Blooming Knit Flowers: Loop-Linked Soft Morphing Structures for Soft Robotics

Fully autonomous water monitoring by plant-inspired robots

Developing countries struggle with water quality management owing to poor infrastructure, limited expertise, and financial constraints. Traditional water testing, relying on periodic site visits and manual sampling, is impractical for continuous wide-area monitoring and fails to detect sudden heavy metal contamination. To address this, plant-inspired robots capable of fully autonomous water quality monitoring are proposed. Constructed from paper, the robot absorbs surrounding water through its roots. This paper robot is controlled by paper-based microfluidic logic that sends absorbed water to petal-shaped actuators only when the water is polluted by heavy metals. This triggers the actuators to swell and bend like a blooming flower, visually signaling contamination to local residents. In tests with copper-contaminated water, the robotic flower's diameter increased from 4.69 cm to 14.89 cm, a more than threefold expansion (217.25 %). This significant blooming movement serves as a highly visible and easily recognizable indicator of water pollution, even for the public. Furthermore, the paper robot can be mass-produced at a low cost (∼$0.2 per unit) and deployed over large areas. Once installed, the paper robot operates autonomously using surrounding water as a power source, eliminating the need for external electrical infrastructure and expert intervention. Therefore, this autonomous robot offers a new approach to water quality monitoring suitable for resource-limited environments, such as Sub-Saharan Africa.

Knitting Elastic Conductive Fibers of MXene/Natural Rubber for Multifunctional Wearable Sensors

Wearable electronic sensors have recently attracted tremendous attention in applications such as personal health monitoring, human movement detection, and sensory skins as they offer a promising alternative to counterparts made from traditional metallic conductors and bulky metallic conductors. However, the real-world use of most wearable sensors is often hindered by their limited stretchability and sensitivity, and ultimately, their difficulty to integrate into textiles. To overcome these limitations, wearable sensors can incorporate flexible conductive fibers as electrically active components. In this study, we adopt a scalable wet-spinning approach to directly produce flexible and conductive fibers from aqueous mixtures of Ti3C2Tx MXene and natural rubber (NR). The electrical conductivity and stretchability of these fibers were tuned by varying their MXene loading, enabling knittability into textiles for wearable sensors. As individual filaments, these MXene/NR fibers exhibit suitable conductivity dependence on strain variations, making them ideal for motivating sensors. Meanwhile, textiles from knitted MXene/NR fibers demonstrate great stability as capacitive touch sensors. Collectively, we believe that these elastic and conductive MXene/NR-based fibers and textiles are promising candidates for wearable sensors and smart textiles.

Knittable Electrochemical Yarn Muscle for Morphing Textiles

Morphing textiles, crafted using electrochemical artificial muscle yarns, boast features such as adaptive structural flexibility, programmable control, low operating voltage, and minimal thermal effect. However, the progression of these textiles is still impeded by the challenges in the continuous production of these yarn muscles and the necessity for proper structure designs that bypass operation in extensive electrolyte environments. Herein, a meters-long sheath-core structured carbon nanotube (CNT)/nylon composite yarn muscle is continuously prepared. The nylon core not only reduces the consumption of CNTs but also amplifies the surface area for interaction between the CNT yarn and the electrolyte, leading to an enhanced effective actuation volume. When driven electrochemically, the CNT@nylon yarn muscle demonstrates a maximum contractile stroke of 26.4%, a maximum contractile rate of 15.8% s-1, and a maximum power density of 0.37 W g-1, surpassing pure CNT yarn muscles by 1.59, 1.82, and 5.5 times, respectively. By knitting the electrochemical CNT@nylon artificial muscle yarns into a soft fabric that serves as both a soft scaffold and an electrolyte container, we achieved a morphing textile is achieved. This textile can perform programmable multiple motion modes in air such as contraction and sectional bending.

