Biological ferroelectrics

The phenomenon of ferroelectricity has been demonstrated in a biological system at the molecular scale for the first time and could lead to a better understanding of how the heart and lungs work.

Ferroelectricity is a property of some materials, mostly those that ironically do not contain iron, that display reversible electric polarization in an external electric field. It is analogous to ferromagnetism. Now, researchers at the University of Washington have studied the ferroelectric properties of the smallest unit of the elastic protein found in tissues that expand and contract repeatedly, tropoelastin. Elastin itself is an important component of the lung, heart and arteries. This demonstration, reported in the Proceedings of the National Academy of Sciences, is the first to show ferroelectric switching in a biological material occurring at the molecular level. [Li et al., (2014) Proc Natl Acad Sci; DOI: 10.1073/pnas.1402909111]

The effect was first detected in 2012 in biological tissues by mechanical engineer Jiangyu Li and colleagues; in 2013 they went on to show that the phenomenon is suppressed by glucose. They now suspect that ferroelectricity helps to build and support healthy connective tissue in mammals. “We wanted to bring in different experimental techniques, evidence and theoretical understanding of ferroelectricity in biological functions,” explains mechanical engineer Jiangyu Li. “We certainly have much more confidence now in the phenomenon itself.”

The team tested tropoelastin using piezoresponse force microscopy and by molecular dynamic simulations. They also carried out high-temperature studies on whole elastin from porcine aorta. The combined experimental and computational studies led them to conclude that elastin is somewhat similar to classical ferroelectrics in structure, and that the switching phenomena is intrinsic to the tropoelastin, the building block, Li told Materials Today.

“When we looked at the smallest structural unit of the biological tissue and how it was organized into a larger protein fiber, we then were able to see similarities to the classic ferroelectric model found in solids,” Li explains. Ferroelectric behavior was apparent in whole elastin, but by also testing the smallest possible unit of the protein, in the form of tropoelastin, the team was able to prove that the switching behavior is “intrinsic” to the molecular make-up of elastin itself.

The team now needs to explain the physiological significance of ferroelectricity in elastin. Li suggests that this switching property helps elastin stay flexible and functional in the body. It might be that when it fails, this could have a direct effect on the process of atherosclerosis, hardening of arteries. Ultimately, it might be possible exploit ferroelectricity to probe the artery wall in a novel imaging technique to reveal the earliest stages of disease. Similarly, diseases of the heart and lung might be imaged in ways that are not currently possible.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".