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Soft actuators for real-world applications
Abstract
Inspired by physically adaptive, agile, reconfigurable and multifunctional soft-bodied animals and human muscles, soft actuators have been developed for a variety of applications, including soft grippers, artificial muscles, wearables, haptic devices and medical devices. However, the complex performance of biological systems cannot yet be fully replicated in synthetic designs. In this Review, we discuss new materials and structural designs for the engineering of soft actuators with physical intelligence and advanced properties, such as adaptability, multimodal locomotion, self-healing and multi-responsiveness. We examine how performance can be improved and multifunctionality implemented by using programmable soft materials, and highlight important real-world applications of soft actuators. Finally, we discuss the challenges and opportunities for next-generation soft actuators, including physical intelligence, adaptability, manufacturing scalability and reproducibility, extended lifetime and end-of-life strategies. Soft actuators are flexible and compliant and thus perfectly suited to interact with the human body. This Review discusses tethered, untethered and biohybrid soft actuation strategies, highlights promising real-world applications of soft robots and identifies key future challenges, such as implementing physical intelligence and end-of-life strategies.
... Artificial and biologically-inspired microfluidic networks are rapidly evolving to incorporate nonlinear elements and more complex topologies [30][31][32][33][34][35][36][37][38][39][40][41][42], including several examples of artificial valves, some of which exhibit NDR [14,33,35,36,[42][43][44][45][46][47][48]. Although connecting these nonlinear valves in fluid networks could be straightforward, we will show that complex phenomena emerges when: (i) the system is able to locally store volume and (ii) the local volume changes are coupled to the pressure distribution along the system. ...
... Artificial and biologically-inspired microfluidic networks are rapidly evolving to incorporate nonlinear elements and more complex topologies [30][31][32][33][34][35][36][37][38][39][40][41][42], including several examples of artificial valves, some of which exhibit NDR [14,33,35,36,[42][43][44][45][46][47][48]. Although connecting these nonlinear valves in fluid networks could be straightforward, we will show that complex phenomena emerges when: (i) the system is able to locally store volume and (ii) the local volume changes are coupled to the pressure distribution along the system. ...
Fluid flow networks are ubiquitous and can be found in a broad range of contexts, from human-made systems such as water supply networks to living systems like animal and plant vasculature. In many cases, the elements forming these networks exhibit a highly non-linear pressure-flow relationship. Although we understand how these elements work individually, their collective behavior remains poorly understood. In this work, we combine experiments, theory, and numerical simulations to understand the main mechanisms underlying the collective behavior of soft flow networks with elements that exhibit negative differential resistance. Strikingly, our theoretical analysis and experiments reveal that a minimal network of nonlinear resistors, which we have termed a `fluidic memristor', displays history-dependent resistance. This new class of element can be understood as a collection of hysteresis loops that allows this fluidic system to store information. Our work provides insights that may inform new applications of fluid flow networks in soft materials science, biomedical settings, and soft robotics, and may also motivate new understanding of the flow networks involved in animal and plant physiology.
... Soft actuators are a subject of intense research and have been designed to respond to a range of stimuli, such as pressure, heat, chemical reactions, and magnetic or electric fields (16)(17)(18)(19)(20). Previous works have successfully leveraged the mechanical properties of biodegradable materials and implemented them into several unique soft actuator designs: Pneumatically driven actuators can consist of fully biodegradable components, using materials like biogels, cotton fibers, self-healing proteins, or seed-germinating foams (21)(22)(23)(24) as mediums that enable large deformations in response to pressure; some thermally driven actuators can even harness the bursting of popcorn kernels to actuate (25). ...
Combating environmental pollution demands a focus on sustainability, in particular from rapidly advancing technologies that are poised to be ubiquitous in modern societies. Among these, soft robotics promises to replace conventional rigid machines for applications requiring adaptability and dexterity. For key components of soft robots, such as soft actuators, it is thus important to explore sustainable options like bioderived and biodegradable materials. We introduce systematically determined compatible materials systems for the creation of fully biodegradable, high-performance electrohydraulic soft actuators, based on various biodegradable polymer films, ester-based liquid dielectric, and NaCl-infused gelatin hydrogel. We demonstrate that these biodegradable actuators reliably operate up to high electric fields of 200 V/μm, show performance comparable to nonbiodegradable counterparts, and survive more than 100,000 actuation cycles. Furthermore, we build a robotic gripper based on biodegradable soft actuators that is readily compatible with commercial robot arms, encouraging wider use of biodegradable materials systems in soft robotics.
... They can also mimic the movement and behavior of various animals and plants and can be used for pollination, seed dispersal, and soil aeration for regeneration and restoration in hard-to-reach environments (Valdes et al., 2012;Hartmann et al., 2021;Kim et al., 2021). There are already promising examples of soft robots being used to address major challenges in real-world applications that align with the SDGs and CPA (Tolley et al., 2014;Amend et al., 2016;Ng et al., 2021;Elfferich et al., 2022;Li et al., 2022). ...
Soft robotics technology can aid in achieving United Nations Sustainable Development Goals (SDGs) and the Paris Climate Agreement through development of autonomous, environmentally responsible machines powered by renewable energy. By utilizing soft robotics, we can mitigate the detrimental effects of climate change on human society and the natural world through fostering adaptation, restoration, and remediation. Moreover, the implementation of soft robotics can lead to groundbreaking discoveries in material science, biology, control systems, energy efficiency, and sustainable manufacturing processes. However, to achieve these goals, we need further improvements in understanding biological principles at the basis of embodied and physical intelligence, environment-friendly materials, and energy-saving strategies to design and manufacture self-piloting and field-ready soft robots. This paper provides insights on how soft robotics can address the pressing issue of environmental sustainability. Sustainable manufacturing of soft robots at a large scale, exploring the potential of biodegradable and bioinspired materials, and integrating onboard renewable energy sources to promote autonomy and intelligence are some of the urgent challenges of this field that we discuss in this paper. Specifically, we will present field-ready soft robots that address targeted productive applications in urban farming, healthcare, land and ocean preservation, disaster remediation, and clean and affordable energy, thus supporting some of the SDGs. By embracing soft robotics as a solution, we can concretely support economic growth and sustainable industry, drive solutions for environment protection and clean energy, and improve overall health and well-being.
... They can also mimic the movement and behavior of various animals and plants and can be used for pollination, seed dispersal, and soil aeration for regeneration and restoration in hard-to-reach environments (Valdes et al., 2012;Hartmann et al., 2021;Kim et al., 2021). There are already promising examples of soft robots being used to address major challenges in real-world applications that align with the SDGs and CPA (Tolley et al., 2014;Amend et al., 2016;Ng et al., 2021;Elfferich et al., 2022;Li et al., 2022). ...
Soft robotics technology can aid in achieving United Nations' Sustainable Development Goals (SDGs) and the Paris Climate Agreement through development of autonomous, environmentally responsible machines powered by renewable energy. By utilizing soft robotics, we can mitigate the detrimental effects of climate change on human society and the natural world through fostering adaptation, restoration, and remediation. Moreover, the implementation of soft robotics can lead to groundbreaking discoveries in material science, biology, control systems, energy efficiency, and sustainable manufacturing processes. However, to achieve these goals, we need further improvements in understanding biological principles at the basis of embodied and physical intelligence, environment-friendly materials, and energy-saving strategies to design and manufacture self-piloting and field-ready soft robots. This paper provides insights on how soft robotics can address the pressing issue of environmental sustainability. Sustainable manufacturing of soft robots at a large scale, exploring the potential of biodegradable and bioinspired materials, and integrating onboard renewable energy sources to promote autonomy and intelligence are some of the urgent challenges of this field that we discuss in this paper. Specifically, we will present field-ready soft robots that address targeted productive applications in urban farming, healthcare, land and ocean preservation, disaster remediation, and clean and affordable energy, thus supporting some of the SDGs. By embracing soft robotics as a solution, we can concretely support economic growth and sustainable industry, drive solutions for environment protection and clean energy, and improve overall health and well-being.
... That is, a soft-then-hard stiffness state is used for attachment and a sole soft for detachment. This transition of muscle stiffness is usually on the millisecond scale (100 to 500 ms) (39,40), which provides the rapid adhesion switching ability of the sole to the interface. Another critical factor related to the climbing behavior of reptiles is determining when to soften and when to harden the muscles, which is triggered by the nervous system. ...
Artificial dry adhesives have exhibited great potential in the field of robotics. However, there is still a wide gap between bioinspired adhesives and living tissues, especially regarding the surface adaptability and switching ability of attachment/detachment. Here, we propose a sensing-triggered stiffness-tunable smart adhesive material, combining the functions of muscle tissues and sensing nerves rather than traditional biomimetic adhesive strategy that only focuses on structural geometry. Authorized by real-time perception of the interface contact state, conformal contact, shape locking, and active releasing are achieved by adjusting the stiffness based on the magnetorheological effect. Because of the fast switching of the magnetic field, a millisecond-level attachment/detachment response is successfully achieved, breaking the bottleneck of adhesive materials for high-speed manipulation. The innovative design can be applied to any toe's surface structure, opening up a previously unknown avenue for the development of adhesive materials.
... Research on robots with rigid components has a long history. Designing and controlling soft robots for a variety of tasks -from crawling on surfaces with different frictions to jumping on various substrates or carrying different payloads -is just beginning to be understood [1], [2]. Soft robots are attractive because (1) they are deformable and can closely mimic animal behavior; (2) they are soft and thus more collision-proof than traditional rigid-body robots; (3) they can perform tasks that cannot be performed by rigid robots [3]- [6]. ...
Soft robots present unique capabilities, but have been limited by the lack of scalable technologies for construction and the complexity of algorithms for efficient control and motion, which depend on soft-body dynamics, high-dimensional actuation patterns, and external/on-board forces. This paper presents scalable methods and platforms to study the impact of weight distribution and actuation patterns on fully untethered modular soft robots. An extendable Vibrating Intelligent Piezo-Electric Robot (eViper), together with an open-source Simulation Framework for Electroactive Robotic Sheet (SFERS) implemented in PyBullet, was developed as a platform to study the sophisticated weight-locomotion interaction. By integrating the power electronics, sensors, actuators, and batteries on-board, the eViper platform enables rapid design iteration and evaluation of different weight distribution and control strategies for the actuator arrays, supporting both physics-based modeling and data-driven modeling via on-board automatic data-acquisition capabilities. We show that SFERS can provide useful guidelines for optimizing the weight distribution and actuation patterns of the eViper to achieve the maximum speed or minimum cost-of-transportation (COT).
