Analyzing the Mesoscopic Structure of Pericellular Coats on Living Cells

We employed passive particle-tracking microrheology to map the micromechanical structure of the hyaluronan-rich pericellular coat enveloping chondrocytes. Therefor we exploited the technique’s position sensitivity to gain radial information on the coat. We observed a linear increase in viscoelasticity from the coat’s rim towards the cell membrane. This gradient corresponds to hyaluronan concentration profiles observed in confocal fluorescent microscopy with small, specific hyaluronan markers. These results suggest that the structural basis of the pericellular coat is formed by grafted hyaluronan of different effective lengths stretched out by a homogenous decoration with hyaladherins such as aggrecan. The different effective lengths could be caused either by different lengths of the HA chains or by “side-on” attachments within the chain. Remarkably, the hyaluronan-rich coat increases the viscosity of the pericellular space only by about a factor of about two at 100 and at 20 Hz compared to pure media and an increasing elastic component is observed. Both the viscoelasticity as well as the hyaluronan concentration decrease linearly or slightly exponential from the cell membrane towards the PCC’s rim. These observations could be obtained on living cells exploiting this unintrusive measurement techniques.