The objective of this study was to compare micro-scale friction coefficients with and without synovial fluid, and micro-scale measurements were performed using atomic force microscopy (AFM) with a 5 ㎛ spherical probe. Four cylindrical cartilage specimens were harvested from two fresh bovine humeral heads (4-6 months old). Average±standard deviation values of the micro-scale AFM frictional coefficients calculated from the linear fit of friction versus normal force was 0.177±0.012 and 0.130±0.010 with and without synovial fluid coating on AFM probe respectively, showing its reduction by ~27% with synovial fluid. To the best of our knowledge, this experimental study investigates the first such comparisons of frictional response of articular cartilage with and without synovial fluid coating on AFM probe, and provides significant insights into the role of synovial fluid in the articular cartilage friction and lubrication independently of the confounding effect of fluid pressurization in the articular cartilage.