Programming mechanics in knitted materials, stitch by stitch

Knitting turns yarn, a 1D material, into a 2D fabric that is flexible, durable, and can be patterned to adopt a wide range of 3D geometries. Like other mechanical metamaterials, the elasticity of knitted fabrics is an emergent property of the local stitch topology and pattern that cannot solely be attributed to the yarn itself. Thus, knitting can be viewed as an additive manufacturing technique that allows for stitch-by-stitch programming of elastic properties and has applications in many fields ranging from soft robotics and wearable electronics to engineered tissue and architected materials. However, predicting these mechanical properties based on the stitch type remains elusive. Here we untangle the relationship between changes in stitch topology and emergent elasticity in several types of knitted fabrics. We combine experiment and simulation to construct a constitutive model for the nonlinear bulk response of these fabrics. This model serves as a basis for composite fabrics with bespoke mechanical properties, which crucially do not depend on the constituent yarn.

Self-Locking Pneumatic Actuators Formed from Origami Shape-Morphing Sheets

The art of origami has gained traction in various fields such as architecture, the aerospace industry, and soft robotics, owing to the exceptional versatility of flat sheets to exhibit complex shape transformations. Despite the promise that origami robots hold, their use in high-capacity environments has been limited due to the lack of rigidity. This article introduces novel, origami-inspired, self-locking pneumatic modular actuators (SPMAs), enabling them to operate in such environments. Our innovative approach is based on origami patterns that allow for various types of shape morphing, including linear and rotational motion. We have significantly enhanced the stiffness of the actuators by embedding magnets in composite sheets, thus facilitating their application in real-world scenarios. In addition, the embedded self-adjustable valves facilitate the control of sequential origami actuations, making it possible to simplify the pneumatic system for actuating multimodules. With just one actuation source and one solenoid valve, the valves enable efficient control of our SPMAs. The SPMAs can control robotic arms operating in confined spaces, and the entire system can be modularized to accomplish various tasks. Our results demonstrate the potential of origami-inspired designs to achieve more efficient and reliable robotic systems, thus opening up new avenues for the development of robotic systems for various applications.

Encoded sewing soft textile robots

Incorporating soft actuation with soft yet durable textiles could effectively endow the latter with active and flexible shape morphing and motion like mollusks and plants. However, creating highly programmable and customizable soft robots based on textiles faces a longstanding design and manufacturing challenge. Here, we report a methodology of encoded sewing constraints for efficiently constructing three-dimensional (3D) soft textile robots through a simple 2D sewing process. By encoding heterogeneous stretching properties into three spatial seams of the sewed 3D textile shells, nonlinear inflation of the inner bladder can be guided to follow the predefined spatial shape and actuation sequence, for example, tendril-like shape morphing, tentacle-like sequential manipulation, and bioinspired locomotion only controlled by single pressure source. Such flexible, efficient, scalable, and low-cost design and formation methodology will accelerate the development and iteration of soft robots and also open up more opportunities for safe human-robot interactions, tailored wearable devices, and health care.

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.

Design and Evaluation of Smart Textile Actuator with Chain Structure

Textiles composed of fibers can have their mechanical properties adjusted by changing the arrangement of the fibers, such as strength and flexibility. Particularly, in the case of smart textiles incorporating active materials, various deformations could be created based on fiber patterns that determine the directivity of active materials. In this study, we design a smart fiber-based textile actuator with a chain structure and evaluate its actuation characteristics. Smart fiber composed of shape memory alloy (SMA) generates deformation when the electric current is applied, causing the phase transformation of SMA. We fabricated the smart chain column and evaluated its actuating mechanism based on the size of the chain and the number of rows. In addition, a crochet textile actuator was designed using interlooping smart chains and developed into a soft gripper that can grab objects. With experimental verifications, this study provides an investigation of the relationship between the chain actuator's deformation, actuating force, actuator temperature, and strain. The results of this study are expected to be relevant to textile applications, wearable devices, and other technical fields that require coordination with the human body. Additionally, it is expected that it can be utilized to configure a system capable of flexible operation by combining rigid elements such as batteries and sensors with textiles.

