Programming 3D curved mesosurfaces using microlattice designs

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.

Achieving symmetric snap-through buckling via designed magnetic actuation

Symmetric snap-through buckling, although both theoretically achievable and practically advantageous, has remained rare in bistable systems, with most studies favoring asymmetric snapping due to its lower energy barrier. Previous observations of symmetric snapping have been limited to high loading rates. In this work, we present a universal strategy to achieve symmetric snapping under quasi-static conditions by designing magnetization (M)-interface patterns that effectively suppress asymmetric modes. A simplified theoretical model demonstrates that this behavior results from the interplay between pitchfork and saddle-node bifurcations, with predictions validated through simulations and experiments using hard magnetic elastomers. Resisting forces generated by multiple M-interfaces counteract asymmetric snapping, enabling distinct symmetric configurations. Extending this approach to higher-order symmetric snapping, we uncover a quasi-linear scaling law between critical fields and snapping order. These findings establish a robust framework for designing snapping systems with enhanced control and predictability, as demonstrated by a mechanical-magnetic snapping switch, paving the way for advanced applications in precision engineering and magnetic-mechanical actuation.

Bionic Microstructure/Nanofiller Heterogeneous Ultradurable Superhydrophobic Surface Based on Metal Additive Manufacturing

Metallic superhydrophobic surfaces often encounter several challenges, including poor durability, limited functionality, and difficulties in application to complex curved structures. Therefore, we propose a novel strategy for surface biomimetic interpenetrating phase composites (S-BIPC). This approach employs laser powder bed fusion (LPBF) technology to create biomimetic microstructures as the primary phase on the Ti6Al4V surface in a single step. Subsequently, functional nanofillers synthesized via the sol-gel method serve as the secondary phase, interpenetrating with the biomimetic microstructures to form a biomimetic heterogeneous superhydrophobic surface (BHS). The interaction among these heterogeneous surface materials endows the BHS with exceptional durability, allowing it to retain superhydrophobicity after at least 5000 cycles of sandpaper abrasion and approximately 200% compressive strain. Furthermore, the BHS exhibits self-cleaning properties, wear resistance, corrosion resistance, anti-icing capabilities, and can be applied to complex curved structures, making the S-BIPC strategy one of the most promising candidates for metallic superhydrophobic surfaces.

Theoretical Model of the Island Effect in Flexible Electronics under Equal Biaxial Stretching

Island-bridge architecture represents a widely used structural design strategy in the field of stretchable inorganic electronics, where flexible serpentine interconnects function as bridges to accommodate most of the deformation, while the islands residing functional devices exhibit minimal deformation. The mismatch of Young's modulus between the elastic substrate and the rigid islands usually leads to stress concentration, which is named the island effect. This phenomenon can significantly increase the risk of interfacial damage, such as debonding and tearing failure near the island. In this work, the mechanical model of the island effect under equal biaxial stretching is developed based on theoretical analysis, simulation, and experimental measurement. The scaling law of the displacement and strain distributions on the substrate surface illustrates that the ratio of the island radius to the substrate length is the main controlling parameter of the island effect, proved by the experimental and numerical results. The criterion distinguishing whether the island effect problem is axisymmetric is derived from this. Further, the deformation field in periodic array structure is predicted based on the theoretical model, demonstrating its potential for application in flexible electronic devices.

Modeling and design of 3D printed hyperelastic lattice metamaterials with bionic S-shaped stress-strain behaviors

Lattice metamaterials made of stiff polymers, ceramics, and metals have been extensively designed to reproduce the mechanical behaviors of biological tissues, holding promising applications in biomedical devices and tissue engineering. However, lattice metamaterials composed of soft materials have been far less explored due to challenges posed by material nonlinearity and large deformations. Here, hyperelastic lattice metamaterials with curved microstructures are fabricated by 3D printing elastomers and are developed to mimic bionic S-shaped stress-strain behaviors. We propose a design framework for 3D printed hyperelastic lattice metamaterials that integrates digital geometry generation, hierarchical mechanics modeling, and validation by finite element (FE) simulations and experiments. The microstructures are modeled through deriving a Timoshenko-type beam theory governed by hyperelastic strain energy potentials. The model is then combined with the deformation and equilibrium analysis considering non-rigid connections between microstructures to predict the mechanical responses of hyperelastic lattice metamaterials. Using the developed design framework, programmable S-shaped stress-strain behaviors and high fracture strains (over 800%) are achieved. We demonstrate S-shaped stress-strain curves that match skeletal and cardiac muscles and highly stretchable lattice sensors for remote controls. This study provides design methods and theoretical guidelines for hyperelastic lattice metamaterials, holding promise for robotic sensors with bionic performance and functionality.

Three-Dimensionally Architected Tactile Electronic Skins

Tactile electronic skins (e-skins) are flexible electronic devices that aim to replicate tactile sensing capabilities of the human skin, while possessing skin-like geometric features and materials properties. Since the human skin is composed of complex 3D constructions, where the various types of mechanoreceptors are distributed in a spatial layout, an important trend of tactile e-skin development involves introduction of 3D device architectures that can replicate certain structural features of human skins. The resulting 3D architected e-skins have demonstrated advantages in the detection of shear forces and the decoupled perception of multiple mechanical stimuli, which are of pivotal importance in many application scenarios. In this perspective, we summarize the main biological prototypes of existing 3D architected e-skins, and focus on the key 3D architectures related to tactile sensing capabilities. Then we highlight the enhanced tactile perception of 3D architected e-skins in terms of the super-resolution tactile sensing and predictions of diverse physical properties and surface features of an object, which allow for a broad spectrum of practical applications, such as object recognition, human-machine interactions, dexterous manipulation, and health monitoring. Finally, we discuss scientific challenges and opportunities for future developments of 3D architected tactile e-skins.

