Multimode Hydraulically Amplified Electrostatic Actuators for Wearable Haptics

Shape-morphing bioelectronic devices

Shape-morphing bioelectronic devices, which can actively transform their geometric configurations in response to external stimuli (e.g., light, heat, electricity, and magnetic fields), have enabled many unique applications in different areas, ranging from human-machine interfaces to biomedical applications. These devices can not only realize in vivo deformations to execute specific tasks, form conformal contacts with target organs for real-time monitoring, and dynamically reshape their structures to adjust functional properties, but also assist users in daily activities through physical interactions. In this review, we provide a comprehensive overview of recent advances in shape-morphing bioelectronic devices, covering their fundamental working principles, representative deformation modes, and advanced manufacturing methodologies. Then, a broad range of practical applications of shape-morphing bioelectronics are summarized, including electromagnetic devices, optoelectronic devices, biological devices, biomedical devices, and haptic interfaces. Finally, we discuss key challenges and emerging opportunities in this rapidly evolving field, providing insights into future research directions and potential breakthroughs.

A metaverse laboratory setup for interactive atom visualization and manipulation with scanning probe microscopy

We present a metaverse laboratory system that integrates mixed reality (MR) technologies with scanning probe microscopy (SPM) for interactive atomic-scale visualization and manipulation. In order to accommodate both the visualization and input of SPM data in a virtual environment and the physical interaction with SPM-related equipment in the laboratory, the system incorporates a virtual reality (VR) and augmented reality (AR) framework to enable seamless switching between these two environments. Utilizing the pose-tracking capabilities in AR, users can intuitively interact with virtual interface elements and three-dimensional objects through physical hand gesture input to control SPM parameters and probe positioning. The system provides real-time visualization of scanned surfaces at the atomic scale in the virtual environment, enabling immediate feedback during experiments. To demonstrate the system's capabilities, we performed atomic manipulation experiments using hand gestures for lateral probe positioning, showing how MR-enhanced SPM can simplify nanoscale operations and improve experimental efficiency. Our integrated MR-SPM system allows users to conduct experiments via the metaverse platform while enhancing the human-instrument interaction experience. It extends the practical utility required for both real-time physical and virtual environment SPM operations in the laboratory, making nanoscale research more accessible and intuitive.

Soft Materials and Devices Enabling Sensorimotor Functions in Soft Robots

Sensorimotor functions, the seamless integration of sensing, decision-making, and actuation, are fundamental for robots to interact with their environments. Inspired by biological systems, the incorporation of soft materials and devices into robotics holds significant promise for enhancing these functions. However, current robotics systems often lack the autonomy and intelligence observed in nature due to limited sensorimotor integration, particularly in flexible sensing and actuation. As the field progresses toward soft, flexible, and stretchable materials, developing such materials and devices becomes increasingly critical for advanced robotics. Despite rapid advancements individually in soft materials and flexible devices, their combined applications to enable sensorimotor capabilities in robots are emerging. This review addresses this emerging field by providing a comprehensive overview of soft materials and devices that enable sensorimotor functions in robots. We delve into the latest development in soft sensing technologies, actuation mechanism, structural designs, and fabrication techniques. Additionally, we explore strategies for sensorimotor control, the integration of artificial intelligence (AI), and practical application across various domains such as healthcare, augmented and virtual reality, and exploration. By drawing parallels with biological systems, this review aims to guide future research and development in soft robots, ultimately enhancing the autonomy and adaptability of robots in unstructured environments.

Full freedom-of-motion actuators as advanced haptic interfaces

The sense of touch conveys critical environmental information, facilitating object recognition, manipulation, and social interaction, and can be engineered through haptic actuators that stimulate cutaneous receptors. An unfulfilled challenge lies in haptic interface technologies that can engage all the various mechanoreceptors in a programmable, spatiotemporal fashion across large areas of the body. Here, we introduce a small-scale actuator technology that can impart omnidirectional, superimposable, dynamic forces to the surface of skin, as the basis for stimulating individual classes of mechanoreceptors or selected combinations of them. High-bit haptic information transfer and realistic virtual tactile sensations are possible, as illustrated through human subject perception studies in extended reality applications that include advanced hand navigation, realistic texture reproduction, and sensory substitution for music perception.

Enhancing haptic continuity in virtual reality using a continuity reinforcement skeleton

Haptic displays are crucial for facilitating an immersive experience within virtual reality. However, when displaying continuous movements of contact, such as stroking and exploration, pixel-based haptic devices suffer from losing haptic information between pixels, leading to discontinuity. The trade-off between the travel distance of haptic elements and their pixel size in thin wearable devices hinders solutions that solely rely on increasing pixel density. Here we introduce a continuity reinforcement skeleton, which employs physically driven interpolation to enhance haptic information. This design enables the off-plane displacement to move conformally and display haptic information between pixel gaps. Efforts are made to quantify haptic display quality using geometric, mechanical, and psychological criteria. The development and integration of one-dimensional, two-dimensional, and curved haptic devices with virtual reality systems highlight the impact of the continuity reinforcement skeleton on haptic display, showcasing its potential for improving haptic experience.

Skin-attached haptic patch for versatile and augmented tactile interaction

Wearable tactile interfaces can enhance immersive experiences in virtual/augmented reality systems by adding tactile stimulation to the skin along with the visual and auditory information delivered to the user. We introduce a flat cone dielectric elastomer actuator (FCDEA) array that is thin, soft, and capable of producing spatiotemporally adjustable and large static-to-dynamic force in response to electric voltage signals on large areas of the skin. Integration of the FCDEA array into a photomicrosensor array enables the implementation of a wearable wireless communication haptic patch. We demonstrate that the developed haptic patch allows users to communicate tactile information in real time while maintaining conformal contact with the skin. The haptic patch can also express the topology of 3D structures and render textures of virtual objects in response to localized vibration of the FCDEA array. We expect that the developed haptic patch will provide an immersive touching experience in virtual reality and facilitate tactile communication between users in various applications.

