Functional hydrogel structures for autonomous flow control inside microfluidic channels

Beebe, David J.
Moore, Jeffrey S.
Bauer, Joseph M.
Yu, Qing
Liu, Robin H.
Devadoss, Chelladurai
Jo, Byung-Ho

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

Received 17 December 1999; accepted 16 February 2000.

Correspondence and requests for materials should be addressed to D.J.B.

Nature 404(6778):p 588-590, April 6, 2000.

Hydrogels have been developed to respond to a wide variety of stimuli, 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 response. 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.