Electric Tears?

“We’ve known since the 1950’s that some biological materials, such as bone and wood, are piezoelectric – meaning they generate an electrical charge when pressed,” says Aimee Stapleton of the University of Limerick, Ireland. According to Stapleton, bone piezoelectricity is thought to contribute to bone regeneration and healing, but the mechanisms that allow bone and other biological materials to be piezoelectric is not fully understood.  Inspired to find an answer, Stapleton and her team were moved to tears…

“In non-biological materials, we know that a certain type of crystal structure is needed for piezoelectricity,” says Stapleton. “The protein lysozyme – which is found in tears, saliva and egg whites – can be easily crystallized, so we decided to investigate if it showed piezoelectricity.” The team grew crystals of lysozyme and measured their direct piezoelectric effect, finding that they could produce an electric charge when they applied pressure (1). “Although we hypothesized that crystals of lysozyme should be piezoelectric, we were surprised at the magnitude of the response we saw – lysozyme’s effect was comparable to that of quartz, a material exclusively used for its piezoelectric properties.” The upshot? As well as the team’s findings bridging the gap in understanding piezoelectricity in biological tissues, identifying the magnitude of lysozyme’s piezoelectric effect has opened up the potential for its use in a multitude of applications including biomedical devices. The authors also write that “future applications may include controlling the release of drugs in vivo by using lysozyme as a physiologically mediated pump that scavenges energy from its surroundings” (1).  Stapleton says that the team are next interested in studying the converse piezoelectric effect in lysozyme. “We want to investigate if an electric field applied across the protein will deform or change its shape, because this finding could open even more potential applications for lysozyme.”