Ionic polymer–metal composites (IPMC) are smart material transducers that bend in response to low-voltage stimuli and generate voltage in response to bending. IPMCs are mechanically compliant, simple in construction, and easy to cut into desired shape. This allows the designing of novel sensing and actuation systems, e.g., for soft and bio-inspired robotics. IPMC sensing can be implemented in multiple ways, resulting in significantly different sensing characteristics. This paper will review the methods and research efforts to use IPMCs as deformation sensors. We will address efforts to model the IPMC sensing phenomenon, and implementation and characteristics of different IPMC sensing methods. Proposed sensing methods are divided into active sensing, passive sensing, and self-sensing actuation (SSA), whereas the active sensing methods measure one of IPMC-generated voltage, charge, or current; passive methods measure variations in IPMC impedances, or use it in capacitive sensor element circuit, and SSA methods implement simultaneous sensing and actuation on the same IPMC sample. Frequency ranges for reliable sensing vary among the methods, and no single method has been demonstrated to be effective for sensing in the full spectrum of IPMC actuation capabilities, i.e., from DC to ∼100 Hz. However, this limitation can be overcome by combining several sensing methods.

Ionic electroactive polymers (IEAPs), particularly ionic polymer-metal composites (IPMCs) and carbon-polymer composites (CPCs), bend when a voltage is applied on their electrodes, and conversely, they generate an electrical signal when subjected to a mechanical bending. In this work we study and compare the capabilities of IPMC and CPC actuators and sensors in closed-loop control applications. We propose and realize an integrated IEAP sensor–actuator design, characterize its performance using three different materials, and compare the results. The design consists of two short IEAP actuators and one sensor mechanically coupled together in a parallel configuration, and an attached rigid extension significantly longer than the IEAPs. This allows the device to be compliant, simple to construct, lightweight, easy to miniaturize, and functionally similar to a one-degree-of-freedom rotational joint. For control design and accurate position sensing in feedback experiments, we adapt physics-based and control-oriented models of actuation and sensing dynamics, and perform experiments to identify their parameters. In performance characterization, both model-based control and proportional-integral control are explored. System responses to step inputs, sinusoids, and random references are measured, and long-duration sinusoidal tracking experiments are performed. The results show that, while IEAP position sensing is stable for only a limited time-span, H _∞ control significantly improves the performance of the device.

Microfluidic devices and micro-pumps are increasingly necessitated in many fields ranging from untethered soft robots, to pharmaceutical and biomedical technology. While realization of such devices is limited by miniaturization constraints of conventional actuators, these restrictions can be resolved by using smart material transducers instead. This paper proposes and investigates the first ionic polymer metal composite (IPMC) actuator-driven linear peristaltic pump. With the aim of designing a monolithic device, our concept is based on a single IPMC actuator that is etched on both sides and cut with kirigami-inspired slits by laser ablation. Our pump has a planar configuration, operates with low activation voltages (< 5 V) and is simple to manufacture and thus miniaturize. We build proof-of-principle prototypes of an open and closed design of our proposed pump concept, model the closed design, and evaluate both configurations experimentally. Results show the feasibility of the proposed IPMC-driven pump. Without any optimization, the open pump achieved pumping rates of 669 pL/s, while the closed pump configuration attained a 4.57 Pa pressure buildup and 9.18 nL/s pumping rate. These results indicate feasibility of the concept, and future work will focus on design optimization.

The development of high fidelity, anthropomorphically shaped physical phantom organs has a great potential to benefit novel robotic surgical systems by acting as a pre-clinical test bed to validate robotic performance. We present a manufacturing process and methodology to create inexpensive, anatomically accurate kidney and liver phantom organs from gelatin gel with Young's moduli and ultrasound (US) attenuation coefficients matched to those of a porcine kidney and liver. The ration of gelatin to water was varied in order to produce eight gelatin gel samples with a Young's modulus ranging from 8.88 kPa to 76.84. Fresh porcine liver and kidney organs were tested ex vivo to determine their Young's moduli and US attenuation coefficients. A 3D printer created an anthropomorphically accurate kidney mold based on x-ray computed tomography images of a human abdomen. The difference between the porcine and gelatin phantom Young's modulus was less than 2.1 kPa for both the kidney and liver. The US attenuation differed at most by 0.577 dB(cm·MHz) ^-1 when comparing the phantom material to the porcine organs. The volume of anthropomorphically shaped gelatin phantom kidney was within 5% of the volume of the virtual kidney organ which was constructed from x-ray computed tomography. With a total material cost of approximately $0.70 per organ we foresee these organs to be used in a disposable fashion to facilitate the development of novel surgical robotic systems.

Metamaterials are artificially structured materials and exhibit properties that are uncommon or non-existent in nature. Mechanical metamaterials show exotic mechanical properties, such as negative stiffness, vanishing shear modulus, or negative Poisson’s ratio. These properties stem from the geometry and arrangement of the metamaterial unit elements and, therefore, cannot be altered after fabrication. Active mechanical metamaterials aim to overcome this limitation by embedding actuation into the metamaterial unit elements to alter the material properties or mechanical state. This could pave the way for a variety of applications in industries, such as aerospace, robotics, and high-tech engineering. This work proposes and studies an active mechanical metamaterial concept that can actively control the force and deformation distribution within its lattice. Individually controllable actuation units are designed based on piezostack actuators and compliant mechanisms and interconnected into an active metamaterial lattice. Both the actuation units and the metamaterial lattice are modeled, built, and experimentally studied. In experiments, the actuation units attained 240 and 1510 µm extensions, respectively, in quasi-static and resonant operation at 81 Hz, and 0.3 N blocked force at frequencies up to 100 Hz. Quasi-static experiments on the active metamaterial lattice prototype demonstrated morphing into four different configurations: Tilt left, tilt right, convex, and concave profiles. This demonstrated the feasibility of altering the force and deformation distribution within the mechanical metamaterial lattice. Much more research is expected to follow in this field since the actively tuneable mechanical state and properties can enable qualitatively new engineering solutions.