A team of Irish scientists has discovered that applying pressure to a protein that is found in egg whites and tears can produce electricity. The team from the Bernal Institute, University of Limerick (UL), Ireland, has seen the crystals of lysozyme generate electricity. Lysozyme is in tears, saliva and milk of mammals.
Piezoelectricity is a property of materials that can convert mechanical energy into electrical energy and vice versa. These materials are used in many applications ranging from resonators and vibrators in mobile phones to deep ocean sonars to ultrasound imaging. Bone, tendon and wood have piezoelectricity.
"While piezoelectricity is used all around us, the capacity to generate electricity from this particular protein had not been explored. The extent of the piezoelectricity in lysozyme crystals is significant. It is of the same order of magnitude found in quartz. However, because it is a biological material, it is non-toxic so could have many innovative applications such as electroactive, anti-microbial coatings for medical implants," said Aimee Stapleton, the lead author and an Irish Research Council EMBARK Postgraduate Fellow in the Department of Physics and Bernal Institute of UL.
Crystals of lysozyme are easy to make from natural sources.
"The high precision structure of lysozyme crystals has been known since 1965," said structural biologist at UL and co-author Professor Tewfik Soulimane. "In fact, it is the second protein structure and the first enzyme structure that was ever solved," he added, "but we are the first to use these crystals to show the evidence of piezoelectricity".
Professor Tofail Syed, of UL’s Department of Physics and team leader, said, "Crystals are the gold-standard for measuring piezoelectricity in non-biological materials. Our team has shown that the same approach can be taken in understanding this effect in biology. This is a new approach as scientists so far have tried to understand piezoelectricity in biology using complex hierarchical structures such as tissues, cells or polypeptides rather than investigating simpler fundamental building blocks."
This discovery has wide-reaching applications and could lead to further research in the area of energy harvesting and flexible electronics for the biomedical field. Future applications of the discovery might include controlling the release of drugs in the body by using lysozyme as a physiologically mediated pump that gathers energy from its surroundings. It is naturally biocompatible and piezoelectric, so lysozyme may be an alternative to the conventional piezoelectric energy harvesters which have toxic elements, like lead.
A paper on this research was published in Applied Physics Letters.