| Abstract
| - Using a surface forces apparatus, we have measured the normal and shear forces betweensurfaces containing physisorbed hyaluronic acid (HA), which is a major component of synovial fluid andwhich is believed to play a role in joint lubrication. The adsorption mechanisms involved the ionic bindingof negatively charged HA (i) to positively charged surfactant bilayers supported on mica substrates and(ii) to negatively charged mica surfaces via Ca2+ bridges. Our results show that physisorbed HA fails asa lubricant when surfaces are pressed strongly together and/or sheared due to the squeezing out of theHA from between the surfaces. On the basis of these and previous studies, we conjecture that HA mightfunction as an effective boundary biolubricant, exhibiting both low friction and low wear, but only if it ischemically or specifically bound exclusively to each surface, but not to both surfaces.
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