Review of Electrohydraulic Actuators Inspired by the HASEL Actuator

The muscle-like movement and speed of the electrohydraulic actuator have granted it much attention in soft robotics. Our aim is to review the advancements in electrohydraulic actuators inspired by the Hydraulically Amplified Self-healing Electrostatic (HASEL) actuator. With this paper, we focus on the performance of 21 electrohydraulic actuator designs developed across five Universities, ranging from the earliest HASEL designs to the latest electrohydraulic designs. These actuators reported up to 60 N forces and contracting strains of up to 99%. The actuators with the best overall performance so far have been the Quadrant HASEL actuator and the HEXEL actuator, developed at the University of Colorado Boulder. However, notable is also the HALVE actuator (produced by ETH Zürich, Switzerland), which, by using a 5 µm PVDF-TrFE-CTFE film with a relative permittivity of 40, produced 100 times the electrostatic force of any of the electrohydraulic actuators under review. The latter shows that there is room for improvement as low force and displacement still limit the viability of the soft actuators in real-life applications.

Highly agile flat swimming robot

Navigating and exploring the surfaces of bodies of water allow swimming robots to perform a range of measurements while efficiently communicating and harvesting energy from the Sun. Such environments are often highly unstructured and cluttered with plant matter, animals, and debris, which require robots to move swiftly. We report a fast (5.1 centimeters per second translation and 195 degrees per second rotation), centimeter-scale swimming robot with high maneuverability and autonomous untethered operation. Locomotion is enabled by a pair of soft, millimeter-thin, undulating pectoral fins, in which traveling waves are electrically excited to generate propulsion. The actuators, robot design, and power supply are codesigned to enable high-performance locomotion in a scaled-down system. A single soft electrohydraulic actuator per side generates the traveling wave. A compact and lightweight power supply enables untethered operation, made possible by decreasing the operating voltage of the electrohydraulic actuators to below 500 volts and their power consumption to 35 milliwatts. By an experimental study and by modeling, we determined optimum dimensions and operating conditions across designs and size scales. The robots navigate through narrow spaces and through grassy plants and push objects weighing more than 16 times their body weight. Such robots can allow exploration of complex environments as well as continuous measurement of plant and water parameters for aquafarming.

A self-powered soft triboelectric-electrohydrodynamic pump

Soft pumps have the potential to transform industries including soft robotics, wearable devices, microfluidics and biomedical devices, but their efficiency and power supply limitations hinder prolonged operation. Here, we report a self-powered triboelectric-electrohydrodynamic pump, which combines a soft electrohydrodynamic pump driven by an electrostatic generator, specifically a triboelectric nanogenerator. The triboelectric nanogenerator collects ambient energy and converts it into high-voltage power source, allowing it to self-power an electrohydrodynamic pump and thus eliminating the need for external power supply. Using power management circuit, geometric shape optimization, and stacking methods, we achieve a maximum pressure of 4.49 kPa and a maximum flow rate of 502 mL/min. We demonstrate the pump's versatility in applications such as self-powered soft actuators, oil pumping in microfluidics, and oil purification. The triboelectric-electrohydrodynamic pump holds promising applications, and offers new insights for the development of fully self-powered systems.

Wearable Haptics for Orthotropic Actuation Based on Perpendicularly Nested Auxetic SMA Knotting

Smart wearable tactile systems, designed to deliver different types of touch feedback on human skin, can significantly improve engagement through diverse actuation patterns in virtual or augmented reality environments. Here, a perpendicularly nested auxetic wearable haptic interface is reported for orthotropically decoupled multimodal actuation (WHOA), capable of producing diverse tactile feedback modes with 3D sensory perception. WHOA incorporates shape memory alloy wires that are intricately knotted into an auxetic structure oriented along orthotropic dual axes. Its perpendicularly nested auxetic structure enables orthotropic actuation, allowing independent expansion and contraction along both x and y-axes, as confirmed by force-strain and displacement-time performance tests. Additionally, the perylene coating provides orthogonal electrical isolation to WHOA, allowing for stripe-specific localized actuation and enabling multiple tactile feedback modes. As an orthotropic wearable haptic interface, WHOA distinguishes between x-axis and y-axis directions and ultimately delivers multi-dimensional information regarding movements in 3D space through tactile feedback. As a result, when worn on the foot or arm, WHOA naturally delivers spatiotemporal tactile information to the user, facilitating navigation and teleoperation with 3D sensory perception.

Haptiknit: Distributed stiffness knitting for wearable haptics

Haptic devices typically rely on rigid actuators and bulky power supply systems, limiting wearability. Soft materials improve comfort, but careful distribution of stiffness is required to ground actuation forces and enable load transfer to the skin. We present Haptiknit, an approach in which soft, wearable, knit textiles with embedded pneumatic actuators enable programmable haptic display. By integrating pneumatic actuators within high- and low-stiffness machine-knit layers, each actuator can transmit 40 newtons in force with a bandwidth of 14.5 hertz. We demonstrate the concept with an adjustable sleeve for the forearm coupled to an untethered pneumatic control system that conveys a diverse array of social touch signals. We assessed the sleeve's performance for discriminative and affective touch in a three-part user study and compared our results with those of prior electromagnetically actuated approaches. Haptiknit improves touch localization compared with vibrotactile stimulation and communicates social touch cues with fewer actuators than pneumatic textiles that do not invoke distributed stiffness. The Haptiknit sleeve resulted in similar recognition of social touch gestures compared to a voice-coil array but represented a more portable and comfortable form factor.

Cutaneous Electrohydraulic (CUTE) Wearable Devices for Pleasant Broad-Bandwidth Haptic Cues

By focusing on vibrations, current wearable haptic devices underutilize the skin's perceptual capabilities. Devices that provide richer haptic stimuli, including contact feedback and/or variable pressure, are typically heavy and bulky due to the underlying actuator technology and the low sensitivity of hairy skin, which covers most of the body. This article presents a system architecture for compact wearable devices that deliver salient and pleasant broad-bandwidth haptic cues: Cutaneous Electrohydraulic (CUTE) devices combine a custom materials design for soft haptic electrohydraulic actuators that feature high stroke, high force, and electrical safety with a comfortable mounting strategy that places the actuator in a non-contact resting position. A prototypical wrist-wearable CUTE device produces rich tactile sensations by making and breaking contact with the skin (2.44 mm actuation stroke), applying high controllable forces (exceeding 2.3 N), and delivering vibrations at a wide range of amplitudes and frequencies (0-200 Hz). A perceptual study with 14 participants achieves 97.9% recognition accuracy across six diverse cues and verifies their pleasant and expressive feel. This system architecture for wearable devices gives unprecedented control over the haptic cues delivered to the skin, providing an elegant and discreet way to activate the user's sense of touch.