... For robots pursuing more DOFs by adding motors, there are usually sharp increases in the material cost, the control complexity and bulky robot sizes. Bioinspired actuators [13][14][15] may be low-cost approaches for robot dexterity, but they sacri ce the inherit precision and consistency introduced by motors. ...
Handheld robots are welcome solutions with a short learning curve to extend operator capabilities. However, the controllable degree-of-freedoms are limited due to scarce space for actuators. Inspired by muscle movements stimulated by nerves, we report a handheld time-share driven robot composed of several motion modules powered by only one motor. The modules are connected to shape memory alloy wires as nerves for activation, to be actuated by the motor. The robot contains a 202-gram motor base and a 1.2 cm diameter manipulator consisting of serially socketed bending modules. The manipulator can be tailored in length and integrated with various instruments in situ, for non-invasive access and high-dexterous operation on remote surgical sites. The applicability was demonstrated in clinical scenarios, where a surgeon held the robot to perform transluminal experiments on a human stomach model and an ex vivo porcine stomach. The time-share driven mechanism provides a practical way to build a multi-degree-of-freedom robot for broader applications.
... As an emerging type of actuation, soft actuators have been widely explored and applied to intelligent actuators [1][2][3], deep-sea exploration [4,5], bionic robotics [6][7][8], tunable optical devices [9,10], and morphological control [11,12] due to their outstanding features such as softness and flexibility, strong environmental adaptability, and excellent biocompatibility. Among the various soft actuation principles [13], dielectric elastomers have attracted great attention due to their large actuation deformation, fast response, and high energy density [14]. Existing research has shown that dielectric elastomers can produce area strains of up to 380% [15], and even more than 2000% under voltage [16]. ...
Dielectric elastomer actuation has been extensively investigated and applied to bionic robotics and intelligent actuators due to its status as an excellent actuation technique. As a conical dielectric elastomer actuator (DEA) structure extension, push-pull DEA has been explored in controlled acoustics, microfluidics, and multi-stable actuation due to its simple fabrication and outstanding performance. In this paper, a theoretical model is developed to describe the electromechanical behavior of push-pull DEA based on the force balance of the mass block in an actuator. The accuracy of the proposed model is experimentally validated by employing the mass block in the construction of the actuator as the object of study. The actuation displacement of the actuator is used as the evaluation indication to investigate the effect of key design parameters on the actuation performance of the actuator, its failure mode, and critical failure voltage. A dynamic actuator model is proposed and used with experimental data to explain the dynamic response of the actuator, its natural frequency, and the effect of variables. This work provides a strong theoretical background for dielectric elastomer actuators, as well as practical design and implementation experience.
... Recently, significant efforts have been made to develop soft robots or wearable devices with strain sensors for position and force feedback. These strain sensors, typically made from polymers or liquid metals, have been co-fabricated or post-integrated into soft robots and wearables 60,61 . However, the softness of the polymer-based sensors is usually higher than that of the structural material (e.g., Ecoflex and PDMS) of soft robots, thus imposing additional mechanical constraints on the robotic actuation. ...
Understanding biological systems and mimicking their functions require electronic tools that can interact with biological tissues with matched softness. These tools involve biointerfacing materials that should concurrently match the softness of biological tissue and exhibit suitable electrical conductivities for recording and reading bioelectronic signals. However, commonly employed intrinsically soft and stretchable materials usually contain solvents that limit stability for long-term use or possess low electronic conductivity. To date, an ultrasoft (i.e., Young’s modulus <30 kPa), conductive, and solvent-free elastomer does not exist. Additionally, integrating such ultrasoft and conductive materials into electronic devices is poorly explored. This article reports a solvent-free, ultrasoft and conductive PDMS bottlebrush elastomer (BBE) composite with single-wall carbon nanotubes (SWCNTs) as conductive fillers. The conductive SWCNT/BBE with a filler concentration of 0.4 − 0.6 wt% reveals an ultralow Young’s modulus (<11 kPa) and satisfactory conductivity (>2 S/m) as well as adhesion property. Furthermore, we fabricate ultrasoft electronics based on laser cutting and 3D printing of conductive and non-conductive BBEs and demonstrate their potential applications in wearable sensing, soft robotics, and electrophysiological recording.
... Mechano-sensors are a kind of sensor that can convert a variety of mechanical signals (such as air/water flow, vibration, touch, acoustic signal, and so on) into electrical signals [1][2][3][4]. In the engineering field, mechano-sensors are important for engineering equipment to detect mechanical signals in the internal and external environment, because mechanical signals contain a lot of information for rehabilitation monitoring of advanced equipment, guiding the control of mechanical actuators, and precise motion control of intelligent robots in complex working conditions [5][6][7][8]. Recently, there has been an urgent need to further significantly improve the sensing performance of mechano-sensors. However, after decades of research, the mechano-sensors based on traditional design methods are quickly approaching their performance limits. ...
Internal mechano-sensors, as an indispensable part of the proprioceptive system of intelligent equipment, have attracted enormous research interest because of their extremely crucial role in monitoring machining processes, real-time diagnosis of equipment faults, adaptive motor control and so on. The mechano-sensory structure with signal-transduction function is an important factor in determining the sensing performance of a mechano-sensor. However, contrary to the wide application of the cantilever beam as the sensory structure of external mechano-sensors in order to guarantee their exteroceptive ability, there is still a lack of an effective and widely used sensory structure to significantly improve the sensing performance of internal mechano-sensors. Here, inspired by the scorpion using the specialized slit as the sensory structure of internal mechano-sensilla, the slit is ingeniously used in the design of the engineered internal mechano-sensor. In order to improve the deformability of the slit wake, the hollowed-out design around the slit tail of biological mechano-sensilla is researched. Meanwhile, to mimic the easily deformed flexible cuticular membrane covering the slit, the ultrathin, flexible, crack-based strain sensor is used as the sensing element to cover the controllable slit wake. Based on the coupling deformation of the slit wake, as well as the flexible strain sensor, the slit-based mechano-sensor shows excellent sensing performance to various mechanical signals such as displacement and vibration signals.
... 2−6 Soft robots are driven by continuously deformable soft artificial muscles instead of conventional rigid motors, which provides the possibility of miniaturization. 7,8 In the natural world, a small and light insect can move fast in a narrow space. If insect-like soft robots could be batch-made, they would be very promising to participate in many scenarios like exploration and rescue. ...
Insects with small and light bodies possess the capability of agile and fast movement in a small space. Inspired by nature, an insect-like soft robot may update the strategies in many scenarios like exploration, rescue, etc. However, the design and mass manufacture of soft robots combining insect size, fast mobility, good robustness, and impact-perception capability still present great engineering challenges. Herein, we report an insect-scale (15 mm body length (BL), 450 mg body weight) and ultrafast (∼4.0 BL s–1) soft robot. The remarkable motion performance is attributed to the high-frequency (760 Hz) operation as well as the long lifetime (>one million cycles) of its artificial muscle, which is a coil dielectric elastomer actuator (DEA) made by multimaterial coaxial three-dimensional printing with well-designed highly elastic materials and 5-inlets nozzle structure. The current robot is not only the smallest and fastest among the reported DEA-driven robots but also obtains high robustness, good environmental adaptability, and impact-perception capability: It can run on various grounds and complex paths, climb inside small pipes, work in robot swarms, and sustain and perceive the impact of the external environment.
... Inspired by numerous soft actuator projects that are integrated into textile-based objects by international research teams [9][10][11][12][13], such as the MIT Tangible Media Group or Harvard BioDesign Lab, an intensive literature study was carried out. Several relevant scientific articles were studied, and expert interviews were conducted, including with the Fraunhofer ISC Smart Materials Centre, MIT, and the RCA Soft System Research Group. ...
The process of making adaptive and responsive wearables on the scale of the body has often been a process where designers use off-the-shelf parts or hand-crafted electronics to fabricate garments. However, recent research has shown the importance of emergence in the process of making. Second Skins is a multistakeholder exploration into the creation of those garments where the designers and engineers work together throughout the design process so that opportunities and challenges emerge with all stakeholders present in the process. This research serves as a case study into the creation of adaptive caring garments for sustainable wardrobes from a multistakeholder design team. The team created a garment that can customize the colors, patterns, structures, and other properties dynamically. A reflection on the multi-stakeholder process unpacks the process to explore the challenges and opportunities in adaptable e-textiles.
... Its physical parameters, such as intensity, wavelength, and polarization, can be easily tailored with high spatial and temporal resolution (155). The on-demand control techniques enable light-driven robots' versatile, sophisticated, and multifunctional motions (156). Light can trigger macroscopic deformation, an inequivalent thermal strain, 15. 16 Wang water desorption, a change of hydrophobicity, a change of surface tension, a phase transition, or a change of magnetic properties. ...
Soft robotic systems are human friendly and can mimic the complex motions of animals, which introduces promising potential in various applications, ranging from novel actuation and wearable electronics to bioinspired robots operating in unstructured environments. Due to the use of soft materials, the traditional fabrication and manufacturing methods for rigid materials are unavailable for soft robots. 3D printing is a promising fabrication method for the multifunctional and multimaterial demands of soft robots, as it enables the personalization and customization of the materials and structures. This review provides perspectives on the manufacturing methods for various types of soft robotic systems and discusses the challenges and prospects of future research, including in-depth discussion of pneumatic, electrically activated, magnetically driven, and 4D-printed soft actuators and integrated soft actuators and sensors. Finally, the challenges of realizing multimaterial, multiscale, and multifunctional 3D-printed soft robots are discussed.
Expected final online publication date for the Annual Review of Control, Robotics, and Autonomous Systems, Volume 14 is May 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Actuators, which turn control signals to mechanical actions, are key drivers in advancing modern technology and shaping our future. In recent years, enormous efforts have been put into the development of soft actuators [1][2][3][4][5] made of stimuli-responsive polymers, hydrogels, liquid metals, phase-change materials, and composites, [6][7][8][9][10][11][12][13] due to their flexibility, adaptability, biocompatibility, and multi-functionality. Substantial progress has been made on the deformation of the macroscopic material/system under external stimuli. ...
