Mimicking tissue surfaces by supported membrane coupled ultrathin layer of hyaluronic acid

We describe a technique of anchoring ultrathin (50-250 nm) layers of the extracellular matrix polysaccharide hyaluronic acid (HA) on solid supported fluid lipid bilayers through a recombinant HA-binding protein (p32) which is coupled to lipid molecules by reversible histidine-chelator bonds. A novel technique, the dual wavelength reflection interference contrast microscopy (DW-RICM), was applied to measure the local absolute thickness of the soft polymer cushions by measuring the height of the colloidal beads hovering over the surface. By analysis of the mean-square out-of-plane fluctuations of the beads, the surface elasticity and friction of the HA films can be measured as a function of the film thickness. The technique is applied to study the influence of excess salt and the cross-linkers on the film thickness and viscoelastic parameters of membrane coupled HA layer. The mean-square displacement of the lateral diffusion of the colloidal beads over the HA film obeys a non-Brownian power law (〈|x(t) - x(0)|²〉 ∞ t^α) with α = 0.70 ± 0.05 attributed to the time-dependent friction of the viscoelastic HA film.