Interactive design modeling of 3D styling combining Bezier curve and Harris corner point detection algorithm

Enhancing the effectiveness and precision of 3D modeling design has become the main focus of current research due to the ongoing development of 3D modeling applications in numerous fields. In this study, an interactive 3D modeling design model based on Bezier curve and Harris corner detection algorithm is constructed. First, the output image is denoised, and then the improved Harris corner detection algorithm is used to obtain the feature points, which ensures the clarity of the image while extracting the key features. Second, a new sketch contour generation method is proposed by combining feature points with Bezier curves. Finally, a combination of Bezier surfaces and Delaunay triangulation is used for surface reconstruction and 3D modeling of the image is rendered. The results revealed that the improved Harris corner point detection algorithm could detect 120 3D image features of a kettle in 3.2s, and detect 50 3D image feature points of a vase in only 0.43s, which had very high detection speed and accuracy. The total time for surface reconstruction of a mechanical part model by combining Bezier surface and Delaunay triangulation was 0.524s, which met the basic user requirements. The teapot image modeling experiment proves the feasibility of the overall design method of the study. Moreover, through the 3D modeling interaction design model designed by the study, the designer can construct the accurate 3D modeling based on the real thing faster, which greatly saves time, improves efficiency, and pushes forward the development of 3D modeling design technology.

Strut-Buckling Transformation Enabling Anomalous Density-Scaling Toughening Law in Ultralight Lattice Metamaterials

Lightweight lattice metamaterials attract considerable attention due to their exceptional and tunable mechanical properties. However, their practical application is ultimately limited by their tolerance to inevitable manufacturing defects. Traditional fracture mechanics of lattice metamaterials are confined to localized tensile failure of a crack-tip strut, overlooking the toughening effect of buckling instability in discrete struts around the crack front. Here, via a combination of additive manufacturing, numerical simulation, and theoretical analysis, this work identifies an anomalous power scaling law of specific fracture energy with relative density, where the scaling exponent shifts to negative values below a critical relative density. This anomalous toughening law stems from crack-tip blunting triggered by delocalized strut-buckling transformation at ultralow densities, which is universal across various lattice metamaterials with varying length scales, crack orientations, node connectivity, and component properties. By strategically harnessing strut buckling mechanisms, exceptionally high specific fracture toughness can be achieved at extremely low relative density, thereby addressing gaps in the material property design space. These findings not only provide physical insights into discrete lattice fracture but also offer design motifs for ultralight, ultra-tough lattice metamaterials.

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.

Long-term adhesion durability revealed through a rheological paradigm

The question of how long an object can adhere to a surface has intrigued scientists for centuries. Traditional studies focus on rapid crack-propagation detachment and account only for short-term adhesion governed by interfacial-viscoelastic dissipation, failing to explain long-term phenomena like sudden detachment after prolonged adherence and to predict corresponding adhesion lifetimes. Here, we investigate the long-term adhesion through a rheological paradigm using both theory and experiment. By considering both the bulk rheology and interfacial viscoelasticity mechanisms, we show that long-term adhesion durability is governed by the competition between them. This understanding leads to accurate lifetime predictions, which we validate through experiments. In addition, our study reveals a previously undocumented, counterintuitive phenomenon unique to long-term adhesion: the expansion of the contact area under tensile forces, in contrast to short-term adhesion in which the contact area always shrinks during detachment. This research fills a critical gap in adhesion physics.

Mechanically Stable and Damage Resistant Freestanding Ultrathin Silver Nanowire Films with Closely Packed Crossed-Lamellar Structure

One-dimensional (1D) functional nanowires are widely used as nanoscale building blocks for assembling advanced nanodevices due to their unique functionalities. However, previous research has mainly focused on nanowire functionality, while neglecting the structural stability and damage resistance of nanowire assemblies, which are critical for the long-term operation of nanodevices. Biomaterials achieve excellent mechanical stability and damage resistance through sophisticated structural design. Here, we successfully prepared a mechanically stabilized monolamella silver nanowire (Ag NW) film, based on a facile bubble-mediated assembly and nondestructive transfer strategy with the assistance of a porous mixed cellulose ester substrate, inspired by the hierarchical structure of biomaterial. Owing to the closely packed arrangement of Ag NWs combined with their weak interfaces, the monolamellar Ag NW film can be transferred to arbitrary substrates without damage. Furthermore, freestanding multilamellar Ag NW films with impressive damage resistance can be obtained from the monolamellar Ag NW film, through the introduction of bioinspired closely packed crossed-lamellar (CPCL) structure. This CPCL structure maximizes intra- and interlamellar interactions among Ag NWs ensuring efficient stress transfer and uniform electron transport, resulting in excellent mechanical durability and stable electrical properties of the multilamellar Ag NW films.

An agile multimodal microrobot with architected passively morphing wheels

Multimodal microrobots are of growing interest due to their capabilities to navigate diverse terrains, with promising applications in inspection, exploration, and biomedicine. Despite remarkable progress, it remains challenging to combine the attributes of excellent maneuverability, low power consumption, and high robustness in a single multimodal microrobot. We propose an architected design of a passively morphing wheel that can be stabilized at distinct geometric configurations, relying on asymmetric bending stiffness of bioinspired tentacle structures. By integrating such wheels with electromagnetic motors and a flexible body, we develop a highly compact, lightweight, multimodal microrobot (length ~32 mm and mass ~4.74 g) with three locomotion gaits. It has high motion speed (~21.2 BL/s), excellent agility (relative centripetal acceleration, ~206.9 BL/s2), low power consumption (cost of transport, ~89), high robustness, and strong terrain adaptabilities. Integration of batteries and a wireless control module enables developments of an untethered microrobot that maintains high motion speed and excellent agility, with capabilities of traveling in hybrid terrains.