Localized actuation is an important goal of nanotechnology broadly impacting applications such as programmable materials, soft robotics, and nanolithography. Despite significant recent advances, actuation with high temporal and spatial resolution remains challenging to achieve. Herein, we demonstrate strongly localized photoactuation of polymer pens made of polydimethylsiloxane (PDMS) and surface-functionalized short carbon nanotubes based on a fundamental understanding of the nanocomposite chemistry and device innovations in directing intense light with digital micromirrors to microscale domains. We show that local illumination can drive a small group of pens (3 × 3 over 170 μm × 170 μm) within a massively two-dimensional array to attain an out-of-plane motion by more than 7 μm for active molecular printing. The observed effect marks a striking three-order-of-magnitude improvement over the state of the art and suggests new opportunities for active actuation.
... The introducing of twisting into those fibers greatly enhances the contraction effect, and the actuation properties of the resulted muscles could be regulated via the degree of twisting and the tightness of the resulting coil [11]. In comparison to other artificial muscles e.g., dielectric elastomers, conductive polymers, hydrogels and shape memory polymers, artificial coiled yarn muscles offer unparalleled advantages regarding low voltage, reversibility, high specific energy density and economy [12][13][14]. In particular, with the optimization of materials, structures and stimuli, recent artificially curled muscles have shown higher performance in terms of actuation stroke, speed, response time, specific energy density and specific work output [15,16]. ...
Muscles are capable of modulating the body and adapting to environmental changes with a highly integrated sensing and actuation. Inspired by biological muscles, coiled/twisted fibers are adopted that can convert volume expansion into axial contraction and offer the advantages of flexibility and light weight. However, the sensing-actuation integrated fish line/yarn-based artificial muscles are still barely reported due to the poor actuation-sensing interface with off-the-shelf fibers. We report herein artificial coiled yarn muscles with self-sensing and actuation functions using the commercially available yarns. Via a two-step process, the artificial coiled yarn muscles are proved to obtain enhanced electrical conductivity and durability, which facilitates the long-term application in human-robot interfaces. The resistivity is successfully reduced from 172.39 Ω·cm (first step) to 1.27 Ω·cm (second step). The multimode sense of stretch strain, pressure, and actuation-sensing are analyzed and proved to have good linearity, stability and durability. The muscles could achieve a sensitivity (gauge factor, GF) of the contraction strain perception up to 1.5. We further demonstrate this self-aware artificial coiled yarn muscles could empower non-active objects with actuation and real-time monitoring capabilities without causing damage to the objects. Overall, this work provides a facile and versatile tool in improving the actuation-sensing performances of the artificial coiled yarn muscles and has the potential in building smart and interactive soft actuation systems.
... Control of these robust structures necessarily focuses only on the dynamics at the transitions, that is, near the saddles, eliminating the need for active control during the remainder of the response. This type of control strategy, through the use of long-term robust responses, has inspired the emerging fields of physical intelligence 10,11 and soft-robotics [12][13][14] in which simple actuators generate complex behavior by utilizing the inherent dynamics of their structural components and material properties 15 . Understanding these systems through accurate models of their responses, would enable unique methods to control them and stimulate further development in these fields. ...
In lieu of continuous time active feedback control in complex systems, nonlinear dynamics offers a means to generate desired long-term responses using short-time control signals. This type of control has been proposed for use in resonators that exhibit a plethora of complex dynamic behaviors resulting from energy exchange between modes. However, the dynamic response and, ultimately, the ability to control the response of these systems remains poorly understood. Here, we show that a micromechanical resonator can generate diverse, robust dynamical responses that occur on a timescale five orders of magnitude larger than the external harmonic driving and these responses can be selected by inserting small pulses at specific branching points. We develop a theoretical model and experimentally show the ability to control these response patterns. Hence, these mechanical resonators may represent a simple physical platform for the development of springboard concepts for nonlinear, flexible, yet robust dynamics found in other areas of physics, chemistry, and biology.
... The first two are EC plasticizers, 53-55 while citric acid is a cellulose cross linker 56,57 and AC modifier. 58,59 The ability to modify and tune the mechanical properties of the films by simply incorporating edible additives is interesting for the production of materials with multiple functionalities and easily adaptable to a specific application and surface 60,61 . ...
Edible electronics will enable systems that can be safely ingested and degraded in the human body after completing their function, such as sensing physiological parameters or biological markers in the gastrointestinal tract, without risk of retention or need of recollection. The same systems are potentially suitable for directly tagging food, monitoring its quality, and developing edible soft actuators control and sensing abilities. Designing appropriate edible power sources is critical to turn such a vision into real opportunities. We propose electrically conductive edible composites based on ethylcellulose and activated carbon as enabling materials for energy harvesting and storage. Free-standing, phase-separated bi-layered films, insulating at the top and with low electrical resistivity (∼10 Ω cm) at the bottom, were produced with a scalable single-step process. Food additives can tune the mechanical and triboelectrical properties of the proposed edible films. We demonstrated their successful operation as electropositive elements in organic triboelectric nanogenerators (TENGs) and as electrodes in fully edible supercapacitors (SC). The TENGs showed ∼60 V peak voltage (root mean square power density ∼2.5 μW cm⁻² at 5 Hz), while the SC achieved an energy density of 3.36 mW h g⁻¹, capacity of ∼ 9 mAh g−1, and stability for more than 1000 charge-discharge cycles. These results show that the combination of ethyl cellulose and activated carbon, and the control over their mixture, allow on-demand edible devices for energy generation and storage, serving future edible and green electronics scenarios.
... The study of grippers in service robots using smart actuation materials and flexible jaws has recently attracted increasing interest (Sriskandarajah and Shetty, 2018;Zhang et al., 2020a;Shintake et al., 2018;Rodrigue et al., 2017;Li et al., 2021). Compared with traditional rigid grippers actuated by electric motors (S and R, 2018), pneumatic (Walker et al., 2020;Zhong et al., 2019;Zhong et al., 2021) and electrohydraulic (Park et al., 2020), etc., the flexible grippers actuated by smart materials are smaller, more adaptable and safer to better interact with unstructured environments and can perform tasks with more postures (Yoon, 2019;Shintake et al., 2018;Ogawa et al., 2022;Wang et al., 2022;Cardin-Catalan et al., 2022;Pi et al., 2021). ...
Purpose
The paper aims to propose a novel dual-stage shape memory alloy (SMA) actuated gripper (DAG), of which the grasp performance is improved through primary and secondary actuation.
Design/methodology/approach
This paper presents a method of integrating the design of dual-stage actuation modules based on the SMA bias actuation principle to enhance the grasping shape adaptability and force modulation of a DAG. The actuation angle range and grasping performance of the DAG are investigated by thermomechanical analysis and the finite element method based numerical simulation.
Findings
The results of present experiments and simulations indicate that the actuation angle scope of the DAG is about 20° under no load, which enables the grasping space occupied by an object in the DAG from 60 mm to 120 mm. The grasping force adjusted by changing the input power of the primary main actuation module and secondary fine-tuning actuation module can reach a maximum of 2 N, which is capable of grasping objects of various sizes, weights, shapes, etc.
Originality/value
The contribution of this paper is to design a DAG based on SMA, and establish the solution methods for the primary main actuation module and secondary fine-tuning actuation module, respectively. It lays a foundation for the research of lightweight and intelligent robotic grippers.
Magnetoactive soft materials, typically composed of magnetic particles dispersed in a soft polymer matrix, are finding many applications in soft robotics due to their reversible and remote shape transformations under magnetic fields. To achieve complex shape transformations, anisotropic, and heterogeneous magnetization profiles must be programmed in the material. However, once programmed and assembled, magnetic soft actuators cannot be easily reconfigured, repurposed, or repaired, which limits their application, their durability, and versatility in their design. Here, magnetoactive soft composites are developed from squid‐derived biopolymers and NdFeB microparticles with tunable ferromagnetic and thermomechanical properties. By leveraging reversible crosslinking nanostructures in the biopolymer matrix, a healing‐assisted assembly process is developed that allows for on‐demand reconfiguration and magnetic reprogramming of magnetoactive composites. This concept in multi‐material modular actuators is demonstrated with programmable deformation modes, self‐healing properties to recover their function after mechanical damage, and shape‐memory behavior to lock in their preferred configuration and un‐actuated catch states. These dynamic magnetic soft composites can enable the modular design and assembly of new types of magnetic actuators, not only eliminating device vulnerabilities through healing and repair but also by providing adaptive mechanisms to reconfigure their function on demand.
A novel soft actuator is designed, fabricated, and optimized for applied use in soft robotics and biomedical applications. The soft actuator is powered by the expansion and contraction of a graphene‐containing and encased liquid marble using the photothermal effect. Unfortunately, conventional liquid marbles are found to be too fragile and prone to cracking and failure for such applications. After experimentation, it is possible to remedy this problem by synthesizing liquid marbles encased with polymeric shells–polymerized in situ–for added mechanical strength and robustness. These marbles are shown to have intrinsic photothermal activity. They are then situated in bimorph‐type soft actuators where one side of the actuator has a dramatically different Young's modulus than the other, leading to directional actuation which is successfully demonstrated in multistep walking soft robots. The soft actuators are shown to successfully activate the mechanosensitive Piezo protein in a transfected human cell line with high effectiveness and no toxicity. Overall, the liquid marble‐powered soft actuators described here represent a new soft actuation methodology and a novel tool for mechanobiological studies, such as stem cell fate and organoid differentiation.
In recent years, soft electrothermal actuators (ETAs) with low voltage drives have been applied in the field of human‐machine interface (iHMI) because of their safety and low power consumption. However, great challenges remain for achieving high‐performance, low‐cost and low‐voltage ETAs manufacturing. Herein, an ETA embedded with a conductive circuit fabricated using the liquid metal of eutectic gallium‐indium alloy (EGaIn), was developed using the 3D printing technology. Resistance stability, transmittance (92.1 %), and heat generation capacity (246 °C at 1.484 V) of the ETAs were investigated to evaluate its performance. when the thickness ratio is 10:1, and the length‐width is 8:1, ETAs with U‐shaped conductive circuit structures shows higher bending performance. Three different categories of deformative structures (S‐shaped, flower‐shaped, and bridge‐shaped) were designed via planning the PI position of ETAs to investigate the deformation possibility of multiple structural deformations of ETA. Finally, a flexible smart gripper consisting of five ETAs was developed to demonstrate its potential application. Our study demonstrates that the developed ETA has high heat production capacity, high resistance stability and excellent bending performance at low voltage drives. This article is protected by copyright. All rights reserved.
