Protein solutions are complex fluids in which the rheology can change as the concentration changes. These solutions, used for a wide range of applications in bio-pharmaceutical and biotechnology industries, can be solubilized in a variety of solvents — including water and organic solvents. At low concentrations, protein solutions can behave like Newtonian fluids over a wide range of shear rates, while at high concentrations of protein these solutions can be non-Newtonian at sufficiently high shear rates. The shear rates where non-Newtonian behavior are observed are totally dependent on the protein and its concentration. This is why we recommend testing viscosity at multiple shear rates from low to high. It will give you a more complete understanding of your proteins! Proteins are naturally metastable in solution, however, too much protein instability in solution is detrimental to their effectiveness. Protein stability depends on temperature, pH, concentration, as well as intra- and intermolecular interactions and is a critical factor in protein drug formulation, drug efficacy, and storage shelf life.
In an ideal scenario we would formulate protein solutions and immediately use them but this is rarely the case. In practical applications, protein solutions are formulated and then stored for long periods of time - sometimes even months - before use. Interactions between proteins and their microstructure in solutions are dynamic as time passes. Hence, these solutions can experience age related changes during storage. For instance, the effects of protein ageing can include aggregation, as well as flocculation, which can be detected using viscosity measurements (Dickinson E, 2010).
In our protein ageing application note we show that age-related changes in protein solutions can be detected using automated viscosity measurements. We go a step further, showing that the shelf life of protein solutions can be increased with minor changes to the formulation. In particular, this application note primarily focuses on the incorporation of arginine-HCl into formulations.
Download the full application note to learn how we used automated viscosity measurements with VROC® initium to show how the incorporation of arginine-HCl into protein formulations reduced initial viscosity, inhibited flocculation, and kept viscosity stable for longer.