Shape Memory Alloy (SMA) Actuators: The Role of Material, Form, and Scaling Effects

Shape memory alloys (SMAs) are smart materials that are widely used to create intelligent devices because of their high energy density, actuation strain, and biocompatibility characteristics. Given their unique properties, SMAs are found to have significant potential for implementation in many emerging applications in mobile robots, robotic hands, wearable devices, aerospace/automotive components, and biomedical devices. Here, the state-of-the-art of thermal and magnetic SMA actuators in terms of their constituent materials, form, and scaling effects are summarized, including their surface treatments and functionalities. The motion performance of various SMA architectures (wires, springs, smart soft composites, and knitted/woven actuators) is also analyzed. Based on the assessment, current challenges of SMAs that need to be addressed for their practical application are emphasized. Finally, how to advance SMAs by synergistically considering the effects of material, form, and scale is suggested.

Programmable spatial deformation by controllable off-center freestanding 4D printing of continuous fiber reinforced liquid crystal elastomer composites

Owing to their high deformation ability, 4D printed structures have various applications in origami structures, soft robotics and deployable mechanisms. As a material with programmable molecular chain orientation, liquid crystal elastomer is expected to produce the freestanding, bearable and deformable three-dimensional structure. However, majority of the existing 4D printing methods for liquid crystal elastomers can only fabricate planar structures, which limits their deformation designability and bearing capacity. Here we propose a direct ink writing based 4D printing method for freestanding continuous fiber reinforced composites. Continuous fibers can support freestanding structures during the printing process and improve the mechanical property and deformation ability of 4D printed structures. In this paper, the integration of 4D printed structures with fully impregnated composite interfaces, programmable deformation ability and high bearing capacity are realized by adjusting the off-center distribution of the fibers, and the printed liquid crystal composite can carry a load of up to 2805 times its own weight and achieve a bending deformation curvature of 0.33 mm^-1 at 150 °C. This research is expected to open new avenues for creating soft robotics, mechanical metamaterials and artificial muscles.

A Shape Memory Alloy-Based Soft Actuator Mimicking an Elephant's Trunk

Soft actuators that execute diverse motions have recently been proposed to improve the usability of soft robots. Nature-inspired actuators, in particular, are emerging as a means of accomplishing efficient motions based on the flexibility of natural creatures. In this research, we present an actuator capable of executing multi-degree-of-freedom motions that mimics the movement of an elephant's trunk. Shape memory alloys (SMAs) that actively react to external stimuli were integrated into actuators constructed of soft polymers to imitate the flexible body and muscles of an elephant's trunk. The amount of electrical current provided to each SMA was adjusted for each channel to achieve the curving motion of the elephant's trunk, and the deformation characteristics were observed by varying the quantity of current supplied to each SMA. It was feasible to stably lift and lower a cup filled with water by using the operation of wrapping and lifting objects, as well as effectively performing the lifting task of surrounding household items of varying weights and forms. The designed actuator is a soft gripper that incorporates a flexible polymer and an SMA to imitate the flexible and efficient gripping action of an elephant trunk, and its fundamental technology is expected to be used as a safety-enhancing gripper that requires environmental adaptation.

Origami and Kirigami Structure for Impact Energy Absorption: Its Application to Drone Guards

As the use of drones grows, so too does the demand for physical protection against drone damage resulting from collisions and falls. In addition, as the flight environment becomes more complicated, a shock absorption system is required, in which the protective structure can be deformed based on the circumstances. Here, we present an origami- and kirigami-based structure that provides protection from various directions. This research adds a deformation capacity to existing fixed-shape guards; by using shape memory alloys, the diameter and height of the protective structure are controlled. We present three protective modes (1: large diameter/low height; 2: small diameter/large height; and 3: lotus shaped) that mitigate drone falls and side collisions. From the result of the drop impact test, mode 2 showed a 78.2% reduction in the maximum impact force at side impact. We incorporated kirigami patterns into the origami structures in order to investigate the aerodynamic effects of the hollow patterns. Airflow experiments yielded a macro understanding of flow-through behaviors on each kirigami pattern. In the wind speed experiment, the change in airflow velocity induced by the penetration of the kirigami pattern was measured, and in the force measurement experiment, the air force applied to the structure was determined.

