Illustrating Ultra-Low-Volume Rheology on a Conventional Rheometer: Charting the Development of Hyaluronan During Fermentation

Abstract

We provide methodologies to characterise the rheology of ultra-low volumes of polymer solutions and biological fluids (10- 100μL) on a rotational rheometer. The technique utilises a parallel plate geometry with narrow gaps of 20- 100 micrometers, which is an order of magnitude less than conventional methods. Despite the complications these gaps present, the use of appropriate protocols ensures reliable and accurate rheological characterisation of fluids, including shear-dependent viscosity, normal stresses and linear viscoelasticity. This rheological technique’s usefulness is further demonstrated by showing how the rheology of hyaluronan solutions evolve during fermentation. The intrinsic viscosity of the hyaluronan macromolecule is determined using less than 100 μL of solution extracted directly from the bioreactor, and this is used to provide a reasonable indicator of its molecular weight as it develops during the fermentation process. The ability to measure rheology of ultra-low volumes has applications in the characterisation of biological fluids and high value macromolecules, as well as generally in biotechnology and nanotechnology research fields.

Keywords

• ultra-low-volume rheology
• narrow gap
• hyaluronan
• intrinsic viscosity
• molecular weight