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Functional hydrogel structures for autonomous flow control inside microfluidic channels


Hydrogels have been developed to respond to a wide variety of stimuli1,2,3,4,5,6, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response7. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.

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Figure 1: A diagram of the fabrication method and images demonstrating a variety of shapes that were polymerized within 35 seconds.
Figure 2: Prefabricated posts in a microchannel serve as supports for the hydrogels, improving stability during volume changes.
Figure 3: A shut-off valve.
Figure 4: The volume response of two different hydrogels with respect to the pH of the surrounding fluid.

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This work was supported by DARPA-MTO.

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Correspondence to David J. Beebe.

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Beebe, D., Moore, J., Bauer, J. et al. Functional hydrogel structures for autonomous flow control inside microfluidic channels. Nature 404, 588–590 (2000).

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