Shape Memory Alloys in Textile Platform: Smart Textile-Composite Actuator and Its Application to Soft Grippers

In recent years, many researchers have aimed to construct robotic soft grippers that can handle fragile or unusually shaped objects without causing damage. This study proposes a smart textile-composite actuator and its application to a soft robotic gripper. An active fiber and an inactive fiber are combined together using knitting techniques to manufacture a textile actuator. The active fiber is a shape memory alloy (SMA) that is wire-wrapped with conventional fibers, and the inactive fiber is a knitting yarn. A knitted textile structure is flexible, with an excellent structure retention ability and high compliance, which is suitable for developing soft grippers. A driving source of the actuator is the SMA wire, which deforms under heating due to the shape memory effect. Through experiments, the course-to-wale ratio, the number of bundling SMA wires, and the driving current value needed to achieve the maximum deformation of the actuator were investigated. Three actuators were stitched together to make up each finger of the gripper, and layer placement research was completed to find the fingers' suitable bending angle for object grasping. Finally, the gripping performance was evaluated through a test of grasping various object shapes, which demonstrated that the gripper could successfully lift flat/spherical/uniquely shaped objects.

Radio Frequency Heating of Washable Conductive Textiles for Bacteria and Virus Inactivation

The ongoing COVID-19 pandemic has increased the use of single-use medical fabrics such as surgical masks, respirators, and other personal protective equipment (PPE), which have faced worldwide supply chain shortages. Reusable PPE is desirable in light of such shortages; however, the use of reusable PPE is largely restricted by the difficulty of rapid sterilization. In this work, we demonstrate successful bacterial and viral inactivation through remote and rapid radio frequency (RF) heating of conductive textiles. The RF heating behavior of conductive polymer-coated fabrics was measured for several different fabrics and coating compositions. Next, to determine the robustness and repeatability of this heating response, we investigated the textile's RF heating response after multiple detergent washes. Finally, we show a rapid reduction of bacteria and virus by RF heating our conductive fabric. 99.9% of methicillin-resistant Staphylococcus aureus (MRSA) was removed from our conductive fabrics after only 10 min of RF heating; human cytomegalovirus (HCMV) was completely sterilized after 5 min of RF heating. These results demonstrate that RF heating conductive polymer-coated fabrics offer new opportunities for applications of conductive textiles in the medical and/or electronic fields.

Design and development of non-magnetic hierarchical actuator powered by shape memory alloy based bipennate muscle

Actuators are ubiquitous to generate controlled motion through the application of suitable excitation force or torque to perform various operations in manufacturing and industrial automation. The demands placed on faster, smaller, and efficient actuators drive innovation in actuator development. Shape memory alloy (SMA) based actuators have multiple advantages over conventional actuators, including high power-to-weight ratio. This paper integrates the advantages of pennate muscle of a biological system and the unique properties of SMA to develop SMA-based bipennate actuator. The present study explores and expands on the previous SMA actuators by developing the mathematical model of the new actuator based on the bipennate arrangement of the SMA wires and experimentally validating it. The new actuator is found to deliver at least five times higher actuation forces (up to 150 N) in comparison to the reported SMA-based actuators. The corresponding weight reduction is about 67%. The results from the sensitivity analysis of the mathematical model facilitates customization of the design parameters and understanding critical parameters. This study further introduces an Nth level hierarchical actuator that can be deployed for further amplification of actuation forces. The SMA-based bipennate muscle actuator has broad applications ranging from building automation controls to precise drug delivery systems.