A high-response-frequency bimodal network polyacrylate elastomer with ultrahigh power density under low electric field

Dielectric elastomers, used as driver modules, require high power density to enable fast movement and efficient work of soft robots. Polyacrylate elastomers usually suffer from low power density under low electric fields due to limited response frequency. Here, we propose a bimodal network polyacrylate dielectric elastomer which breaks the intrinsic coupling relationship between dielectric and mechanical properties, featuring relatively high dielectric constant, low Young's modulus, and wide driving frequency bandwidth (~200 Hz) like silicones. Therefore, an ultrahigh power density (154 W kg-1@20 MV m-1, 200 Hz) is realized at low electric field and high resonance frequency, 75 times greater than at 10 Hz. Further, a rotary motor is developed, reaching an impressive speed of 1245 rpm at 19.6 MV m-1 and 125 Hz, surpassing previous acrylate-based motors and entering the high-speed domain of silicone-based motors. These findings offer a versatile strategy to fabricate high-power-density dielectric elastomers for low-electric-field soft actuators.

Haptic artificial muscle skin for extended reality

Existing haptic actuators are often rigid and limited in their ability to replicate real-world tactile sensations. We present a wearable haptic artificial muscle skin (HAMS) based on fully soft, millimeter-scale, multilayer dielectric elastomer actuators (DEAs) capable of significant out-of-plane deformation, a capability that typically requires rigid or liquid biasing. The DEAs use a thickness-varying multilayer structure to achieve large out-of-plane displacement and force, maintaining comfort and wearability. Experimental results demonstrate that HAMS can produce complex tactile feedback with high perception accuracy. Moreover, we show that HAMS can be integrated into extended reality (XR) systems, enhancing immersion and offering potential applications in entertainment, education, and assistive technologies.

Wearable and Implantable Soft Robots

Soft robotics presents innovative solutions across different scales. The flexibility and mechanical characteristics of soft robots make them particularly appealing for wearable and implantable applications. The scale and level of invasiveness required for soft robots depend on the extent of human interaction. This review provides a comprehensive overview of wearable and implantable soft robots, including applications in rehabilitation, assistance, organ simulation, surgical tools, and therapy. We discuss challenges such as the complexity of fabrication processes, the integration of responsive materials, and the need for robust control strategies, while focusing on advances in materials, actuation and sensing mechanisms, and fabrication techniques. Finally, we discuss the future outlook, highlighting key challenges and proposing potential solutions.

Neural interfaces: Bridging the brain to the world beyond healthcare

Neural interfaces, emerging at the intersection of neurotechnology and urban planning, promise to transform how we interact with our surroundings and communicate. By recording and decoding neural signals, these interfaces facilitate direct connections between the brain and external devices, enabling seamless information exchange and shared experiences. Nevertheless, their development is challenged by complexities in materials science, electrochemistry, and algorithmic design. Electrophysiological crosstalk and the mismatch between electrode rigidity and tissue flexibility further complicate signal fidelity and biocompatibility. Recent closed-loop brain-computer interfaces, while promising for mood regulation and cognitive enhancement, are limited by decoding accuracy and the adaptability of user interfaces. This perspective outlines these challenges and discusses the progress in neural interfaces, contrasting non-invasive and invasive approaches, and explores the dynamics between stimulation and direct interfacing. Emphasis is placed on applications beyond healthcare, highlighting the need for implantable interfaces with high-resolution recording and stimulation capabilities.

A Multi-Layer Stacked Microfluidic Tactile Display With High Spatial Resolution

Pneumatic tactile displays dynamically customize surface morphological features with reconfigurable arrays of independently addressable actuators. However, their ability to render detailed tactile patterns or fine textures is limited by the low spatial resolution. For pneumatic tactile displays, the high-density integration of pneumatic actuators within a small space (fingertip) poses a significant challenge in terms of pneumatic circuit wiring. In contrast to the structure with a single-layer layout of pipes, we propose a multi-layered stacked microfluidic pipe structure that allows for a higher density of actuators and retains their independent actuation capabilities. Based on the proposed structure, we developed a soft microfluidic tactile display with a spatial resolution of 1.25 mm. The device consists of a 5 × 5 array of independently addressable microactuators, driven by pneumatic pressure, each of which enables independent actuation of the surface film and continuous control of the height. At a relative pressure of 1000 mbar, the actuator produced a perceptible out-of-plane deformation of 0.145 mm and a force of 17.7 mN. User studies showed that subjects can easily distinguish eight tactile patterns with 96% accuracy.

Dynamically reconfigurable shape-morphing and tactile display via hydraulically coupled mergeable and splittable PVC gel actuator

Shape-morphing displays alter their surface geometry to convey information through three-dimensional shapes. However, rapid transformation into seamless shapes with multimodal tactile sensations poses challenges. Here, we introduce a versatile soft shape-morphing and tactile display, using a novel actuator that combines a PVC gel composite, dielectric liquid, and an electrode array. Proposed device facilitates on-demand liquid flow control through electrohydraulic actuation. Liquid channels within the device can be dynamically reconfigured using localized electrostatic zipping, enabling swift shape morphing and reconfiguration into diverse seamless 3D shapes. Our device achieves a large deformation and high output force, in a slim and lightweight framework. It also offers various haptic feedback, including dynamic tactile patterns and vibrations for localizable surface textures on the morphed shape. Additionally, its potential in robotics was demonstrated through high-speed object manipulation, leveraging liquid flow-induced inertia. In summary, our innovative soft shape-morphing tactile display could open new ways that we interact with technology, offering a more immersive and intuitive experience.

Hexagonal electrohydraulic modules for rapidly reconfigurable high-speed robots

Robots made from reconfigurable modular units feature versatility, cost efficiency, and improved sustainability compared with fixed designs. Reconfigurable modules driven by soft actuators provide adaptable actuation, safe interaction, and wide design freedom, but existing soft modules would benefit from high-speed and high-strain actuation, as well as driving methods well-suited to untethered operation. Here, we introduce a class of electrically actuated robotic modules that provide high-speed (a peak contractile strain rate of 4618% per second, 15.8-hertz bandwidth, and a peak specific power of 122 watts per kilogram), high-strain (49% contraction) actuation and that use magnets for reversible mechanical and electrical connections between neighboring modules, thereby serving as building blocks for rapidly reconfigurable and highly agile robotic systems. The actuation performance of each hexagonal electrohydraulic (HEXEL) module is enabled by a synergistic combination of soft and rigid components; a hexagonal exoskeleton of rigid plates amplifies the motion produced by soft electrohydraulic actuators and provides a mechanical structure and connection platform for reconfigurable robots composed of many modules. We characterize the actuation performance of individual HEXEL modules, present a model that captures their quasi-static force-stroke behavior, and demonstrate both a high-jumping and a fast pipe-crawling robot. Using embedded magnetic connections, we arranged multiple modules into reconfigurable robots with diverse functionality, including a high-stroke muscle, a multimodal active array, a table-top active platform, and a fast-rolling robot. We further leveraged the magnetic connections for hosting untethered, snap-on driving electronics, together highlighting the promise of HEXEL modules for creating rapidly reconfigurable high-speed robots.

