Confocal Microrheology of biopolymer Hyaluronan

Hyaluronan is a biopolymer that is found throughout the human body in connective tissue. To investigate the viscoelastic properties of this material the diffusion of carboxylate spheres in buffered solutions containing varying concentrations of 60 kDa Hyaluronan was monitored using a confocal microscope. The solutions contained a mix of D2O/H2O to match the density of the spheres. The trajectories of the spheres were analyzed using one- and two-point microrheology analysis methods. At low concentrations of hyaluronan the dynamic viscosity was extracted using the Stokes-Einstein relation. We compare these viscosities with theoretical models and use them to estimate the overlap concentration. At high concentrations, the spheres move in a way that does not correspond to normal diffusion, and the mean-squared displacement vs. lag time displays an interesting concentration-dependent inflection point. We compare results from one- and two-point particle tracking analysis.