Existing stretchable, transparent conductors are mostly electronic conductors. They limit the performance of interconnects, sensors, and actuators as components of stretchable electronics and soft machines. We describe a class of devices enabled by ionic conductors that are highly stretchable, fully transparent to light of all colors, and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilovolts. We demonstrate a transparent actuator that can generate large strains and a transparent loudspeaker that produces sound over the entire audible range. The electromechanical transduction is achieved without electrochemical reaction. The ionic conductors have higher resistivity than many electronic conductors; however, when large stretchability and high transmittance are required, the ionic conductors have lower sheet resistance than all existing electronic conductors.

It is a challenge to synthesize materials that possess the properties of biological muscles-strong, elastic and capable of self-healing. Herein we report a network of poly(dimethylsiloxane) polymer chains crosslinked by coordination complexes that combines high stretchability, high dielectric strength, autonomous self-healing and mechanical actuation. The healing process can take place at a temperature as low as -20 °C and is not significantly affected by surface ageing and moisture. The crosslinking complexes used consist of 2,6-pyridinedicarboxamide ligands that coordinate to Fe(III) centres through three different interactions: a strong pyridyl-iron one, and two weaker carboxamido-iron ones through both the nitrogen and oxygen atoms of the carboxamide groups. As a result, the iron-ligand bonds can readily break and re-form while the iron centres still remain attached to the ligands through the stronger interaction with the pyridyl ring, which enables reversible unfolding and refolding of the chains. We hypothesize that this behaviour supports the high stretchability and self-healing capability of the material.

Our skin is a stretchable, large-area sheet of distributed sensors. These properties of skin have inspired the development of mimics, with differing levels of sophistication, to enable wearable or implantable electronics for entertainment and healthcare. [1][2][3][4] "Electronic skin" is generally taken to be a stretchable sheet with area above 10 cm 2 carrying sensors for various stimuli, including deformation, pressure, light and temperature. The sensors report signals through stretchable electrical conductors [5] (e.g., carbon grease, [6] microcraked metal films, [1] serpentine metal lines, [2] graphene sheets, [7] carbon nanotubes, [8][9][10] silver nanowires, [11] gold nanomeshes, [12] and liquid metals [13,14] ). These conductors transmit signals using electrons.They meet the essential requirements of conductivity and stretchability, but struggle to meet additional requirements in specific applications, such as biocompatibility in biometric sensors, [15] and transparency in tunable optics. [16,17] By contrast, sensors in our skin report signals using ions. Here we explore the potential of ionic conductors in the development of a new type of sensory sheet, which we call "ionic skin".The sensory sheet is highly stretchable, transparent, and biocompatible. It readily monitors large deformation, such as that generated by the bending of a finger. It detects stimuli with wide dynamic range (strains from 1% to 500%). It measures pressure as low as 1 kPa, with small drift over many cycles. A sheet of distributed sensors covering a large area can report the location and pressure of touch. High transparency allows the sensory sheet to transmit electrical signals without impeding optical signals.Many ionic conductors, such as hydrogels and ionogels, are highly stretchable and transparent. [18][19][20] These gels are polymeric networks swollen with water or ionic liquids. They behave like elastic solids and eliminate the need for containers as required in the case of liquid metal conductors. Whereas familiar elastic gels, such as Jell-O, are brittle and easily rupture, the recent decade has seen the development of hydrogels and ionogels as tough as elastomers. [20][21][22] Many hydrogels are biocompatible. They can be made softer than tissues, achieving the "mechanical invisibility" required for biometric sensors, which monitor soft tissues without 3 constraining them. Although most hydrogels dry out in open air, hydrogels containing humectants retain water in environment of low humidity, and ionogels are nonvolatile in vacuum. [18][19][20] We have recently used ionic conductors-together with stretchable and transparent dielectrics-to make actuators, which deform in response to high voltages, on the order of kilovolts. [18] By contrast, the sensors described here deform in response to applied forces, giving signals that can be measured using voltages below 1 volt. To illustrate principles in our design of the ionic skin, consider a simple example-a dielectric sandwiched between two ionic conductors (Figure 1). In many...

Soft robots actuated by pressurization and inflation of a pneumatic network (a "pneunet") of small channels in elastomeric materials are appealing for their ability to produce sophisticated motions with simple controls. Although current designs of pneu-nets achieve motion with large amplitudes, they do so relatively slowly (that is, over seconds). This paper describes a new design for pneu-nets that reduces the amount of gas that must be transported for inflation of the pneu-net, and thus increases its speed of actuation. A simple actuator can bend from a linear shape to a quasi-circular shape in 50 milliseconds when pressurized at ΔP = 345 kPa. At high rates of pressurization and inflation, the path along which the actuator bends depends on this rate. When inflated fully, the channels and chambers of this new pneu-net design experience only one-tenth the change in volume of that required for a motion of equal amplitude using the previous design. This small change in volume requires comparably low levels of strain in the material at maximum amplitudes of actuation, and commensurately low rates of fatigue and failure. This actuator can operate over a million cycles without significant degradation of performance. This design for soft robotic actuators combines high rates of actuation with high reliability of the actuator, and opens new areas of application for them.