Proliferation and migration of endothelial cells play an important role in many biological activities, and they can be regulated by various microenvironmental factors. In this paper, a novel microfluidic collective cell migration assay is developed to study endothelial cell migration and proliferation under combinations of three oxygen conditions: normoxia, oxygen gradient, and hypoxia and three medium compositions: normal growth medium, the medium with cytochalasin-D for actin polymerization inhibition, and with YC-1 for hypoxia-inducible factor (HIF) inhibition. The microfluidic device designed in the paper allows cell patterns formed with consistent dimensions using laminar flow patterning. In addition, stable oxygen gradients can be generated within the device by a spatially confined chemical reaction method. The device can be operated in conventional cell incubators with minimal chemical reagents and instrumentation for practical applications. The results show directional collective cell migration of the endothelial cells under the oxygen gradients for all the medium compositions. The directional behavior has never been discussed before, and indicates critical roles of oxygen gradients in guiding endothelial cell migration during various biological activities. The developed assay provides a practical yet powerful tool for further i n vitro study of endothelial cell behaviors under various physiological microenvironments.

A widefield FD-FLIM system with fast acquisition speed is utilized to accurately characterize oxygen gradient distributions within microfluidic devices.

This paper reports a microfluidic viscometer with an integrated pressure sensor based on electrofluidic circuits, which are electrical circuits constructed by ionic liquid-filled microfluidic channels. The electrofluidic circuit provides a pressure-sensing scheme with great long-term and thermal stability. The viscosity of the tested fluidic sample is estimated by its flow resistance, which is a function of pressure drop, flow rate, and the geometry of the microfluidic channel. The viscometer can be exploited to measure viscosity of either Newtonian or non-Newtonian power-law fluid under various shear rates (3-500 1/s) and temperatures (4-70 °C) with small sample volume (less than 400 μL). The developed sensor-integrated microfluidic viscometer is made of poly(dimethylsiloxane) (PDMS) with transparent electrofluidic circuit, which makes it feasible to simultaneously image samples under tests. In addition, the entire device is disposable to prevent cross-contamination between samples, which is desired for various chemical and biomedical applications. In the experiments, viscosities of Newtonian fluids, glycerol water solutions with different concentrations and a mixture of pyrogallol and sodium hydroxide (NaOH), and non-Newtonian fluids, xanthan gum solutions and human blood samples, have been characterized. The results demonstrate that the developed microfluidic viscometer provides a convenient and useful platform for practical viscosity characterization of fluidic samples for a wide variety of applications.

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