Microrheological studies offer insights into polysaccharide gels

Microrheological measurements have been carried out on a series of model systems of increasing structural and temporal complexity using multiple particle tracking (MPT). Purely viscous media, entangled polymeric solutions, and subsequently a biologically relevant polysaccharide gel have all been studied. In addition, the gelled sample has been mechanically disrupted in order to induce a transient heterogeneous microstructure. For the polysaccharide sample MPT results are analysed in order to yield both one- and two-point microrheological measurements and these are compared with those obtained by additional experiments carried out using diffusing wave spectroscopy (DWS) and those obtained using a conventional rheometer. Results from glycerol/water mixtures and polyethylene oxide solutions agree with expectations, providing confidence both in the techniques used and the analysis employed. Moreover, a calcium-induced gel of the polysaccharide pectin yields similar results to those published recently on actin, with the elastic modulus being frequency independent at low frequency, and both elastic and viscous moduli exhibiting a high frequency scaling with omega(3/4). Furthermore, preliminary results reported here indicate that these techniques are ideally suited to the study of the temporal evolution of the spatial distribution of mechanical properties in such samples, for example during gelation or digestion. (c) 2007 Published by Elsevier B.V.