Denaturation and graphitization of albumin molecules induced by mechanical shear stress via in-situ point contact

Abstract

Many well functioned explants have shown that a gaphitized tribofilm formed on the bearing surfaces providing excellent lubrication effects, greatly improves the longevity and service safety of the joint prosthesis. Tribofilms are generally believed to be generated from protein molecules in the pseudo-synovial fluid. In this study, a modified atomic force microscopy with an alumina microsphere tip was used to articulate against low-carbon wrought CoCrMo alloy pins in protein solution. We successfully studied the process of tribofilm formation in-situ, with the results demonstrating that a critical compressive stress (>136 MPa) was required for tribofilm formation. Increasing compressive stress reduced tribofilm thickness but expanded its area and increased its modulus. In addition, with prolonged friction, the proteins gradually shifted toward graphitization. This in-situ study revealed that tribofilm growth in the articular prostheses is manifested as the expansion of the coverage area, rather than the continuous increase of thickness.