Microrheology of Concentrated Protein Solutions

Abstract: The behavior of concentrated protein solutions is of general high interest due to implications in, for example, biological systems and medical applications. It is necessary to investigate the rheological properties of such systems to understand how parameters, such as stability, are affected by the high concentrations. Unfortunately, studies are often hindered by the lack of sufficient quantities of the protein of interest. A collection of techniques have been suggested as a way to circumvent this issue by requiring much smaller sample volumes. These techniques are commonly collated by the term "microrheology" and are based on observing the motion of tracer particles immersed in a sample. This thesis describes the work of preparing tracer particles suitable for scattering- and microscopy-based microrheology of concentrated protein solutions. Different proteins were investigated using the aforementioned methods, including several present in the eye lens system which has a necessity of high protein concentrations to function optimally. Employing a secondary sample preparation step involving evaporation made it possible to reach into the arrested regime of close-packed proteins. Samples in this region are of high scientific interest but commonly difficult to produce and investigate.