Abstract

The Focusing of cells is an important part of cytometry applications and can be achieved by different techniques. 3D hydrodynamic focusing has generated considerable interest over the last few years, owing to its simplicity and its independence from an electric potential for focusing. Current 3D hydrodynamic focusing devices require multilayer structures necessitating complex fabrication. Moreover, the existing designs show poor efficiencies in focusing. In the present work, three novel 3D hydrodynamic focusing designs consisting of a main channel for sample fluid flow and three pairs of side channels for focusing are proposed and modelled. A novel three dimensional hydrodynamic focusing design is proposed and simulated. In order to develop the numerical model for three dimensional focusing designs, a theoretical review of parameters affecting the fluid flow in microfluidic structure has been performed.
Simulation was performed using COMSOL Multiphysics with diluted glycerol as the sample fluid and DI water as sheath flow fluid. The effects of fluid velocities in the channels were studied. In Design III, the overall efficiency is less than that in the first two designs, but the advantage of this design lies in the possibility of a simpler fabrication. Subsequently, parameters such as velocity and viscosity were studied in the case of Design III, and the ideal velocity condition was identified as 150 m/sec for the sample flow, 350µm/sec for the first sheath flow, and 550µm/sec for the second sheath. Simulations were carried out with sample and sheath flow fluids that have different viscosities. It was concluded that the effect of focusing is primarily dependent on the velocity rather than on the viscosity of the fluid.