Jai A. Pathak

A Microliter Capillary Rheometer for Characterization of Protein Solutions

Rheometry is an important characterization tool for therapeutic protein solutions because it determines syringeability and relates indirectly to solution stability and thermodynamic interactions. Despite the maturity of rheometry, there remains a need for a rheometer that meets the following three needs of the biopharamaceutical industry: small volume; large dynamic range of shear rates; and no air-sample interface. Here, we report the development of a miniaturized capillary rheometer that meets these needs and is potentially scalable to a multiwell format. These measurements consume only a few microliters of sample and have an uncertainty of a few percent. We demonstrate its performance on monoclonal antibody solutions at different concentrations and temperatures. The instrument has a dynamic range of approximately three decades (in shear rate) and can measure Newtonian, shear thinning, and yielding behaviors, which are representative of the different solution behaviors typically encountered. We compare our microliter capillary rheometer with existing instruments to describe the range of parameter space covered by our device.

Rheology of a miscible blend of SAN and SMA

We present results of oscillatory shear rheology experiments on miscible blends of commercial styrene-acrylonitrile (SAN) and styrene-maleic anhydride (SMA) copolymers. We find that this blend system upholds the empirical time-temperature superposition principle. We compare the thermorheological behavior in this system with other blends, on which oscillatory shear data have been published in the literature. We show that thermorheological behavior in these blends is indeed comparable to other known thermorheologically simple blends. Thermorheological simplicity in this blend is nicely anticipated by a thermorheological phase diagram in the parameter space of dynamic asymmetry and free volume, which we have recently proposed.