Several microvalves utilizing stimuli-responsive hydrogel materials have been developed. The hydrogel components are fabricated inside microchannels using a liquid phase polymerization process. In-channel processing greatly simplifies device construction, assembly, and operation since the functional components are fabricated in situ and can perform both sensing and actuation functions. Two in situ photopolymerization techniques, "laminar stream mode" and "mask mode," have been explored. Three two-dimensional (2-D) valves were fabricated and tested (response time, pressure drop, maximum differential pressure). In addition, a hydrogel/PDMS three-dimensional (3-D) hybrid valve that physically separates the sensing and regulated streams was demonstrated. Analytical modeling was performed on the 3-D valve. Hydrogel-based microvalves have a number of advantages over conventional microvalves, including relatively simple fabrication, no external power requirement, no integrated electronics, large displacement (185 m), and large force generation (22 mN).[597]

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A mixing technique based on bubble-induced acoustic microstreaming principle was developed. A mixer consists of a piezoelectric disk that is attached to a reaction chamber, which has a set of air bubbles with desirable size trapped in the solution. Fluidic experiments showed that air bubbles resting on a solid surface and set into vibration by the sound field generated circulatory flows, resulting in global convection flows and thus rapid mixing. The time to fully mix a 100 chamber is significantly reduced from hours (diffusiononly) to tens of seconds. CFD modeling showed that the induced flowfield and thus degree of mixing strongly depends on bubble positions. Immuno-magnetic cell capture experiments showed acoustic microstreaming provided efficient mixing of bacterial cell (E. coli K12) matrix suspendedin blood with magnetic capture beads, resulting highly effective immuno-magnetic cell capture. Bacterial viability assay experiments showed that acoustic microstreaming has a relatively low shear strain field since the blood cells and bacteria remained intact after mixing. Acoustic microstreaming has many advantages over most existing chamber micromixing techniques, including simple apparatus, ease of implementation, low power consumption (2 mW), and low cost.

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