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hubie writes:

A memristor (memory resistor) is a hypothetical circuit element that, in principle, would make up the fourth basic circuit element joining the resistor, capacitor, and inductor. One of the more interesting properties of an ideal memristor is that there exists a non-liner relationship between the applied voltage and current which gives rise to non-volatile memory behavior. This has resulted in a lot of exciting research in the semiconductor industry for new and improved memory chips.

The hallmark of a memristor is that the non-linear relationship between the electric flux and charge gives rise to a voltage-current plot that exhibits a pinched hysteresis behavior, namely that it looks like a frequency-dependent Lissajous figure that always crosses the plot at the origin. If one takes a step back from solid state devices and defines memristors in terms of this voltage/current behavior, there are a number of biologic-based systems that qualify, including human skin. If skin is a memristor, does that mean that it acts like non-volatile memory? In a new paper published in Nature's open-access journal Scientific Reports, Pabst et al show that this is indeed the case. They applied direct current voltage pulses to various parts of the human skin and show that analog information can be stored for at least three minutes.

DOI: https://doi.org/10.1038/s41598-019-55749-9

Paper Abstract
Much is already understood about the anatomical and physiological mechanisms behind the linear, electrical properties of biological tissues. Studying the non-linear electrical properties, however, opens up for the influence from other processes that are driven by the electric field or movement of charges. An electrical measurement that is affected by the applied electrical stimulus is non-linear and reveals the non-linear electrical properties of the underlying (biological) tissue; if it is done with an alternating current (AC) stimulus, the corresponding voltage current plot may exhibit a pinched hysteresis loop which is the fingerprint of a memristor. It has been shown that human skin and other biological tissues are memristors. Here we performed non-linear electrical measurements on human skin with applied direct current (DC) voltage pulses. By doing so, we found that human skin exhibits non-volatile memory and that analogue information can actually be stored inside the skin at least for three minutes. As demonstrated before, human skin actually contains two different memristor types, one that originates from the sweat ducts and one that is based on thermal changes of the surrounding tissue, the stratum corneum; and information storage is possible in both. Finally, assuming that different physiological conditions of the skin can explain the variations in current responses that we observed among the subjects, it follows that non-linear recordings with DC pulses may find use in sensor applications.

Original Submission