Advances in High-Performance Autonomous Energy and Self-Powered Sensing Textiles with Novel 3D Fabric Structures

The seamless integration of emerging triboelectric nanogenerator (TENG) technology with traditional wearable textile materials has given birth to the next-generation smart textiles, i.e., textile TENGs, which will play a vital role in the era of Internet of Things and artificial intelligences. However, low output power and inferior sensing ability have largely limited the development of textile TENGs. Among various approaches to improve the output and sensing performance, such as material modification, structural design, and environmental management, a 3D fabric structural scheme is a facile, efficient, controllable, and scalable strategy to increase the effective contact area for contact electrification of textile TENGs without cumbersome material processing and service area restrictions. Herein, the recent advances of the current reported textile TENGs with 3D fabric structures are comprehensively summarized and systematically analyzed in order to clarify their superiorities over 1D fiber and 2D fabric structures in terms of power output and pressure sensing. The forward-looking integration abilities of the 3D fabrics are also discussed at the end. It is believed that the overview and analysis of textile TENGs with distinctive 3D fabric structures will contribute to the development and realization of high-power output micro/nanowearable power sources and high-quality self-powered wearable sensors.

Methods for numerical simulation of knit based morphable structures: knitmorphs

Shape morphing behavior has applications in many fields such as soft robotics, actuators and sensors, solar cells, tight packaging, flexible electronics, and biomedicine. The most common approach to achieve shape morphing structures is through shape memory alloys or hydrogels. These two materials undergo differential strains which generate a variety of shapes. In this work, we demonstrate the novel concept that 2D knits comprising of yarns from different materials can be morphed into different three-dimensional shapes thereby forming a bridge between traditional knitting and shape changing structures. This concept is referred to as Knitmorphs. Our computational analysis acts as the proof of concept revealing that knitted patterns of varying materials morph into complex shapes, such as saddle, axisymmetric cup, and a plate with waves when subjected to thermal loads. Two-dimensional circular models of plain and rib developed on CAD packages are imported to the finite element analysis software Abaqus, followed by post-processing into wires and assigning fiber material properties of different thermal coefficients of expansion and stiffness. We also propose potential applications for the concept of programmable knits for developing robots based upon jellyfish like locomotion, and complex structures similar to wind turbine blades. This novel concept is meant to introduce a new field for design when considering morphable structures.

Textiles in soft robots: Current progress and future trends

Soft robotics have substantial benefits of safety, adaptability, and cost efficiency compared to conventional rigid robotics. Textiles have applications in soft robotics either as an auxiliary material to reinforce the conventional soft material or as an active soft material. Textiles of various types and configurations have been fabricated into key components of soft robotics in adaptable formats. Despite significant advancements, the efficiency and characteristics of textile actuators in practical applications remain unsatisfactory. To address these issues, novel structural and material designs as well as new textile technologies have been introduced. Herein, we aim at giving an insight into the current state of the art in textile technology for soft robotic manufacturing. We firstly discuss the fundamental actuation mechanisms for soft robotics. We then provide a critical review on the recently developed functional textiles as reinforcements, sensors, and actuators in soft robotics. Finally, the future trends and current strategies that can be employed in textile-based actuator manufacturing process have been explored to address the critical challenges in soft robotics.

Functional Fibers and Fabrics for Soft Robotics, Wearables, and Human-Robot Interface

Soft robotics inspired by the movement of living organisms, with excellent adaptability and accuracy for accomplishing tasks, are highly desirable for efficient operations and safe interactions with human. With the emerging wearable electronics, higher tactility and skin affinity are pursued for safe and user-friendly human-robot interactions. Fabrics interlocked by fibers perform traditional static functions such as warming, protection, and fashion. Recently, dynamic fibers and fabrics are favorable to deliver active stimulus responses such as sensing and actuating abilities for soft-robots and wearables. First, the responsive mechanisms of fiber/fabric actuators and their performances under various external stimuli are reviewed. Fiber/yarn-based artificial muscles for soft-robots manipulation and assistance in human motion are discussed, as well as smart clothes for improving human perception. Second, the geometric designs, fabrications, mechanisms, and functions of fibers/fabrics for sensing and energy harvesting from the human body and environments are summarized. Effective integration between the electronic components with garments, human skin, and living organisms is illustrated, presenting multifunctional platforms with self-powered potential for human-robot interactions and biomedicine. Lastly, the relationships between robotic/wearable fibers/fabrics and the external stimuli, together with the challenges and possible routes for revolutionizing the robotic fibers/fabrics and wearables in this new era are proposed.

