and surface modification of Mg implants, treated with the PEO method. The addition of Ca2+ ions resulted in more intense oxidation of the Mg surface and growth of the oxide layer with a higher active surface area. Cell culture experiments demonstrated appropriate cell adhesion to all investigated coatings with a significantly better proliferation rate for the samples treated in Ca(OH)2-containing electrolyte. In contrast, NaOH-based electrolyte provided more relevant antibacterial effects but did not support cell proliferation. In conclusion, it should be noted that PEO of Mg alloy in silicate baths containing Ca(OH)2 provided the formation of stable biocompatible oxide coatings that could be used in the development of commercial degradable implants.

Biological Performance of Duplex PEO + CNT/PCL Coating on AZ31B Mg Alloy for Orthopedic and Dental Applications

“…After 15 days, surface degradation and ensuing corrosion lead to complete cell death in both cell types, regardless of the coating differences (data not shown). Previous studies have demonstrated that the corrosion process can significantly change the pH of the medium and affect cell metabolism [ 57 , 58 ]. The pH value of human tissue is in the range of 7 ~ 7.4.…”

“…Tiny pores on the order of a few microns were shown to facilitate cell attachment by providing anchoring sites [ 64 ]. A previous study demonstrated efficient adhesion of human sarcoma U2OS cells to the PEO surface [ 57 ]. A different cell response was observed with the PEO + CNT surface: the thick filopodia were not observed despite the presence of irregular openings.…”

Electrochemistry of Thin Films and Nanostructured Materials

“…This process is called plasma electrolytic oxidation (PEO), and the resulting oxide layer forms a porous ceramic coating on the metal surface. Husak et al [ 137 ] studied PEO of pure Mg in different silicate-based solutions with different concentrations of sodium silicate, sodium fluoride, calcium hydroxide, and sodium hydroxide. To form a ceramic coating on the Mg surface, a potential of 200–300 V was applied for 10 min.…”

Overview on plasma electrolytic oxidation of magnesium alloys for medical and engineering applications

“…Application of pure Mg for biodegradable implants was studied by Y. Husak et al ( 2021) [13]. The bioactive coatings were obtained using silicate-based electrolytes with the following composition: 10 g/L sodium silicate, 5 g/L sodium fluoride, and 10g/L sodium hydroxide for one electrolyte and, 10g/L calcium hydroxide for another one.…”