Stanford researchers have developed a flexible material made from glycine, the simplest amino acid, that generates electricity when it is pressed or bent. They say it could eventually be used in medical and environmental sensors that biodegrade once their job is done.

The work comes from the lab of Vivian Feig, an assistant professor of mechanical engineering, and was published in Advanced Functional Materials, according to Stanford Report. Postdoctoral scholar Zhuomin Zhang is the first author. The Stanford Daily included the study in its Oct. 25 research roundup.

Why glycine

The body makes glycine, it helps form skin, bones and ligaments, and it has even been found in samples returned from comets. "We know how to process it, our bodies know how to break it down, and it's cheap and really accessible," Feig told Stanford Report.

Scientists already knew glycine could be a very good piezoelectric material, meaning it produces energy from mechanical stress. Piezoelectric parts are used in smoke alarms, watches, ultrasound imaging and diagnostic sensors. But glycine falls apart within seconds in water, and the crystal form it naturally prefers isn't piezoelectric.

What the team did

  • Locked in the useful crystal form: the team applied an electric field while glycine crystallized in extremely small spaces, lining the crystals up by polarity. Molecular stabilizers kept them from shifting into a non-piezoelectric form.
  • Slowed the breakdown: borrowing from Feig's earlier work on delayed drug delivery, they encased the glycine in a polymer matrix. After 60 days the material still performed as a piezoelectric.
  • Kept it flexible: Stanford's photo shows a patterned film conforming to the surface of a leaf.

Zhang called the progress "a huge leap" that moves the field "one step closer toward practical biomedical applications."

What's next

This is a materials platform, not a finished device. The team plans to test it at body temperature and at pH levels like those in the digestive tract. It is also exploring work with Stanford's School of Medicine on biodegradable sensors that could replace devices used to monitor patients after surgery or around implants.