Reducing the hydrodynamic resistance of viscous flows through needles*

Reducing the hydrodynamic resistance of viscous flows through confined geometries is of practical importance for a variety of applications such as drug delivery, additive manufacturing, and food processing. In the context of drug delivery, high concentration protein-based drugs are desirable due to their ability to be delivered subcutaneously, eliminating the need for the intravenous injections. However, high viscosity prevents manual injectability through standard medical needles; hence restricting the practical use of many such biologics. In this work, we present approaches to enhance the manual injectability of drug formulations through the use of multi-phase flows. Core annular flows and other lubrication techniques are used to achieve large reductions in hydrodynamic resistance. In addition, the dependence of resistance on (i) flow regimes, (ii) fluid properties such as viscosity and density and, (iii) interfacial parameters such as wettability and surface tension are characterized. Finally, we establish a regime map to minimize the hydrodynamic resistance of viscous flows through needles.