Automated discovery of reprogrammable nonlinear dynamic metamaterials

Harnessing the rich nonlinear dynamics of highly deformable materials has the potential to unlock the next generation of functional smart materials and devices. However, unlocking such potential requires effective strategies to spatially engineer material architectures within the nonlinear dynamic regime. Here we introduce an inverse-design framework to discover flexible mechanical metamaterials with a target nonlinear dynamic response. The desired dynamic task is encoded via optimal tuning of the full-scale metamaterial geometry through an inverse-design approach powered by a fully differentiable simulation environment. By deploying such a strategy, mechanical metamaterials are tailored for energy focusing, energy splitting, dynamic protection and nonlinear motion conversion. Furthermore, our design framework can be expanded to automatically discover reprogrammable architectures capable of switching between different dynamic tasks. For instance, we encode two strongly competing tasks-energy focusing and dynamic protection-within a single architecture, using static precompression to switch between these behaviours. The discovered designs are physically realized and experimentally tested, demonstrating the robustness of the engineered tasks. Our approach opens an untapped avenue towards designer materials with tailored robotic-like reprogrammable functionalities.

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.

Damage-free dry transfer method using stress engineering for high-performance flexible two- and three-dimensional electronics

Advanced transfer printing technologies have enabled the fabrication of high-performance flexible and stretchable devices, revolutionizing many research fields including soft electronics, optoelectronics, bioelectronics and energy devices. Despite previous innovations, challenges remain, such as safety concerns due to toxic chemicals, the expensive equipment, film damage during the transfer process and difficulty in high-temperature processing. Thus a new transfer printing process is needed for the commercialization of high-performance soft electronic devices. Here we propose a damage-free dry transfer printing strategy based on stress control of the deposited thin films. First, stress-controlled metal bilayer films are deposited using direct current magnetron sputtering. Subsequently, mechanical bending is applied to facilitate the release of the metal bilayer by increasing the overall stress. Experimental and simulation studies elucidate the stress evolution mechanisms during the processes. By using this method, we successfully transfer metal thin films and high-temperature-treated oxide thin films onto flexible or stretchable substrates, enabling the fabrication of two-dimensional flexible electronic devices and three-dimensional multifunctional devices.

Phase-Change Stamp with Highly Switchable Adhesion and Stiffness for Damage-Free Multiscale Transfer Printing

Transfer printing is a technology widely used in the production of flexible electronics and vertically stacked devices, which involves the transfer of predefined electronic components from a rigid donor substrate to a receiver substrate with a stamp, potentially avoiding the limitations associated with lithographic processes. However, the stamps typically used in transfer printing have several limitations related to unwanted organic solvents, substantial loading, film damage, and inadequate adhesion switching ratios. This study introduces a thermally responsive phase-change stamp for efficient and damage-free transfer printing inspired by the adhesion properties observed during water freezing and ice melting. The stamp employs phase-change composites and simple fabrication protocols, providing robust initial adhesion strength and switchability. The underlying mechanism of switchable adhesion is investigated through experimental and numerical studies. Notably, the stamp eliminates the need for extra preload by spontaneously interlocking with the ink through in situ melting and crystallization. This minimizes ink damage and wrinkle formation during pickup while maintaining strong initial adhesion. During printing, the stamp exhibits a sufficiently weak adhesion state for reliable and consistent release, enabling multiscale, conformal, and damage-free transfer printing, ranging from nano- to wafer-scale. The fabrication of nanoscale short-channel transistors, epidermal electrodes, and human-machine interfaces highlights the potential of this technique in various emerging applications of nanoelectronics, nano optoelectronics, and soft bioelectronics.

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.

Marangoni-driven deterministic formation of softer, hollow microstructures for sensitivity-enhanced tactile system

Microengineering the dielectric layers with three-dimensional microstructures has proven effective in enhancing the sensitivity of flexible pressure sensors. However, the widely employed geometrical designs of solid microstructures exhibit limited sensitivity over a wide range of pressures due to their inherent but undesired structural compressibility. Here, a Marangoni-driven deterministic formation approach is proposed for fabricating hollow microstructures, allowing for greater deformation while retarding structural stiffening during compression. Fluid convective deposition enables solute particles to reassemble in template microstructures, controlling the interior cavity with a void ratio exceeding 90%. The hollow micro-pyramid sensor exhibits a 10-fold sensitivity improvement across wider pressure ranges over the pressure sensor utilizing solid micro-pyramids, and an ultra-low detect limit of 0.21 Pa. With the advantages of facilitation, scalability, and large-area compatibility, such an approach for hollow microstructures can be expanded to other sensor types for superior performance and has considerable potential in robotic tactile and epidermal devices.

