Artificial soft robotic elephant trunk made with ionic polymer-metal nanocomposites (IPMCs)

IPMCs or Ionic polymer–metal composites are electro active polymers (EAPs) and are capable of actuation, energy harvesting, and sensing capabilities among other properties. Thus, they are multi–functional smart materials that can be used in biomimetic soft robotics. They normally require a small electric field of a few V/mm and generate spectacular bending and flexing under small electric fields and generate transient voltage and currents output due to dynamic interaction with the environment. Environmental dynamics, like wind or ocean waves, makes them generate an output voltage and transient current of a few mVs for small samples (10mm x 40mm x 0.2mm). IPMCs are capable of operating in or under water or other polar liquids, like blood. Due to the imposed electric field, the conjugated cations electrophoretically migrate towards the cathode and thus expand the cathode side of the ionic membrane and thus bending towards the anode electrode is observed. Osmotic pressures are also instrumental in the migration of cations towards the cathode electrode. Shahinpoor, Bar–Cohen, Xue, Simpson, and Smith1–2 published an early version and review of IPMCs in 1998.1–2 See the pioneering works of Osada, Oguro, Kawami, Asaka, Takenaka and Shahinpoor,3–14 in the 1992–93periods. The electrodynamics of cations generation and transportation in IPMCs are governed by the Poisson– Nernst–Planck field equations15–24 Biomimetic soft robotic actuation like artificial muscles and sensing of these materials display artificial muscle behavior. For example, an applied voltage of 1 to 4 volts for a typical sample of the size 10mm x 80mm x 0.2mm typically produces spectacular bending (Figure 1).