Replicating the natural ability to perceive softness in skin-inspired tactile sensors is vital for the advancement of robotic manipulation and object classification. Humans sense softness through the activation of specific skin receptors, which are sensitive to pressure and lateral strain. Current electronic skins (eSkin) mimic this dual functionality by detecting both normal pressure and lateral strain. However, these sensors are challenging to fabricate and often have large spatial footprints, limiting their integration into high-density arrays. To overcome these challenges, this work presents an all-elastomer sensor for tactile detection of softness, combining a parallel-plate capacitor structure with a serpentine piezoresistive strain sensor in a vertically stacked design. Conductive carbon structures, digitally laser patterned and embedded in a styrene-ethylene-butylene-styrene (SEBS) thermoplastic elastomer, serve as robust and modifiable electrodes. The device displays the ability to differentiate moduli between 74 kPa and 1.49 MPa. We conduct a parametric study to evaluate the effects of object dimensions, materials choices, and design parameters on sensor performance. Importantly, we investigate the sensor performance when mounted onto a soft substrate, analogous to the human fingertip or robotic digit. Overall, this work highlights the potential of z-directionally stacked sensing components with tunable properties to realize compact, multimodal devices.

There is an increasing demand for multimodal sensing and stimulation bioelectronic fibres for both research and clinical applications1,2. However, existing fibres suffer from high rigidity, low component layout precision, limited functionality and low density of active components. These limitations arise from the challenge of integrating many components into one-dimensional fibre devices, especially owing to the incompatibility of conventional microfabrication methods (for example, photolithography) with curved, thin and long fibre structures2. As a result, limited applications have been demonstrated so far. Here we use 'spiral transformation' to convert two-dimensional thin films containing microfabricated devices into one-dimensional soft fibres. This approach allows for the fabrication of high-density multimodal soft bioelectronic fibres, termed Spiral-NeuroString (S-NeuroString), while enabling precise control on the longitudinal, angular and radial positioning and distribution of the functional components. Taking advantage of the biocompatibility of our soft fibres with the dynamic and soft gastrointestinal system, we proceed to show the feasibility of our S-NeuroString for post-operative multimodal continuous motility mapping and tissue stimulation in awake pigs. We further demonstrate multi-channel single-unit electrical recording in mouse brain for up to 4 months, and a fabrication capability to produce 1,280 channels within a 230-μm-diameter soft fibre. Our soft bioelectronic fibres offer a powerful platform for minimally invasive implantable electronics, where diverse sensing and stimulation functionalities can be effectively integrated.

In living tissue, pain provides a localized alert to damage and elicits an adaptive response, including the ability to heal. Mimicking these abilities in soft robotics is a key challenge. Here, we design a self-healing, multilayer electronic skin capable of sensing three-dimensional damage inflicted by scalpels and needles at similar to 1-mm resolution. In our design, unidirectional, linear voltage gradients are applied across resistive "drive" layers. Analog "sense" layers detect lateral position and depth of metallic objects by sensing voltage upon electrical contact between layers. The multilayer sensing principle is validated through experiments with device designs of increasing functionality-including with one-, two-, and three-dimensional damage sensing-with synchronized measurements made using an underlying precision six-axis force sensor. The ability to detect punctures and incisions in soft, self-healable materials at millimeter resolution may enable the development of reusable, sensory surgical simulation technology for training medical personnel and evaluating efficacy of surgical robots.

Bioelectronic devices and components made from soft, polymer-based and hybrid electronic materials form natural interfaces with the human body. Advances in the molecular design of stretchable dielectric, conducting and semiconducting polymers, as well as their composites with various metallic and inorganic nanoscale or microscale materials, have led to more unobtrusive and conformal interfaces with tissues and organs. Nonetheless, technical challenges associated with functional performance, stability and reliability of integrated soft bioelectronic systems still remain. This Review discusses recent progress in biomedical applications of soft organic and hybrid electronic materials, device components and integrated systems for addressing these challenges. We first discuss strategies for achieving soft and stretchable devices, highlighting molecular and materials design concepts for incorporating intrinsically stretchable functional materials. We next describe design strategies and considerations on wearable devices for on-skin sensing and prostheses. Moving beneath the skin, we discuss advances in implantable devices enabled by materials and integrated devices with tissue-like mechanical properties. Finally, we summarize strategies used to build standalone integrated systems and whole-body networks to integrate wearable and implantable bioelectronic devices with other essential components, including wireless communication units, power sources, interconnects and encapsulation. Soft bioelectronic devices are made from polymer-based and hybrid electronic materials that form natural interfaces with the human body. In this Review, the authors present recent developments in soft bioelectronic sensors and actuators, and discuss system-level integration for wearable and implantable medical applications.

