Hydrolytic instability of laser-ablatively deposited CaSi2 coatings in air and neutral water affects the behavior of bone healing-related cell types

Abstract

Calcium silicide (CaSi2) instability in humid air or pH-neutral water remains unknown, although the topochemical formation of silicene from CaSi2 in various aqueous phases is a well-known process. Here we report on laser ablation of CaSi2 in the vacuum and ethanol, characterize coatings deposited on titanium substrates with electron microscopy, X-ray photoelectron, Raman, and infrared spectroscopy, and examine the instability of the deposited coatings in humid air and neutral water. We further investigate the behavior of human mesenchymal stromal cells (hMSCs), vascular cells (HUVECS, human umbilical vein endothelial cells), and macrophages (derived from THP-1 cell line) in contact with the deposited coatings submerged in cell culture medium. The observed results indicate that the CaSi2 coatings undergo topochemical conversion to silicene, which is accompanied by hydrolytic reactions leading to inorganic Ca compounds and SiO2, and that the response of all cell types in the hydrolyzed CaSi2 surface domain is negatively affected by the nature of the hydrolytic products. In contrast, cells showed a tendency for enhanced biocompatibility towards the CaSi2 particles ablated in the vacuum. The results suggest that coating approaches can significantly influence cell behavior outcomes.