This study demonstrates that commercial Nafion membranes exhibit anisotropic swelling behavior. Nafion is widely used as the base material in Ionic Polymer-Metal Composite (IPMC) actuators and is also broadly utilized in electrochemical applications, for example, as a proton exchange membrane in fuel cells. IPMCs consist of an ion-exchange polymer membrane, typically Nafion, sandwiched between metal electrodes. Initial experimental results revealed anisotropic swelling in the Nafion membrane, indicating that deformation within the material depends on direction. Consequently, the in-plane swelling is anisotropic, with the expansion along one axis being roughly 20% greater than along the perpendicular axis. Exploiting this anisotropy enables the design of IPMC actuators with novel, precisely controlled deformation modes, opening possibilities for soft robotics and smart materials applications. Since Nafion is also widely used as a proton-exchange membrane in fuel cells and other electrochemical systems, the findings of this work may likewise be applicable to Nafion-based electrochemical devices.

Triboelectric pressure sensors suffer from significant performance degradation in humid environments, which limits their reliability in wearable and outdoor applications. Most see a drop of more than 70% in voltage output when humidity exceeds 90%. Here, we demonstrate a triboelectric fabric pressure sensor operating even under ultra-high humidity conditions (at least 98% RH) through a materials–structure synergistic design. It is a fabric, combining PTFE and nylon 6,6 multifilament yarns that can be integrated into clothing. In this structure, the material's intrinsic hydrophobicity works in conjunction with the fabric's dense structure to help inhibit water penetration, at the same time, the multi-filament structure increases the effective contact area. The output exhibits a non-monotonic variation with humidity, decreasing in the range of 24–89% RH and partially recovering as humidity approaches saturation. This is studied by quantifying the evolution of the dielectric constant (εr) and the short-circuit transferred charge (Qsc) of dielectric layers under varying humidity levels, showing that the non-monotonic response of the open-circuit voltage (Voc) is primarily due to the dominant role of Qsc. The formation of microscale water droplets at the interface observed near saturation humidity is consistent with this phenomenon, suggesting that it may contribute to enhanced charge transfer and output response. The device retains 54.2% of its low-humidity output while maintaining reliable pressure-sensing performance at 98% RH, more than other reports, and achieves a high area-normalized output of 3.82 V cm−2.

Skin-level force detection in humanoid robotics is a demanding design problem benefitting from soft sensors that are compact, conform to curved surfaces, and sense multi-axis forces. Interactions with people and fragile objects make the ability to detect multi-axis force important for dexterous manipulation and safety. This work presents a 3-axis capacitive force sensing soft skin integrated into the fingertips of the PowerHand, a 1-degree-of-freedom prosthetic/robotic hand, enabling real-time measurement of directional interaction forces during object manipulation. Advances include the integration of a curved and compact sensor into the five fingers of the hand, along with wireless communication. Composed of stretchable electrodes and a soft dielectric on a flexible printed circuit board, the capacitive sensor is unobtrusively mounted on the finger, with a 2 mm ‘skin’ thickness and a 6 mm radius of curvature. It has low power consumption (<5 mW) and can employ wireless communication (15 mW Bluetooth Low Energy). The outer surface of the sensor is soft due to the elastomer substrate and elastomer-carbon blend electrodes. The sensitivity at 6 mm radius of curvature is 2%/N normal force and 7.2%/N in shear up to 1.75 N and 0.6 N in each – ranges typical for fine dexterous manipulation. The wireless readout system refreshes at 34 Hz. The hand is used to demonstrate 3 axis forces involved in gently grasping a soft rubber ball and a paper cup. Multi-axis grasping forces may inform development of sophisticated closed-loop control in the future, including slip detection and adaptive grasp stabilization.

Abstract Injectable biomaterials with aligned microstructures play a critical role in tissue engineering and drug-delivery applications where control over the position and orientation of cells and nano/micron-scale architectures enhance intervention efficacy. Patients are often subject to MRI scans; for patient safety and treatment efficacy, we investigated the effects of MRI on a biomaterial treatment consisting of aligned magnetic microstructures being developed for guiding cell growth. Under MRI exposure, potential movement of aligned structures could be detrimental to nearby cells, and potential MRI-induced heating could adversely affect traumatized tissue. In this work, the alignment state and heat conduction of such a treatment were studied using a 9.4 T preclinical MRI. The treatment comprises short magnetic rod-shaped polycaprolactone fibers (rods) with embedded magnetic nanoparticles in a surrounding hydrogel (gelatin methacrylate), with rod alignment observed before and after a 45-minute MRI scan. No change in rod alignment state was observed, and no heat generation was measured. A theoretical framework was developed which supports the experimental observation that the biomaterial is stable under MRI. This work can be extended to other biomaterial systems with aligned architectures used in tissue engineering applications such as spinal cord, muscle and tendon.

