Monolithic fabrication of ionic polymer–metal composite actuators capable of complex deformation

Ionic polymer–metal composites (IPMCs) are soft actuation materials with promising applications in robotics and biomedical devices. However, traditional IPMC actuators can generate the bending motion only. In this paper, a lithography-based approach is presented for monolithic, batch-fabrication of IPMC actuators that are capable of complex deformation. Such an actuator consists of multiple, individually controlled IPMC regions that are mechanically coupled through compliant, passive regions. Two novel techniques have been introduced to overcome challenges in fabrication of patterned IPMCs: (1) selectively thinning down Nafion using reactive ion etch, to make the passive areas thin and compliant, and (2) modulating the stiffness and swellability of Nafion with ion-exchange. Ion-exchanged Nafion shows almost 300% increase in stiffness, and over 94% reduction in swellability in water and acetone, which facilitates lithography and other critical fabrication steps. Prototypes of artificial pectoral fins have been fabricated with the proposed method, and sophisticated deformation modes, including bending, twisting, and cupping, have been demonstrated. For example, a peak-to-peak twisting angle of 16 ° is achieved under 3 V, 0.3 Hz actuation voltages, showing the promise of the fabricated device in robotic fish applications.