Scientists at Northwestern University are discovering how porous polymers mixed with liquid metals are giving medical monitoring devices unprecedented elasticity so that they can be more easily integrated into the human body.
People with chronic medical conditions that require constant monitoring frequently have to visit doctors or hospitals. Current medical devices that conduct that 
monitoring are rigid. But the flexible technology developed by Northwestern’s McCormick School of Engineering may mean that monitoring devices could work with the body’s natural ability to move. Patients could therefore have their medical condition monitored while they are at home, the office, or in the car, and their vital signs could be transmitted to the doctors.
The porous polymer and liquid metal allow electronics to bend and stretch to more than 200% of their original size, the researchers at the school say. That is four times greater than what is possible with today’s technology.
“With current technology, electronics are able to stretch a small amount, but many potential applications require a device to stretch like a rubber band,” says Yonggang Huang, a professor of civil, environmental, and mechanical engineering at the school, in a school news article. “With that level of stretchability we could see medical devices integrated into the human body.”
A problem in designing stretchable electronics is overcoming a loss of conductivity. Circuits available today can handle a small amount of flexibility, but their electrical conductivity plummets by 100 times when stretched. “This conductivity loss really defeats the point of stretchable electronics,” Huang says.
But his team found a way to overcome these challenges. The scientists created a porous three-dimensional structure using a polymer material, polydimethylsiloxane, that can stretch to three times its original size. Then, they placed a liquid metal inside the pores, which allowed electricity to flow consistently even when the material is excessively stretched. The work was published in a June issue of Nature Communications.
The new material is both highly stretchable and extremely conductive, Huang says. “By combining a liquid metal in a porous polymer, we achieved 200 percent stretchability in a material that does not suffer from stretch. Once you achieve that technology, any electronic can behave like a rubber band,” he notes.
Source: “Northwestern Researchers Create ‘Rubber-Band Electronics,’” Northwestern University press release, 7/2/12
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.