Soft sensors that can perceive multiaxial forces, such as normal and shear, are of interest for dexterous robotic manipulation and monitoring of human performance. Typical planar fabrication techniques have substantial design constraints that often prohibit the creation of functionally compelling and complex architectures. Moreover, they often require multiple-step operations for production. Here, we use an additive manufacturing process based on continuous liquid interface production to create high-resolution (30-micrometer) three-dimensional elastomeric polyurethane lattices for use as dielectric layers in capacitive sensors. We show that the capacitive responses and sensitivities are highly tunable through designs of lattice type, thickness, and material-void volume percentage. Microcomputed tomography and finite element simulation are used to elucidate the influence of lattice design on the deformation mechanism and concomitant sensing behavior. The advantage of three-dimensional printing is exhibited with examples of fully printed representative athletic equipment with integrated sensors.

Dielectric elastomer actuators (DEAs) offer versatile applications including haptics, soft robotics and smart lenses. However, due to the lack of conductive electrodes with low modulus and high stretchability, their use is limited by nonsolid electrodes, hindering integration with other systems. In this study, transparent and patternable solid electrodes, achieving actuation performance comparable to a commonly used non-solid counterpart (e.g., carbon grease), with a stretchable and patternable conducting polymer composed of PEDOT:PSS and PEG-PPG-PEG diacrylate (P123DA) are reported. Varying the ratio of P123DA to PEDOT:PSS enables optimization of electrical and mechanical properties to achieve compliant solid electrodes in static and dynamic actuation. The ratio of P123DA to PEDOT:PSS is found to impact PEDOT:PSS nanofiber formation and the associated electrical and mechanical properties. Moreover, the resulting P123DA/PEDOT:PSS-based solid electrode shows excellent optical transmittance exceeding 95%. This work highlights the potential of tuning different solid electrode properties to realize transparent, patternable, and stretchable solid electrodes, enhancing their applicability in diverse fields.

Self-healing soft electronic and robotic devices can, like human skin, recover autonomously from damage. While current devices use a single type of dynamic polymer for all functional layers to ensure strong interlayer adhesion, this approach requires manual layer alignment. In this study, we used two dynamic polymers, which have immiscible backbones but identical dynamic bonds, to maintain interlayer adhesion while enabling autonomous realignment during healing. These dynamic polymers exhibit a weakly interpenetrating and adhesive interface, whose width is tunable. When multilayered polymer films are misaligned after damage, these structures autonomously realign during healing to minimize interfacial free energy. We fabricated devices with conductive, dielectric, and magnetic particles that functionally heal after damage, enabling thin-film pressure sensors, magnetically assembled soft robots, and underwater circuit assembly.

Polymer semiconductors (PSCs) are essential active materials in mechanically stretchable electronic devices. However, many exhibit low fracture strain due to their rigid chain conformation and the presence of large crystalline domains. Here, a PSC/elastomer blend, poly[((2,6‐bis(thiophen‐2‐yl)‐3,7‐bis(9‐octylnonadecyl)thieno[3,2‐b]thieno[2′,3′:4,5]thieno[2,3‐d]thiophene)‐5,5′‐diyl)(2,5‐bis(8‐octyloctadecyl)‐3,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione)‐5,5′‐diyl]] (P2TDPP2TFT4) and polystyrene‐ block ‐poly(ethylene‐ran‐butylene)‐ block ‐polystyrene (SEBS) are systematically investigated. Specifically, the effects of molecular weight of both SEBS and P2TDPP2TFT4 on the resulting blend morphology, mechanical, and electrical properties are explored. In addition to commonly used techniques, atomic force microscopy‐based nanomechanical images are used to provide additional insights into the blend film morphology. Opposing trends in SEBS‐induced aggregation are observed for the different P2TDPP2TFT4 molecular weights upon increasing the SEBS molecular weight from 87 to 276 kDa. Furthermore, these trends are seen in device performance trends for both molecular weights of P2TDPP2TFT4. SEBS molecular weight also has a substantial influence on the mesoscale phase separation. Strain at fracture increases dramatically upon blending, reaching a maximum value of 640% ± 20% in the blended films measured with film‐on‐water method. These results highlight the importance of molecular weight for electronic devices. In addition, this study provides valuable insights into appropriate polymer selections for stretchable semiconducting thin films that simultaneously possess excellent mechanical and electrical properties.

