Optical imaging and analytical modelling of the dynamic concentration gradient of viscous inlet solutions in a microfabricated network design

The design and operation of a gradient network is particularly critical when mixing solutions of different viscosities, which is common with real samples, especially in life science applications. The dynamic concentration gradient formed from mixing equal inlet flow rates of (0.01-1.5 mol/kg) sucrose solution with deionized water in a network was analytically modelled and experimentally investigated. The generation of a stable profile was highly dependent on both the inlet flow rate and the inlet viscosity ratio of the mixed solutions for each case study. The optimum flow rate per inlet for a stable profile was also determined. The experimental investigations show that optimizing the diffusion rate and providing sufficient mixing are key parameters to validate the analytical model. An inlet viscosity ratio of >1.009:1 (with respect to water inlet) was sufficient to perturb the outlet concentration profile. The linearity of the outlet concentration profile decreased and tended towards a sigmoidal profile with increasing sucrose concentration. Enhanced linearity of the outlet concentration profile, through optimizing the inlet flow rate ratio for each case study was also performed. © 2009 Elsevier B.V. All rights reserved.