Life is always defying the boundaries of biology, or at least of biology textbooks. You don’t have to look far to find instances where books from other fields become relevant. Flip open a physics book, say, and you might find some especially pertinent examples in the chapter on magnetism.
There you’ll learn that if you break a bar magnet in two, you get two magnets — the new ends created by the break just become new poles. And that if you heat a magnet up enough, then you have no magnet at all: High temperatures randomly jumble all the bits of magnetic material (ultimately orientations of spinning electrons) that had aligned themselves along the north-to-south-pole axis. Luckily (if you think of the laws of physics as luck), you can restore your bar’s magnetism just by putting it next to another strong magnet, whose field will realign the magnetic materials that the heat had jumbled.
Less familiarly, similar tricks can be performed with electricity. Some materials possess sepa- rated electric charges that flip their orientation in response to an electric field (the electric equivalent of a magnet swapping its north and south poles). Such polarity-reversing materials are called ferroelectric (an analogy with ferromagnetism, even though iron is not involved in the electric version). Scientists discovered ferroelectricity in 1920; since then, dozens of ferroelectric materials have been found. Some even have practical uses — in memory storage devices, for instance. (Flipping polarity makes ferroelectric materials act like on-off switches, corresponding to the 1s and 0s of binary data storage.)
But it turns out that humans are latecomers to ferroelectricity. Life seems to have known about it since the first cells ingested amino acids.
Glycine, the simplest of the 20 naturally occurring amino acids in living things, crystallizes into a form that exhibits ferroelectricity, researchers from Portugal, Rensselaer Polytechnic Institute in Troy, N.Y., and Oak Ridge National Laboratory in Tennessee have found. Other new evidence shows that cells forming the inner wall of a pig’s aorta are also ferroelectric, the first sign of ferroelectricity in mammalian tissue.
Finding ferroelectricity in pig tissue is a big deal because it has been hard to spot in any biological material (some organic substances do possess the property, just not very strongly or stably). And finding it in glycine is doubly exciting because it means the ferroelectric effect can be induced on the nanoscale. Experiments by Alejandro Heredia of the University of Aveiro in Portugal and colleagues show that ferroelectric polarity flipping induced by a tiny electrode operates on an area of glycine crystal less than 100 nanometers across. “This feature could be extremely useful for possible applications in information storage devices,” Heredia and collaborators write in a paper to appear in Advanced Functional Materials.
What’s more, glycine molecules will flip to reorient their electric charges when exposed to the electric field emanating from an electrode tip, theoretical analysis by the researchers showed. In principle, even just one single glycine molecule might flip in response to a sufficiently high electric field. That ability raises the prospect of superdense memory storage, perhaps allowing the construction of nanosized computing devices. You could imagine machines made of natural molecules that could swim through the blood, exploiting their memory storage and computing power to battle bad molecules on the nanoscale.
And ferroelectricity in glycine might have even more profound biological implications, Heredia and colleagues point out. Glycine is an important messenger molecule between nerve cells in the brain, for instance, not to mention its role as a component of proteins. It may be that glycine’s ferroelectric properties played some role in the origin of life, the researchers speculate. Switching of a molecule’s polarity could influence its ability to engage in various chemical reactions, for instance, that might have been important in getting life going.
For that matter, ferroelectric knowledge could also prove practical in keeping life going. Perhaps ferroelectricity plays a role in blood clotting, Yuanming Liu and colleagues point out in the pig aorta paper, published in February in Physical Review Letters.
Let’s also not forget that cholesterol is a polar molecule. Its attachment to blood vessel walls might be influenced by the electric polarity of cells there, note Liu, of the University of Washington in Seattle, and colleagues from Washington and Boston University.
“The discovery of ferroelectricity in blood vessel walls adds an important dimension to the biophysical properties of blood vessel wall, which could lead to the development of new methods in prevention and treatment of cardiovascular diseases,” Liu and collaborators write.
No doubt other implications of bioferroelectricity will emerge as it is studied further, perhaps by biologists as well as physicists and biomechanical engineers. Still, it probably won’t ever be a good idea to go to a physicist instead of a physician for coronary artery disease. But you might want to find a doctor who knows what the physicists are finding out.
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