Bioinspired adaptable multiplanar mechano-vibrotactile haptic system

Several gaps persist in haptic device development due to the multifaceted nature of the sense of touch. Existing gaps include challenges enhancing touch feedback fidelity, providing diverse haptic sensations, and ensuring wearability for delivering tactile stimuli to the fingertips. Here, we introduce the Bioinspired Adaptable Multiplanar Haptic system, offering mechanotactile/steady and vibrotactile pulse stimuli with adjustable intensity (up to 298.1 mN) and frequencies (up to 130 Hz). This system can deliver simultaneous stimuli across multiple fingertip areas. The paper includes a full characterisation of our system. As the device can play an important role in further understanding human touch, we performed human stimuli sensitivity and differentiation experiments to evaluate the capability of delivering mechano-vibrotactile, variable intensity, simultaneous, multiplanar and operator agnostic stimuli. Our system promises to accelerate the development of touch perception devices, providing painless, operator-independent data crucial for researching and diagnosing touch-related disorders.

Energy-efficient dynamic 3D metasurfaces via spatiotemporal jamming interleaved assemblies for tactile interfaces

Inspired by the natural shape-morphing abilities of biological organisms, we introduce a strategy for creating energy-efficient dynamic 3D metasurfaces through spatiotemporal jamming of interleaved assemblies. Our approach, diverging from traditional shape-morphing techniques reliant on continuous energy inputs, utilizes strategically jammed, paper-based interleaved assemblies. By rapidly altering their stiffness at various spatial points and temporal phases during the relaxation of the soft substrate through jamming, we enable the formation of refreshable, intricate 3D shapes with a desirable load-bearing capability. This process, which does not require ongoing energy consumption, ensures energy-efficient and lasting shape displays. Our theoretical model, linking buckling deformation to residual pre-strain, underpins the inverse design process for an array of interleaved assemblies, facilitating the creation of diverse 3D configurations. This metasurface holds notable potential for tactile displays, particularly for the visually impaired, heralding possibilities in visual impaired education, haptic feedback, and virtual/augmented reality applications.

A tactile sensing system capable of recognizing objects based on bioinspired self-sensing soft pneumatic actuator

Tactile sensors play an important role when robots perform contact tasks, such as physical information collection, force or displacement control to avoid collision. For these manipulations, excessive contact may cause damage while poor contact cause information loss between the robotic end-effector and the objects. Inspired by skin structure and signal transmission method, this paper proposes a tactile sensing system based on the self-sensing soft pneumatic actuator (S-SPA) capable of providing tactile sensing capability for robots. Based on the adjustable height and compliance characteristics of the S-SPA, the contact process is safe and more tactile information can be collected. And to demonstrate the feasibility and advantage of this system, a robotic hand with S-SPAs could recognize different textures and stiffness of the objects by touching and pinching behaviours to collect physical information of the various objects under the positive work states of the S-SPA. The result shows the recognition accuracy of the fifteen texture plates reaches 99.4%, and the recognition accuracy of the four stiffness cuboids reaches 100%by training a KNN model. This safe and simple tactile sensing system with high recognition accuracies based on S-SPA shows great potential in robotic manipulations and is beneficial to applications in domestic and industrial fields.

Impact of Solid Materials in the Gap Space between Driving Electrodes in a MEMS Tri-Electrode Electrostatic Actuator

MEMS electrostatic actuators can suffer from a high control voltage and a limited displacement range, which are made more prevalent by the pull-in effect. This study explores a tri-electrode topology to enable a reduction in the control voltage and explores the effect of various solid materials forming the space between the two underlying stationary electrodes. Employing solid dielectric material simplifies fabrication and can reduce the bottom primary electrode's fixed voltage. Through numerical analysis, different materials were examined to assess their impact. The results indicate that the primary electrode's fixed voltage can be reduced with an increase in the dielectric constant, however, with the consequence of reduced benefit to control voltage reduction. Additionally, charge analysis was conducted to compare the actuator's performance using air as the gap-spacing material versus solid materials, from the perspective of energy conservation. It was found that solid materials result in a higher accumulated charge, reducing the need for a high fixed voltage.

Untethered soft actuators for soft standalone robotics

Soft actuators produce the mechanical force needed for the functional movements of soft robots, but they suffer from critical drawbacks since previously reported soft actuators often rely on electrical wires or pneumatic tubes for the power supply, which would limit the potential usage of soft robots in various practical applications. In this article, we review the new types of untethered soft actuators that represent breakthroughs and discuss the future perspective of soft actuators. We discuss the functional materials and innovative strategies that gave rise to untethered soft actuators and deliver our perspective on challenges and opportunities for future-generation soft actuators.

Towards high performance and durable soft tactile actuators

Soft actuators are gaining significant attention due to their ability to provide realistic tactile sensations in various applications. However, their soft nature makes them vulnerable to damage from external factors, limiting actuation stability and device lifespan. The susceptibility to damage becomes higher with these actuators often in direct contact with their surroundings to generate tactile feedback. Upon onset of damage, the stability or repeatability of the device will be undermined. Eventually, when complete failure occurs, these actuators are disposed of, accumulating waste and driving the consumption of natural resources. This emphasizes the need to enhance the durability of soft tactile actuators for continued operation. This review presents the principles of tactile feedback of actuators, followed by a discussion of the mechanisms, advancements, and challenges faced by soft tactile actuators to realize high actuation performance, categorized by their driving stimuli. Diverse approaches to achieve durability are evaluated, including self-healing, damage resistance, self-cleaning, and temperature stability for soft actuators. In these sections, current challenges and potential material designs are identified, paving the way for developing durable soft tactile actuators.

