Tribological Properties and Tribochemistry of Articular Synovial Fluids Made of Physiological Saline and Calf Serum

Articular synovial fluids of different compositions were prepared from calf serum and 0.9%NaCl physiological saline. The anti-wear and friction-reducing properties of the resulting articular synovial fluids were evaluated using a four-ball machine. The worn surfaces of the steel ball lubricated with the synovial fluid were analyzed by means of X-ray photoelectron spectroscopy. It was found that the calf serum had excellent anti-wear and friction-reducing capacities, but the physiological saline was poor in terms of the anti-wear and friction-reducing capacities. Thus the incorporation of the calf serum at different volume fractions contributed to improve the anti-wear and friction-reducing capacities of the physiological saline. The improved anti-wear and friction-reduction of the physiological saline in the presence of the calf serum was attributed to the boundary film composed of the adsorbed protein of the serum, the deposited CaCO_3 layer originated from the serum, and the tribochemical reaction layer containing FePO_4 on the worn steel surface.