Electric Tears

Fantasy is replete with examples of tears possessing magical powers, from the Brothers Grimm to Harry Potter. Yet a new study from the Bernal Institute of the University of Limerick (UL) in Ireland discovered a use for tears stranger than fiction: producing electricity.

According to the research, led by Irish Research Council EMBARK postgraduate fellow Aimee Stapleton, tears are abundant in lyzosome crystals, which are also found in egg whites from birds and in the saliva and milk of mammals. These crystals of lyzosome can generate electricity when put under pressure, a property called direct piezoelectricity that is common in materials like quartz. It works by converting mechanical energy into electrical energy and vice versa.

"While piezoelectricity is used all around us, the capacity to generate electricity from this particular protein had not been explored," Stapleton explained in a UL press release. Significantly, the extent of the piezoelectricity generated by lysozyome crystals is on the same order as that generated by quartz.

"However, because [lysozyome crystals are] a biological material, it is non toxic so could have many innovative applications such as electroactive, anti-microbial coatings for medical implants," Stapleton added.

The team's research appears in the journal Applied Physical Letters.

Reimagining Electronic Devices

Piezoelectric materials are found in mobile phone resonators and vibrators, as well as in deep ocean sonars and even in ultrasound imaging machines. Many of the piezoelectric materials used in these devices, however, contain toxic elements like lead.

In contrast, lyzosome crystals are biocompatible—meaning they can't harm the human body. The discovery of this property in lyzosome crystals, which are easier to make from natural sources like tears, can reinvent how these materials are constructed.

The discovery also opens up possibilities for alternative energy harvesting using biocompatible materials, which can be used to develop flexible electronics for biomedical devices. The researchers are considering possible use in drug release control in the human body, for example.

"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," said Luuk van der Wielen, Bernal Institute director, commenting on the discovery. "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."

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