A team of Irish scientists has discovered that applying pressure to a protein found in egg whites and tears can generate electricity. The researchers from the Bernal Institute, University of Limerick (UL), Ireland, 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 can generate electricity when pressed. Their report is published today (October 2) in the journal, Applied Physics Letters.
The ability to generate electricity by applying pressure, known as direct piezoelectricity, is a property of materials such as quartz that can convert mechanical energy into electrical energy and vice versa. Such materials are used in a variety of applications ranging from resonators and vibrators in mobile phones to deep ocean sonars to ultrasound imaging. Bone, tendon and wood are long known to possess 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," 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 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".
According to team leader Professor Tofail Syed of UL's Department of Physics, "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 have wide reaching applications and could lead to further research in the area of energy harvesting and flexible electronics for biomedical devices. Future applications of the discovery may include controlling the release of drugs in the body by using lysozyme as a physiologically mediated pump that scavenges energy from its surroundings. Being naturally biocompatible and piezoelectric, lysozyme may present an alternative to conventional piezoelectric energy harvesters, many of which contain toxic elements such as lead.
Professor Luuk van der Wielen, Director of Bernal Institute and Bernal Professor of Biosystems Engineering and Design expressed his delight at this breakthrough by UL scientists. "The Bernal Institute has the ambition to impact the world on the basis of top science in an increasingly international context. The impact of this discovery in the field of biological piezoelectricity will be huge and Bernal scientists are leading from the front the progress in this field," he said.
The full paper, The Direct Piezoelectric Effect in the Globular Protein Lysozyme, by Aimee Stapleton, Mohamed R Noor, John Sweeney, Vincent Casey, Andrei Kholkin, Christophe Silien, Abbasi A. Gandhi, Tewfik Soulimane and Syed A M Tofail, is published in Applied Physics Letters (October 02, 2017). The article can be accessed at https://doi.org/10.1063/1.4997446.
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Notes to the editor:
Aimee Stapleton was awarded funding from the Irish Research Council EMBARK Postgraduate Scholarship. Part of this study was also facilitated by a Higher Education Authority grant under the Programme for Research in Third Level Institutions (PRTLI 5) to University of Limerick.
About Aimee Stapleton:
Aimee Stapleton, from Nenagh, County Tipperary, Ireland, has just completed her PhD in the Department of Physics and Energy at University of Limerick. She used a number of methods, including Piezoresponse Force Microscopy, to study piezoelectricity (electromechanical coupling) in proteins. Before starting her doctoral studies, she graduated with a first class honours degree in Applied Physics. During her degree, she interned at 2M Engineering in The Netherlands, researching laser-based technologies. Apart from her research activities, Aimee has a keen interest in science communication as well as teaching and learning. In 2015, she won the Institute of Physics Rosse Medal Award for best communication of postgraduate research.
About the Bernal Institute:
The Bernal Institute at University of Limerick is a research institute comprised of 20,000m2 of high-quality, multi-purpose research space in the new science and engineering zone at UL. The Bernal Institute is named for John Desmond Bernal, one of the most influential scientists of the 20th Century who was born in Nenagh, County Tipperary.
About University of Limerick:
University of Limerick, Ireland, with more than 13,000 students and 1,300 staff is an energetic and enterprising institution with a proud record of innovation and excellence in education, research and scholarship. The dynamic, entrepreneurial and pioneering values which drive UL's mission and strategy ensures that it capitalises on local, national and international engagement and connectivity.
About Applied Physics Letters:
Applied Physics Letters (APL) features concise, up-to-date reports on significant new findings in applied physics. Emphasizing rapid dissemination of key data and new physical insights, APL offers prompt publication of new experimental and theoretical papers reporting applications of physics phenomena to all branches of science, engineering, and modern technology.