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MEDICAL ELECTRONICS Tiny tattoos sense health By Jessica Lipsky Research into nanosensors is bearing fruit at the University of California San Diego. Researchers at the University’s Center for Wearable Sensors have prototypes for several tiny, inexpensive sensors fit for the skin that target a variety of medical uses. Joe Wang, distinguished professor in UCSD’s Department of Nanoengineering and faculty director of its wearables center, showcased temporary tattoos outfitted with electrochemical sensors to monitor electrolytes and metabolites in real-time. The tattoos are screen printed and can be worn for up to a week. “The skin is an important sensory function,” Wang said at TSensors Summit. “The skin is not only our own body, but it could be the body of any host like a building, a tree, or a moving car.” Such sensing devices “couple favorable substrate-skin elasticity along with an attractive electrochemical performance” for highly efficient sensing. Attached sensors did non-invasive diabetes monitoring using tears and were also able to assess endurance and performance through sweat. The tattoos were able to withstand at least 50 manipulations and still retain shape and performance. The sensors allow for measurement of trace heavy metal elements such as lead down to a parts-per-billion level. Wang added that the tattoo sensors could also be used to harvest energy in the form of a printable biofuel or zinc battery, which could potentially power an LED with sweat. Research began with printable textile-based sensors sewn into the elastic waist of underwear to measure performance. Multi-electrode layers on garments were eventually able to sense explosives while a “forensic finger” on a glove could do an on-spot analysis of a crime scene. “The goal was to develop a forensic lab on a sleeve with detection of explosives and gunshot residue all integrated with supporting electronics on a sleeve, on a textile,” Wang said. Wang and team also worked with the Navy to put printable sensors on a wetsuit to monitor underwater security and environmental conditions. Other prototypes monitored saliva in a mouth guard. Minimally invasive micro needle sensors are also under development at the center. Researchers hope to create an array of Several Center for Wearable Sensors research projects. (Image: UCSD) up to 15 carbon based needles with electrodes that can monitor electrolytes under the skin. The needles would sit barely beneath the skin and, in addition to monitoring electrolytes, could more effectively deliver drugs. “We’re working on continuous monitoring of multiple chemical markers under the skin. The ultimate goal is to create a sense, act, treat, and feedback system and integrate sensors with drug delivery actuators,” Wang said. To deliver medications more effectively, each micro needle will be equipped with different reservoirs. A doctor could trigger those reservoirs to send drugs at varying intervals or doses. Students in UCSD’s Bioengineering department showed proof-of-concepts, including a point-of-care system for glucose monitoring. The portable glucose molecule detection platform can be plugged into any smartphone and, eventually, more basic handsets. The goal is to bring the price of the glucose monitor below the current $23 average and enable data to be instantly sent to doctors. Long-term, uninterrupted monitoring of an ECG also necessitates a wearable sensor. The group’s design leverages the “quasi periodicity” of ECGs -- which exhibit data spikes during cardiac incidents -- to create a “dynamically reconfigurable” device. Although still in circuit design, one student said the wearable sensor can go into low power mode when the sensor shows low signal activity. A project in UCSD’s Integrated Systems Neuro-engineering Screen printed tattoos would need to be worn with an additional device that would send data via Bluetooth LE. (Image: UCSD) Jessica Lipsky is Associate Editor at EE Times (Left) Example of needle depth. (Right) A nine-micro needle array. (Image: UCSD) 36 Electronic Engineering Times Europe December 2014 www.electronics-eetimes.com


EETE DEC 2014
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