Strong and Robust Electrochemical Artificial Muscles by Ionic-Liquid-in-Nanofiber-Sheathed Carbon Nanotube Yarns

To address the lack of a suitable electrolyte that supports the stable operation of the electrochemical yarn muscles in air, an ionic-liquid-in-nanofibers sheathed carbon nanotube (CNT) yarn muscle is prepared. The nanofibers serve as a separator to avoid the short-circuiting of the yarns and a reservoir for ionic liquid. The ionic-liquid-in-nanofiber-sheathed yarn muscles are strong, providing an isometric stress of 10.8 MPa (about 31 times the skeletal muscles). The yarn muscles are highly robust, which can reversibly contract stably at such conditions as being knotted, wide-range humidity (30 to 90 RH%) and temperature (25 to 70 °C), and long-term cycling and storage in air. By utilizing the accumulated isometric stress, the yarn muscles achieve a high contraction rate of 36.3% s^-1 . The yarn muscles are tightly bundled to lift heavy weights and grasp objects. These unique features can make the strong and robust yarn muscles as a desirable actuation component for robotic devices.

Programming soft robots with flexible mechanical metamaterials

The complex behavior of highly deformable mechanical metamaterials can substantially enhance the performance of soft robots.

Low-Temperature Triggered Shape Transformation of Liquid Metal Microdroplets

Shape transformable materials that can respond to external environments have attracted widespread interest over the fields of soft robotics, flexible electronics, and tissue engineering. Among stimuli-responsive materials, liquid metals exhibit rather unique characteristics of versatile morphological changes upon diverse stimuli, including chemicals, electrical field, and mechanical force, etc. Herein, a superfast (few milliseconds), large-scaled (13.8% deformation increase), and fierce (cracks formation) transformation of liquid metal microdroplets (LMMs) with strong impulse expanded force due to liquid-solid phase transition in a dual fluid system composed of LMMs and aqueous solution is reported. When subject to low-temperature stimulus, LMM would transform from ellipsoidal shape to amorphous shape induced by thermal stress, driving the shape morphing. Furthermore, the phase changes of LMMs as well as the formation of surrounding ice crystals are proven to be responsible for this phenomenal behavior. The densification of ice crystals is demonstrated to play a significant role in the transformable behavior. In particular, these nonconductive LMMs in aqueous solutions are discovered to turn into conducive materials with an impedance change of about 10⁵ times. The present discovery is of fundamental and practical significance, and would open new venues in fields such as fluid mechanics, thermal science, flexible electronics, biomedicine, and so forth.

An All-Textile Non-muscular Biomimetic Actuator Based on Electrohydrodynamic Swelling

Mass transfer from one part of an organism to another constitutes a fundamental non-muscular movement strategy in living organisms, in particular in plants. The demonstrable simplicity and safety make non-muscular actuators especially attractive for distributed configurations such as in wearable robotic applications on a textile platform. However, practical arrangements for integrating actuators as inherent parts of textiles is an ongoing challenge. Here we demonstrate an electrohydrodynamic ionic actuator that combines two textiles of natural origin. The first textile - viscose-rayon-derived activated carbon cloth - consists of high-surface-area monolithic fibers that provide electrical and mechanical integrity, whereas the other textile - silk - contributes to mechanical integrity in the lateral direction while preventing the conductive textiles from contacting. By injecting an electronic charge into the activated carbon cloth electrodes, the migration of the electrolyte ions is initiated in the porous network in-between the electrodes, causing non-uniform swelling and eventually bending of the laminate. The three-layer laminate composed of integral textile fibers demonstrated a ∼0.8% strain difference. Electrical control over a fluid movement in a textile platform provides a scalable method for functional textiles not limited to actuation.

