Physarum Wires, Sensors and Oscillators

Abstract

To make an electronic wetware device doing something useful we need sensors to input information, wires to transfer information between distant parts of the devices, and an oscillator to act as a clock and synchronise the device. We show how slime mould wires, optical colour and tactile sensors and oscillators can be made. A Physarum wire is a protoplasmic tube. Given two pins to be connected by a wire, we place a piece of slime mould at one pin and an attractant at another pin. Physarum propagates towards the attractant and thus connects the pins with a protoplasmic tube. A protoplasmic tube is conductive, it can survive substantial over-voltage and can be used to transfer electrical current to electronic loads. We demonstrate experimental approaches towards programmable routing of Physarum wires with chemoattractants and electrical fields, show how to grow the slime mould wires on almost bare breadboards and electronic circuits, and insulate the Physarum. We evaluate feasibility of slime-mould based colour sensors by illuminating Physarum with red, green, blue and white colours and analysing patterns of the slime mould’s electrical potential oscillations. We define that the slime mould recognises a colour if it reacts to illumination with the colour by a unique changes in amplitude and periods of oscillatory activity. In laboratory experiments we found that the slime mould recognises red and blue colour. The slime mould does not differentiate between green and white colours. The slime mould also recognises when red colour is switched off. We also map colours to diversity of the oscillations: illumination with a white colour increases diversity of amplitudes and periods of oscillations, other colours studied increase diversity either of amplitude or period. We design experimental laboratory implementation of a slime mould based tactile bristles, where the slime mould responds to repeated deflection of bristle by an immediate high-amplitude spike and a prolonged increase in amplitude and width of its oscillation impulses. We demonstrate that signal strength of the Physarum tactile bristle sensor averages near six for an immediate response and two for a prolonged response. Finally, we show how to make an electronic oscillator from the slime mould. The slime mould oscillator is made of two electrodes connected by a protoplasmic tube of the living slime mould. A protoplasmic tube has an average resistance of 3 MOhm. The tube’s resistance is changing over time due to peristaltic contractile activity of the tube. The resistance of the protoplasmic tube oscillates with average period of 73 s and average amplitude of 0.6 MOhm. We present experimental laboratory results on dynamics of Physarum oscillator under direct current voltage up to 15 V and speculate that slime mould P. polycephalum can be employed as a living electrical oscillator in biological and hybrid circuits.