This paper describes measurements of charge transport by tunneling through molecular junctions comprising a self-assembled monolayer (SAM) supported by a template-stripped metal bottom electrode (MTS), which has been immersed in an organic liquid and contacted by a conical Ga2O3/EGaIn top electrode. These junctions formed in organic liquids are robust; they show stabilities and yields similar to those formed in air. We formed junctions under seven external environments: (I) air, (II) perfluorocarbons, (III) linear hydrocarbons, (IV) cyclic hydrocarbons, (V) aromatic compounds, (VI) large, irregularly shaped hydrocarbons, and (VII) dimethyl siloxanes. Several different lengths of SAMs of n-alkanethiolates, S(CH2)n-1CH3 with n = 4-18, and two different kinds of bottom electrodes (AgTS or AuTS) are employed to assess the mechanism underlying the observed changes in tunneling currents. Measurements of current density through junctions immersed in perfluorocarbons (II) are comparable to junctions measured in air. Junctions immersed in other organic liquids show reductions in the values of current density, compared to the values in air, ranging from 1 (III) to 5 orders of magnitude (IV). We interpret the most plausible mechanism for these reductions in current densities to be an increase in the length of the tunneling pathway, reflecting the formation of thin (0.5-1.5 nm) liquid films at the interface between the SAM and the Ga2O3/EGaIn electrode. Remarkably, the thickness of the liquid film─estimated by the simplified Simmons model, measurements of electrical breakdown of the junction, and simulations of molecular dynamics─is consistent with the existing observations of structured liquid layers that form between two flat interfaces from measurements obtained by the surface force apparatus. These results suggest the use of the EGaIn junction and measurements of charge transport by tunneling as a new form of surface analysis, with the applications in the study of near-surface, weak, molecular interactions and the behavior of liquid films adjacent to non-polar interfaces.

Self-healing soft electronic and robotic devices can recover autonomously from some forms of external damage, analogous to human skin. While current self-healing devices employ a single type of dynamic polymer network for all functional layers to ensure strong interlayer adhesion, this approach requires the manual alignment of layers to ensure functional healing. Here, we use two dynamic polymers, which have immiscible backbones but identical dynamic bonds, to maintain interlayer adhesion while enabling autonomous realignment of functional components during healing. We show that these dynamic polymers exhibit a weakly interpenetrating and adhesive interface, whose width is tunable. Moreover, when multi-layer laminates of these polymers are misaligned after damage, these structures autonomously realign during healing to minimize interfacial area—a phenomena that is also observed in simulations. We demonstrate the broader utility of this strategy by fabricating composite devices with conductive, dielectric, and magnetic particles that functionally heal after damage, enabling thin film pressure sensors, magnetically assembled soft robots, and underwater circuit assembly.

Bioelectronic fibers hold promise for both research and clinical applications due to their compactness, ease of implantation, and ability to incorporate various functionalities such as sensing and stimulation. However, existing devices suffer from bulkiness, rigidity, limited functionality, and low density of active components. These limitations stem from the difficulty to incorporate many components on one-dimensional (1D) fiber devices due to the incompatibility of conventional microfabrication methods (e.g., photolithography) with curved, thin and long fiber structures. Herein, we introduce a fabrication approach, “spiral transformation″, to convert two-dimensional (2D) films containing microfabricated devices into 1D soft fibers. This approach allows for the creation of high density multimodal soft bioelectronic fibers, termed Spiral NeuroString (S-NeuroString), while enabling precise control over the longitudinal, angular, and radial positioning and distribution of the functional components. We show the utility of S-NeuroString for motility mapping, serotonin sensing, and tissue stimulation within the dynamic and soft gastrointestinal (GI) system, as well as for single-unit recordings in the brain. The described bioelectronic fibers hold great promises for next-generation multifunctional implantable electronics.

The selectivity of electrocatalytic reduction of CO2 (CDR) is dictated not only by the intrinsic reactivity of the catalyst but also by the transport of reactants to the catalyst (i.e., mass transport). Current methods for increasing mass transport in CDR rely upon either (1) mechanical agitation or (2) use of gas-diffusion electrodes and are unable to eliminate concentration polarization completely. This work demonstrates that magnetic fields orthogonal to the ionic cur-rent (i.e., the Lorentz force) can be used to increase mass transport during CDR by generating convective flow in the fluid, thus modi-fying the observed selectivity of CDR. This increase in mass transport leads to a corresponding increase in current densities (up to 1.3x higher than the analogous system with no (B) over right arrow -field or agitation) and increased selectivity of CDR relative to the hydrogen evolution reac-tion (up to 2.5 x higher than the system with no (B) over right arrow -field or agitation).

