Microfluidic fuel cells developed by researchers at Brown University may make it practical to devise long-running medical devices, such as implants that monitor glucose levels in diabetics. The Brown fuel cells don't require an ion-conducting membrane or selective catalysts at the electrodes to separate fuel-containing fluids. Instead, the cells exploit the fact that fluids do not mix under certain conditions. "We take advantage of how fuels flow in small channels: They don't mix, which means we can keep fuels separated without a membrane," says Tayhas Palmore, Brown associate professor of engineering, biology, and medicine.

These cells work in tandem to provide power under pulsating conditions that mimic blood flow in the body. Until now, fuel-cell makers have fallen short in their efforts to produce a membraneless device that didn't short circuit under pulsed flow. One of the microfluidic cells features a branched channel, which encloses six electrodes. This cell is suitable for generating electrical power under conditions of pulsed flow, according to Palmore. "The design of the device makes possible the delivery of power to a chip as a result of changes in the concentration of a fuel, such as glucose," he says. "This power feedback is a necessary component in an imbedded sensor for diabetes."