Soft capacitive sensors offer an approach for enhancing real-time measurements of both normal and shear stresses. We have created a 'smart' roller that employs dielectric elastomer sensors. The cylindrical capacitive sensor array is designed for automated fiber placement (AFP) machines, widely used in laying down carbon fibers to create composite parts for aerospace and automotive applications. Available in two variants, the smart roller accommodates distinct measurement needs: one model features 4 x 13 sensing units for normal stress, while the other employs 4 x 7 sensing units for three-axis stress measurement. The roller operates at typical roller stresses of up to 1.5 MPa, with sensitivities of 0.5/MPa. Both variants incorporate Bluetooth Low Energy (BLE) technology for wireless data transmission.

Liquid crystal elastomers show promise for artificial muscles, but challenges remain in achieving excellent actuation performance and controllability under diverse operational conditions. This study presents a novel asymmetric braiding method using a Maypole braiding machine to integrate carbon nanotube yarns with liquid crystal elastomer fibers, producing an electrothermal fiber-shaped actuator. The actuator demonstrates exceptional performance in both air and water. In air, the actuator lifts 261 times its own weight (0.17 MPa) within 2.5 s, achieving a 45% contraction with a strain rate of 18%·s-1. Underwater, it reaches a 32% contraction within 3 s. To enhance controllability under diverse conditions, a long short-term memory (LSTM) model was proposed and applied, accurately predicting actuation strain with a coefficient of determination (R2) of 0.994. Applications in a music robot and underwater claw highlight its potential for flexible robotics, validating its advantages in programmable control, rapid response, and adaptability across environments.

Twisted and coiled polymer fiber actuators can provide a large work output of 2.1-2.6 kJ/kg under constant external force. However, for realistic applications, variable external forces and periodic motion need to be considered. This paper measures the work loops of twisted and coiled polymer fiber actuators to obtain the work output per unit cycle. The paper finds, for the first time, that the softening property of the material with increasing temperature significantly deteriorates the work output. The upper limit of work output is determined by the crossover point of the work loop graph, reaching 0.24 kJ/kg in our initial studies. Deterioration of the work output is also caused by viscoelasticity. This paper further shows a simple graphical method, which can be extended to other actuators, and can be used to estimate the crossover point and the maximum work from stress-strain curves at the low and high temperature operating points.

Fully soft and stretchable sensors are desirable for wearable devices because of their high conformability to human skin, key to providing comfort and untethered user experiences. However, mostly targeting uni-axial stress sensing, few of these sensors have demonstrated design flexibility, manufacturing scalability, and multi-modality sensing. To address these challenges, we present a 3D-printed soft stretchable multi-modality capacitive sensor architecture, leveraging Direct Ink Writing (DIW) technology. DIW's versatility in material compatibility, multi-material printing capability, and ease of setup facilitate the precise deposition of silicone rubber ink for the sensor body and silver paste for electrodes, enabling complex sensor and electrode geometries, tailored to specific use cases. Fabrication of a sensor array is demonstrated. Next steps are to increase printer resolution and improve electrical connections to demonstrate the fully printed sensor array.

Dielectric polymers, particularly thermally stable synthetic types, play a crucial role in capacitors, circuit boards, insulators, and high-frequency devices. However, they also contribute significantly to electronic waste, making up approximately 20% of the 74.7 million metric tons of e-waste generated each year. Unfortunately, less than 18% of this waste is properly recycled, posing serious risks to human health and the environment. To address these challenges, we present a circular approach to fabricating biobased dielectric structures with ultralow dielectric constant and dielectric loss factor. Our method utilizes forestry residues derived from birch bark, after the extraction of high-value bioactive compounds. Specifically, we process the thermally stable, lignin-rich fibers in the residual bark through partial dissolution and cross-linking to produce "birch dielectric (BD)" films. These films exhibit exceptional dielectric properties, with dielectric constant (Dk) and loss factor (Df) values as low as ∼1.8 and ∼0.002, respectively, outperforming or matching the requirements of modern electrical insulators, including advanced polymer blends based on polyimides. In addition to their functional performance, BD films demonstrate remarkable mechanical and thermal stability, photothermal conversion capabilities, strength retention after cycling, and biodegradability. These findings, supported by experimental data and simulation studies of intermolecular interactions, highlight the potential of BD films as a sustainable and efficient alternative to conventional dielectric materials.

