Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. Here, we report an ionic polymer-metal composite actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. This paper introduces a soft multiple-shape-memory polymer-metal composite (MSMPMC) actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of the authors’ knowledge, this MSMPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability.

Ionic polymer-metal composite artificial muscles have received great research attention in the development of robotic manipulators, advanced medical devices, and underwater propulsors, such as artificial fish fins. This is due to their unique properties of large deformation, fast dynamic response, low-power requirements, and the ability to operate in aquatic environments. Recently, locomotion of biological cells and microorganisms through unique motion of cilium (flagellum) has received great interest in the field of biomimetic robotics. It is envisioned that artificial cilia can be an effective strategy for maneuvering and sensing in small-scale bioinspired robotic systems. However, current actuators used for driving the robots are typically rigid, bulky in mechanism and electronics requirements producing some acoustic signatures, and difficult to miniaturize. Herein, we report biomimetic, wirelessly driven, electroactive polymer (EAP) microfibers that actuate in an aqueous medium when subjected to an external electric field of <5 V/mm, which can be realized to create cilia-based robotic systems for aquatic applications. Initial development and manufacturing of these systems is presented in this paper. The EAP fibers are fabricated from ionic polymer precursor resin through melt-drawing process and have a circular cross-section with a diameter of 30‐70 μm. When properly activated and subjected to an electric field with switching polarity, the EAP fibers exhibit cyclic actuation with adequate response time (0.05‐5 Hz). The experimental results are presented and discussed to demonstrate the performance and feasibility of biomimetic cilia-based microactuators. Prospective bioinspired applications of the artificial muscle cilia-based system in marine operations are also discussed.

The work presented in this paper introduces Aquivion as a potential candidate for additive manufacturing of ionomeric polymers for the application of IPMCs. First, Aquivion was characterized and compared with Nafion to show that it has the similar qualities, with the major difference being the ionic conductivity. Ionic polymer–metal composites (IPMCs) were fabricated using off-the-shelf membranes of Nafion and Aquivion. The actuation tests showed improved performance for an IPMC with Aquivion as the base compared to an IPMC with a Nafion base. With these results in mind, additive manufacturing of unique shapes using Aquivion filament was studied. A 3D printer was modified to work with Aquivion filament and the polymer was printed into various shapes. Using the printed membranes, IPMCs were fabricated using an electroless plating process. Nafion-based and printed Aquivion-based IPMCs were tested for their performance in back relaxation, frequency driven actuation, blocking force, and mechano-electric sensing. The printed Aquivion-based IPMCs performed comparably to Nafion-based IPMC in back relaxation and showed significantly improved performance in frequency driven actuation, blocking force generation, and mechano-electric sensing.

Ionic polymer-metal composites (IPMC) are useful actuators because of their ability to be fabricated in different shapes and move in various ways. However, producing unique or intricate shapes can be difficult based upon the current fabrication techniques. Presented here is a fabrication method of producing the Nafion® membrane or thin film through a painting method. Using an airbrush, a Nafion water dispersion is sprayed onto an acrylonitrile butadiene styrene surface with a stencil of the desired shape. To verify that this method of fabrication produces a Nafion membrane similar to that which is commercially available, a sample that was made using the painting method and Nafion 117 purchased from DuPont™ were tested for various characteristics and compared. The results show promising similarities. The painted Nafion sample was chemically plated with platinum and compared with a traditional IPMC for its displacement and blocking force capabilities. The painted IPMC sample showed comparable results.

A biomimetic underwater robot was designed utilizing ionic polymer-metal composite (IPMC) artificial muscles. The actuators were controlled by thermal and electrical inputs, taking advantage of both the shape-memory and electromechanical behavior of the material, to achieve multiple swimming modes in the proposed robot. The design was inspired by the pectoral fish swimming modes, such as stingrays, knifefish, and cuttlefish. The robot was actuated by two soft fins which consisted of multiple embedded IPMC actuators connected with an Eco-Flex membrane. Through electromechanical actuation, a traveling wave was generated on the soft fin. The deformation and the blocking force of the IPMCs on the fin were measured to characterize the actuators. An experimental setup was also designed in a flow channel to measure the thrust force of the robot under different frequencies and traveling wave numbers in a captive state. Experiments determined a peak thrusting force of 12 mN at a frequency of 0.5 Hz and wave number of 1, and twisting deformations of 30°were obtained. Additionally, shape-memory was utilized to change the swimming mode of the robot from Gymnotiform to Mobuliform. The designed underwater robot utilizes IPMC materials with multi-input control, enabling high deformability, with available maneuverability and agility in future studies.