A comprehensive material system is introduced for the additive manufacturing of electrohydraulic (HASEL) tentacle actuators. This material system consists of a photo-curable, elastomeric silicone-urethane with relatively strong dielectric properties (ε r ≈ 8.8 at 1 kHz) in combination with ionically-conductive hydrogel and silver paint electrodes that displace a vegetable-based liquid dielectric under the application of an electric field. The electronic properties of the silicone material as well as the mechanical properties of the constitutive silicone and hydrogel materials are investigated. The hydraulic pressure exerted on the dielectric working fluid in these capacitive actuators is measured in order to characterize their quasi-static behavior. Various design features enabled by 3D printing influence this behavior-decreasing the voltage at which actuation begins or increasing the force density in the system. Using a capacitance change of >35% across the actuators while powered, a demonstration of self-sensing inherent to HASELs is shown. Antagonistic pairs of the 3D printed actuators are shown to exert a blocked force of over 400 mN. An electrohydraulic tentacle actuator is then fabricated to demonstrate the use of this material and actuation system in a synthetic hydrostat. This tentacle actuator is shown to achieve motion in a multi-dimensional space.

Elastomer‐granule composites have been used to switch between soft and stiff states by applying negative pressure differentials that cause the membrane to squeeze the internal grains, inducing dilation and jamming. Applications of this phenomenon have ranged from universal gripping to adaptive mobility. Previously, the combination of this jamming phenomenon with the ability to transport grains across multiple soft actuators for shape morphing has not yet been demonstrated. In this paper, the authors demonstrate the use of hollow glass spheres as granular media that functions as a jammable “quasi‐hydraulic” fluid in a fluidic elastomeric actuator that better mimics a key featur of animal musculature: independent control over i) isotonic actuation for motion; and ii) isometric actuation for stiffening without shape change. To best implement the quasi‐hydraulic fluid, the authors design and build a fluidic device. Leveraging this combination of physical properties creates a new option for fluidic actuation that allows higher specific stiffness actuators using lower volumetric flow rates in addition to independent control over shape and stiffness. These features are showcased in a robotic catcher's mitt by stiffening the fluid in the glove's open configuration for catching, unjamming the media, then pumping additional fluid to the mitt to inflate and grasp.

than their intrinsic material constituents. Metamaterials concepts have been demonstrated in diverse fields, including electromagnetics, acoustics, mechanics and others, exhibiting novel properties such as negative refractive index, perfect absorption, and auxetic behavior. [1][2][3][4][5] Further, metamaterials can be designed with flexible and reconfigurable substrates to achieve physically tunable responses. For instance, several examples of origami and deployable structures exhibit adaptive electromagnetic resonance tuning through physical deformation. [6][7][8][9][10] Strain-tunable dielectric materials and composites are a growing research field with recent demonstrations in optical and millimeter wave regimes. [11,12] For instance, Meerbeek et al., described the macroscopic shape of a porous elastomeric foam by measuring the shift in light reflected internally by its cellular voids during bending and twisting. [11] Zhang et al., synthesized a graphene foam with tunable microwave absorption via solid matrix densification during physical compression. [13] Additional mechanisms for strain-tuning dielectric properties include the use of permanent or induced dipoles at the molecular level; and the distribution of voids and inclusions in host matrices. [14][15][16] Elastomeric metamaterials present a deformation-based tuning strategy for regulating local periodicity and effective dielectric properties. This strategy is particularly useful in deformable electromagnetic devices where the feature size of the dielectric architecture is electrically small and physical reconfiguration of the dielectric structure will facilitate localized and controllable tuning. [14] Materials with mechanically reconfigurable dielectric properties can help address these inherent challenges for flexible hybrid electronics (FHEs) and adaptive communication devices.Elastomers have previously been leveraged for mechanical metamaterials, which are a subset of metamaterial designs with periodic architectures whose elements rotate, buckle, fold, or snap under an external load. [17] Mechanical instabilities present in many of these structures allow their rapid transformation under relatively low strains. They demonstrate unique properties like auxetic behavior, energy absorption, multistability, and nonlinear elastic properties. [18][19][20][21][22][23][24][25] The transformation of these mechanical structures provides a straightforward tuning mechanism for surrounding wave properties in optical, acoustic, and Flexible hybrid electronic (FHE) materials and devices exploit the interaction of mechanical and electromagnetic properties to operate in new form factors and loading environments, which are key for advancing wearable sensors, flexible antennas, and soft robotic skin technologies. Dielectric elastomer (DE) architectures offer a novel substrate material for this application space as they are a class of strain-tolerant and programmable metamaterials that derive their mechanical and dielectric properties from their architecture. Due to the...

Triply periodic minimal surface lattices have mechanical properties that derive from the unit cell geometry and the base material. Through computation software like nTopology and Abaqus, these geometries are used to tune nonlinear stress–strain curves not readily achievable with solid materials alone and to change the compliance by two orders of magnitude compared to the constituent material. In this study, four elastomeric TPMS gyroids undergo large deformation compression and tension testing to investigate the impact of the structure's geometry on the mechanical properties. Among all the samples, the modulus at strain ε varies by over one order of magnitude (7.7–293.4 kPa from FEA under compression). These lattices are promising candidates for designing multifunctional systems that can perform multiple tasks simultaneously by leveraging the geometry's large surface area to volume ratio. For example, the architectural functionality of the lattice to bear loads and store mechanical energy along with the larger surface area for energy storage is combined. A compliant double‐gyroid capacitor that can simultaneously achieve three functions is demonstrated: load bearing, energy storage, and sensing.

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