Study of a Denatured Bovine Serum Albumin Solution Used as Lubricant in Tribological Testing of Total Knee Replacements

The lubricant solution used in tribological testing of total knee replacements must have a 20 g/L (ISO 14243-3:2014) overall value of protein concentration; bovine serums (BSs) are currently used as base fluids to prepare such solution. BSs normally have a higher concentration of bovine serum albumin (BSA) and minor concentration of globulins (α, β and γ). It has been observed that these proteins can be degraded and adsorbed onto the surface of the materials during tribological tests. Therefore, this research is aimed at analyzing the proteins of denatured lubricant BSA-based solutions having a protein concentration of 20 g/L, after 6 h of tribological testing under different conditions. The testing tribological parameters considered were the applied load (L), sliding-to-rolling ratio (SRR), and entrainment speed (V_m). Four combination of parameters were set: (a) 8N-18-80 mm/s, (b) 2N-18-80 mm/s, (c) 8N-0.2-20 mm/s, and (d) 2N-0.2-20 mm/s. All tests carried out at 37 °C. Samples of the solutions were analyzed before and after testing by UV–Vis spectroscopy (range 200–300 nm), Bradford and Ellman methods. The UV–Vis spectroscopy analyzes allowed to determine possible change suffered of the aromatic residues (residues exposed or covered cause an increase or decrease of absorbance). Bradford analysis of solutions indicated similar content of proteins. Therefore, basic amino acid residues in proteins interact and reorganize. Moreover, disulfide bonds involved in tertiary structure of protein remains stable. Finally, COF (Coefficient friction) is dependent on both, protein state as well as the tribological parameters.