Information can be stored in the human skin memristor which has non-volatile memory

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.

The non-linear electrical properties of silver/silver chloride electrodes in sodium chloride solution

“…The changes in measured current here within the DC pulses are relatively small which is different from the recordings on human skin [11]. However, it is likely that the changes of the silver/silver chloride electrodes in sodium chloride solution would be larger with larger DC levels than 0.1 V. The current responses in series 2 were not periodic which is an indication that the electrodes exhibit non-volatile memory [11,16]. However, the current responses in series 1 and 3 are quite periodic in most cases which might be due to the small DC levels.…”

“…It would be interesting to repeat this experiment with longer conductance measurements and also larger DC levels of the applied voltage. The changes in measured current here within the DC pulses are relatively small which is different from the recordings on human skin [ 11 ]. However, it is likely that the changes of the silver/silver chloride electrodes in sodium chloride solution would be larger with larger DC levels than 0.1 V. The current responses in series 2 were not periodic which is an indication that the electrodes exhibit non-volatile memory [ 11 , 16 ].…”

“…We found that information can be stored in human skin [ 11 ]. However, here we found that information can be stored in the electrodes themselves since different conductance values can be set by applying DC voltage pulses (see Fig.…”

“…We therefore did recordings with dry silver/silver chloride (Ag/AgCl) electrodes (same type that was used for the recordings on human skin) in sodium chloride (NaCl) solution that has a similar ion concentration as human sweat. In addition, we used the same instrumentation and similar test protocols as in the studies on human skin (see [ 4 , 11 ]).…”

“…In a second experiment we applied DC voltage pulses and measured the small signal admittance afterwards. We could show that the human skin memristor is non-volatile and that information can actually be stored inside (see [ 11 ]). We were interested here whether it is similar for the silver/silver chloride electrodes in sodium chloride solution.…”