Corrosion Behavior and Biocompatibility of Na2EDTA-Induced Nacre Coatings on AZ91D Alloys Prepared via Hydrothermal Treatment

Abstract

An effective method for controlling the corrosion rate of Mg-based implants must be urgently developed to meet the requirements of clinical applications. As a naturally occurring osteoid material, nacre offers a strategy to endow biomedical Mg alloys with excellent biocompatibility, and corrosion resistance. In this study, pearl powder and NaH2PO4 were used as precursors to deposit coatings on AZ91D alloy substrates hydrothermally based on Na2EDTA-assisted induction. Na2EDTA-induced nacre coatings were fabricated at various pH values, and its chemical composition and microstructure were analyzed via energy-dispersive X-ray, scanning electron microscopy, and X-ray diffraction spectroscopy. The corrosion-resistant performance and cytocompatibility of the samples were evaluated via electrochemical measurements and in vitro cell experiments. Results showed that the samples hydrothermally treated under faint acid conditions present excellent corrosion resistance, whereas the samples treated under slight alkaline conditions demonstrate improved biocompatibility due to high Ca and P content and large Ca/P atomic ratio. This study provides substantial evidence of the potential value of nacre coatings in expanding the biological applications of implanted biomaterials.

An Impact of the Recent Developments in Coating Materials and Techniques on the Corrosion Response of AZ91D Alloy: A Review

“…Even though the emphasis was given to the conventional coating methods during this period, few studies proposed advanced and environment-friendly techniques like the sol-gel deposition [79] and hydrothermal deposition method. [131,132] It can be seen from the previous discussion that the researchers during the first half of the decade (2012-2015) had emphasized the general applications the most, and very few studies focused on specific applications. [102,109,133,134] However, in recent years, coatings developed to meet specific application requirements have become more popular, and this trend can easily be observed in Figure 13.…”

“…The biodegradation behavior of bare and coated AZ91D can be better understood from Figure 21. [132] Generally, the oxidized layer on AZ91D substrate is cracked, and CaP products on such oxidized Mg(OH) 2 layer are unstable. Hence, the Cl À ions from the surrounding solution attack the AZ91D surface, resulting in pitting corrosion within a few hours of exposure to the corrosive environment in the case of uncoated AZ91D.…”

“…However, the second coating layer in the form of ZnO@ZIF-8 core-shell could result in a superhydrophobic surface; hence, the surface damage was comparatively less. [132] Figure 22. Surface morphology of MAO coating on AZ91D with different process parameters: a) 600 Hz, 40% duty cycle, AE20 mA cm À2 and b) 800 Hz, 20% duty cycle, AE10 mA cm À2 .…”

“…Even though the emphasis was given to the conventional coating methods during this period, few studies proposed advanced and environment‐friendly techniques like the sol–gel deposition [ 79 ] and hydrothermal deposition method. [ 131,132 ]…”