The performance of pneumatic artificial muscles (PAMs) depends in large part on the fluidic hardware used to add and remove air from their volume. A complete fluidic system usually contains tubing, pneumatic regulators, pneumatic valves, and pneumatic pumps. However, for most PAMs, the performance of the actuator depends on how fast air can be taken into and out of the chamber as the presence of a single chamber entails relatively simple fluidic strategies. In our previous work, we introduced a type of PAM called Hyperbaric Vacuum Artificial Muscles (Hyper‐VAM) which utilizes a negative pressure inner chamber placed inside a positive pressure outer chamber. This paper investigates advanced fluidic strategies for this actuator by making use of the pressure equilibrium between these two chambers as the building block for advanced fluidic strategies. It is shown that it is possible to operate the Hyper‐VAM in sub‐ and hyper‐atmospheric conditions during closed‐loop actuation and to use the atmosphere as a natural pump starting from a sub‐ or hyper‐atmospheric atmospheric equilibrium. This paper demonstrates and compares these strategies to basic fluidic strategies and demonstrates fluidic systems capable of implementing cyclic actuation using these strategies. This article is protected by copyright. All rights reserved.
Integrating adaptative logic computation directly into soft microrobots is imperative for the next generation of intelligent soft microrobots as well as for the smart materials to move beyond stimulus-response relationships and toward the intelligent behaviors seen in biological systems. Acquiring adaptivity is coveted for soft microrobots that can adapt to implement different works and respond to different environments either passively or actively through human intervention like biological systems. Here, a novel and simple strategy for constructing untethered soft microrobots based on stimuli-responsive hydrogels that can switch logic gates according to the surrounding stimuli of environment is introduced. Different basic logic gates and combinational logic gates are integrated into a microrobot via a straightforward method. Importantly, two kinds of soft microrobots with adaptive logic gates are designed and fabricated, which can smartly switch logic operation between AND gate and OR gate under different surrounding environmental stimuli. Furthermore, a same magnetic microrobot with adaptive logic gate is used to capture and release the specified objects through the change of the surrounding environmental stimuli based on AND or OR logic gate. This work contributes an innovative strategy to integrate computation into small-scale untethered soft robots with adaptive logic gates.
Molecular spin‐crossover (SCO) complexes are phase‐change materials that develop large spontaneous strains across the thermally induced phase transition, which can be advantageously used in designing soft actuators. Herein, a bilayer bending cantilever, made of thermoplastic polyurethane (TPU) with embedded [Fe(NH2trz)3](SO4) SCO particles (25 wt%), is presented. The proposed actuator is fabricated by blade casting an SCO@TPU layer on a conducting Ag@TPU film to convert electrothermal input into mechanical response. Experiments are conducted to characterize the curvature of bilayer beams, which is then further analyzed using the Euler–Bernoulli beam theory. The beam curvature change, free transformation strain, and effective work density associated with the SCO are 0.11 mm−1, 1.6%, and 1.25 mJ cm−3, respectively. Further, the open‐ and closed‐loop response of the actuator is investigated using a custom‐built setup. The open‐loop identification suggests that the actuator gain increases monotonously when the control current increases. This natural adaptive character can explain the drastically diminished response time in closed‐loop proportional–integral–derivative control experiments (2–3 s). Finally, tracking experiments are carried out to evaluate the robustness of the actuator with and without payloads. The results for 30 240 endurance cycles reveal a mean positioning error of 0.8%. Bilayer bending cantilevers, made of thermoplastic polyurethane (TPU) with embedded [Fe(NH2trz)3](SO4) spin‐crossover (SCO) particles and silver flakes, are built to convert electrothermal input into mechanical response. The beam curvature change and response time obtained in closed‐loop proportional–integral–derivative control experiments and the robustness of the actuators demonstrate the potential of the proposed actuator for shape control applications, such as soft morphing.
Committee:
President: Dr. Ramón Eulalia Zaera Polo;
Secretary: Dr. Abdon Pena-Francesch;
Spokesperson: Dr. Laura de Lorenzis.
Cum Laude distinction.
Soft electronics have attracted great interest owing to their potential applications in electronic skins, implanted devices, soft robotics, etc. Among the various soft materials, hydrogels are recognized as an ideal building block of soft electronics due to their tissue‐like physicochemical properties, abundant stimuli‐responses, and excellent mechanical compliances. Compared to elastomers, hydrogels containing large amounts of water exhibit better mechanical match to soft tissues and permeability to hydrophilic molecules. To date, most hydrogel‐based soft electronics (HSE) are facilely developed using a bulk conductive gel as the sensing unit, different from the elastomer‐based soft electronics with sophisticated integration of electronic elements. To advance their applications in engineering and biomedical fields, it is significant to devise hydrogel electronics with distributed sensing units. This Review summarizes the fabrication and applications of HSE, focusing on the multifunctional HSE with patterned conductive circuits and distributed sensing units. First, the fabrication of single‐functional soft electronics is briefly introduced with a bulk gel as the building block, including strain, temperature, chemical, and proximity sensors. Then, the approaches to integrating multiple sensing units into one hydrogel are summarized with examples of applications. Finally, perspectives are given on future directions and potential challenges in this field. Multifunctional hydrogel‐based soft electronics (HSE) attract great attention due to their potential applications in electronic skins, implanted devices, soft robotics, etc. In this Review, strategies to fabricate integrated multifunctional HSE with patterned conductive circuits and distributed sensing elements are highlighted, and perspectives on potential challenges and opportunities are discussed.
Less than 1% of Earth’s freshwater reserves is accessible. Industrialization, population growth and climate change are further exacerbating clean water shortage. Current water-remediation treatments fail to remove most pollutants completely or release toxic by-products into the environment. The use of self-propelled programmable micro- and nanoscale synthetic robots is a promising alternative way to improve water monitoring and remediation by overcoming diffusion-limited reactions and promoting interactions with target pollutants, including nano- and microplastics, persistent organic pollutants, heavy metals, oils and pathogenic microorganisms. This Review introduces the evolution of passive micro- and nanomaterials through active micro- and nanomotors and into advanced intelligent micro- and nanorobots in terms of motion ability, multifunctionality, adaptive response, swarming and mutual communication. After describing removal and degradation strategies, we present the most relevant improvements in water treatment, highlighting the design aspects necessary to improve remediation efficiency for specific contaminants. Finally, open challenges and future directions are discussed for the real-world application of smart micro- and nanorobots. Micro- and nanorobots hold great promise for next-generation water-remediation applications. This Review discusses the development of intelligent micro- and nanoscale systems for the removal and degradation of water contaminants and the challenges toward their practical application.
Small-scale robots capable of remote active steering and navigation offer great potential for biomedical applications. However, the current design and manufacturing procedure impede their miniaturization and integration of various diagnostic and therapeutic functionalities. Here, we present a robotic fiber platform for integrating navigation, sensing, and therapeutic functions at a submillimeter scale. These fiber robots consist of ferromagnetic, electrical, optical, and microfluidic components, fabricated with a thermal drawing process. Under magnetic actuation, they can navigate through complex and constrained environments, such as artificial vessels and brain phantoms. Moreover, we utilize Langendorff mouse hearts model, glioblastoma microplatforms, and in vivo mouse models to demonstrate the capabilities of sensing electrophysiology signals and performing localized treatment. Additionally, we demonstrate that the fiber robots can serve as endoscopes with embedded waveguides. These fiber robots provide a versatile platform for targeted multimodal detection and treatment at hard-to-reach locations in a minimally invasive and remotely controllable manner.
The rapid development in micro‐machinery enabled the investigation of smart materials that can embody fast response, programmable actuation, and flexibility to perform mechanical work. Soft magnetic actuators represent an interesting platform toward combining those properties. This study focuses on the synthesis of micro‐actuators that respond to thermal and magnetic stimuli using micro‐molding with a soft template as a fabrication technique. These microsystems consist of a hydrogel matrix loaded with anisotropic magnetic nanospindles. When a homogeneous magnetic field is applied, the nanospindles initially dispersed in monomer solution, align and assemble into dipolar chains. The ensuing UV‐polymerization creates a network and conveniently arrests these nanostructures. Consequently, the magnetic dipole moment is coplanar with the microgel. Varying the shape, volume, and composition of the micro‐actuators during synthesis provides a temperature‐dependent control over the magnetic response and the polarizability. Beyond isotropic swelling, shaping the hydrogel as long thin ribbons with a passive layer on one side allows for differential swelling leading to bending and twisting deformations, for example, 2D‐ or 3D‐spiral. These deformations involve a reversible amplification of the magnetic response and orientation of the hydrogels under magnetic field. Temperature control herewith determines the conformation and simultaneously the magnetic response of the micro‐actuators. Soft poly(N‐isopropylacrylamide) micro‐actuators with pre‐aligned embedded maghemites spindles are synthesized with different shapes using particle replication in non‐wetting template. Their swelling and magnetic response can be controlled with the temperature, as well as their shape and polarizability by further restricting their swelling with an additional gold coating.
Magnetic soft robots (MSRs) have attracted growing interest due to their unique advantages in untethered actuation and excellent controllability. However, actuation strategies of these robots have long been designed out of heuristics. Herein, it is aimed to develop an intelligent method to solve the inverse problem of finding workable magnetic fields for the actuation of strip‐like soft robots entirely based on deep reinforcement learning algorithms. Magnetic torques and a dissipation force to the Cosserat rod model are introduced, and the developed model to simulate the dynamics of MSRs is utilized. Meanwhile, under the reinforcement learning framework, soft robots to move forward without human guidance are successfully trained, and the results intelligently adapt to different magnetization patterns and magnetic field restrictions. The learned actuation strategies by directly applying simulated magnetic fields to real MSRs in an open loop way are validated. The experimental results show good accordance with simulations. By presenting the first case of using strategies entirely generated by reinforcement learning to control real MSRs, the potential of using reinforcement learning to achieve autonomous actuation of MSRs is demonstrated, which can be used to establish a route for the creation of highly adaptive design framework. An intelligent method is developed to solve the inverse design problem of finding workable magnetic fields for actuation of magnetic soft robots (MSRs) without human guidance, implemented by a brand new simulation platform for MSRs based on Cosserat rod models and a deep reinforcement learning framework, demonstrating the potential of using reinforcement learning to achieve autonomous actuation of magnetic soft robots.
