We describe the design, fabrication and use of a single-layered poly(dimethylsiloxane) microfluidic structure for the entrapment and release of microdroplets in an array format controlled entirely by liquid flow. Aqueous picoliter droplets are trapped en masse and optically monitored for extended periods of time. Such an array-based approach is used to characterize droplet shrinkage, aggregation of encapsulated E. colicells and enzymatic reactions. We also demonstrate that trapped droplets may be recovered from the microfluidic array for further processing.

Although cellular mechanical properties are known to alter during stem cell differentiation, understanding of the functional relevance of such alterations is incomplete. Here, we show that during the course of differentiation of human myeloid precursor cells into three different lineages, the cells alter their viscoelastic properties, measured using an optical stretcher, to suit their ultimate fate and function. Myeloid cells circulating in blood have to be advected through constrictions in blood vessels, engendering the need for compliance at short time-scales (minutes), compared to undifferentiated cells. These findings suggest that reduction in steady-state viscosity is a physiological adaptation for enhanced migration through tissues. Our results indicate that the material properties of cells define their function, can be used as a cell differentiation marker and could serve as target for novel therapies.