An antimicrobial enzyme made from tears, saliva and milk has proven to be a promising biocompatible source of piezoelectricity.
One of the most important components of many body fluids - tears, breast milk, saliva, nasal mucus - is the enzyme lysozyme. It is a protein hydrolase that destroys the cell walls of bacteria, so it is used in the food industry and in medicine. Lysozyme is extracted from the proteins of chicken eggs and is used as an antiseptic and preservative.
Physicists at the University of Limerick investigated pure lysozyme crystals, finding their piezoelectric properties, that is, the ability to accumulate electrical voltage when deformed. Syed Tofail and his colleagues - including Andrey Kholkin from the Institute of Natural Sciences and Mathematics of the Ural Federal University - write about this in an article published by the journal Applied Physics Letters.
The authors placed a thin film of lysozyme crystals between a pair of glasses and applied pressure, measuring the accumulated charges. The magnitude of the direct piezoelectric effect of the protein was comparable to that of quartz crystals (6.5 pC / H). And if quartz piezoelectric elements have already found the broadest application in technology, lysozyme ones can be useful for medicine, since the usual enzyme in our body is completely biocompatible.
"This is a completely new approach," says Said Tofeil, "because until now, scientists have tried to investigate the piezoelectric effect in biology using complex, hierarchically organized systems - such as tissues, cells or large polypeptides - instead of looking at fundamental building blocks." … In the future, scientists are sure, lysozyme will most likely be used to power medical implants, sensors, analyzers and "smart" pills, at the same time providing them with antimicrobial properties.