LAUSR

The human somatosensory network relies on ionic currents to sense, transmit, and process tactile information. We investigate hydrogels that similarly transduce pressure into ionic currents, forming a piezoionic skin. As in rapid- and slow-adapting mechanoreceptors, piezoionic currents can vary widely in duration, from milliseconds to hundreds of seconds. These currents are shown to elicit direct neuromodulation and muscle excitation, suggesting a path toward bionic sensory interfaces. The signal magnitude and duration depend on cationic and anionic mobility differences. Patterned hydrogel films with gradients of fixed charge provide voltage offsets akin to cell potentials. The combined effects enable the creation of self-powered and ultrasoft piezoionic mechanoreceptors that generate a charge density four to six orders of magnitude higher than those of triboelectric and piezoelectric devices. Description Converting forces into ionic signals Piezoelectric materials can convert mechanical forces into electrical signals and are used as the active material in many pressure sensors. However, biological systems tend to be based on the movement of ions rather than electrons. Dobashi et al. looked at the piezoionic effect of several kinds of hydrogels. Hydrogels are designed so that the anions and cations have a different mobility; thus, when the material is squeezed, it causes an ionic gradient that generates voltage. The authors demonstrate several potential applications, including a piezoionic skin and peripheral nerve stimulation, to demonstrate the possibility of self-powered piezoionic neuromodulation. —MSL A hydrogel system converts pressure into ion movement that induces voltage changes.