1. The Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
2. Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA

Correspondence to: David J. Beebe^1,2 Correspondence and requests for materials should be addressed to D.J.B. (e-mail: Email: dbeebe@engr.wisc.edu).

Abstract

Hydrogels have been developed to respond to a wide variety of stimuli^{1, 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.