Atomic Layer Deposition of Oxide-Based Nanocoatings for Regulation of AZ31 Alloy Biocorrosion in Ringer’s Solution

Research into methods for regulating the biocorrosion rate of biodegradable magnesium implants is one of the most urgent tasks in the field of biomedical materials science. Atomic layer deposition (ALD) is a highly effective method for the preparation of nanocoatings, which can be used to regulate the biodegradation rate. The present paper presents the findings of a research study in which the most commonly used simple oxide ALD coatings (Al2O3, TiO2, and ZnO) were examined, in addition to mixed coatings obtained by alternating ALD cycles of the application of ZnO-TiO2 (ZTO) and Al2O3-TiO2 (ATO). The coating thicknesses exhibited a variation within the most typical range for ALD coatings, measuring between 20 and 80 nanometres. The biocorrosion testing was conducted in Ringer’s physiological solution through the measurement of potentiodynamic polarisation curves and impedance spectroscopy. The findings demonstrated that, for Al2O3 coatings, the protective properties exhibited an increase with increasing thickness, while for TiO2, the trend was found to be dependent on the type of precursor utilised. The protective properties of titanium tetraisopropoxide (TTIP) have been observed to increase with increasing thickness. Conversely, the protective properties of titanium tetrachloride (TiCl4) have been observed to decrease. The application of mixed ZTO oxides with a thickness of 40 nm has been demonstrated to reduce the corrosion current by 1.7 and 3.4 times, depending on the use of TiCl4 or TTIP. Furthermore, the effectiveness of ATO coatings of similar thicknesses has been shown to be higher, with a reduction in corrosion currents of 54 and 24 times for samples obtained using TiCl4 and TTIP, respectively. A thorough analysis of the collected data unequivocally demonstrates the superior efficacy of mixed oxides in comparison to their pure oxide counterparts.