Probing biological systems using a microfluidic chemical signal generator: An investigation into the dynamics of ionophore stimulation in NIH-3T3 fibroblasts

The complex signal transduction systems that regulate intracellular calcium are a subject of extensive research in biology. Observations of cellular behavior in response to time-varying stimuli can aid in the modeling and analysis of this and other cell signaling processes. I present an experimental technique to probe the dynamic characteristics of living cells using the phenomenon of parallel laminar flow in a microfluidic channel. Under laminar flow conditions, distinct fluids can flow alongside one another in parallel streams without convective mixing. The resulting concentration gradient will relax into a diffusion boundary layer that grows with downstream distance. If the relative flow rates of the streams are adjusted, the diffusion region will move laterally across the channel's width. As a result, cells adherent to the channel surface will be exposed to a chemical environment that varies continuously in time, a "chemical signal" which can be used to study a cell's dynamic behavior.; I employed this technique to perturb intracellular calcium concentration in NIH-3T3 fibroblasts with ionophores while observing their response with fluorescence microscopy. Using feedback control of reservoir pressure to modulate fluid flow rates in a microfluidic device, I stimulated target cells with approximate impulse functions and oscillatory signals. Cells were observed to release and then re-sequester calcium from an internal store after a short exposure. The observed cellular response can be closely modeled as a low-order linear dynamic system whose parameters are roughly consistent across the population studied. Physical measurements of the calcium regulatory system can be extracted from the model.