Maintaining stimulant waveforms in large-volume microfluidic cell chambers
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RESEARCH PAPER
Maintaining stimulant waveforms in large-volume microfluidic cell chambers Xinyu Zhang • Raghuram Dhumpa Michael G. Roper
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Received: 28 August 2012 / Accepted: 13 December 2012 / Published online: 28 December 2012 Ó Springer-Verlag Berlin Heidelberg 2012
Abstract Stimulation of cells with temporal waveforms can be used to observe the frequency-dependent nature of cellular responses. The ability to produce and maintain the temporal waveforms in spite of the broadening processes that occur as the wave travels through the microfluidic system is critical for observing dynamic behaviors. Broadening of waves in microfluidic channels has been examined, but the effect that large-volume cell chambers have on the waves has not. In this report, a sinusoidal glucose wave delivered to a 1-mm diameter cell chamber using various microfluidic channel structures was simulated by finite element analysis with the goal of minimizing the broadening of the waveform in the chamber and maximizing the homogeneity of the concentration in the chamber at any given time. Simulation results indicated that increasing the flow rate was the most effective means to achieve these goals, but at a given volumetric flow rate, geometries that deliver the waveform to multiple regions in the chamber while maintaining a high linear velocity produced sufficient results. A 4-inlet geometry with a 220-lm channel width gave the best result in the simulation and was used to deliver glucose waveforms to a population of pancreatic islets of Langerhans. The result was a stronger and more robust synchronization of the islet population as compared with when a non-optimized chamber was used. This general strategy will be useful in other microfluidic systems examining the frequency-dependence nature of cellular behavior.
Keywords Dynamic stimulation Microfluidic perfusion Finite element analysis Broadening and delay Islets of Langerhans
1 Introduction Microfluidic systems are increasingly used to evaluate the dynamic nature of biological systems, for example, genetic networks (Lucchetta et al. 2005; Danino et al. 2010), transcriptional responses (King et al. 2008), or protein expression (Mondragon-Palomino et al. 2011). In these investigations, temporally varying concentrations of stimulant are used to probe the frequency-dependence of cellular responses, which can reveal features of cellular responses not observed by stimulation with a single concentration of stimulant (Jovic et al. 2010; Dhumpa and Roper 2012). One challenge in using temporal gradients is dispersion of the waveform as they pass through the fluidic system. All dispersive channels are low-pass filters since highfrequency chemical waves will disperse at a greater rate than low-frequency waves (Azizi and Mastrangelo 2008). The result of this low-pass filtering is broadening and amplitude attenuation of the output waveforms. The amount of attenuation, described as the ratio of the output to input concentrations, is a function of channel length (L) and input frequency (f) (Aziz
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