Skin is soft yet strong - a combination achieved by integrating compliant elastin with stiff but wavy collagen, producing non-linear mechanical properties. Inspired by this structure, stiff conductive wires are engineered into sinusoidal patterns and mechanically interlocked them with highly elastic fibers using a reimagined woven fabric approach. The result is a highly conducting and stretchable yarn that also has high tensile strength - a combination that is attractive for wearable applications where comfort and durability are valued. With a diameter of ≈1 mm-comparable to many commercial yarns-the fabric-based yarn exhibits low stiffness across a broad strain range (up to 270% under 2 N of force) while demonstrating a self-protective transition to high stiffness and strength (up to 30 MPa) as it nears failure. Additionally, this yarn offers excellent flexibility, high strain tolerance (exceeding 500%), inherent breathability, and superior weavability. By tuning the number of elastic fibers and electrode fibers, it can further tailor these stretchable conductive yarns into strain-insensitive connecting yarns (low impedance at MHz frequencies, GF = 0.0003) and mechanical sensing yarns with dual strain and proximity sensing capabilities. The integration of these functional yarns enables system-level smart textile applications, such as wristband controllers.

Wearable devices that combine flexibility, stretchability, breathability, sweat permeability, and sensing functionality are highly desirable for long-term health monitoring and seamless human-computer interaction. Herein, we developed a smart conducting fabric based on the widely used plain-woven structure, achieving these characteristics while enabling both sweat monitoring and haptic sensing. The fabric is designed with elastic filaments in the warp direction and two electrically conductive nylon fibers in the weft direction. This multi-fiber hybrid assembly strategy enhances breathability and sweat permeability while ensuring excellent stretchability (more than 60%). We demonstrated sensitivity to stretch and proximity by measuring capacitance between fibers, allowing measurement of respiratory, and monitoring of joint movement. When sweat penetrates the fabric, the impedance baseline drops significantly, enabling the detection of sweat. These properties make it amenable to integration into smart garments, and scaling up for mass production. Next steps include the addition of more conducting fibers, enabling localization of touch and sweat.

Marine plastic waste is a global environmental issue that needs urgent attention as it adversely affects the environment and living organisms, including human beings. More than 32–280 million metric tons of plastic are produced every year; however plastic production decreased in 2020 owing to a drop in demand caused by COVID-19[1-4]. Plastic production is expected to reach 53 million metric tons by 2030[5] and 155–265 million metric tons by 2060[3]. As the amount of plastic waste from sources other than packaging is decreasing, most of the waste is not treated as waste and is discharged into the ocean. Approximately 4.7–12.7 million metric tons of plastic waste is dumped into the sea annually[4,6], covering an area of 1.6 million km2[2]. About 150 million tons of plastic waste is reportedly present in the sea, which will likely remain in the sea until at least 2050. Properties of plastic further exacerbate this problem. Plastic shopping bags take more than a thousand years to completely decompose naturally, and plastics that have once entered the sea continue to harm the environment for an extremely long time[7]. Approximately 700 species, including endangered marine species, have been injured and killed[8]. Such deaths were attributed to glass and trees in the past; however, in recent years, 92% of these deaths have occurred owing to marine plastic waste/microplastic particles[8-10]. The effects of plastic waste and microplastic particles also affect coral reefs[11] and the Arctic[12]. This research will increase the applicability of activated carbon (AC) in marine plastic recycling. However, marine plastics are a mixture of various plastics, and it is difficult to recycle all of them from deposits, additives, and paints. Therefore, a recycling destination with high added value is required. In contrast, applications of AC have evolved from those in improving water quality to those in electrode materials, and especially as a storage battery. Its application prospects differ from other storage batteries in terms of charge and discharge characteristics; therefore, it is regarded as a power storage device whose demand will continue to rise in the future. Moreover, impurities in the electrode materials of ordinary secondary batteries can have a large adverse effect on battery capacity, internal resistance, and cycle life. Supercapacitors with carbon electrodes can be charged and discharged even if some impurities are present. Therefore, this study presented the production of AC as one of the treatment methods for marine plastic waste and evaluated the performance of AC and its performance as a supercapacitor electrode. The aim of this study was to develop methods to manage marine plastic waste (Fig.1(A)) through the production of activated carbon (AC). The specific surface area, micropore volume, and mesopore volume of marine plastic AC prepared under arbitrary temperature and activator weight ratio were measured (Fig1(B),(C)), and the specific capacitance and supercapacitor electrode performance were evaluated. At an activation temperature of 800 °C and a weight ratio of 1:7 between the raw material and 8 M KOH solution, a specific capacitance of 201 F/g and a high surface area of 2389 m2/g were obtained. Accordingly, marine plastic waste-based AC can be used as the electrode material in supercapacitors. [1] C. M. Rochman, et al., Policy: Classify plastic waste as hazardous, Nature 494 (2013), 169–171. [2] L. Lebreton, et al., Evidence that the Great Pacific Garbage Patch is rapidly accumulating plastic, Sci. Rep. 8 (2018), 4666. [3] L. Lebreton, A. Andrady, Future scenarios of global plastic waste generation and disposal, Palgrave Commun. 5 (2019), 6. [4] J. R. Jambeck, et al., Marine pollution. Plastic waste inputs from land into the ocean, Science 347 (2015), 768–771. [5] T. M. Adyel, Accumulation of plastic waste during COVID-19, Science 369 (2020), 1314–1315. [6] E. MacArthur, Beyond plastic waste, Science 358 (2017), 843. [7] C. Giacovelli, Single-use plastics: A roadmap for sustainability. International Environmental Technology Centre (2018). [8] S. C. Gall, R. C. Thompson. The impact of debris on marine life. Mar. Pollut. Bull. 92 (2015), 170–179. [9] O. M. Lonnstedt, P. Eklov, Environmentally relevant concentrations of microplastic particles influence larval fish ecology, Science 352 (2016), 1213–1216. [10] Animal behaviour: Plastic smells good to marine birds, Nature 539 (2016), 332. [11] J. B. Lamb, et al., Plastic waste associated with disease on coral reefs, Science 359 (2018), 460–462. [12] M. Bergmann, et al., Plastic pollution in the Arctic, Nat. Rev. Earth Environ. 3 (2022), 323–337. Figure 1

