Polymer Probe Diffusion in Globular Protein Gels and Aggregate Suspensions

Transport properties of macromolecules in dense aggregate suspensions and gels of proteins are important for usage of these biomaterials in areas such as pharmaceutics, food, and cosmetics. The mobility of polymers in protein gels has received some attention in the past, but the mobility in dense aggregate suspensions has not yet been investigated. In this study, self diffusion of probe dextran chains was studied in suspensions of aggregates with different size and morphology and in gels using fluorescence recovery after photobleaching over a wide range of concentrations. Brownian diffusion of the probes was observed in aggregate suspensions as well as in weak gels formed just beyond the critical gel concentration. Diffusion of polymers in dense suspensions of protein aggregates depends not only on the concentration but also on the size and morphology of the aggregates. It is not directly related to the viscosity or the dynamic correlation length. Diffusion of polymers in protein gels is anomalous and occurs on logarithmic time scales. The recovery of the fluorescence for densely cross-linked gels was logarithmic with time, suggesting an exponential distribution of diffusion coefficients.