Soft Robotic Pad Maturing for Practical Applications

Soft pneumatic actuators (SPAs) have existed for many years as one of the mainstream actuators. Along with the rise of soft robotics, the development in SPA designs in recent years was especially rapid and diverse. Particularly with innovations in SPA fabrication, there is an increasing variety of SPAs with different air chamber designs, varied scales, and distinctive motion modalities. Collectively, it can be seen that the majority of the SPAs come in the format of a finger-like one-dimensional actuator. To expand the SPA spectrum, this article gives a detailed and thorough introduction of a new class of SPA, called soft robotic pad (SRP). SRP is a silicone-based two-dimensional (2D) pad-like actuator that can be programmed to do a multiplicity of surface morphing without any change in thickness. We have previously reported a novel fabrication technique for SRP. However, it also came with a major issue-premature failure. Therefore, in this article, we present significant improvements in the fabrication that substantially strengthen the SRPs so that they can withstand higher pressure for future applications. In addition, shape and force modeling are also provided to predict the corresponding outputs upon different pressures. Motion tracking using Vicon system is proposed for the characterization of the 2D surface morphing. As a pioneering step, we also propose one SRP application, a soft wearable assistive pad for elbow flexion, to demonstrate its capabilities. As a new and unique member in the SPA family, SRP brings new dimension and more motion varieties to SPAs, a substantial boost to the application scope for SPAs and soft robots.

Long Shape Memory Alloy Tendon-based Soft Robotic Actuators and Implementation as a Soft Gripper

Shape memory alloy (SMA) wire-based soft actuators have had their performance limited by the small stroke of the SMA wire embedded within the polymeric matrix. This intrinsically links the bending angle and bending force in a way that made SMA-based soft grippers have relatively poor performance versus other types of soft actuators. In this work, the use of free-sliding SMA wires as tendons for soft actuation is presented that enables large increases in the bending angle and bending force of the actuator by decoupling the length of the matrix and the length of the SMA wires while also allowing for the compact packaging of the driving SMA wires. Bending angles of 400° and tip forces of 0.89 N were achieved by the actuators in this work using a tendon length up to 350 mm. The tendons were integrated as a compact module using bearings that enables the actuator to easily be implemented in various soft gripper configurations. Three fingers were used either in an antagonistic configuration or in a triangular configuration and the gripper was shown to be capable of gripping a wide range of objects weighing up to 1.5 kg and was easily installed on a robotic arm. The maximum pulling force of the gripper was measured to be 30 N.

Suit-type Wearable Robot Powered by Shape-memory-alloy-based Fabric Muscle

A suit-type wearable robot (STWR) is a new type of soft wearable robot (SWR) that can be worn easily anywhere and anytime to assist the muscular strength of wearers because it can be worn like normal clothes and is comfortable to wear even with no power supply. This paper proposes an STWR, in which a shape-memory-alloy-based fabric muscle (SFM) is used as the actuator. The STWR, which weighs less than 1 kg, has a simple structure, with the following components: SFMs, wire encoders for measuring the contraction length of the SFMs, and BOA that fix the actuators on the forearms. In this study, a position controller for the SFM using the wire encoder was developed, and a prototype STWR was fabricated using this position controller. Moreover, by putting the STWR on a mannequin, step-response experiments were performed in which the arms of the mannequin lifted barbells weighing 2 kg and 4 kg to a certain target position. A fast response of moving to the target position in less than 1 s was observed in all steps except for the initial heating step for the 2 kg barbell. The response speed of the SFM was noticeably slower for the 4 kg barbell compared to that for the 2 kg barbell; it moved to the target position in approximately 3 s in all the steps except for the initial heating step. The SFM-applied STWR could overcome the limitations of conventional robots in terms of weight and inconvenience, thereby demonstrating the application potential of STWRs.