Humans physically express emotion by modulating parameters that register on mammalian skin mechanoreceptors, but are unavailable in current touch-sensing technology. Greater sensory richness combined with data on affect-expression composition is a prerequisite to estimating affect from touch, with applications including physical human-robot interaction. To examine shear alongside more easily captured normal stresses, we tailored recent capacitive technology to attain performance suitable for affective touch, creating a flexible, reconfigurable and soft 36-taxel array that detects multitouch normal and 2-dimensional shear at ranges of 1.5kPa-43kPa and +/- 0.3-3.8kPa respectively, wirelessly at 43Hz (1548 taxels/s). In a deep-learning classification of 9 gestures (N=16), inclusion of shear data improved accuracy to 88%, compared to 80% with normal stress data alone, confirming shear stress's expressive centrality. Using this rich data, we analyse the interplay of sensed-touch features, gesture attributes and individual differences, propose affective-touch sensing requirements, and share technical considerations for performance and practicality.

The future of wearable technology lies in the seamless integration of devices into our everyday clothing. It unlocks new possibilities by reimagining the electronic textiles through the lens of their intrinsic fiber interwoven structure. Currently, the interplay between textile structure design and wearable device functionality is not well understood, hindering the progress of electronic textiles. Inspired by human muscle architectures, we developed a tensile-responsive triboelectric yarn using a Janus tubular braided structure and hierarchical fiber composite-intertwining approach. This innovative yarn exhibits exceptional stretchability (i.e., strain up to 50 % with a 2 N force), favorable mechanical perception, remarkable washability, and adaptability for weaving, positioning it as a competitive candidate for self-powered wearable sensors. The fibrous intertwining architecture ensures excellent durability, retaining over 85 % electrical output ability after 3000 folding cycles. Additionally, we addressed triboelectric signal noise due to power frequency interference by implementing a band-stop filter. We developed a deep learning model based on a long short-term memory neural network, which can achieve highly accurate classification (accuracy > 99 %) of J-TENG signals within a time-span of 1 second. By integrating this yarn with a data transmission module and battery unit, we showcased the potential application of wireless wearable systems for physiological monitoring.