A Versatile Synthesis Platform Based on Polymer Cubosomes for a Library of Highly Ordered Nanoporous Metal Oxides Particles

Polymer cubosomes (PCs) have well-defined inverse bicontinuous cubic mesophases formed by amphiphilic block copolymer bilayers. The open hydrophilic channels, large periods, and robust physical properties of PCs are advantageous to many host-guest interactions and yet not fully exploited, especially in the fields of functional nanomaterials. Here, the self-assembly of poly(ethylene oxide)-block-polystyrene block copolymers is systematically investigated and a series of robust PCs is developed via a cosolvent method. Ordered nanoporous metal oxide particles are obtained by selectively filling the hydrophilic channels of PCs via an impregnation strategy, followed by a two-step thermal treatment. Based on this versatile PC platform, the general synthesis of a library of ordered porous particles with different pore structures3 ¯ $\bar{3}$ 3 ¯ $\bar{3}$ , tunable large pore size (18-78 nm), high specific surface areas (up to 123.3 m2 g-1 for WO3) and diverse framework compositions, such as transition and non-transition metal oxides, rare earth chloride oxides, perovskite, pyrochlore, and high-entropy metal oxides is demonstrated. As typical materials obtained via this method, ordered porous WO3 particles have the advantages of open continuous structure and semiconducting properties, thus showing superior gas sensing performances toward hydrogen sulfide.

Machine learning-enabled forward prediction and inverse design of 4D-printed active plates

Shape transformations of active composites (ACs) depend on the spatial distribution of constituent materials. Voxel-level complex material distributions can be encoded by 3D printing, offering enormous freedom for possible shape-change 4D-printed ACs. However, efficiently designing the material distribution to achieve desired 3D shape changes is significantly challenging yet greatly needed. Here, we present an approach that combines machine learning (ML) with both gradient-descent (GD) and evolutionary algorithm (EA) to design AC plates with 3D shape changes. A residual network ML model is developed for the forward shape prediction. A global-subdomain design strategy with ML-GD and ML-EA is then used for the inverse material-distribution design. For a variety of numerically generated target shapes, both ML-GD and ML-EA demonstrate high efficiency. By further combining ML-EA with a normal distance-based loss function, optimized designs are achieved for multiple irregular target shapes. Our approach thus provides a highly efficient tool for the design of 4D-printed active composites.

Skin Comfort Sensation with Mechanical Stimulus from Electronic Skin

The field of electronic skin has received considerable attention due to its extensive potential applications in areas including tactile sensing and health monitoring. With the development of electronic skin devices, electronic skin can be attached to the surface of human skin for long-term health monitoring, which makes comfort an essential factor that cannot be ignored in the design of electronic skin. Therefore, this paper proposes an assessment method for evaluating the comfort of electronic skin based on neurodynamic analysis. The holistic analysis framework encompasses the mechanical model of the skin, the modified Hodgkin-Huxley model for the transduction of stimuli, and the gate control theory for the modulation and perception of pain sensation. The complete process, from mechanical stimulus to the generation of pain perception, is demonstrated. Furthermore, the influence of different factors on pain perception is investigated. Sensation and comfort diagrams are provided to assess the mechanical comfort of electronic skin. The comfort assessment method proposed in this paper provides a theoretical basis when assessing the comfort of electronic skin.

An all-metallic nanovesicle for hydrogen oxidation

Vesicle, a microscopic unit that encloses a volume with an ultrathin wall, is ubiquitous in biomaterials. However, it remains a huge challenge to create its inorganic metal-based artificial counterparts. Here, inspired by the formation of biological vesicles, we proposed a novel biomimetic strategy of curling the ultrathin nanosheets into nanovesicles, which was driven by the interfacial strain. Trapped by the interfacial strain between the initially formed substrate Rh layer and subsequently formed RhRu overlayer, the nanosheet begins to deform in order to release a certain amount of strain. Density functional theory (DFT) calculations reveal that the Ru atoms make the curling of nanosheets more favorable in thermodynamics applications. Owing to the unique vesicular structure, the RhRu nanovesicles/C displays excellent hydrogen oxidation reaction (HOR) activity and stability, which has been proven by both experiments and DFT calculations. Specifically, the HOR mass activity of RhRu nanovesicles/C are 7.52 A mg(Rh+Ru)-1 at an overpotential of 50 mV at the rotating disk electrode (RDE) level; this is 24.19 times that of commercial Pt/C (0.31 mA mgPt-1). Moreover, the hydroxide exchange membrane fuel cell (HEMFC) with RhRu nanovesicles/C displays a peak power density of 1.62 W cm-2 in the H2-O2 condition, much better than that of commercial Pt/C (1.18 W cm-2). This work creates a new biomimetic strategy to synthesize inorganic nanomaterials, paving a pathway for designing catalytic reactors.

Bio-Inspired Dynamically Morphing Microelectronics toward High-Density Energy Applications and Intelligent Biomedical Implants

Choreographing the adaptive shapes of patterned surfaces to exhibit designable mechanical interactions with their environment remains an intricate challenge. Here, a novel category of strain-engineered dynamic-shape materials, empowering diverse multi-dimensional shape modulations that are combined to form fine-grained adaptive microarchitectures is introduced. Using micro-origami tessellation technology, heterogeneous materials are provided with strategic creases featuring stimuli-responsive micro-hinges that morph precisely upon chemical and electrical cues. Freestanding multifaceted foldable packages, auxetic mesosurfaces, and morphable cages are three of the forms demonstrated herein of these complex 4-dimensional (4D) metamaterials. These systems are integrated in dual proof-of-concept bioelectronic demonstrations: a soft foldable supercapacitor enhancing its power density (≈108 mW cm-2), and a bio-adaptive device with a dynamic shape that may enable novel smart-implant technologies. This work demonstrates that intelligent material systems are now ready to support ultra-flexible 4D microelectronics, which can impart autonomy to devices culminating in the tangible realization of microelectronic morphogenesis.