The control of pneumatically driven soft robots typically requires electronics. Microcontrollers are connected to power electronics that switch valves and pumps on and off. As a recent alternative, fluidic control methods have been introduced, in which soft digital logic gates permit multiple actuation states to be achieved in soft systems. Such systems have demonstrated autonomous behaviors without the use of electronics. However, fluidic controllers have required complex fabrication processes. To democratize the exploration of fluidic controllers, we developed tube-balloon logic circuitry, which consists of logic gates made from straws and balloons. Each tube-balloon logic device takes a novice five minutes to fabricate and costs $0.45. Tube-balloon logic devices can also operate at pressures of up to 200 kPa and oscillate at frequencies of up to 15 Hz. We configure the tube-balloon logic device as NOT-, NAND-, and NOR-gates and assemble them into a three-ring oscillator to demonstrate a vibrating sieve that separates sugar from rice. Because tube-balloon logic devices are low-cost, easy to fabricate, and their operating principle is simple, they are well suited for exploring fundamental concepts of fluidic control schemes while encouraging design inquiry for pneumatically driven soft robots.

The problem this paper addresses is the origin of the hysteretic behavior in two-terminal molecular junctions made from an EGaIn electrode and self-assembled monolayers of alkanethiolates terminated in chelates (transition metal dichlorides complexed with 2,2'-bipyridine; BIPY-MCl2). The hysteresis of conductance displayed by these BIPY-MCl2 junctions changes in magnitude depending on the identity of the metal ion (M) and the window of the applied voltage across the junction. The hysteretic behavior of conductance in these junctions appears only in an incoherent (Fowler-Nordheim) tunneling regime. When the complexed metal ion is Mn(II), Fe(II), Co(II), or Ni(II), both incoherent tunneling and hysteresis are observed for a voltage range between +1.0 V and -1.0 V. When the metal ion is Cr(II) or Cu(II), however, only resonant (one-step) tunneling is observed, and the junctions exhibit no hysteresis and do not enter the incoherent tunneling regime. Using this correlation, the conductance characteristics of BIPY-MCl2 junctions can be controlled. This voltage-induced change of conductance demonstrates a simple, fast, and reversible way (i.e., by changing the applied voltage) to modulate conductance in molecular tunneling junctions.

Traditional orthopedic casting strategies used in the treatment of fractured limbs, such as fiberglass and plaster‐based tapes, suffer from several drawbacks, including technically challenging molding for application, occurrence of skin complications, and the requirement of a potentially hazardous oscillatory saw for removal, which is frightening for pediatric patients. This work presents the design and evaluation of a foam‐fabric cast (FFC) to overcome these drawbacks by integrating strategies from soft materials engineering and functional apparel design. A fabric sleeve is designed to enable the reactive injection molding of a polymer foam and provide a form‐fitting orthopedic cast for the human forearm—with sufficient mechanical reinforcement to stabilize a fractured limb. Through testing with a replica limb and human subjects with a range of forearm volumes, the FFC application process is demonstrated and characterized. The thermal, pressural, chemical, and hygienic safety are comparable to or safer than existing clinical technologies. The FFC weighs only ≈150 g, is water resistant, and represents a robust alternative to traditional casts that can be i) manufactured at a large scale for a low cost; ii) applied to patients simply, rapidly (≈5 min), and reliably; and iii) removed easily with a pair of scissors.

This work demonstrates how the application of a magnetic field during electrocatalysis can affect the transport of reactants and products at the electrode surface and, under certain conditions, generate complex, oscillatory behavior in amperometric experiments. During the electrocatalytic oxidation of glycerol (EOG), the Lorentz force acts upon hydronium and hydroxide ionic currents to produce fluidic convection, which serves to enhance the mass transport of glycerol and glyceraldehyde. Particle imaging velocimetry shows that the convective fluid flow field depends nonlinearly on the viscosity of the solution (dictated by the concentration of glycerol, which ranged from 2.5% to 40% v/v, to give a viscosity range of 1.3-5.3 mPa s). The nonlinear dependence of velocity of the fluid flow on the viscosity of the electrolyte generates time-delayed negative feedback during EOG and results in chemical oscillations. This time-delayed feedback is due to two coupled steps: (i) oxidation of glycerol rapidly decreases the viscosity of the electrolyte near the anode and (ii) at low viscosities magnetic fields increase the rate of mass transport, which subsequently increases the viscosity of the electrolyte near the anode (by increasing the concentration of glycerol). These chemical oscillations can be used to enhance the selectivity of EOG to glyceric acid by a factor of 2.1. This work focuses on the effects of magnetic fields on EOG using a combination of fluid flow analysis, rotating-disk electrode experiments, and electrochemical simulations.