A new type of soft actuators based on a vertical stack of nanoporous 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐oxidized cellulose nanofibers (TOCNs) and atomically thin 2D platinum ditelluride (PtTe2) layers is reported. The actuation of TOCNs is driven by the interfacing 2D PtTe2 layers whose electrothermal proficiency precisely controls their hydration/dehydration states sensitive to mechanical deformation. These vertically stacked TOCN/2D PtTe2 actuators present excellent actuation characteristics such as high linearity of bending curvature versus applied voltage and well‐preserved reversibility during cyclic operations. Most notably, they exhibit an extremely large weight‐lifting ratio, i.e., ≈1000 times the mass of the TOCN layers, confirming superior mechanical robustness. Furthermore, complicated actuations such as twisting in a 3D manner are demonstrated by judiciously controlling the surface wettability of TOCN layers. This study unveils opportunities for CNFs and 2D materials for actuator applications, as well as suggests new design strategies broadly applicable to soft robotics and biomimetic devices. A new type of bimorph actuator operated by the actuation of cellulose nanofibers (CNFs) driven by the Joule heating of ultrathin 2D PtTe2 layers sandwiched between CNFs and the polymer is reported.
Human finger excels at delicate and dynamic gripping tasks via coordinating soft tissues and rigid components, which is yet considerably challenging for robotic grippers. Herein, inspired by the human finger, a soft‐rigid structured gripper composed of three variable‐stiffness fingers with the antagonistic mechanism is proposed. Each finger can change its joint stiffness by selectively applying pretension to the springs so that it can exhibit different stiffness gradients to conform to the surfaces. Theoretical models are established to evaluate both the deformation and stiffness properties, and several experiments verify that it can increase the stiffness to 6.4 times after aggravating the antagonistic effect. Based on the variable stiffness, the finger performs sequential motion to conform to different curvatures, resulting in a larger contact area. Moreover, by stiffening joints, the proposed gripper can improve its grasping performance with a large grasping force while providing gentle contact. Furthermore, the gripper presents the capability of handling various objects with the optimal posture and gently grasping fragile objects like the paper ring and plasticine cylinder. Whereas this gripper can coordinate the relationship between high compliance and variable stiffness, the exploration of the gripper provides shed light on robotic design and practical application. The coordination between high compliance and variable stiffness is quite challenging. Herein, a soft‐rigid structured gripper with variable stiffness is reported to achieve sequential motion and mutable posture. Leveraging the antagonistic mechanism, this gripper is capable of high conformability and grasping ability for objects with various shapes and weights, moreover, can offer safe interaction without compromising its stiffness.
Thermoresponsive polymer‐based bilayer bending actuators rely on the dissimilar thermal expansion of the polymers that form the two layers. To maximize the heat‐induced change in curvature, the thermal expansion shall be large in one and small in the other material. Semicrystalline polymers display a large nonlinear thermal expansion across their melting transition, but as their mechanical integrity is lost upon melting, they cannot readily be used in bilayer actuators. To overcome this limitation, segmented polyurethanes (PUs) with crystallizable polyethylene glycol (PEG) soft segments and hard segments formed by the reaction of 1,6‐hexane diisocyanate and 1,4‐butanediol (BDO) is developed. The latter serve as physical cross‐links and inhibit flow at temperatures where the domains formed by the PEG segments have melted. The molecular weight of the PEG segments and the hard‐segment content in the polymer are systematically varied. As the nonlinear expansion of the PEG–PUs is associated with the melting of the crystalline PEG domains, the thermal expansion of these materials is correlated with their crystallinity and is highest for the polymers with the lowest BDO content and the highest PEG molecular weight. Electro‐thermally controlled bilayer bending actuators based on the new materials display high deflection and low switching temperatures. A series of polyurethane elastomers with large nonlinear thermal expansion is reported. The materials feature crystallizable polyether soft segments and hydrogen‐bonding hard segments that act as physical cross‐links and preserve mechanical stability above the melt temperature. The polymers are used to fabricate electrothermally controlled bilayer bending actuators with a high deflection and a low switching temperature.
Soft robots capable of flexible deformations and agile locomotion similar to biological systems are highly desirable for promising applications, including safe human-robot interactions and biomedical engineering. Their achievable degree of freedom and motional deftness are limited by the actuation modes and controllable dimensions of constituent soft actuators. Here, we report self-vectoring electromagnetic soft robots (SESRs) to offer new operational dimensionality via actively and instantly adjusting and synthesizing the interior electromagnetic vectors (EVs) in every flux actuator sub-domain of the robots. As a result, we can achieve high-dimensional operation with fewer actuators and control signals than other actuation methods. We also demonstrate complex and rapid 3D shape morphing, bioinspired multimodal locomotion, as well as fast switches among different locomotion modes all in passive magnetic fields. The intrinsic fast (re)programmability of SESRs, along with the active and selective actuation through self-vectoring control, significantly increases the operational dimensionality and possibilities for soft robots.
Functional soft materials, exhibiting multiple types of deformation, have shown their potential/abilities to achieve complicated biomimetic behaviors (soft robots). Inspired by the locomotion of earthworm, which is conducted through the contraction and stretching between body segments, this study proposes a type of one-piece-mold folded diaphragm, consisting of the structure of body segments with radial magnetization property, to achieve large 3D and bi-directional deformation with inside-volume change capability subjected to the low homogeneous magnetically driving field (40 mT). Moreover, the appearance based on the proposed magnetic-driven folded diaphragm is able to be easily customized to desired ones and then implanted into different untethered soft robotic systems as soft drivers. To verify the above points, we design the diaphragm pump providing unique properties of lightweight, powerful output and rapid response, and the soft robot including the bio-earthworm crawling robot and swimming robot inspired by squid to exhibit the flexible and rapid locomotion excited by single homogeneous magnetic fields.
On-skin wearable systems for biofluid sampling and biomarker sensing can revolutionize the current practices in healthcare monitoring and personalized medicine. However, there is still a long path toward complete market adoption and acceptance of this fascinating technology. Accordingly, microfluidic science and technology can provide excellent solutions for bridging the gap between basic research and clinical research. The research gap has led to the emerging field of epidermal microfluidics. Moreover, recent advances in the fabrication of highly flexible and stretchable microfluidic systems have revived the concept of micro elastofluidics, which can provide viable solutions for on-skin wearable biofluid handling. In this context, this review highlights the current state-of-the-art platforms in this field and discusses the potential technologies that can be used for on-skin wearable devices. Toward this aim, we first compare various microfluidic platforms that could be used for on-skin wearable devices. These platforms include semiconductor-based, polymer-based, liquid metal-based, paper-based, and textile-based microfluidics. Next, we discuss how these platforms can enhance the stretchability of on-skin wearable biosensors at the device level. Next, potential microfluidic solutions for collecting, transporting, and controlling the biofluids are discussed. The application of finger-powered micropumps as a viable solution for precise and on-demand biofluid pumping is highlighted. Finally, we present the future directions of this field by emphasizing the applications of droplet-based microfluidics, stretchable continuous-flow micro elastofluidics, stretchable superhydrophobic surfaces, liquid beads as a form of digital micro elastofluidics, and topological liquid diodes that received less attention but have enormous potential to be integrated into on-skin wearable devices.
Catastrophically mechanical failure of soft self-healing materials is unavoidable due to their inherently poor resistance to crack propagation. Here, with a model system, i.e., soft self-healing polyurea, we present a biomimetic strategy of surpassing trade-off between soft self-healing and high fracture toughness, enabling the conversion of soft and weak into soft yet tough self-healing material. Such an achievement is inspired by vascular smooth muscles, where core-shell structured Galinstan micro-droplets are introduced through molecularly interfacial metal-coordinated assembly, resulting in an increased crack-resistant strain and fracture toughness of 12.2 and 34.9 times without sacrificing softness. The obtained fracture toughness is up to 111.16 ± 8.76 kJ/m2, even higher than that of Al and Zn alloys. Moreover, the resultant composite delivers fast self-healing kinetics (1 min) upon local near-infrared irradiation, and possesses ultra-high dielectric constants (~14.57), thus being able to be fabricated into sensitive and self-healing capacitive strain-sensors tolerant towards cracks potentially evolved in service. Catastrophically mechanical failure, of soft self-healing materials often stems from its poor resistance to crack, propagation. Here, the authors present a strategy of surpassing trade-off, between soft self-healing and high fracture toughness, enabling the, conversion of soft and weak into soft yet tough self-healing materials.
The driving principle of a thermal-responsive hydrogel that loses water at high temperature and absorbs water at low temperature limits its application in an aqueous environment. Here, a gradient hydrogel actuator was developed by introducing sodium hyaluronate into poly(N-isopropylacrylamide) hydrogel by an asymmetric mold method. The hydrogel exhibited a fast response above the LCST in air and unusual self-recovery without the need for further temperature stimuli. The actuation behavior was related to conversion from free water to bound water and water retention within the gradient matrix. The self-recovery mechanism was explored. This work provides a new insight into designing bionic hydrogels applied in a non-aqueous environment.
Smart molecular actuators have become a cutting-edge theme due to their ability to convert chemical energy into mechanical energy under external stimulations. However, realizing actuation at the molecular level and elucidating the mechanisms for actuating still remain challenging. Herein, we design and fabricate a novel nanoscaled polyoxometalate-based humidity-responsive molecular actuator {Bi8Mo48} through the assembly of [Mo2O2S2]2+ units, transition metals, and flexible phosphonic acid ligands. {Bi8Mo48} exhibits a semi-flexible cage-like architecture with oxygen-rich surfaces and highly negative charges 72-. The nanoscaled molecular actuator shows reversible expansion and contraction behavior under humidity variations due to lattice expansion and contraction induced by hydrogen bonding and solvation interactions between {Bi8Mo48} and water molecules. Molecular dynamics simulation was further employed to study these processes, which provides a fundamental understanding for the mechanism of humidity actuation at the molecular level.
Reversible thermoresponsive hydrogels, which swell and shrink (deswell) in the temperature range of 30° to 60°C, provide an attractive material class for operating untethered soft robots in human physiological and ambient conditions. Crawling has been demonstrated previously with thermoresponsive hydrogels but required patterned or constrained gels or substrates to break symmetry for unidirectional motion. Here, we demonstrate a locomotion mechanism for unidirectionally crawling gels driven by spontaneous asymmetries in contact forces during swelling and deswelling of segmented active thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) and passive polyacrylamide (pAAM) bilayers with suspended linkers. Actuation studies demonstrate the consistent unidirectional movement of these gel crawlers across multiple thermal cycles on flat, unpatterned substrates. We explain the mechanism using finite element simulations and by varying experimental parameters such as the linker stiffness and the number of bilayer segments. We elucidate design criteria and validate experiments using image analysis and finite element models. We anticipate that this mechanism could potentially be applied to other shape-changing locomotors.
