Viscous Behavior of Different Concentrations of Bovine Calf Serum Used to Lubricate the Micro-textured CoCrMo Alloy Material before and after Wear Testing

Bovine calf serum is a common lubricant used to test the rheological properties of synovial fluid; however the rheological properties of the serum and their effect on testing the wear behavior of artificial joints are not fully understood. Bovine calf serum (BCS) is used as a model lubricant for testing artificial joints because the natural human synovial fluid is not readily available. Synovial fluid is the lubricant for joints and the source of nutrition for articular cartilage. The purpose of the present paper is to provide a comprehensive examination of the flow properties of bovine calf serum, with and without antibacterial agents, to determine whether it can be used as appropriate model for synovial fluid when testing the wear of artificial joint materials. We hypothesized that the viscosity of a mixture of bovine calf serum and water changes as the concentration of bovine calf serum changes before and after wear testing the lubricants. The steady-shear viscosity and storage and loss moduli were evaluated in BCS from fifteen lubricant compositions, with and without antibacterial agents, before and after wear testing the lubricant. The steady-shear viscosity varied over two orders of magnitude for both lubricants samples with and without antibacterial agent, with a greater variation for the samples with antibacterial agents. Bovine calf serum without antibacterial agents was more likely to exhibit normal viscous properties than bovine calf serum with antibacterial agents (p <0.001). The non-worn "before wear" BCS lubricants were less viscous than the worn "after wear" lubricants. Other parameters distinguished the two groups, and showed statistical significance. Both groups exhibited degenerate flow properties when compared to the synovial fluid from healthy individuals. Further examination of the connection between flow properties of BCS, other joint fluids commonly used to test artificial joints and the tribology of joint replacement prostheses should be studied.