A team of Irish scientists from the Bernal Institute, University of Limerick (UL) has observed that crystals of lysozyme, a model protein that is abundant in egg whites of birds as well as in the tears, saliva, and milk of mammals could generate electricity when pressed.
Piezoelectricity, or the ability to generate electricity by applying pressure, is a property of materials such as quartz that can convert mechanical energy into electrical energy and vice versa. Bone, tendon and wood are long known to possess piezoelectricity.
These materials are used in applications varying from resonators and vibrators in mobile phones to deep ocean sonars and ultrasound imaging.
“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 it could have many innovative applications such as electroactive anti-microbial coatings for medical implants,” explained 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 can be easily made from natural sources and the high precision of their structure has been known since 1965.
Structural biologist at UL and co-author Professor Tewfik Soulimane commented: “In fact, it is the second protein structure and the first enzyme structure that was ever solved”, adding that their team is the first to use these crystals to show the evidence of piezoelectricity.
The team leader, Professor Tofail Syed, stated: “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”.
The discovery may lead to further research in the area of energy harvesting and flexible electronics for biomedical devices.
The discover may be applied in the future to control the release of drugs in the body by using lysozyme as a physiologically mediated pump that scavenges energy from its surroundings.
As it is naturally biocompatible and piezoelectric, lysozyme could present an alternative to conventional piezoelectric energy harvesters, and the toxic elements, such as lead, that many of them contain.
The report is published today (October 2) in the journal, Applied Physics Letters (https://doi.org/10.1063/1.4997446).