Statistical field theory of polarizable polymer chains with nonlocal dipolar interactions

The electromechanical response of polymeric soft matter to applied electric fields is of fundamental scientific interest as well as relevant to technologies for sensing and actuation. Several existing theoretical and numerical approaches for polarizable polymers subject to a combined applied electric field and stretch are based on discrete monomer models. In these models, accounting for the interactions between the induced dipoles on monomers is challenging due to the nonlocality of these interactions. On the other hand, the framework of statistical field theory provides a continuous description of polymer chains that potentially enables a tractable way to account for these interactions. However, prior formulations using this framework have been restricted to the case of weak anisotropy of the monomer polarizability. This paper formulates a general approach based in the framework of statistical field theory to account for the nonlocal nature of the dipolar interactions without any restrictions on the anisotropy or nonlinearity of the polarizability of the monomer. The approach is based on three key elements: (1) the statistical field theory framework, in which the discrete monomers are regularized to a continuous dipole distribution, (2) a replacement of the nonlocal dipole-dipole interactions by the local electrostatics partial differential equation with the continuous dipole distribution as the forcing, and (3) the use of a completely general relation between the polarization and the local electric field. Rather than treat the dipole-dipole interactions directly, the continuous description in the field theory enables the computationally tractable nonlocal-to-local transformation. Further, it enables the use of a realistic statistical-mechanical ensemble wherein the average far-field applied electric field is prescribed, rather than prescribing the applied field at every point in the polymer domain. The model is applied, using the finite element method, to study the electromechanical response of a polymer chain in the ensemble with fixed far-field applied electric field and fixed chain stretch. The nonlocal dipolar interactions are found to increase, over the case where dipole-dipole interactions are neglected, the magnitudes of the polarization and electric field by orders of magnitude as well as significantly change their spatial distributions. Next, the effect of the relative orientation between the applied field and the chain on the local electric field and polarization is studied. The model predicts that the elastic response of the polymer chain is linear, consistent with the Gaussian approximation, and largely unchanged by the orientation of the applied electric field, though the polarization and local electric field distributions are significantly impacted.

Haptic Sensing and Feedback Techniques toward Virtual Reality

Haptic interactions between human and machines are essential for information acquisition and object manipulation. In virtual reality (VR) system, the haptic sensing device can gather information to construct virtual elements, while the haptic feedback part can transfer feedbacks to human with virtual tactile sensation. Therefore, exploring high-performance haptic sensing and feedback interface imparts closed-loop haptic interaction to VR system. This review summarizes state-of-the-art VR-related haptic sensing and feedback techniques based on the hardware parts. For the haptic sensor, we focus on mechanism scope (piezoresistive, capacitive, piezoelectric, and triboelectric) and introduce force sensor, gesture translation, and touch identification in the functional view. In terms of the haptic feedbacks, methodologies including mechanical, electrical, and elastic actuators are surveyed. In addition, the interactive application of virtual control, immersive entertainment, and medical rehabilitation is also summarized. The challenges of virtual haptic interactions are given including the accuracy, durability, and technical conflicts of the sensing devices, bottlenecks of various feedbacks, as well as the closed-loop interaction system. Besides, the prospects are outlined in artificial intelligence of things, wise information technology of medicine, and multimedia VR areas.

Height-renderable morphable tactile display enabled by programmable modulation of local stiffness in photothermally active polymer

Reconfigurable tactile displays are being used to provide refreshable Braille information; however, the delivered information is currently limited to an alternative of Braille because of difficulties in controlling the deformation height. Herein, we present a photothermally activated polymer-bilayer-based morphable tactile display that can programmably generate tangible three-dimensional topologies with varying textures on a thin film surface. The morphable tactile display was composed of a heterogeneous polymer structure that integrated a stiffness-tunable polymer into a light-absorbing elastomer, near-infra-red light-emitting diode (NIR-LED) array, and small pneumatic chamber. Topological expression was enabled by producing localized out-of-plane deformation that was reversible, height-adjustable, and latchable in response to light-triggered stiffness modulation at each target area under switching of stationary pneumatic pressure. Notably, the tactile display could express a spatial softness map of the latched topology upon re-exposing the target areas to modulated light from the NIR-LED array. We expect the developed tactile display to open a pathway for generating high-dimensional tactile information on electronic devices and enable realistic interaction in augmented and virtual environments.

Reprogrammable Metamaterial Processors for Soft Machines

Soft metamaterials have attracted extensive attention due to their remarkable properties. These materials hold the potential to program and control the morphing behavior of soft machines, however, their combination is limited by the poor reprogrammability of metamaterials and incompatible communication between them. Here, printable and recyclable soft metamaterials possessing reprogrammable embedded intelligence to regulate the morphing of soft machines are introduced. These metamaterials are constructed from interconnected and periodically arranged logic unit cells that are able to perform compound logic operations coupling multiplication and negation. The scalable computation capacity of the unit cell empowers it to simultaneously process multiple fluidic signals with different types and magnitudes, thereby allowing the execution of sophisticated and high-level control operations. By establishing the laws of physical Boolean algebra and formulating a universal design route, soft metamaterials capable of diverse logic operations can be readily created and reprogrammed. Besides, the metamaterials' potential of directly serving as fluidic processors for soft machines is validated by constructing a soft latched demultiplexer, soft controllers capable of universal and customizable morphing programming, and a reprogrammable processor without reconnection. This work provides a facile way to create reprogrammable soft fluidic control systems to meet on-demand requirements in dynamic situations.

Soft Sensors and Actuators for Wearable Human-Machine Interfaces

Haptic human-machine interfaces (HHMIs) combine tactile sensation and haptic feedback to allow humans to interact closely with machines and robots, providing immersive experiences and convenient lifestyles. Significant progress has been made in developing wearable sensors that accurately detect physical and electrophysiological stimuli with improved softness, functionality, reliability, and selectivity. In addition, soft actuating systems have been developed to provide high-quality haptic feedback by precisely controlling force, displacement, frequency, and spatial resolution. In this Review, we discuss the latest technological advances of soft sensors and actuators for the demonstration of wearable HHMIs. We particularly focus on highlighting material and structural approaches that enable desired sensing and feedback properties necessary for effective wearable HHMIs. Furthermore, promising practical applications of current HHMI technology in various areas such as the metaverse, robotics, and user-interactive devices are discussed in detail. Finally, this Review further concludes by discussing the outlook for next-generation HHMI technology.

