Liquid Metals as Responsive Components for Building Intelligent Systems

Most machines rely on a “sense-compute-respond” model. That is, sensors send inputs (sense) to a centralized processor (compute) which determines how to respond appropriately (respond). Such machines use rigid, centralized electronic components to make these ‘intelligent’ decisions. Here, we show a way to perform simple logical functions on the “material-level” in soft materials based on the way the material is touched without relying on semiconductor-based transistors. We were inspired, in part, by an octopus, which is capable of locally processing tactile information through the use of neurons distributed in the appendages. To this end, we present a completely soft, stretchable silicone composite innervated with liquid metal as a conceptual demonstrator. When touched, the liquid metal circuits change their local resistance, thereby changing the way electrical energy distributes in the embedded circuit. That electrical energy can be used to cause Joule heating (for thermochromic responses), for powering circuit components such as LEDs, or to power electromechanical motors. The response of the material converts analog tactile ‘inputs’ into digital ‘outputs’, such as the “on/off” state of a motor. This concept can be implemented to perform simple logic that breaks the typical ‘sense-compute-respond’ paradigm used in both natural and synthetic control systems by removing the need for a centralized processor. More generally, liquid metals can be used as responsive materials as components for ‘intelligent systems’. These liquid alloys of gallium are noted for their metallic conductivity, low viscosity, low toxicity, and near-zero vapor pressure. I will share several examples that take advantage of these properties to create stimuli-responsive systems. For example, metallically conductive inks that can be 3D printed and change shape in response to heat (so-called 4D printing where the 4^th dimension is time), printed conductors that can “grow”, conductive inks that autonomously heal when cut, and soft actuators that utilize the surface tension of liquid metal to convert electrical stimuli into mechanical motion. In general, these examples are united by their simplicity and use of soft materials, which may be useful for new types of electronics, actuators, and sensors in intelligent systems.