Functional hydrogel structures for autonomous flow control inside microfluidic channels

Hydrogels have been developed to respond to a wide variety of stimuli(1-6), but their use in macroscopic systems has been hindered by slow response ti mes (diffusion being the rate-limiting factor governing the swelling proces s). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response(7). It is t herefore expected that scaling down hydrogel objects to the micrometre scal e should greatly improve response times. At these scales, stimuli-responsiv e hydrogels could enhance the capabilities of microfluidic systems by allow ing self-regulated flow control. Here we report the fabrication of active h ydrogel components inside microchannels via direct photopatterning of a liq uid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-respo nsive 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.