A three-dimensionally architected electronic skin mimicking human mechanosensation

Human skin sensing of mechanical stimuli originates from transduction of mechanoreceptors that converts external forces into electrical signals. Although imitating the spatial distribution of those mechanoreceptors can enable developments of electronic skins capable of decoupled sensing of normal/shear forces and strains, it remains elusive. We report a three-dimensionally (3D) architected electronic skin (denoted as 3DAE-Skin) with force and strain sensing components arranged in a 3D layout that mimics that of Merkel cells and Ruffini endings in human skin. This 3DAE-Skin shows excellent decoupled sensing performances of normal force, shear force, and strain and enables development of a tactile system for simultaneous modulus/curvature measurements of an object through touch. Demonstrations include rapid modulus measurements of fruits, bread, and cake with various shapes and degrees of freshness.

Transient charge-driven 3D conformal printing via pulsed-plasma impingement

Seamless integration of microstructures and circuits on three-dimensional (3D) complex surfaces is of significance and is catalyzing the emergence of many innovative 3D curvy electronic devices. However, patterning fine features on arbitrary 3D targets remains challenging. Here, we propose a facile charge-driven electrohydrodynamic 3D microprinting technique that allows micron- and even submicron-scale patterning of functional inks on a couple of 3D-shaped dielectrics via an atmospheric-pressure cold plasma jet. Relying on the transient charging of exposed sites arising from the weakly ionized gas jet, the specified charge is programmably deposited onto the surface as a virtual electrode with spatial and time spans of ~mm in diameter and ~μs in duration to generate a localized electric field accordantly. Therefore, inks with a wide range of viscosities can be directly drawn out from micro-orifices and deposited on both two-dimensional (2D) planar and 3D curved surfaces with a curvature radius down to ~1 mm and even on the inner wall of narrow cavities via localized electrostatic attraction, exhibiting a printing resolution of ~450 nm. In addition, several conformal electronic devices were successfully printed on 3D dielectric objects. Self-aligned 3D microprinting, with stacking layers up to 1400, is also achieved due to the electrified surfaces. This microplasma-induced printing technique exhibits great advantages such as ultrahigh resolution, excellent compatibility of inks and substrates, antigravity droplet dispersion, and omnidirectional printing on 3D freeform surfaces. It could provide a promising solution for intimately fabricating electronic devices on arbitrary 3D surfaces.

A mechanically robust and facile shape morphing using tensile-induced buckling

Inspired by the adaptive mechanisms observed in biological organisms, shape-morphing soft structures have emerged as promising platforms for many applications. In this study, we present a shape-morphing strategy to overcome existing limitations of the intricate fabrication process and the lack of mechanical robustness against mechanical perturbations. Our method uses tensile-induced buckling, achieved by attaching restraining strips to a stretchable substrate. When the substrate is stretched, the stiffness mismatch between the restraining strips and the substrate, and the Poisson's effect on the substrate cause the restraining strips to buckle, thereby transforming initially flat shapes into intricate three-dimensional (3D) configurations. Guided by an inverse design method, we demonstrate the capability to achieve complicated and diverse 3D shapes. Leveraging shape morphing, we further develop soft grippers exhibiting outstanding universality, high grasping efficiencies, and exceptional durability. Our proposed shape-morphing strategy is scalable and material-independent, holding notable potential for applications in soft robotics, haptics, and biomedical devices.

AI-Driven Sensing Technology: Review

Machine learning and deep learning technologies are rapidly advancing the capabilities of sensing technologies, bringing about significant improvements in accuracy, sensitivity, and adaptability. These advancements are making a notable impact across a broad spectrum of fields, including industrial automation, robotics, biomedical engineering, and civil infrastructure monitoring. The core of this transformative shift lies in the integration of artificial intelligence (AI) with sensor technology, focusing on the development of efficient algorithms that drive both device performance enhancements and novel applications in various biomedical and engineering fields. This review delves into the fusion of ML/DL algorithms with sensor technologies, shedding light on their profound impact on sensor design, calibration and compensation, object recognition, and behavior prediction. Through a series of exemplary applications, the review showcases the potential of AI algorithms to significantly upgrade sensor functionalities and widen their application range. Moreover, it addresses the challenges encountered in exploiting these technologies for sensing applications and offers insights into future trends and potential advancements.

Somatosensory Electro-Thermal Actuator through the Laser-Induced Graphene Technology

The biological system realizes the unity of action and perception through the muscle tissue and nervous system. Correspondingly, artificial soft actuators realize the unity of sensing and actuating functions in a single functional material, which will have tremendous potential for developing intelligent and bionic soft robotics. This paper reports the design of a laser-induced graphene (LIG) electrothermal actuator with self-sensing capability. LIG, a functional material formed by a one-step direct-write lasing procedure under ambient air, is used as electrothermal conversion materials and piezoresistive sensing materials. By transferring LIG to a flexible silicone substrate, the design ability of the LIG-based actuator unit is enriched, along with an effectively improved sensing sensitivity. Through the integration of different types of well-designed LIG-based actuator units, the transformations from multidimensional precursors to 2D and 3D structures are realized. According to the piezoresistive effect of the LIG units during the deformation process, the visual synchronous deformation state feedback of the LIG-based actuator is proposed. The multimodal crawling soft robotics and the switchable electromagnetic shielding cloak serve as the demonstrations of the self-sensing LIG-based actuator, showing the advantage of the design in remote control of the soft robot without relying on the assistance of visual devices.

