Effect of hyaluronic acid on phospholipid model membranes.

The role of hyaluronic acid (HA) in supporting low friction and low abrasion during movement in synovial joints is still not fully understood. In this study, we set out to investigate the interaction between HA and representative lipid model membranes, bilayers as well as monolayers, in detail using a variety of calorimetric, spectroscopic, scattering and microscopic techniques, to explore their role in lubrication of articular cartridge. We also cover a wide range of pressures to mimic pressures occurring upon joint movement, aiming at elucidating a possible mechanism for the low friction forces in synovial joints. Effects of HA on lipid bilayer membranes, encompassing significant adsorption at the membrane, penetration of the hydrophobic regions of the HA between lipid head groups, or changes of the temperature- and pressure dependent phase behavior of the membrane or mechanical properties could not be observed. High molecular weight HA at physiological NaCl concentrations might rather operate independently, via an entropy-driven excluded volume effect, to control the hydrodynamics of the synovial fluid. Minor effects are observed only at domain boundaries using lipid monolayers. As lubrication of natural joints is a synergistic effect, other components of the synovial fluid, such as proteoglycans, might play a more active role.