Polymer brush in articular cartilage lubrication: Nanoscale modelling and simulation

Human knee joints move smoothly under high load conditions due to articular cartilage and synovial fluid. Much attention is paid to the role of proteoglycans. It is suggested that a part of proteoglycan forms aggregate on the cartilage surface, making a polymer brush, which has an important role in lubrication. In order to examine the lubrication mechanism in detail, we constructed a full atom model of a polymer brush system, and carried out a series of molecular dynamics simulations to analyze its frictional properties under constant shear. We use chondroitin 6-sulfate molecules grafted on resilient surface as the polymer brush and water with sodium ions as the synovial liquid. In the steady state, polymers have large deformation and the flow of synovial fluid becomes deviate from the Coutette flow, leading to a drastic reduction of friction. Longer chains have larger reduction.