Magnetopolymers are of interest in smart material applications; however, changing their magnetic properties post synthesis is complicated. In this study, we introduce easily programmable polymer magnetic composites comprising 2D lattices of droplets of solid-liquid phase change material, with each droplet containing a single magnetic dipole particle. These composites are ferromagnetic with a Curie temperature defined by the rotational freedom of the particles above the droplet melting point. We demonstrate magnetopolymers combining high remanence characteristics with Curie temperatures below the composite degradation temperature. We easily reprogram the material between four states: (1) a superparamagnetic state above the melting point which, in the absence of an external magnetic field, spontaneously collapses to; (2) an artificial spin ice state, which after cooling forms either; (3) a spin glass state with low bulk remanence, or; (4) a ferromagnetic state with high bulk remanence when cooled in the presence of an external magnetic field. We observe the spontaneous emergence of 2D magnetic vortices in the spin ice and elucidate the correlation of these vortex structures with the external bulk remanence. We also demonstrate the easy programming of magnetically latching structures.
Hysteresis is the inherent characteristic of soft actuator, which seriously weakens its closed-loop control accuracy and applications in soft grippers, medical equipments and detection devices. Inspired by the hydraulic joint in spider leg, a soft joint actuator with dexterous structure and powerful driving is designed. Aiming at the problem that hysteresis characteristics of this pneumatic joint are difficult to be accurately obtained during dynamic rotation, a novel hysteresis measurement method of soft actuator is proposed. And an improved Prandtl-Ishlinskii (PI) model with a one-sided dead-zone operator is investigated to overcome the asymmetry of the force-angle hysteresis of the proposed joint actuator. The improved PI model is compared with the conventional PI model, Bouc-Wen model and experimental data, the results show that the maximum relative error of the improved PI-based force hysteresis model for the soft joint actuator under each inflation pressure is only 5.70%, the average deviation remained within 0.27 N, and the model fitting goodness is more than 0.99. It demonstrates that the improved PI model can accurately describe the non-singular and non-convex hysteresis characteristics of soft actuators, and provide a promising hysteresis modeling method for soft actuators made of hyperelastic materials to satisfy many more possible applications.
Polyvinylidene difluoride (PVDF)-based polymers have been extensively investigated as a type of electroactive polymer because of their wide applications in flexible sensors, actuators, and transducers. In this work, we demonstrate a new functionality of the PVDF-based polymer-shape memory effect (SME). We show that this effect mainly originates from the ferroelectric-paraelectric phase transition and that shape recovery can be realized at a high speed (< 100 ms), superior to most of the existing shape memory polymers. We synthesize modified Schiff base light-sensitive materials and compound them with the polymer to achieve composites exhibiting light-activated SME in the visible light range by exploiting the photothermal effect of the Schiff base compounds. Furthermore, the composites possess light-induced deformation because of the isomerization-induced volume change of the Schiff base molecules under light illumination. To demonstrate the application potential of the multifunctional composites, flexible actuators and robots were designed by combining the thermal-, light-, and electric field-activated SME or deformation. This study not only proposes new multifunctional composites with good application potential, but also presents a new mechanism to design shape memory polymers and expands the functionality of PVDF-based ferroelectric polymers.
Energy-efficient propulsion is a critical design target for robotic swimmers. Although previous studies have pointed out the importance of nonuniform body bending stiffness distribution (k) in improving the undulatory swimming efficiency of adult fish-like robots in the inertial flow regime, whether such an elastic mechanism is beneficial in the intermediate flow regime remains elusive. Hence, we develop a class of untethered soft milliswimmers consisting of a magnetic composite head and a passive elastic body with different k These robots realize larval zebrafish-like undulatory swimming at the same scale. Investigations reveal that uniform k and high swimming frequency (60 to 100 Hz) are favorable to improve their efficiency. A shape memory polymer-based milliswimmer with tunable k on the fly confirms such findings. Such acquired knowledge can guide the design of energy-efficient leading edge-driven soft undulatory milliswimmers for future environmental and biomedical applications in the same flow regime.
Intelligence of physical agents, such as human-made (e.g., robots, autonomous cars) and biological (e.g., animals, plants) ones, is not only enabled by their computational intelligence (CI) in their brain, but also by their physical intelligence (PI) encoded in their body. Therefore, it is essential to advance the PI of human-made agents as much as possible, in addition to their CI, to operate them in unstructured and complex real-world environments like the biological agents. This article gives a perspective on what PI paradigm is, when PI can be more significant and dominant in physical and biological agents at different length scales and how bioinspired and abstract PI methods can be created in agent bodies. PI paradigm aims to synergize and merge many research fields, such as mechanics, materials science, robotics, mechanical design, fluidics, active matter, biology, self-assembly and collective systems, to enable advanced PI capabilities in human-made agent bodies, comparable to the ones observed in biological organisms. Such capabilities would progress the future robots and other machines beyond what can be realized using the current frameworks.
The rapidly expanding field of soft robotics has provided multiple examples of how entirely soft machines and actuators can outperform conventional rigid robots in terms of adaptability, maneuverability, and safety. Unfortunately, the soft and flexible materials used in their construction impose intrinsic limitations on soft robots, such as low actuation speeds and low output forces. Nature offers multiple examples where highly flexible organisms exploit mechanical instabilities to store and rapidly release energy. Guided by these examples, researchers have recently developed a variety of strategies to overcome speed and power limitations in soft robotics using mechanical instabilities. These mechanical instabilities provide, through rapid transitions from structurally stable states, a new route to achieve high output power amplification and attain impressive actuation speeds. Here, an overview of the literature related to the development of soft robots and actuators that exploit mechanical instabilities to expand their actuation speed, output power, and functionality is presented. Additionally, strategies using structural phase transitions to address current challenges in the area of soft robotic control, sensing, and actuation are discussed. Approaches using instabilities to create entirely soft logic modules to imbue soft robots with material intelligence and distributed computational capabilities are also reviewed. Mechanical instabilities provide a novel route to achieve power amplification and attain impressive actuation speeds. An overview of the development of soft robots and actuators that exploit mechanical instabilities to expand their actuation speed, output power, and functionality is presented. These strategies have the potential to address the current challenges in the areas of soft robotic control, sensing, and actuation.
Natural systems display sophisticated control of light-matter interactions at multiple length scales for light harvesting, manipulation, and management, through elaborate photonic architectures and responsive material formats. Here, we combine programmable photonic function with elastomeric material composites to generate optomechanical actuators that display controllable and tunable actuation as well as complex deformation in response to simple light illumination. The ability to topographically control photonic bandgaps allows programmable actuation of the elastomeric substrate in response to illumination. Complex three-dimensional configurations, programmable motion patterns, and phototropic movement where the material moves in response to the motion of a light source are presented. A “photonic sunflower” demonstrator device consisting of a light-tracking solar cell is also illustrated to demonstrate the utility of the material composite. The strategy presented here provides new opportunities for the future development of intelligent optomechanical systems that move with light on demand.
The deep sea remains the largest unknown territory on Earth because it is so difficult to explore1–4. Owing to the extremely high pressure in the deep sea, rigid vessels5–7 and pressure-compensation systems8–10 are typically required to protect mechatronic systems. However, deep-sea creatures that lack bulky or heavy pressure-tolerant systems can thrive at extreme depths11–17. Here, inspired by the structure of a deep-sea snailfish¹⁵, we develop an untethered soft robot for deep-sea exploration, with onboard power, control and actuation protected from pressure by integrating electronics in a silicone matrix. This self-powered robot eliminates the requirement for any rigid vessel. To reduce shear stress at the interfaces between electronic components, we decentralize the electronics by increasing the distance between components or separating them from the printed circuit board. Careful design of the dielectric elastomer material used for the robot’s flapping fins allowed the robot to be actuated successfully in a field test in the Mariana Trench down to a depth of 10,900 metres and to swim freely in the South China Sea at a depth of 3,224 metres. We validate the pressure resilience of the electronic components and soft actuators through systematic experiments and theoretical analyses. Our work highlights the potential of designing soft, lightweight devices for use in extreme conditions.
Stimuli‐responsive and active materials promise radical advances for many applications. In particular, soft magnetic materials offer precise, fast, and wireless actuation together with versatile functionality, while liquid crystal elastomers (LCEs) are capable of large reversible and programmable shape‐morphing with high work densities in response to various environmental stimuli, e.g., temperature, light, and chemical solutions. Integrating the orthogonal stimuli‐responsiveness of these two kinds of active materials could potentially enable new functionalities and future applications. Here, magnetic microparticles (MMPs) are embedded into an LCE film to take the respective advantages of both materials without compromising their independent stimuli‐responsiveness. This composite material enables reconfigurable magnetic soft miniature machines that can self‐adapt to a changing environment. In particular, a miniature soft robot that can autonomously alter its locomotion mode when it moves from air to hot liquid, a vine‐like filament that can sense and twine around a support, and a light‐switchable magnetic spring are demonstrated. The integration of LCEs and MMPs into monolithic structures introduces a new dimension in the design of soft machines and thus greatly enhances their use in applications in complex environments, especially for miniature soft robots, which are self‐adaptable to environmental changes while being remotely controllable.
Robots are increasingly assisting humans in performing various tasks. Like special agents with elite skills, they can venture to distant locations and adverse environments, such as the deep sea and outer space. Micro/nanobots can also act as intrabody agents for healthcare applications. Self‐healing materials that can autonomously perform repair functions are useful to address the unpredictability of the environment and the increasing drive toward the autonomous operation. Having self‐healable robotic materials can potentially reduce costs, electronic wastes, and improve a robot endowed with such materials longevity. This review aims to serve as a roadmap driven by past advances and inspire future cross‐disciplinary research in robotic materials and electronics. By first charting the history of self‐healing materials, new avenues are provided to classify the various self‐healing materials proposed over several decades. The materials and strategies for self‐healing in robotics and stretchable electronics are also reviewed and discussed. It is believed that this article encourages further innovation in this exciting and emerging branch in robotics interfacing with material science and electronics.
Dry adhesion is governed by physical rather than chemical interactions. Those may include van der Waals and electrostatic forces, friction, and suction. Soft dry adhesives, which can be repeatedly attached to and detached from surfaces, can be useful for many exciting applications including reversible tapes, robotic footpads and grippers, and bio-integrated electronics. So far, the most studied Soft dry adhesives are gecko-inspired micro-pillar arrays, but they suffer from limited reusability and weak adhesion underwater. Recently cratered surfaces emerged as an alternative to micro-pillar arrays, as they exhibit many advantageous properties, such as tunable pressure-sensitive adhesion, high underwater adhesive strength, and good reusability. This review summarizes recent work of the authors on mechanical characterization of cratered surfaces, which combines experimental, modeling, and computational components. Using fundamental relationships describing air or liquid inside the crater, we examine the effects of material properties, crater shapes, air vs. liquid ambient environments, and surface patterns. We also identify some unresolved issues and limitations of the current approach, and provide an outlook for future research directions.
