We introduce a novel phase-changing particulate that amplifies a composite's modulus change in response to thermal stimulus. This particulate additive consists of a low melting point alloy (Field's Metal; FM) formed into microparticles using a facile fabrication method, which enables its incorporation into polymer matrices using simple composite manufacturing processes. The effect of the solid-liquid phase change of the FM particles is demonstrated in two host materials: a thermally responsive epoxy and a silicone elastomer. In the epoxy matrix, this thermal response manifests as an amplified change in flexural modulus when heated, which is highly desirable for stiffness-changing move-and-hold applications. In the silicone matrix, the stretchability can be switched depending on the phase of the FM particles. This phenomenon allows the silicone to stretch and hold a strained configuration, and gives rise to mechanically programmable anisotropy as the FM inclusions are reshaped. FM particles present many opportunities where on-demand tunable modulus is required, and is particularly relevant to soft robotics. Because the melting temperature of FM is relatively close to room temperature, triggering the phase change, and thereby modulating the modulus, can be accomplished with low power consumption. We demonstrate the utility of these FM particle-containing composites as variable stiffness and variable stretchability elements targeting applications in the field of soft robotics.

Compliant, continuum structures allow living creatures to perform complex tasks inaccessible to artificial rigid systems. Although advancements in hyper-elastic materials have spurred the development of synthetic soft structures (i.e., artificial muscles), these structures have yet to match the precise control and diversity of motions witnessed in living creatures. Cephalopods tentacles, for example, can undergo multiple trajectories using muscular hydrostat, a structure consisting of aggregated laminae of unidirectional muscle fibers. Here, we present a self-adhesive composite lamina inspired by the structural morphology of the muscular hydrostat, which adheres to any volumetrically expanding soft body to govern its motion trajectory. The composite lamina is stretchable only in one direction due to inextensible continuous fibers unidirectionally embedded within its hyper-elastic matrix. We showcase reconfiguration of inflation trajectories of two- and three-dimensional soft bodies by simply adhering laminae to their surfaces.

Fabrics are ubiquitous materials that have conventionally been passive assemblies of interlacing, inactive fibers. However, the recent emergence of active fibers with actuation, sensing, and structural capabilities provides the opportunity to impart robotic function into fabric substrates. Here we present an implementation of robotic fabrics by integrating functional fibers into conventional fabrics using typical textile manufacturing techniques. We introduce a set of actuating and variable-stiffness fibers, as well as printable in-fabric sensors, which allows for robotic closed-loop control of everyday fabrics while remaining lightweight and maintaining breathability. Finally, we demonstrate the utility of robotic fabrics through their application to an active wearable tourniquet, a transforming and load-bearing deployable structure, and an untethered, self-stowing airfoil.

Electrospun fibers are a promising method for encapsulation of reactive agents in selfhealing coatings. Healing is initiated by mechanical damage to the coating causing the fibers to rupture and release their core materials into the damage region. Prior work has demonstrated autonomous healing in coatings containing electrospun fibers, but full characterization of the electrospun fiber microstructure and healing performance of the coating is lacking. In this study, we utilize electrospun fibers containing liquid healing agents to achieve a crosslinking reaction of poly(dimethylsiloxane) (PDMS) to a crosslinking agent poly(diethoxysiloxane) (PDES), initiated by the catalyst dibutyltindilaurate (DBTL), to fill a damaged region and reseal the metal substrate. Fiber morphology is characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal fluorescence microscopy (CFM). Successful delivery of healing agents to the damage region and subsequent crosslinking reaction is observed using SEM and chemically using infrared spectroscopy. The performance of the healed coating is evaluated electrochemically using linear polarization, where the coatings were subjected to a corrosive environment. The self-healing electrospun coating exhibits lower corrosion current than in control cases, resulting in an 88% corrosion inhibition efficiency.

Compliant sensors based on composite materials are necessary components for geometrically complex systems such as wearable devices or soft robots. Composite materials consisting of polymer matrices and conductive fillers have facilitated the manufacture of compliant sensors due to their potential to be scaled in printing processes. Printing composite materials generally entails the use of solvents, such as toluene or cyclohexane, to dissolve the polymer resin and thin down the material to a printable viscosity. However, such solvents cause swelling and decomposition of most polymer substrates, limiting the utility of the composite materials. Moreover, many such conventional solvents are toxic or otherwise present health hazards. Here, sustainable manufacturing of sensors is reported, which uses an ethanol-based Pickering emulsion that spontaneously coagulates and forms a conductive composite. The Pickering emulsion consists of emulsified polymer precursors stabilized by conductive nanoparticles in an ethanol carrier. Upon evaporation of the ethanol, the precursors are released, which then coalesce amid nanoparticle networks and spontaneously polymerize in contact with the atmospheric moisture. We printed the self-coagulating conductive Pickering emulsion onto a variety of soft polymeric systems, including all-soft actuators and conventional textiles, to sensitize these systems. The resulting compliant sensors exhibit high strain sensitivity with negligible hysteresis, making them suitable for wearable and robotic applications.