Short-term bio sensors monitor from afar

A temporary under-the-skin sensor could monitor a variety of health indicators for soldiers, athletes, diabetics, infants, and critically ill patients without wires and at a distance, according to a team of Penn State chemical engineers.

"We were asked to develop micro sensors for metabolic monitoring of troops," says Dr. Michael Pishko, professor of chemical engineering and materials science and engineering. "These implantable sensors are intended to monitor the physiology of troops in the field."

By monitoring glucose, oxygen, lactose and pyruvate, the U.S. Army hopes to be able to assess the metabolic health of troops in the field and improve the response to the injured.

The researchers, who include Pishko, Dr. Amos M. Mugweru, postdoctoral researcher, and Becky Clark, graduate student in chemical engineering, designed an implantable glucose sensor of glucose oxidase molecules – the enzyme that reacts to glucose – immobilized in photopolymerized and microlithographically patterned film. The polymer exchanges electrons with the glucose oxide to produce a current, which is the signal that can be monitored from afar.

"We cannot make the sensors too small, because they need to be big enough to handle and sturdy enough to be inserted without bending or breaking," says Pishko. "We do want to have two to four sensors per indicator so that the signal is verifiable and viable even if one sensor fails."

Sensors could be bundled in groups depending on the metabolite to be monitored.

"The enzymes entrapped in these polymer films and containing biocompatible hydrogels show good stability and sensitivity," the researchers told attendees today (Aug. 31) at the 230th American Chemical Society National Meeting in Washington, D.C.

The military is interested in monitoring glucose, pyruvate, lactate and oxygen for an overall metabolic picture, so four separate sets of sensors would be necessary, each individually addressable. Personnel in a distant base camp could monitor the soldiers’ health and relay information into the field. These metabolic readings would also help medics decide who to treat first and assess the severity of injuries.

Individual sensors also have their place. The researchers are working with the Juvenile Diabetes Foundation on glucose sensors. Exercise physiologists would like to be able to monitor lactate as a measure of how hard muscles are working. Pediatricians would also like to be able to monitor the functions of the tiniest of newborns.

Because these sensors would be implantable and temporary, one day, marathon runners might need not only to pin on their numbers, but also to receive their implantable metabolic sensor array before approaching the starting line.

"The body is hostile to this kind of implant and the sensors will eventually wear out," says Pishko. "For these applications, the sensors only need to work for a short period of time. Even for the soldiers, 24 to 72 hours is sufficient."