Microfluidic Strategies to Mix Highly Viscous and/or Non-Newtonian Fluids

The decreases in volume and improvements in system control afforded by microfluidics have been taken advantage of by researchers in fields ranging from cell biology to catalysis with the idea of a complete “lab on a chip” becoming a realistic goal.  However, the application of microfluidics has been limited in cases where the fluids involved are highly viscous, are of significantly different viscosities and/or are non-Newtonian in nature.  This is especially true of strategies for mixing highly viscous fluids on the microscale.

Functionally, the rate of fluid flow in a microfluidic device can be affected by the applied pressure, the device geometry, the viscosity of the fluid, and the time for flow.  Thus, in order to successfully maintain flow in a microfluidic environment with increasingly viscous fluids there are a limited number of parameters which must be considered during the device design.  We discuss here these design rules and apply them to drive fluid flow in a microfluidic mixer capable of mixing fluids at the 20 nL level [1].  The viscosities of the solutions to be mixed here differ by a factor of ~30; 2.45×10^-2 Pa-s for a monoolein lipid phase (1-monooleoyl-rac-glycerol, Fluka), versus 7.98×10^-4 Pa-s for an aqueous phase.  Furthermore, the resulting mixture has a viscosity that is a factor of ~10⁵ larger (~48.3 Pa-s at a shear rate of 71.4 s^-1) than the viscosity of the aqueous phase and exhibits non-Newtonian behavior [2].

References:

[1]  Perry, S. L.; Roberts, G. W.; Tice, J. D.; Gennis, R. B.; Kenis, P. J. A., Cryst Growth Des 2009 (in press, DOI: 10.1021/cg900289d).

[2]  Bonacucina, G.; Palmieri, G. F.; Craig, D. Q. M., Journal of Pharmaceutical Sciences 2005, 94, 2452-2462.