Gravity driven flow for the precise control of hydrodynamic focusing

OLIVARES, MARÍA LAURA; BERLI, CLAUDIO L. A.; MINETTI, FLORENCIA

Cordoba

Congreso; II Brazil-Argentine Microfluidics Congress; 2019

UNC - FAMAF y UFA

Hydrodynamic focusing is a key operation inmicrofluidics, with applications that range from cell sorting and counting tomixing and reactions. For most of these operations, both stability and precisehandling of the focused stream are essential. However, these requirements arehardly attained when fluids are supplied by syringe pumps, due to theunavoidable fluctuations associated to the driving mechanical system, namelythe stepper motor and the lead screw. As an alternative, this work presents aplatform for controlled hydrodynamic focusing driven by gravity. In advance toprevious works were the use of hydrostatic pressure has been proposed, here wedescribe a mathematical model to quantitatively handle the flow stream widthsas a function of the fluid reservoir heights. The model enables a fine tuningof flow rates, provided the hydrodynamic resistance of the whole circuit isknown.Focusing experiments were carried out atdifferent flow rate ratios in PMMA/OCA film hybrid chips with slit microchannelsforming cross-shaped intersections. Results were compared to those obtainedwhen fluids are infused by syringe pumps to the same chips. It is demonstratedthat the gravity driven system is successful for attaining highly stable andwell-defined flow streams. Then, the crystallization of calcium carbonate wasimplemented in the gravity-driven systemas example of application. The reactiontake place at the interface of co-flowing streams that transport the respectivereactants, hence different final products are attained for different reservoirheights. Apart from enabling accurate fluid handling and stability, themodel-controlled platform is highly versatile to design new experiments, aswell as to assist the operator in practice.