Devices that continuously monitor blood sugar levels are replacing painful finger-stick tests for many of the United States' 18.2 million diabetics, but they typically must be implanted under the skin by medical technicians. A prototype developed by engineers at the University of California, Berkeley, could provide a way around this inconvenience. Stefan Zimmermann, Boris Stoeber, and Dorian Liepmann at the Berkeley Sensor and Actuator Center employed the same lithographic techniques used to create microchips to build an array of silicon microneedles, each about 200 micrometers long. The array is simply placed on top of the skin, where the needles puncture deeply enough to reach the fluid between cells, but not deep enough to hit nerves or blood vessels. A sensing device above the needles analyzes the fluid to determine blood sugar levels. Zimmermann says Berkeley is in negotiations to license the technology to medical-device makers.