In soft devices, complex actuation sequences and precise force control typically require hard electronic valves and microcontrollers. Existing designs for entirely soft pneumatic control systems are capable of either digital or analog operation, but not both, and are limited by speed of actuation, range of pressure, time required for fabrication, or loss of power through pull-down resistors. Using the nonlinear mechanics intrinsic to structures composed of soft materials—in this case, by leveraging membrane inversion and tube kinking—two modular soft components are developed: a piston actuator and a bistable pneumatic switch. These two components combine to create valves capable of analog pressure regulation, simplified digital logic, controlled oscillation, nonvolatile memory storage, linear actuation, and interfacing with human users in both digital and analog formats. Three demonstrations showcase the capabilities of systems constructed from these valves: 1) a wearable glove capable of analog control of a soft artificial robotic hand based on input from a human user’s fingers, 2) a human-controlled cushion matrix designed for use in medical care, and 3) an untethered robot which travels a distance dynamically programmed at the time of operation to retrieve an object. This work illustrates pathways for complementary digital and analog control of soft robots using a unified valve design.

With the help of machine learning, electronic devices-including electronic gloves and electronic skins-can track the movement of human hands and perform tasks such as object and gesture recognition. However, such devices remain bulky and lack an ability to adapt to the curvature of the body. Furthermore, existing models for signal processing require large amounts of labelled data for recognizing individual tasks for every user. Here we report a substrate-less nanomesh receptor that is coupled with an unsupervised meta-learning framework and can provide user-independent, data-efficient recognition of different hand tasks. The nanomesh, which is made from biocompatible materials and can be directly printed on a person's hand, mimics human cutaneous receptors by translating electrical resistance changes from fine skin stretches into proprioception. A single nanomesh can simultaneously measure finger movements from multiple joints, providing a simple user implementation and low computational cost. We also develop a time-dependent contrastive learning algorithm that can differentiate between different unlabelled motion signals. This meta-learned information is then used to rapidly adapt to various users and tasks, including command recognition, keyboard typing and object recognition.

While the density is a central property of a polymer film, it can be difficult to measure in films with a thickness of similar to 100 nm or less, where the structure of the interfaces and the confinement of the polymer chains may perturb the packing and dynamics of the polymers relative to the bulk. This Article demonstrates the use of magneto-Archimedes levitation (MagLev) to estimate the density of thin films of hydrophobic polymers ranging from similar to 10 to 1000 nm in thickness by employing a substrate with a water-soluble sacrificial release layer to delaminate the films. We validate the performance of MagLev for this application in the similar to 1 mu m thickness range by comparing measurements of the densities of several different films of amorphous hydrophobic polymers with their bulk values of density. We apply the technique to films < 100 nm and observe that, in several polymers, there are substantial changes in the levitation height, corresponding to both increases and decreases in the apparent density of the film. These apparent changes in density are verified with a buoyancy control experiment in the absence of paramagnetic ions and magnetic fields. We measure the dependence of density upon thickness for two model polymeric films: poly(styrene) (PS) and poly(methyl methacrylate) (PMMA). We observe that, as the films are made thinner, PS increases in density while PMMA decreases in density and that both exhibit a sigmoidal dependence of density with thickness. Such changes in density with thickness of PS have been previously observed with reflectometric measurements (e.g., ellipsometry, X-ray reflectivity). The interpretation of these measurements, however, has been the subject of an ongoing debate. MagLev is also compatible with nontransparent, rough, heterogeneous polymeric films, which are extremely difficult to measure by alternative means. This technique could be useful to investigate the properties of thin films for coatings, electronic devices, and membrane-based separations and other uses of polymer films.

The rapidly increasing use of digital technologies requires the rethinking of methods to store data. This work shows that digital data can be stored in mixtures of fluorescent dye molecules, which are deposited on a surface by inkjet printing, where an amide bond tethers the dye molecules to the surface. A microscope equipped with a multichannel fluorescence detector distinguishes individual dyes in the mixture. The presence or absence of these molecules in the mixture encodes binary information (i.e., "0" or "1"). The use of mixtures of molecules, instead of sequence-defined macromolecules, minimizes the time and difficulty of synthesis and eliminates the requirement of sequencing. We have written, stored, and read a total of approximately 400 kilobits (both text and images) with greater than 99% recovery of information, written at an average rate of 128 bits/s (16 bytes/s) and read at a rate of 469 bits/s (58.6 bytes/s).