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.

Highlights

  • Much is already understood about the anatomical and physiological mechanisms behind the linear, electrical properties of biological tissues

  • These properties were explained by electro-osmosis that changes the degree of sweat duct filing[3]

  • It was later concluded that the sweat ducts and the stratum corneum can both be modelled as memristors

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Summary

Introduction

Much is already understood about the anatomical and physiological mechanisms behind the linear, electrical properties of biological tissues. We performed non-linear electrical measurements on human skin with applied direct current (DC) voltage pulses. Non-linear electrical properties have been demonstrated for human skin ( for the sweat ducts) in[3] (using a constant amplitude voltage stimulus) and in[4] (using a constant amplitude current stimulus). These properties were explained by electro-osmosis (directed motion of liquids forced by an electric field) that changes the degree of sweat duct filing[3]. The recorded currents changed with each DC pulse but the state of the skin memristor changed after the voltage was turned off

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