The advancement of technology has a profound and far‐reaching impact on the society, now penetrating all areas of life. From cradle to grave, one is supported by and depends on a wide range of electronic and robotic appliances, with an ever more intimate integration of the digital and biological spheres. These advances, however, often come at the price of negatively impacting our ecosystem, with growing demands on energy, contributions to greenhouse gas emissions and environmental pollution—from production to improper disposal. Mitigating these adverse effects is among the grand challenges of the society and at the forefront of materials research. The currently emerging forms of soft, biologically inspired electronics and robotics have the unique potential of becoming not only like their natural antitypes in performance and capabilities, but also in terms of their ecological footprint. This review outlines the rise of sustainable materials in soft and bioinspired robotics, targeting all robotic components from actuators to energy storage and electronics. The state‐of‐the‐art in biobased robotics spans flourishing fields and applications ranging from microbots operating in vivo to biohybrid machines and fully biodegradable yet resilient actuators. These first steps initiate the evolution of robotics and guide them into a sustainable future.
Minimally invasive medical procedures, such as endovascular catheterization, have considerably reduced procedure time and associated complications. However, many regions inside the body, such as in the brain vasculature, still remain inaccessible due to the lack of appropriate guidance technologies. Here, experimentally and through numerical simulations, we show that tethered ultra-flexible endovascular microscopic probes can be transported through tortuous vascular networks with minimal external intervention by harnessing hydrokinetic energy. Dynamic steering at bifurcations is performed by deformation of the probe head using magnetic actuation. We developed an endovascular microrobotic toolkit with a cross-sectional area that is orders of magnitude smaller than the smallest catheter currently available. Our technology has the potential to improve state-of-the-art practices as it enhances the reachability, reduces the risk of iatrogenic damage, significantly increases the speed of robot-assisted interventions, and enables the deployment of multiple leads simultaneously through a standard needle injection and saline perfusion.
Textiles have emerged as a promising class of materials for developing wearable robots that move and feel like everyday clothing. Textiles represent a favorable material platform for wearable robots due to their flexibility, low weight, breathability, and soft hand‐feel. Textiles also offer a unique level of programmability because of their inherent hierarchical nature, enabling researchers to modify and tune properties at several interdependent material scales. With these advantages and capabilities in mind, roboticists have begun to use textiles, not simply as substrates, but as functional components that program actuation and sensing. In parallel, materials scientists are developing new materials that respond to thermal, electrical, and hygroscopic stimuli by leveraging textile structures for function. Although textiles are one of humankind's oldest technologies, materials scientists and roboticists are just beginning to tap into their potential. This review provides a textile‐centric survey of the current state of the art in wearable robotic garments and highlights metrics that will guide materials development. Recent advances in textile materials for robotic components (i.e., as sensors, actuators, and integration components) are described with a focus on how these materials and technologies set the stage for wearable robots programmed at the material level.
Responsive soft materials capable of exhibiting various three-dimensional (3D) shapes under the same stimulus are desirable for promising applications including adaptive and reconfigurable soft robots. Here, we report a laser rewritable magnetic composite film, whose responsive shape-morphing behaviors induced by a magnetic field can be digitally and repeatedly reprogrammed by a facile method of direct laser writing. The composite film is made from an elastomer and magnetic particles encapsulated by a phase change polymer. Once the phase change polymer is temporarily melted by transient laser heating, the orientation of the magnetic particles can be re-aligned upon change of a programming magnetic field. By the digital laser writing on selective areas, magnetic anisotropies can be encoded in the composite film and then reprogrammed by repeating the same procedure, thus leading to multimodal 3D shaping under the same actuation magnetic field. Furthermore, we demonstrated their functional applications in assembling multistate 3D structures driven by the magnetic force-induced buckling, fabricating multistate electrical switches for electronics, and constructing reconfigurable magnetic soft robots with locomotion modes of peristalsis, crawling, and rolling.
A design, manufacturing, and control methodology is presented for the transduction of ultrasound into frequency-selective actuation of multibody hydrogel mechanical systems. The modular design of compliant mechanisms is compatible with direct laser writing and the multiple degrees of freedom actuation scheme does not require incorporation of any specific material such as air bubbles. These features pave the way for the development of active scaffolds and soft robotic microsystems from biomaterials with tailored performance and functionality. Finite element analysis and computational fluid dynamics are used to quantitatively predict the performance of acoustically powered hydrogels immersed in fluid and guide the design process. The outcome is the remotely controlled operation of a repertoire of untethered biomanipulation tools including monolithic compound micromachinery with multiple pumps connected to various functional devices. The potential of the presented technology for minimally invasive diagnosis and targeted therapy is demonstrated by a soft microrobot that can on-demand collect, encapsulate, and process microscopic samples.
Devices that perform cardiac mapping and ablation to treat atrial fibrillation provide an effective means of treatment. Current devices, however, have limitations that either require tedious point-by-point mapping of a cardiac chamber or have limited ability to conform to the complex anatomy of a patient’s cardiac chamber. In this work, a detailed, scalable, and manufacturable technique is reported for fabrication of a multielectrode, soft robotic sensor array. These devices exhibit high conformability (~85 to 90%) and are equipped with an array of stretchable electronic sensors for voltage mapping. The form factor of the device is intended to match that of the entire left atrium and has a hydraulically actuated soft robotic structure whose profile facilitates deployment from a 13.5-Fr catheter. We anticipate that the methods described in this paper will serve a new generation of conformable medical devices that leverage the unique characteristics of stretchable electronics and soft robotics.
Soft robotic grippers are shown to be high effective for grasping unstructured objects with simple sensing and control strategies. However, they are still limited by their speed, sensing capabilities and actuation mechanism. Hence, their usage have been restricted in highly dynamic grasping tasks. This paper presents a soft robotic gripper with tunable bistable properties for sensor-less dynamic grasping. The bistable mechanism allows us to store arbitrarily large strain energy in the soft system which is then released upon contact. The mechanism also provides flexibility on the type of actuation mechanism as the grasping and sensing phase is completely passive. Theoretical background behind the mechanism is presented with finite element analysis to provide insights into design parameters. Finally, we experimentally demonstrate sensor-less dynamic grasping of an unknown object within 0.02 seconds, including the time to sense and actuate.
Colorful changes
Distributed fiber-optic sensors have been used for monitoring mechanical deformations in stiff infrastructures such as bridges, roads, and buildings, but they either are limited to measuring one variable or require complex optics to measure multiple properties. Bai et al. now demonstrate dual-core elastomeric optical fibers, one of which contains patterned dye regions. The waveguides are fabricated by molding out of commercially available elastomers and integrate a clear core and an adjacent core doped with up to three macroscale dye regions. Changes in optical paths in the two cores detect deformation and map it onto a color space. By monitoring changes in the color and intensity in both elastomer-based fibers, the researchers could distinguish bending, stretching, and localized pressing with a spatial resolution down to ∼1 centimeter.
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Future robots and intelligent systems will autonomously navigate in
unstructured environments and closely collaborate with humans; integrated
with our bodies and minds, they will allow us to surpass our physical
limitations. Traditional robots are mostly built from rigid, metallic components
and electromagnetic motors, which make them heavy, expensive, unsafe
near people, and ill-suited for unpredictable environments. By contrast,
biological organisms make extensive use of soft materials and radically
outperform robots in terms of dexterity, agility, and adaptability. Particularly,
natural muscle—a masterpiece of evolution—has long inspired researchers
to create “artificial muscles” in an attempt to replicate its versatility, seamless
integration with sensing, and ability to self-heal. To date, natural muscle
remains unmatched in all-round performance, but rapid advancements in soft
robotics have brought viable alternatives closer than ever. Herein, the recent
development of hydraulically amplified self-healing electrostatic (HASEL)
actuators, a new class of high-performance, self-sensing artificial muscles
that couple electrostatic and hydraulic forces to achieve diverse modes of
actuation, is discussed; current designs match or exceed natural muscle
in many metrics. Research on materials, designs, fabrication, modeling,
and control systems for HASEL actuators is detailed. In each area, research
opportunities are identified, which together lays out a roadmap for actuators
with drastically improved performance. With their unique versatility and wide
potential for further improvement, HASEL actuators are poised to play an
important role in a paradigm shift that fundamentally challenges the current
limitations of robotic hardware toward future intelligent systems that replicate
the vast capabilities of biological organisms.
Coordinated nonreciprocal dynamics in biological cilia is essential to many living systems, where the emergentmetachronal waves of cilia have been hypothesized to enhance net fluid flows at low Reynolds numbers (Re). Experimental investigation of this hypothesis is critical but remains challenging. Here, we report soft miniature devices with both ciliary nonreciprocal motion and metachronal coordination and use them to investigate the quantitative relationship between metachronal coordination and the induced fluid flow. We found that only antiplectic metachronal waves with specific wave vectors could enhance fluid flows compared with the synchronized case. These findings further enable various bioinspired cilia arrays with unique functionalities of pumping and mixing viscous synthetic and biological complex fluids at low Re. Our design method and developed soft miniature devices provide unprecedented opportunities for studying ciliary biomechanics and creating cilia-inspired wireless microfluidic pumping, object manipulation and lab- and organ-on-a-chip devices, mobile microrobots, and bioengineering systems.
Haptic actuators generate touch sensations and provide realism and depth in human–machine interactions. A new generation of soft haptic interfaces is desired to produce the distributed signals over large areas that are required to mimic natural touch interactions. One promising approach is to combine the advantages of organic actuator materials and additive printing technologies. This powerful combination can lead to devices that are ergonomic, readily customizable, and economical for researchers to explore potential benefits and create new haptic applications. Here, an overview of emerging organic actuator materials and digital printing technologies for fabricating haptic actuators is provided. In particular, the focus is on the challenges and potential solutions associated with integration of multi‐material actuators, with an eye toward improving the fidelity and robustness of the printing process. Then the progress in achieving compact, lightweight haptic actuators by using an open‐source extrusion printer to integrate different polymers and composites in freeform designs is reported. Two haptic interfaces—a tactile surface and a kinesthetic glove—are demonstrated to show that printing with organic materials is a versatile approach for rapid prototyping of various types of haptic devices. An overview of emerging organic actuator materials and digital printing technologies for fabricating soft organic haptic actuators to emulate touch sensations is provided. In particular, the focus is on the challenges and potential solutions associated with integration of multi‐material actuators. The progress in achieving compact, lightweight haptic actuators by combining different polymers and composites in freeform designs is reported.
