Development of Ultra-Low Friction Coefficient Films and Their Effect on the Biocompatibility of Biomedical Steel

Abstract

This study evaluates the effect of a self-lubricant film with ultra-low friction coefficient on the biocompatibility of the AISI 316L. The samples were thermochemically treated to generate a hard surface layer of iron borides followed by a secondary process. The purpose of the secondary process was to generate a self-lubricant film of boric acid. The ultra-low friction coefficient of boric acid films was estimated in 0.02 compared to 0.2 and 0.8 for borided and as-received AISI 316L steel respectively. The effect of the boric acid films on the steel’s biocompatibility was evaluated by the culture of Madin-Darby canine kidney II (MDCK II) cells with exposure times of 0, 4, 8, 12, 24, 48 and 72 h. The In vitro tests revealed the absence of cytotoxic effect by the direct exposure of the cells to the samples. Additionally, the presence of signs early apoptosis by the determination of the expression of the cysteinyl proteases termed caspase-3 and -9 was determined. Their presence was assessed by indirect immunofluorescence in cells in direct contact with the samples. No significant expression of the proteolytic enzymes was detected. All these results suggest that the surface film of boric acid does not induce any cytotoxic effect and does not inhibit the cell-cell adhesion.

Graphical Abstract