PopTouch: A Submillimeter Thick Dynamically Reconfigured Haptic Interface with Pressable Buttons

The interactions with touchscreens rely heavily on vision: The virtual buttons and virtual sliders on a touchscreen provide no mechanical sense of the object they seek to represent. This work presents PopTouch: a 500 µm thick flexible haptic display that creates pressable physical buttons on demand. PopTouch can be mounted directly on touchscreens or any other smooth surface, flat, or curved. The buttons of PopTouch are independently controlled hydraulically amplified electrostatic zipping taxels (tactile pixels) that generate 1.5 mm of out of plane displacement. When pressed by the user, the buttons provide intuitive mechanical feedback thanks to a snap-through characteristic in their force-displacement profile. The snap-through threshold can be as high as 4 N, and is tuned by design and actuation parameters. This work presents two versions of PopTouch: a transparent PopTouch for integration on Touchscreens with built-in touch sensing, such as smartphones and a sensorized PopTouch, with embedded thin-film piezoelectric sensors on each taxel, for integration on substrates without built-in touch sensing, such as a steering wheel. PopTouch adds static and vibrating button-like haptics to any device thanks to its thin profile, flexibility, low power consumption (6 mW per button), rapid refresh rate (2 Hz), and freely configured array format.

Adaptive tactile interaction transfer via digitally embroidered smart gloves

Human-machine interfaces for capturing, conveying, and sharing tactile information across time and space hold immense potential for healthcare, augmented and virtual reality, human-robot collaboration, and skill development. To realize this potential, such interfaces should be wearable, unobtrusive, and scalable regarding both resolution and body coverage. Taking a step towards this vision, we present a textile-based wearable human-machine interface with integrated tactile sensors and vibrotactile haptic actuators that are digitally designed and rapidly fabricated. We leverage a digital embroidery machine to seamlessly embed piezoresistive force sensors and arrays of vibrotactile actuators into textiles in a customizable, scalable, and modular manner. We use this process to create gloves that can record, reproduce, and transfer tactile interactions. User studies investigate how people perceive the sensations reproduced by our gloves with integrated vibrotactile haptic actuators. To improve the effectiveness of tactile interaction transfer, we develop a machine-learning pipeline that adaptively models how each individual user reacts to haptic sensations and then optimizes haptic feedback parameters. Our interface showcases adaptive tactile interaction transfer through the implementation of three end-to-end systems: alleviating tactile occlusion, guiding people to perform physical skills, and enabling responsive robot teleoperation.

Low-voltage electrohydraulic actuators for untethered robotics

Rigid robots can be precise but struggle in environments where compliance, robustness to disturbances, or energy efficiency is crucial. This has led researchers to develop biomimetic robots incorporating soft artificial muscles. Electrohydraulic actuators are promising artificial muscles that perform comparably to mammalian muscles in speed and power density. However, their operation requires several thousand volts. The high voltage leads to bulky and inefficient driving electronics. Here, we present hydraulically amplified low-voltage electrostatic (HALVE) actuators that match mammalian skeletal muscles in average power density (50.5 watts per kilogram) and peak strain rate (971% per second) at a 4.9 times lower driving voltage (1100 volts) compared to the state of the art. HALVE actuators are safe to touch, are waterproof, and exhibit self-clearing properties. We characterize, model, and validate key performance metrics of our actuator. Last, we demonstrate the utility of HALVE actuators on a robotic gripper and a soft robotic swimmer.

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

Polydimethylsiloxane (PDMS)-the simplest and most common silicone compound-exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS-based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS-based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS-based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next-generation soft materials and devices.

Easy-To-Wear Auxetic SMA Knot-Architecture for Spatiotemporal and Multimodal Haptic Feedbacks

Wearable haptic interfaces prioritize user comfort, but also value the ability to provide diverse feedback patterns for immersive interactions with the virtual or augmented reality. Here, to provide both comfort and diverse tactile feedback, an easy-to-wear and multimodal wearable haptic auxetic fabric (WHAF) is prepared by knotting shape-memory alloy wires into an auxetic-structured fabric. This unique meta-design allows the WHAF to completely expand and contract in 3D, providing superior size-fitting and shape-fitting capabilities. Additionally, a microscale thin layer of Parylene is coated on the surface to create electrically separated zones within the WHAF, featuring zone-specified actuation for conveying diverse spatiotemporal information to users with using the WHAF alone. Depending on the body part it is worn on, the WHAF conveys either cutaneous or kinesthetic feedback, thus, working as a multimodal wearable haptic interface. As a result, when worn on the forearm, the WHAF intuitively provides spatiotemporal information to users during hands-free navigation and teleoperation in virtual reality, and when worn on the elbow, the WHAF guides users to reach the desired elbow flexion, like a personal exercise advisor.

Derivation of Ultra-High Gain Hybrid Converter Families for HASEL Actuators Used in Soft Mobile Robots

This work proposes, analyzes, designs, and validates superior topologies of UHGH converters that are capable of supporting extremely large conversion ratios up to ∼2000× and output voltage up to ∼4-12 kV for future mobile soft robots from an input voltage as low as the range of a 1-cell battery pack. Thus, the converter makes soft robots standalone systems that can be untethered and mobile. The extremely large voltage gain is enabled by a unique hybrid combination of a high-gain switched magnetic element (HGSME) and a capacitor-based voltage multiplier rectifier (CVMR) that, together, achieve small overall size, efficient operation, and output voltage regulation and shaping with simple duty-cycle modulation. With superior performance, power density, and compact size, the UHGH converters prove to be a promising candidate for future untethered soft robots.

HaptGlove-Untethered Pneumatic Glove for Multimode Haptic Feedback in Reality-Virtuality Continuum

Novel haptics technologies are urgently needed to bridge the gap between entirely physical world and fully digital environment to render a more realistic and immersive human-computer interaction. Current virtual reality (VR) haptic gloves either deliver limited haptic feedback or are bulky and heavy. The authors develop a haptic glove or HaptGlove, an untethered and lightweight pneumatic glove, that allows users to "physically" interact in a VR environment and enables both kinesthetic and cutaneous sensations naturally and realistically. Integrated with five pairs of haptic feedback modules and fiber sensors, HaptGlove provides variable stiffness force feedback and fingertip force and vibration feedback, allowing users to touch, press, grasp, squeeze, and pull various virtual objects and feel the dynamic haptic changes. Significant improvements in VR realism and immersion are observed in a user study with participants achieving 78.9% accuracy in sorting six virtual balls of different stiffnesses. Importantly, HaptGlove facilitates VR training, education, entertainment, and socialization in a reality-virtuality continuum.