Soft Tendril-Inspired Grippers: Shape Morphing of Programmable Polymer-Paper Bilayer Composites

Nastic movements in plants that occur in response to environmental stimuli have inspired many man-made shape-morphing systems. Tendril is an exemplification serving as a parasitic grasping component for the climbing plants by transforming from a straight shape into a coiled configuration via the asymmetric contraction of internal stratiform plant tissues. Inspired by tendrils, this study using a three-dimensional (3D) printing approach developed a class of soft grippers with preprogrammed deformations being capable of imitating the general motions of plant tendrils, including bending, spiral, and helical distortions for grasping. These grippers initially in flat configurations were tailored from a polymer-paper bilayer composite sheet fabricated via 3D printing a polymer on the paper substrate with different patterns. The rough and porous paper surface provides a printed polymer that is well-adhered to the paper substrate which in turn serves as a passive strain-limiting layer. During printing, the melted polymer filament is stretched, enabling the internal strain to be stored in the printed polymer as memory, and then it can be thermally released, which will be concurrently resisted by the paper layer, resulting in various transformations based on the different printed geometries. These obtained transformations were then used for designing grippers to grasp objects with corresponding motions. Furthermore, a fully equipped robotic tendril with three segments was reproduced, where one segment was used for grasping the object and the other two segments were used for forming a tendril-like twistless spring-like structure. This study further helps in the development of soft robots using active polymer materials for engineered systems.

Scalable and facile synthesis of stretchable thermoelectric fabric for wearable self-powered temperature sensors

Wearable sensor systems with ultra-thinness, light weight, high flexibility, and stretchability that are conformally in contact with the skin have advanced tremendously in many respects, but they still face challenges in terms of scalability, processibility, and manufacturability. Here, we report a highly stretchable and wearable textile-based self-powered temperature sensor fabricated using commercial thermoelectric inks. Through various combinations of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS), silver nanoparticles (AgNPs), and graphene inks, we obtained linear temperature-sensing capability. The optimized sensor generates a thermoelectric voltage output of 1.1 mV for a temperature difference of 100 K through a combination of PEDOT:PSS and AgNPs inks and it shows high durability up to 800 cycles of 20% strain. In addition, the knitted textile substrate exhibits temperature-sensing properties that are dependent upon the stretching directions. We believe that stretchable thermoelectric fabric has broader potential for application in human–machine interfaces, health-monitoring technologies, and humanoid robotics.

A highly stretchable and wearable textile-based self-powered temperature sensor fabricated using commercial thermoelectric inks is presented.

Biomimicry, Biofabrication, and Biohybrid Systems: The Emergence and Evolution of Biological Design

The discipline of biological design has a relatively short history, but has undergone very rapid expansion and development over that time. This Progress Report outlines the evolution of this field from biomimicry to biofabrication to biohybrid systems' design, showcasing how each subfield incorporates bioinspired dynamic adaptation into engineered systems. Ethical implications of biological design are discussed, with an emphasis on establishing responsible practices for engineering non-natural or hypernatural functional behaviors in biohybrid systems. This report concludes with recommendations for implementing biological design into educational curricula, ensuring effective and responsible practices for the next generation of engineers and scientists.

A Highly Stretchable and Washable All-Yarn-Based Self-Charging Knitting Power Textile Composed of Fiber Triboelectric Nanogenerators and Supercapacitors

Rapid advancements in stretchable and multifunctional wearable electronics impose a challenge on corresponding power devices that they should have comparable portability and stretchability. Here, we report a highly stretchable and washable all-yarn-based self-charging knitting power textile that enables both biomechanical energy harvesting and simultaneously energy storing by hybridizing triboelectrical nanogenerator (TENG) and supercapacitor (SC) into one fabric. With the weft-knitting technique, the power textile is qualified with high elasticity, flexibility, and stretchability, which can adapt to complex mechanical deformations. The knitting TENG fabric is able to generate electric energy with a maximum instantaneous peak power density of ∼85 mW·m^-2 and light up at least 124 light-emitting diodes. The all-solid-state symmetrical yarn SC exhibits lightweight, good capacitance, high flexibility, and excellent mechanical and long-term stability, which is suitable for wearable energy storage devices. The assembled knitting power textile is capable of sustainably driving wearable electronics (for example, a calculator or temperature-humidity meter) with energy converted from human motions. Our work provides more opportunities for stretchable multifunctional power sources and potential applications in wearable electronics.