Porifera-Inspired Lightweight, Thin, Wrinkle-Resistance, and Multifunctional MXene Foam

Transition metal carbides/nitrides (MXenes) demonstrate a massive potential in constructing lightweight, multifunctional wearable electromagnetic interference (EMI) shields for application in various fields. Nevertheless, it remains challenging to develop a facile, scalable approach to prepare the MXene-based macrostructures characterized by low density, low thickness, high mechanical flexibility, and high EMI SE at the same time. Herein, the ultrathin MXene/reduced graphene oxide (rGO)/Ag foams with a porifera-inspired hierarchically porous microstructure are prepared by combining Zn2+ diffusion induction and hard template methods. The hierarchical porosity, which includes a mesoporous skeleton and a microporous MXene network within the skeleton, not only exerts a regulatory effect on stress distribution during compression, making the foams rubber-like resistant to wrinkling but also provides more channels for multiple reflections of electromagnetic waves. Due to the interaction between Ag nanosheets, MXene/rGO, and porous structure, it is possible to produce an outstanding EMI shielding performance with the specific surface shielding effectiveness reaching 109152.4 dB cm2 g-1. Furthermore, the foams exhibit multifunctionalities, such as transverse Joule heating, longitudinal heat insulation, self-cleaning, fire resistance, and motion detection. These discoveries open up a novel pathway for the development of lightweight MXene-based materials with considerable application potential in wearable electromagnetic anti-interference devices.

Do medical devices contribute to sustainability? The role of innovative polymers and device design

Sustainability of a medical device has not yet become a major issue in public discussions compared to other topics with impact to material performance, clinical application, production economy and environmental pollution. Due to their unique properties, polymers (plastics) allow for multiple, flexible applications in medical device technology. Polymers are part of the majority of disposable and single use medical device and contribute with 3% to the worldwide production of plastics. The global medical polymer market size was valued 19.9 billion US-$ in 2022 and its value projection for 2023 is expected to reach 43.03 billion US-$ Here, a wider concept of related sustainability is introduced for medical devices and their polymer components. A close look on medical device specification reveals that additional properties are required to provide sustainability, such as biodegradability, quality by device design (QbD), as well as an inbuild performance service for patients, healthcare professionals and healthcare providers. The increasing global numbers for chronic and non-communicable diseases require a huge demand for single use medical devices. A careful look at polymer specification and its performance properties is needed, including possible chemical modifications and degradation processes during waste disposal. Bioengineers in charge of design and production of medical devices will only be successful when they apply a holistic and interdisciplinary approach to medical device sustainability.

A three-dimensional liquid diode for soft, integrated permeable electronics

Wearable electronics with great breathability enable a comfortable wearing experience and facilitate continuous biosignal monitoring over extended periods1-3. However, current research on permeable electronics is predominantly at the stage of electrode and substrate development, which is far behind practical applications with comprehensive integration with diverse electronic components (for example, circuitry, electronics, encapsulation)4-8. Achieving permeability and multifunctionality in a singular, integrated wearable electronic system remains a formidable challenge. Here we present a general strategy for integrated moisture-permeable wearable electronics based on three-dimensional liquid diode (3D LD) configurations. By constructing spatially heterogeneous wettability, the 3D LD unidirectionally self-pumps the sweat from the skin to the outlet at a maximum flow rate of 11.6 ml cm-2 min-1, 4,000 times greater than the physiological sweat rate during exercise, presenting exceptional skin-friendliness, user comfort and stable signal-reading behaviour even under sweating conditions. A detachable design incorporating a replaceable vapour/sweat-discharging substrate enables the reuse of soft circuitry/electronics, increasing its sustainability and cost-effectiveness. We demonstrated this fundamental technology in both advanced skin-integrated electronics and textile-integrated electronics, highlighting its potential for scalable, user-friendly wearable devices.

Fully Transient 3D Origami Paper-Based Ammonia Gas Sensor Obtained by Facile MXene Spray Coating

Developing high-performance chemiresistive gas sensors with mechanical compliance for environmental or health-related biomarker monitoring has recently drawn increasing research attention. Among them, two-dimensional MXene materials hold great potential for room-temperature hazardous gas (e.g., NH3) monitoring regardless of the complicated fabrication process, insufficient 2D/3D flexibilities, and poor environmental sustainability. Herein, a Ti3C2Tx MXene/gelatin ink was developed for patterning electrodes through a facile spray coating. Particularly, the patterned Ti3C2Tx-based coating exhibited good adhesion on the paper substrate against repeated peeling-off and excellent mechanical flexibility against 1000 cyclic stretching. The porous morphology of the coating facilitated the NH3 sensing ability. As a result, the 2D kirigami-shaped NH3 sensor exhibited a good response of 7% to 50 ppm of NH3 with detectable concentrations ranging from 5-500 ppm, decent selectivity over interferences, etc., which could be well-maintained even at 50% stretched state. In addition, with the help of mechanically guided compressive buckling, 3D mesostructured MXene origamis could be obtained, holding promise for detecting the coming direction and height distribution of hazardous gas, e.g., the NH3. More importantly, the as-fabricated MXene/gelatin origami paper could be fully degraded in PBS/H2O2/cellulase solution within 19 days, demonstrating its potential as a high-performance, shape morphable, and environmentally friendly wearable gas sensor.

Directional actuation and phase transition-like behavior in anisotropic networks of responsive microfibers

Two-dimensional shape-morphing networks are common in biological systems and have garnered attention due to their nontrivial physical properties that emanate from their cellular nature. Here, we present the fabrication and characterization of anisotropic shape-morphing networks composed of thermoresponsive polymeric microfibers. By strategically positioning fibers with varying responses, we construct networks that exhibit directional actuation. The individual segments within the network display either a linear extension or buckling upon swelling, depending on their radius and length, and the transition between these morphing behaviors resembles Landau's second-order phase transition. The microscale variations in morphing behaviors are translated into observable macroscopic effects, wherein regions undergoing linear expansion retain their shape upon swelling, whereas buckled regions demonstrate negative compressibility and shrink. Manipulating the macroscale morphing by adjusting the properties of the fibrous microsegments offers a means to modulate and program morphing with mesoscale precision and unlocks novel opportunities for developing programmable microscale soft robotics and actuators.

