Building microfluidic circuits is generally a multi-day process, requiring a clean room and specialized manufacturing equipment. A new study suggests a quicker alternative using fluid walls to define the circuit instead of solid ones. The authors refer to their technique as “Freestyle Fluidics”. As seen above, the shape of the circuit is printed in the operating fluid, then covered by a layer of immiscible, transparent fluid. This outer layer help prevent evaporation. Underneath, the circuit holds its shape due to interfacial forces pinning it in place. Those same forces can be used to passively drive flow in the circuit, as shown in the lower animation, where fluid is pumped from one droplet to the other by pressure differences due to curvature. Changing the width of connecting channels can also direct flow in the circuits. This technique offers better biocompatibility than conventional microfluidic circuits, and the authors hope that this, along with simplified manufacturing, will help the technique spread. (Image and research credit: E. Walsh et al., source)