Closed-loop microfluidic control for probing multicellular dynamics

Long-term spatiotemporal control of chemical environments in and around living cells or tissues is critical in probing multicellular dynamics such as embryonic development where dynamic responses of localized cells during developmental stages direct the eventual states. Understanding multicellular signaling during embryonic development also has important implications for studies on stem cells, regenerative tissue engineering, cancer growth and metastasis. While studies on signaling in single cells have made significant advances, it is still challenging to investigate biochemical signaling in multicellular systems under dynamically regulated chemical environments. I present a new microfluidic methodology for long-term and high-speed control of microfluidic flow patterns to enable spatiotemporal regulation of chemical environments in the Animal Cap (AC) tissues isolated from gastrulating Xenopus embryos. Using this microfluidic control, I first investigate dynamic responses of glucocorticoid receptors to periodic stimulation of steroid hormone dexamethasone (DEX) in AC tissues by tracking the redistribution of a GFP-tagged DEX-reporter constructed from the human glucocorticoid receptor (GR). I find that stimulation with localized bursts versus continuous stimulation can result in highly distinct responses but even within a complex embryonic tissue the overall system can converge toward a predictive first-order response. I next examine dynamic responses of epithelial contraction to spatiotemporally controlled extracellular ATP environments in AC tissues by observing localized cell contractions, analyzing time response profiles of the contractility, and constructing AC tissue strain maps that can reveal the morphogenetic response of cells to both immediate stimulation and the transmission of the signal across multiple cells. This approach will deliver new information inaccessible by existing technologies and enhance the understanding of biochemical signaling mechanisms in multicellular environments. I believe this work will have a significant impact on areas spanning dynamic systems and control engineering integrated with microfluidics to biomedical/clinical applications.