Functional bio-inspired hybrid fliers with separated ring and leading edge vortices

Recent advances in passive flying systems inspired by wind-dispersed seeds contribute to increasing interest in their use for remote sensing applications across large spatial domains in the Lagrangian frame of reference. These concepts create possibilities for developing and studying structures with performance characteristics and operating mechanisms that lie beyond those found in nature. Here, we demonstrate a hybrid flier system, fabricated through a process of controlled buckling, to yield unusual geometries optimized for flight. Specifically, these constructs simultaneously exploit distinct fluid phenomena, including separated vortex rings from features that resemble those of dandelion seeds and the leading-edge vortices derived from behaviors of maple seeds. Advanced experimental measurements and computational simulations of the aerodynamics and induced flow physics of these hybrid fliers establish a concise, scalable analytical framework for understanding their flight mechanisms. Demonstrations with functional payloads in various forms, including bioresorbable, colorimetric, gas-sensing, and light-emitting platforms, illustrate examples with diverse capabilities in sensing and tracking.

Bioinspired 3D flexible devices and functional systems

Flexible devices and functional systems with elaborated three-dimensional (3D) architectures can endow better mechanical/electrical performances, more design freedom, and unique functionalities, when compared to their two-dimensional (2D) counterparts. Such 3D flexible devices/systems are rapidly evolving in three primary directions, including the miniaturization, the increasingly merged physical/artificial intelligence and the enhanced adaptability and capabilities of heterogeneous integration. Intractable challenges exist in this emerging research area, such as relatively poor controllability in the locomotion of soft robotic systems, mismatch of bioelectronic interfaces, and signal coupling in multi-parameter sensing. By virtue of long-time-optimized materials, structures and processes, natural organisms provide rich sources of inspiration to address these challenges, enabling the design and manufacture of many bioinspired 3D flexible devices/systems. In this Review, we focus on bioinspired 3D flexible devices and functional systems, and summarize their representative design concepts, manufacturing methods, principles of structure-function relationship and broad-ranging applications. Discussions on existing challenges, potential solutions and future opportunities are also provided to usher in further research efforts toward realizing bioinspired 3D flexible devices/systems with precisely programmed shapes, enhanced mechanical/electrical performances, and high-level physical/artificial intelligence.

Iontronic Dynamic Sensor with Broad Bandwidth and Flat Frequency Response Using Controlled Preloading Strategy

Rapid advancements in human-machine interaction and voice biometrics impose desirability on soft mechanical sensors for sensing complex dynamic signals. However, existing soft mechanical sensors mainly concern quasi-static signals such as pressure and pulsation for health monitoring, limiting their applications in emerging wearable electronics. Here, we propose a hydrogel-based soft mechanical sensor that enables recording a wide range of dynamic signals relevant to humans by combining a preloading design strategy and iontronic sensing mechanism. The proposed sensor offers a two-orders-of-magnitude larger working bandwidth (up to 1000 Hz) than most of the reported soft mechanical sensors and meanwhile provides a high sensitivity (-23 dB) that surpasses the common commercial microphone. The amplitude-frequency characteristic of the proposed sensor can be precisely tuned to meet the desired requirement by adjusting the preloads and the parameters of the microstructured hydrogel. The sensor is capable of recording instrumental sounds with high fidelity from simple pure tones to melodic songs. Demonstration of a skin-mountable sensor used for human-voice-based remote control of a toy car shows great potential for applications in the voice user interface of human-machine interactions.

Rational Design of Flexible Mechanical Force Sensors for Healthcare and Diagnosis

Over the past decade, there has been a significant surge in interest in flexible mechanical force sensing devices and systems. Tremendous efforts have been devoted to the development of flexible mechanical force sensors for daily healthcare and medical diagnosis, driven by the increasing demand for wearable/portable devices in long-term healthcare and precision medicine. In this review, we summarize recent advances in diverse categories of flexible mechanical force sensors, covering piezoresistive, capacitive, piezoelectric, triboelectric, magnetoelastic, and other force sensors. This review focuses on their working principles, design strategies and applications in healthcare and diagnosis, with an emphasis on the interplay among the sensor architecture, performance, and application scenario. Finally, we provide perspectives on the remaining challenges and opportunities in this field, with particular discussions on problem-driven force sensor designs, as well as developments of novel sensor architectures and intelligent mechanical force sensing systems.

3D Chiral Energy-Absorbing Structures with a High Deformation Recovery Ratio Fabricated via Selective Laser Melting of the NiTi Alloy

Excellent energy-absorbing structures have been highly sought after in engineering applications to improve devices and personal safety. The ideal energy absorption mechanism should exhibit characteristics such as lightweight, high energy absorption capacity, and efficient reusability. To address this demand, a novel three-dimensional (3D) chiral lattice structure with compression-twist coupling deformation is fabricated by combining the left and right chiral units. The proposed structure was fabricated in NiTi shape memory alloys (SMAs) by using laser powder bed fusion technology. The compression experiment result indicates that the shape recovery ratio is as high as 94% even when the compression strain is over 80%. Additionally, the platform strain reaches as high as 66%, offering high-level specific energy absorption, i.e., 213.02 J/g. The obtained results are of great significance for basic research and engineering applications of energy-absorbing structures with high deformation recovery ratios.

