The nonlinear viscoelasticity of hyaluronic acid and its role in joint lubrication

Hyaluronic acid solutions have been widely studied due to their relevance to the rheological behavior of synovial fluid and joint lubrication. Ambulatory joint motion is typically large oscillatory deflections; therefore, large amplitude oscillatory shear strain experiments are used to examine the relevant non-linear viscoelastic properties of these solutions. Using the sequence of physical processes method to analyze data provides time dependent viscoelastic moduli, which exhibit a clear physiologically relevant behavior to hyaluronic acids non-linear viscoelasticity. In particular, it is seen that during peak strain/acceleration, the time dependent elastic modulus peaks and the loss modulus is at a minimum. The hyaluronic acid can provide an immediate elastic response to sudden forces, acting like a shock absorber during sudden changes in direction of motion or maximum deflection. However, during peak rate, the elastic modulus is at a minimum and the loss modulus is at a maximum, which provides greater efficacy to hydrodynamic shear lubrication.