Tech & Science

Piezoelectricity: Tears and Egg Whites Used to Generate Electricity

Scientists harness the power of lysozyme, a protein found in tears and egg whites, to make energy. MarLeah Cole on Flickr

The science is in: Your sadness is electric.

Research published yesterday in the journal Applied Physical Letters shows that lysozyme, a protein found in tears and bird egg whites, can produce electricity. This discovery has potential future applications in medicine and medical devices.

Researchers at the University of Limerick were searching for new ways to generate electricity and wondered if lysozyme might work. (The protein is both well studied and readily available. Anyone wanting some does not have to turn on Old Yeller and harvest their own tears. Companies extract the protein from chicken eggs—not human tears—and sell it to scientists and the food industry.)

The scientists crystallized the protein with heat and used an actuator to apply pressure. Then, they used electrodes to measure the voltage that the protein generated. They measured the pressure being applied from below and controlled the tools exactly by using software. It turned out that lysozyme has a “piezoelectric effect,” meaning that it can generate charge when mechanical stress is applied. Materials with a piezoelectric effect can convert mechanical energy into electrical energy, and electrical energy into mechanical energy. The pressure disturbs their electrical neutrality, and polarization runs to the surface of the material. Only crystals with a lack of central symmetry can have piezoelectricity.

“While the response is not huge, it’s comparable with traditional electrical materials,” says materials physicist Aimee Stapleton, one of the study authors.

Scientists have observed piezoelectic activity in several other biological elements, such as wood, bone, tendons and keratin, the material that fingernails are made of. However, lysozyme is an ideal molecule because it can easily be crystallized, which is integral for obtaining charge from it.

The benefit of a biologically based electricity source is that it could be used more safely in medical devices. For example, pacemakers could be more biocompatible if they used lysozyme to power them instead of lead from traditional batteries, reducing infections.

Alternatively, lysozyme power could be used in several other ways, including as an antimicrobial coating for medical devices, because it inherently has antibacterial properties. “The application could be anything really,” says Stapleton.

However, we won't necessarily see egg-powered pacemakers soon. “This is very much a starting point,” Stapleton says. “We haven’t looked at other proteins. They might have an even bigger electric response.”

Stapleton hopes that this research can pave the way for the future of piezoelectric effects in proteins.