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We present and characterize cotton yarn and knots as building blocks for making microfluidic circuits from the bottom up. The yarn used is made up of 200–300 fibres, each with a lumen. Liquid applied at the extremity of the yarn spontaneously wets the yarn, and the wetted length increases linearly over time in untreated yarn, but progresses according to a square root relationship as described by Washburn's equation upon plasma activation of the yarn. Knots are proposed for combining, mixing and splitting streams of fluids. Interestingly, the topology of the knot controls the mixing ratio of two inlet streams into two outlet yarns, and thus the ratio can be adjusted by choosing a specific knot. The flow resistance of a knot is shown to depend on the force used to tighten it and the flow resistance rapidly increases for single-stranded knots, but remains low for double-stranded knots. Finally, a serial dilutor is made with a web made of yarns and double-stranded overhand knots. These results suggest that yarn and knots may be used to build low cost microfluidic circuits. [ABSTRACT FROM AUTHOR]

High resolution live cell microscopy is increasingly used to detect cellular dynamics in response to drugs and chemicals, but it depends on complex and expensive liquid handling devices that have limited its wider adoption. Here, we present a microfluidic perfusion system that is built without using specialized microfabrication infrastructure, simple to use because only a pipette is needed for liquid handling, and yet allows for rapid media exchange and simultaneous fluorescence microscopy imaging. Yeast cells may be introduced from a culture, or spotted as arrays on a coverslip, and are sandwiched with a 20 μm thick track-etched membrane. A second coverslip and a mesh with 120 μm porosity are placed on top, forming a microfluidic conduit for lateral flow of solutions by capillary effects. Solutions introduced through the inlet flow through the mesh and chemicals diffuse vertically across the membrane to the cells trapped below. Solutions are exchanged by adding a new sample to the inlet. Using this system, we studied the dynamic response of F-actin in living yeast expressing Sac6-EGFP—a protein associated with discrete F-actin structures called “patches”—to the drug latrunculin A, a well known inhibitor of actin polymerization. We observed that the patches disappeared in 85% of the cells within 5 min, and re-assembled in 45 min following exchange of the drug with media. The perfusion system presented here is a simple, inexpensive device suited for analysis of drug dose-response and regeneration of single cells and arrays of cells. [ABSTRACT FROM AUTHOR]