Like microscopic floodgates, Biomedical Engineering Assistant Professor David Beebe's hydrogel valves regulate fluid flow through channels in microfluidic systems, or thumbnail-sized "laboratories," without the help of external controls.

While conventional microactuators require external power to operate, Beebe's pH-sensitive hydrogel valves are "smart"; they swell and contract in response to changes in their environment, performing both sensing and actuation functions. Collaborating with Professor Jeff Moore of the University of Illinois, Beebe's group makes the valves-tiny hydrogel pillars-right inside the microchannels by flowing a mixture of monomers and a photoinitiator into the channels and irradiating the combination through a photomask. This capability to fabricate functional structures within microfluidic channels will make it significantly easier for scientists to build complex microfluidic systems, which can monitor, pump, mix or control small quantities of fluids.

Although a common example of a microfluidic system is an inkjet-printer nozzle, researchers can use microfluidic systems for on-the-spot analyses and in situations where substances or dangerous chemicals are only available or needed in small quantities. Beebe's work, funded by a DARPA grant, could extend to antigen-responsive hydrogels that could be devices in self-regulated drug delivery or biosensors.