Surface Modification of Mg0.8Ca Alloy via Wollastonite Micro-Arc Coatings: Significant Improvement in Corrosion Resistance

Abstract

Biodegradable materials are currently attracting the attention of scientists as materials for implants in reconstructive medicine. At the same time, ceramics based on calcium silicates are promising materials for bone recovery, because Ca2+ and Si2+ ions are necessary for the mineralization process, and they take an active part in the formation of apatite. In the presented research, the protective silicate biocoatings on a Mg0.8Ca alloy were formed by means of the micro-arc oxidation method, and the study of their morphology, structure, phase composition, corrosion, and biological properties was carried out. Elongated crystals and pores were uniformly distributed over the surface of the coatings. The coated samples exhibited remarkable anti-corrosion properties in comparison with bare magnesium alloy because their corrosion current decreased 10 times, and their corrosion resistance increased almost 100 times. The coatings did not significantly affect the viability of the cells, even without the additional dilution of the extract, and were non-toxic according to ISO 10993-5: 2009. In this case, there was a significant difference in toxicity of the pure Mg0.8Ca alloy and the coated samples. Thus, the results demonstrated that the applied coatings significantly reduced the toxicity of the alloy.

The Role of Microparticles of β-TCP and Wollastonite in the Creation of Biocoatings on Mg0.8Ca Alloy

“…Plasmachemical processes occurred with the formation of new phases [52,53], while rapid cooling resulted in the formation of an amorphous phase. The regularities of the formation of micro-arc coatings in the anodic potentiostatic regime, in electrolytes containing microparticles, were established in previous studies [18][19][20]30,38,39]. They were as follows: In the first period of coating deposition (up to 50 s in Figure 3a) the most powerful micro-arc discharges were realized and a porous coating layer was formed.…”

“…β-TCP particles were isometric, while wollastonite particles were elongated (Figure 1). The elongated shape of the natural wollastonite particles was its characteristic feature and was due to the chain structure of the calcium orthosilicate [30,40]. The ζ-potential of powder samples was measured at a pH range of 6-11 (ZetaSizer Nano ZSP, Malvern Instruments Ltd., Malvern, UK).…”

“…Calcium silicates, such as wollastonite (CaSiO 3 ), is a promising material for medical application due to its excellent bioactivity and biocompatibility [27][28][29][30]. Ca and Si ions took an active part in the process of biomineralization and new bone formation [27,28].…”

“…Ca and Si ions took an active part in the process of biomineralization and new bone formation [27,28]. Moreover, wollastonite could be used as a component of the coating formed on the surface of bioinert alloys [29,30] to improve their mechanical and biological properties. Calcium and magnesium silicates, such as bredigite (Ca 7 MgSi 4 O 16 ), akermanite (Ca 2 MgSi 2 O 7 ), and diopside (CaMgSi 2 O 6 ), demonstrated remarkable biocompatibility, osteogenesis, and angiogenesis capabilities [31,32].…”

Mg-Ca0.3 Electrochemical Activity Exposed to Hank’s Physiological Solution and Properties of Ag-Nano-Particles Deposits

“…One approach for a significant decrease of the corrosion degradation rate has been the modification of the Mg-Ca0.8 surface by wollastonite (CaSiO 3 ) and β-tricalcium phosphate [Ca 3 (PO 4 ) 2 ] micro-arc coatings [72,73]. Reported studies compare the degradation behavior of Mg-Ca alloys (0.3, 0.6, and 0.9 %Ca) under physiological conditions, such as the culture medium DMEM glutamax + 10% FBS-Fetal serum bovine + 1% penicillin streptomycin) [74][75][76].…”