Soft force sensors have many applications in robotics and industrial environments. One challenge is obtaining a wide force range from common compliant materials. The capacitive sensor presented expands the range of measurable forces, while also detecting normal and shear forces. Mutual capacitance sensors are created from patterned silicone with stretchable electrodes. Capacitance changes between electrodes measure displacements and forces. A two-layer dielectric between the electrodes has one layer that is compliant to small forces, and stiff at higher forces. A second stiffer layer enables reasonable sensitivity at higher forces. This dielectric design results in a soft sensor with a normal force range of 0.03 N–50 N, with distinct low- and high-force ranges. At low forces, the sensor is able to distinguish normal forces of 31 mN and shear displacements of 10.8 µm. This approach enables a soft sensor for combining high normal and shear force measurement.

The low power consumption of electrochromism makes it widely used in actively shaded windows and mirrors, while flexible versions are attractive for use in wearable devices. Initial demonstration of stretchable electrochromic elements promises good conformability to complex surfaces. Here, fully integrated intrinsically stretchable electrochromic devices are demonstrated as single elements and 3 × 3 displays. Conductive and electrochromic ionic liquid-doped poly(3,4-ethylenedioxythiophene) polystyrene sulfonate is combined with poly(vinyl alcohol)-based electrolyte to form complete cells. A transmission change of 15% is demonstrated, along with a reflectance change of 25% for opaque reflective devices, with <7 s switching time, even under 30% strain. Stability under both electrochemical and mechanical strain cycling is demonstrated. A passive matrix display exhibits addressability and low cross-talk under strain. Comparable optical performance to flexible electrochromics and higher deformability provide attractive qualities for use in wearable, biometric monitoring, and robotic skin devices.

Existing smartwatches offer convenient health monitoring and interfaces with mobile devices. However, the interactivity between a user and a smartwatch suffers from the limited size of the screen and buttons. To improve the usability of smartwatches, novel human-computer interaction methods are introduced into the watchband. To this end, we present a modular lightweight watchband consisting of various capacitive sensing modules—TouchBand. It is made with a flexible printed circuit board (PCB) supporting the bottom electrodes, silver-coated conductive fabric as the top electrodes, and Eco-Flex as the dielectric to electrically separate the PCB and fabric. The watchband incorporates three control modules—(i) two shear-sensitive pressure sensing buttons, (ii) two capacitive sliders, and (iii) one proximity sensing array for hand gesture recognition. Shear forces are captured by analyzing the asymmetric changes in multiple mutual-capacitance readings produced by a shear motion between the top and bottom layers, where overlapped electrodes reside. Sliders pick up changes in proximity as fingers are moved across the sensor surfaces. Hand gestures could be recognized by monitoring the capacitance-based proximity readings between the watchband electrodes and the user’s skin. Eyes-free input to the watch becomes feasible by providing a shear/sliding touch input to the watchband as well as performing a free-hand gesture on the wearing hand. With a flexible printed circuit (FPC) connection to the compact custom electronics, all modules of the watchband were sampled at 50 Hz while consuming 30 mW of power. Meanwhile, the measurement data was wirelessly transmitted through Bluetooth Low-Energy 5.0 (BLE) to a nearby mobile device for real-time data analysis and visualization.

Nylon actuators yield a large reversible strain (5-20%+), are compact (300-µm) and provide a low-cost option for biomedical applications. We propose to develop an active textile composed of cotton, silver-coated nylon, and nylon actuators. We will assess the feasibility of nylon actuators to generate effective cycle rates and compression pressures similar to those of clinically effective pneumatic compression pumps. Our aim is to establish correlations between three nylon actuator configurations (parallel, parallel at 30°, and crisscrossed at 30°), thermal distribution, and compression pressure, as well as between power input and nylon actuator cycle rate. A microcontroller unit (MCU) and a pressure sensor will be developed for the nylon actuators to ensure that the actuators are under constant strain, while monitoring pressure, current, voltage and temperature. The development of an actively contracting textile could have significant benefits for portable compression therapies.

Soft sensors that can discriminate shear and normal force could help provide machines the fine control desirable for safe and effective physical interactions with people. A capacitive sensor is made for this purpose, composed of patterned elastomer and containing both fixed and sliding pillars that allow the sensor to deform and buckle, much like skin itself. The sensor differentiates between simultaneously applied normal force and shear using summation and differences of signals from four deformable capacitors. Cross talk from shear to normal force is less than 2.5%, and between shear axes is less than 10%. Normal and shear stress sensitivity is 0.49 kPa and 0.31 kPa respectively, with a minimum displacement resolution of 40 μm. In addition, finger proximity is detectable at a range of up to 15 mm. The operation is demonstrated on a simple gripper holding a cup. The combination of features and the straightforward fabrication method make this sensor a candidate for implementation as a sensing skin for humanoid robotics applications.