A multifunctional soft robotic shape display with high-speed actuation, sensing, and control

Shape displays which actively manipulate surface geometry are an expanding robotics domain with applications to haptics, manufacturing, aerodynamics, and more. However, existing displays often lack high-fidelity shape morphing, high-speed deformation, and embedded state sensing, limiting their potential uses. Here, we demonstrate a multifunctional soft shape display driven by a 10 × 10 array of scalable cellular units which combine high-speed electrohydraulic soft actuation, magnetic-based sensing, and control circuitry. We report high-performance reversible shape morphing up to 50 Hz, sensing of surface deformations with 0.1 mm sensitivity and external forces with 50 mN sensitivity in each cell, which we demonstrate across a multitude of applications including user interaction, image display, sensing of object mass, and dynamic manipulation of solids and liquids. This work showcases the rich multifunctionality and high-performance capabilities that arise from tightly-integrating large numbers of electrohydraulic actuators, soft sensors, and controllers at a previously undemonstrated scale in soft robotics.

Soft, miniaturized, wireless olfactory interface for virtual reality

Recent advances in virtual reality (VR) technologies accelerate the creation of a flawless 3D virtual world to provide frontier social platform for human. Equally important to traditional visual, auditory and tactile sensations, olfaction exerts both physiological and psychological influences on humans. Here, we report a concept of skin-interfaced olfactory feedback systems with wirelessly, programmable capabilities based on arrays of flexible and miniaturized odor generators (OGs) for olfactory VR applications. By optimizing the materials selection, design layout, and power management, the OGs exhibit outstanding device performance in various aspects, from response rate, to odor concentration control, to long-term continuous operation, to high mechanical/electrical stability and to low power consumption. Representative demonstrations in 4D movie watching, smell message delivery, medical treatment, human emotion control and VR/AR based online teaching prove the great potential of the soft olfaction interface in various practical applications, including entertainment, education, human machine interfaces and so on.

Biodegradable electrohydraulic actuators for sustainable soft robots

Combating environmental pollution demands a focus on sustainability, in particular from rapidly advancing technologies that are poised to be ubiquitous in modern societies. Among these, soft robotics promises to replace conventional rigid machines for applications requiring adaptability and dexterity. For key components of soft robots, such as soft actuators, it is thus important to explore sustainable options like bioderived and biodegradable materials. We introduce systematically determined compatible materials systems for the creation of fully biodegradable, high-performance electrohydraulic soft actuators, based on various biodegradable polymer films, ester-based liquid dielectric, and NaCl-infused gelatin hydrogel. We demonstrate that these biodegradable actuators reliably operate up to high electric fields of 200 V/μm, show performance comparable to nonbiodegradable counterparts, and survive more than 100,000 actuation cycles. Furthermore, we build a robotic gripper based on biodegradable soft actuators that is readily compatible with commercial robot arms, encouraging wider use of biodegradable materials systems in soft robotics.

Localized Photoactuation of Polymer Pens for Nanolithography

Localized actuation is an important goal of nanotechnology broadly impacting applications such as programmable materials, soft robotics, and nanolithography. Despite significant recent advances, actuation with high temporal and spatial resolution remains challenging to achieve. Herein, we demonstrate strongly localized photoactuation of polymer pens made of polydimethylsiloxane (PDMS) and surface-functionalized short carbon nanotubes based on a fundamental understanding of the nanocomposite chemistry and device innovations in directing intense light with digital micromirrors to microscale domains. We show that local illumination can drive a small group of pens (3 × 3 over 170 μm × 170 μm) within a massively two-dimensional array to attain an out-of-plane motion by more than 7 μm for active molecular printing. The observed effect marks a striking three-order-of-magnitude improvement over the state of the art and suggests new opportunities for active actuation.

Dynamic control of high-voltage actuator arrays by light-pattern projection on photoconductive switches

The ability to control high-voltage actuator arrays relies, to date, on expensive microelectronic processes or on individual wiring of each actuator to a single off-chip high-voltage switch. Here we present an alternative approach that uses on-chip photoconductive switches together with a light projection system to individually address high-voltage actuators. Each actuator is connected to one or more switches that are nominally OFF unless turned ON using direct light illumination. We selected hydrogenated amorphous silicon (a-Si:H) as our photoconductive material, and we provide a complete characterization of its light to dark conductance, breakdown field, and spectral response. The resulting switches are very robust, and we provide full details of their fabrication processes. We demonstrate that the switches can be integrated into different architectures to support both AC and DC-driven actuators and provide engineering guidelines for their functional design. To demonstrate the versatility of our approach, we demonstrate the use of the photoconductive switches in two distinctly different applications-control of µm-sized gate electrodes for patterning flow fields in a microfluidic chamber and control of cm-sized electrostatic actuators for creating mechanical deformations for haptic displays.

Wrapping Haptic Displays Around Robot Arms to Communicate Learning

Humans can leverage physical interaction to teach robot arms. As the human kinesthetically guides the robot through demonstrations, the robot learns the desired task. While prior works focus on how the robot learns, it is equally important for the human teacher to understand what their robot is learning. Visual displays can communicate this information; however, we hypothesize that visual feedback alone misses out on the physical connection between the human and robot. In this paper we introduce a novel class of soft haptic displays that wrap around the robot arm, adding signals without affecting that interaction. We first design a pneumatic actuation array that remains flexible in mounting. We then develop single and multi-dimensional versions of this wrapped haptic display, and explore human perception of the rendered signals during psychophysic tests and robot learning. We ultimately find that people accurately distinguish single-dimensional feedback with a Weber fraction of 11.4%, and identify multi-dimensional feedback with 94.5% accuracy. When physically teaching robot arms, humans leverage the single- and multi-dimensional feedback to provide better demonstrations than with visual feedback: our wrapped haptic display decreases teaching time while increasing demonstration quality. This improvement depends on the location and distribution of the wrapped haptic display.