Application and Development of EEG Acquisition and Feedback Technology: A Review

This review focuses on electroencephalogram (EEG) acquisition and feedback technology and its core elements, including the composition and principles of the acquisition devices, a wide range of applications, and commonly used EEG signal classification algorithms. First, we describe the construction of EEG acquisition and feedback devices encompassing EEG electrodes, signal processing, and control and feedback systems, which collaborate to measure faint EEG signals from the scalp, convert them into interpretable data, and accomplish practical applications using control feedback systems. Subsequently, we examine the diverse applications of EEG acquisition and feedback across various domains. In the medical field, EEG signals are employed for epilepsy diagnosis, brain injury monitoring, and sleep disorder research. EEG acquisition has revealed associations between brain functionality, cognition, and emotions, providing essential insights for psychologists and neuroscientists. Brain-computer interface technology utilizes EEG signals for human-computer interaction, driving innovation in the medical, engineering, and rehabilitation domains. Finally, we introduce commonly used EEG signal classification algorithms. These classification tasks can identify different cognitive states, emotional states, brain disorders, and brain-computer interface control and promote further development and application of EEG technology. In conclusion, EEG acquisition technology can deepen the understanding of EEG signals while simultaneously promoting developments across multiple domains, such as medicine, science, and engineering.

A 4D-Printing Inverse Design Strategy for Micromachines with Customized Shape-Morphing

An active heterostructure with smart-response material used as "muscle" and inactive material as "skeleton" can deform over time to respond to external stimuli. 4D printing integrated with two-photon polymerization technology and smart material allows the material or characteristic distribution of active heterostructures to be defined directly at the microscale, providing a huge programmable space. However, the high degree of design freedom and the microscale pose a challenge to the construction of micromachines with customized shape morphing. Here, a reverse design strategy based on multi-material stepwise 4D printing is proposed to guide the structural design of biomimetic micromachines. Inspired by the piecewise constant curvature model of soft robot, a reverse design algorithm based on the Timoshenko model is developed. The algorithm can approximate 2D features to a constant-curvature model and determine an acceptable material distribution within the explored printing range. Three Chinese "Long" (Chinese dragon heralds of good fortune) designed by the strategy can deform to the customized shape. In addition, a microcrawler printed using this method can imitate a real inchworm gait. These results demonstrate that this method can be an efficient tool for the action or shape design of bionic soft microrobots or micromachines with predetermined functions.

Mechanically-Guided 3D Assembly for Architected Flexible Electronics

Architected flexible electronic devices with rationally designed 3D geometries have found essential applications in biology, medicine, therapeutics, sensing/imaging, energy, robotics, and daily healthcare. Mechanically-guided 3D assembly methods, exploiting mechanics principles of materials and structures to transform planar electronic devices fabricated using mature semiconductor techniques into 3D architected ones, are promising routes to such architected flexible electronic devices. Here, we comprehensively review mechanically-guided 3D assembly methods for architected flexible electronics. Mainstream methods of mechanically-guided 3D assembly are classified and discussed on the basis of their fundamental deformation modes (i.e., rolling, folding, curving, and buckling). Diverse 3D interconnects and device forms are then summarized, which correspond to the two key components of an architected flexible electronic device. Afterward, structure-induced functionalities are highlighted to provide guidelines for function-driven structural designs of flexible electronics, followed by a collective summary of their resulting applications. Finally, conclusions and outlooks are given, covering routes to achieve extreme deformations and dimensions, inverse design methods, and encapsulation strategies of architected 3D flexible electronics, as well as perspectives on future applications.

Mechanical metamaterials and beyond

Mechanical metamaterials enable the creation of structural materials with unprecedented mechanical properties. However, thus far, research on mechanical metamaterials has focused on passive mechanical metamaterials and the tunability of their mechanical properties. Deep integration of multifunctionality, sensing, electrical actuation, information processing, and advancing data-driven designs are grand challenges in the mechanical metamaterials community that could lead to truly intelligent mechanical metamaterials. In this perspective, we provide an overview of mechanical metamaterials within and beyond their classical mechanical functionalities. We discuss various aspects of data-driven approaches for inverse design and optimization of multifunctional mechanical metamaterials. Our aim is to provide new roadmaps for design and discovery of next-generation active and responsive mechanical metamaterials that can interact with the surrounding environment and adapt to various conditions while inheriting all outstanding mechanical features of classical mechanical metamaterials. Next, we deliberate the emerging mechanical metamaterials with specific functionalities to design informative and scientific intelligent devices. We highlight open challenges ahead of mechanical metamaterial systems at the component and integration levels and their transition into the domain of application beyond their mechanical capabilities.

Flexible Impact-Resistant Composites with Bioinspired Three-Dimensional Solid-Liquid Lattice Designs

The ubiquitous solid-liquid systems in nature usually present an interesting mechanical property, the rate-dependent stiffness, which could be exploited for impact protection in flexible systems. Herein, a typical natural system, the durian peel, has been systematically characterized and studied, showing a solid-liquid dual-phase cellular structure. A bioinspired design of flexible impact-resistant composites is then proposed by combining 3D lattices and shear thickening fluids. The resulting dual-phase composites offer, simultaneously, low moduli (e.g., 71.9 kPa, lower than those of many reported soft composites) under quasi-static conditions and excellent energy absorption (e.g., 425.4 kJ/m³, which is close to those of metallic and glass-based lattices) upon dynamic impact. Numerical simulations based on finite element analyses were carried out to understand the enhanced buffering of the developed composites, unveiling a lattice-guided fluid-structure interaction mechanism. Such biomimetic lattice-based flexible impact-resistant composites hold promising potential for the development of next-generation flexible protection systems that can be used in wearable electronics and robotic systems.