Human–Machine Interaction through Advanced Haptic Sensors: A Piezoelectric Sensory Glove with Edge Machine Learning for Gesture and Object Recognition

Human–machine interaction (HMI) refers to systems enabling communication between machines and humans. Systems for human–machine interfaces have advanced significantly in terms of materials, device design, and production methods. Energy supply units, logic circuits, sensors, and data storage units must be flexible, stretchable, undetectable, biocompatible, and self-healing to act as human–machine interfaces. This paper discusses the technologies for providing different haptic feedback of different natures. Notably, the physiological mechanisms behind touch perception are reported, along with a classification of the main haptic interfaces. Afterward, a comprehensive overview of wearable haptic interfaces is presented, comparing them in terms of cost, the number of integrated actuators and sensors, their main haptic feedback typology, and their future application. Additionally, a review of sensing systems that use haptic feedback technologies—specifically, smart gloves—is given by going through their fundamental technological specifications and key design requirements. Furthermore, useful insights related to the design of the next-generation HMI devices are reported. Lastly, a novel smart glove based on thin and conformable AlN (aluminum nitride) piezoelectric sensors is demonstrated. Specifically, the device acquires and processes the signal from the piezo sensors to classify performed gestures through an onboard machine learning (ML) algorithm. Then, the design and testing of the electronic conditioning section of AlN-based sensors integrated into the smart glove are shown. Finally, the architecture of a wearable visual-tactile recognition system is presented, combining visual data acquired by a micro-camera mounted on the user’s glass with the haptic ones provided by the piezoelectric sensors.

A mechanics-based approach to realize high–force capacity electroadhesives for robots

Materials with electroprogrammable stiffness and adhesion can enhance the performance of robotic systems, but achieving large changes in stiffness and adhesive forces in real time is an ongoing challenge. Electroadhesive clutches can rapidly adhere high stiffness elements, although their low force capacities and high activation voltages have limited their applications. A major challenge in realizing stronger electroadhesive clutches is that current parallel plate models poorly predict clutch force capacity and cannot be used to design better devices. Here, we use a fracture mechanics framework to understand the relationship between clutch design and force capacity. We demonstrate and verify a mechanics-based model that predicts clutch performance across multiple geometries and applied voltages. On the basis of this approach, we build a clutch with 63 times the force capacity per unit electrostatic force of state-of-the-art electroadhesive clutches. Last, we demonstrate the ability of our electroadhesives to increase the load capacity of a soft, pneumatic finger by a factor of 27 times compared with a finger without an electroadhesive.

Soft Modular Glove with Multimodal Sensing and Augmented Haptic Feedback Enabled by Materials' Multifunctionalities

Immersive communications rely on smart perception based on diversified and augmented sensing and feedback technologies. However, the increasing of functional components also raises the issue of increased system complexity. Here, we propose a modular soft glove with multimodal sensing and feedback functions by exploring and utilizing the multiple properties of glove materials. With a single design of basic structure, the main functional unit possesses triboelectric-based sensing of static and dynamic contact, vibration, strain, and pneumatic actuation. Additionally, the same unit is also capable of offering pneumatic tactile haptic feedback and electroresistive thermal haptic feedback. Together with a machine learning algorithm, the proposed glove not only performs real-time detection of dexterous hand motion and direct feedback but also realizes intelligent object recognition and augmented feedback, which significantly enhance the communication and perception of more comprehensive information. In general, this glove utilizes a facile designed sensing and feedback device to achieve dual-way and multimodal communication among humans, machines, and the virtual world via smart perceptions.

Engineering Liquid-Vapor Phase Transition for Refreshable Haptic Interfaces

Haptics as a communication medium has been increasingly emphasized across various disciplines. Recent efforts have focused on developing various haptic stimulation technologies; however, most of them suffer from critical drawbacks stemming from their bulk, complexity, large power input, or high cost. Here, we describe a strategy to design portable and affordable refreshable haptic interfaces composed of an array of individually addressable and controllable liquid pouch motor-based haptic units embedded in either rigid or flexible substrates for different application contexts. The pouch motor filled with low boiling fluid, under a controlled manner, expands or contracts by Joule heating or cooling, enabling the haptic pin in contact to be protruded or retracted. Programming the actuation sequence of an array of haptic units enables the haptic interface to apply different stimuli to the skin to convey corresponding information. We finally demonstrate the applications to portable rigid braille displays and flexible epidermal VR devices. This study opens the avenue to the design of ubiquitous refreshable haptic interfaces that is portable, affordable, scalable, and uninjurious.

Development of Electrostatic Microactuators: 5-Year Progress in Modeling, Design, and Applications

The implementation of electrostatic microactuators is one of the most popular technical solutions in the field of micropositioning due to their versatility and variety of possible operation modes and methods. Nevertheless, such uncertainty in existing possibilities creates the problem of choosing suitable methods. This paper provides an effort to classify electrostatic actuators and create a system in the variety of existing devices. Here is overviewed and classified a wide spectrum of electrostatic actuators developed in the last 5 years, including modeling of different designs, and their application in various devices. The paper provides examples of possible implementations, conclusions, and an extensive list of references.

Actuating compact wearable augmented reality devices by multifunctional artificial muscle

An artificial muscle actuator resolves practical engineering problems in compact wearable devices, which are limited to conventional actuators such as electromagnetic actuators. Abstracting the fundamental advantages of an artificial muscle actuator provides a small-scale, high-power actuating system with a sensing capability for developing varifocal augmented reality glasses and naturally fit haptic gloves. Here, we design a shape memory alloy-based lightweight and high-power artificial muscle actuator, the so-called compliant amplified shape memory alloy actuator. Despite its light weight (0.22 g), the actuator has a high power density of 1.7 kW/kg, an actuation strain of 300% under 80 g of external payload. We show how the actuator enables image depth control and an immersive tactile response in the form of augmented reality glasses and two-way communication haptic gloves whose thin form factor and high power density can hardly be achieved by conventional actuators.

Artificial muscle actuators enabled by responsive functional materials like shape memory alloys are promising candidates for compact e-wearable devices. Here, authors demonstrate augmented reality glasses and two-way communication haptic gloves capable of image depth control and immersive tactile response.

From passive to emerging smart silicones

Amassing remarkable properties, silicones are practically indispensable in our everyday life. In most classic applications, they play a passive role in that they cover, seal, insulate, lubricate, water-proof, weather-proof etc. However, silicone science and engineering are highly innovative, seeking to develop new compounds and materials that meet market demands. Thus, the unusual properties of silicones, coupled with chemical group functionalization, has allowed silicones to gradually evolve from passive materials to active ones, meeting the concept of “smart materials”, which are able to respond to external stimuli. In such cases, the intrinsic properties of polysiloxanes are augmented by various chemical modifications aiming to attach reactive or functional groups, and/or by engineering through proper cross-linking pattern or loading with suitable fillers (ceramic, magnetic, highly dielectric or electrically conductive materials, biologically active, etc.), to add new capabilities and develop high value materials. The literature and own data reflecting the state-of-the art in the field of smart silicones, such as thermoplasticity, self-healing ability, surface activity, electromechanical activity and magnetostriction, thermo-, photo-, and piezoresponsivity are reviewed.