Many creatures have the ability to traverse challenging environments by using their active muscles with anisotropic structures as the motors in a highly coordinated fashion. However, most artificial robots require multiple independently activated actuators to achieve similar purposes. Here we report a hydrogel-based, biomimetic soft robot capable of multimodal locomotion fueled and steered by light irradiation. A muscle-like poly(N-isopropylacrylamide) nanocomposite hydrogel is prepared by electrical orientation of nanosheets and subsequent gelation. Patterned anisotropic hydrogels are fabricated by multi-step electrical orientation and photolithographic polymerization, affording programmed deformations. Under light irradiation, the gold-nanoparticle-incorporated hydrogels undergo concurrent fast isochoric deformation and rapid increase in friction against a hydrophobic substrate. Versatile motion gaits including crawling, walking, and turning with controllable directions are realized in the soft robots by dynamic synergy of localized shape-changing and friction manipulation under spatiotemporal light stimuli. The principle and strategy should merit designing of continuum soft robots with biomimetic mechanisms.
Small‐scale magnetic soft‐bodied robots based on biocompatible and biodegradable materials are essential for their potential high‐impact minimally invasive medical applications inside the human body. Therefore, a strategy for fully biodegradable untethered soft millirobots with encoded 3D magnetic anisotropy for their static or dynamic shape programming is presented. Such a robot body is comprised of a porcine extracellular matrix‐derived collagen‐based hydrogel network with embedded superparamagnetic iron oxide nanoparticles (SPIONs). 3D magnetization programming inside the hydrogel body is achieved by directionally self‐assembled SPION chains using an external permanent magnet. As a proof‐of‐concept demonstration, a hydrogel milli‐gripper that can undergo flexible and reversible shape deformations inside glycerol and biologically relevant liquid media is presented. The gripper can perform cargo grabbing, transportation by rolling, and release by controlling magnetic field inputs. These milli‐grippers can be completely degraded by the matrix metalloproteinase‐2 enzyme in physiologically relevant concentrations. Furthermore, biocompatibility tests using human umbilical cord vein endothelial cells with the degradation products of the grippers demonstrate no acute toxicity. The approach offers a facile fabrication strategy for designing biocompatible and biodegradable soft robots using nanocomposite materials with programmable 3D magnetic anisotropy toward future medical applications. A biodegradable magnetic milli‐gripper is developed by creating a three‐dimensional magnetic profile in a gelatin hydrogel matrix using directionally self‐assembled superparamagnetic iron oxide nanoparticle chains. It can undergo reversible shape deformations and perform cargo grasping and transportation tasks under controlled magnetic fields. The milli‐gripper can be completely degraded by the matrix metalloproteinase‐2 enzyme in physiologically relevant concentrations.
Shape-morphing magnetic soft machines are highly desirable for diverse applications in minimally invasive medicine , wearable devices, and soft robotics. Despite recent progress, current magnetic programming approaches are inherently coupled to sequential fabrication processes, preventing reprogrammability and high-throughput programming. Here, we report a high-throughput magnetic programming strategy based on heating magnetic soft materials above the Curie temperature of the embedded ferromagnetic particles and reorienting their magnetic domains by applying magnetic fields during cooling. We demonstrate discrete, three-dimensional, and re-programmable magnetization with high spatial resolution (~38 m). Using the reprogrammable magnetization capability, reconfigurable mechanical behavior of an auxetic metamaterial structure, tunable locomotion of a surface-walking soft robot, and adaptive grasping of a soft gripper are shown. Our approach further enables high-throughput magnetic programming (up to 10 samples/min) via contact transfer. Heat-assisted magnetic programming strategy described here establishes a rich design space and mass-manufacturing capability for development of multiscale and reprogrammable soft machines.
The rigidity and relatively primitive modes of operation of catheters equipped with sensing or actuation elements impede their conformal contact with soft-tissue surfaces, limit the scope of their uses, lengthen surgical times and increase the need for advanced surgical skills. Here, we report materials, device designs and fabrication approaches for integrating advanced electronic functionality with catheters for minimally invasive forms of cardiac surgery. By using multiphysics modelling, plastic heart models and Langendorff animal and human hearts, we show that soft electronic arrays in multilayer configurations on endocardial balloon catheters can establish conformal contact with curved tissue surfaces, support high-density spatiotemporal mapping of temperature, pressure and electrophysiological parameters and allow for programmable electrical stimulation, radiofrequency ablation and irreversible electroporation. Integrating multimodal and multiplexing capabilities into minimally invasive surgical instruments may improve surgical performance and patient outcomes.
Artificial microcilia structures have shown potential to incorporate actuators in various applications such as microfluidic devices and biomimetic microrobots. Among the multiple possibilities to achieve cilia actuation, magnetic fields present an opportunity given their quick response and wireless operation, despite the difficulty in achieving localized actuation because of their continuous distribution. In this work, a high‐aspect‐ratio (>8), elastomeric, magnetically responsive microcilia array is presented that allows for wireless, localized actuation through the combined use of light and magnetic fields. The microcilia array can move in response to an external magnetic field and can be locally actuated by targeted illumination of specific areas. The periodic pattern of the microcilia also diffracts light with varying diffraction efficiency as a function of the applied magnetic field, showing potential for wirelessly controlled adaptive optical elements. Chromium dioxide/poly(dimethylsiloxane) composite micropillars with high aspect‐ratio and magnetic properties are presented. The microcilia can be remotely actuated either collectively or selectively by using magnetic fields and light. Light‐driven local actuation enables this microcilia array to function as reconfigurable and controllably moving subsets.
There is ever-increasing interest yet grand challenge in developing programmable untethered soft robotics. Here we address this challenge by applying the asymmetric elastoplasticity of stacked graphene assembly (SGA) under tension and compression. We transfer the SGA onto a polyethylene (PE) film, the resulting SGA/PE bilayer exhibits swift morphing behavior in response to the variation of the surrounding temperature. With the applications of patterned SGA and/or localized tempering pretreatment, the initial configurations of such thermal-induced morphing systems can also be programmed as needed, resulting in diverse actuation systems with sophisticated three-dimensional structures. More importantly, unlike the normal bilayer actuators, our SGA/PE bilayer, after a constrained tempering process, will spontaneously curl into a roll, which can achieve rolling locomotion under infrared lighting, yielding an untethered light-driven motor. The asymmetric elastoplasticity of SGA endows the SGA-based bi-materials with great application promise in developing untethered soft robotics with high configurational programmability. Developing programmable untethered soft robotics remains a challenge. Here the authors apply the asymmetric elastoplasticity of stacked graphene assembly to address this challenge and realize untethered thermoresponsive morphing in tandem with high configurational programmability.
Microrobots offer transformative solutions for non‐invasive medical interventions due to their small size and untethered operation inside the human body. However, they must face the immune system as a natural protection mechanism against foreign threats. Here, non‐immunogenic stealth zwitterionic microrobots that avoid recognition from immune cells are introduced. Fully zwitterionic photoresists are developed for two‐photon polymerization 3D microprinting of hydrogel microrobots with ample functionalization: tunable mechanical properties, anti‐biofouling and non‐immunogenic properties, functionalization for magnetic actuation, encapsulation of biomolecules, and surface functionalization for drug delivery. Stealth microrobots avoid detection by macrophage cells of the innate immune system after exhaustive inspection (>90 hours), which has not been achieved in any microrobotic platform to date. These versatile zwitterionic materials eliminate a major roadblock in the development of biocompatible microrobots, and will serve as a toolbox of non‐immunogenic materials for medical microrobot and other device technologies for bioengineering and biomedical applications. Zwitterionic stealth microrobots avoid detection and capture by immune cells. Zwitterionic microrobots with anti‐biofouling, stealth, and non‐immunogenic properties are 3D‐printed via two‐photon‐polymerization, and are functionalized for magnetic actuation, encapsulation of biomolecules, and drug delivery. The microrobots remain undetected by macrophages and other immune cells for at least 90 hours, overcoming a major roadblock in medical microrobotics.
In the real world, people heavily rely on haptic or touch to manipulate objects. In emerging systems such as assistive devices, remote surgery, self-driving cars and the guidance of human movements, visual or auditory feedback can be slow, unintuitive and increase the cognitive load. Skin stretch devices (SSDs) that apply tangential force to the skin via a tactor can encode a far richer haptic space, not being limited to force, motion, direction, stiffness, indentation and surface geometry. This paper introduces novel hand-worn hydraulic SSDs that can induce 3-axis tangential forces to the skin via a tactor. The developed SSDs are controlled by new soft microtubule muscles (SMMs) which are driven by hydraulic pressure via custom miniature syringes and DC micromotors. An analytical model is developed to characterize the responses of SMM output in terms of force and elongation. A kinematic model for the motion of the 3-axis SSD is also developed. We evaluate the capability of the tactor head to track circular reference trajectories within different working spaces using an optical tracking system. Experimental results show that the developed SSDs have good durability, high-speed, and can generate omnidirectional shear forces and desired displacement up to 1.8 N and 4.5 mm, respectively. The developed SMMs and SSDs created in this paper will enable new forms of haptic communication to augment human performance during daily activities such as tactile textual language, motion guidance and navigational assistance, remote surgical systems, rehabilitation, education, training, entertainment, or virtual and augmented reality.
Tensegrity structures provide both structural integrity and flexibility through the combination of stiff struts and a network of flexible tendons. These structures exhibit useful properties: high stiffness-to-mass ratio, controllability, reliability, structural flexibility, and large deployment. The integration of smart materials into tensegrity structures would provide additional functionality and may improve existing properties. However, manufacturing approaches that generate multimaterial parts with intricate three-dimensional (3D) shapes suitable for such tensegrities are rare. Furthermore, the structural complexity of tensegrity systems fabricated through conventional means is generally limited because these systems often require manual assembly. Here, we report a simple approach to fabricate tensegrity structures made of smart materials using 3D printing combined with sacrificial molding. Tensegrity structures consisting of monolithic tendon networks based on smart materials supported by struts could be realized without an additional post-assembly process using our approach. By printing tensegrity with coordinated soft and stiff elements, we could use design parameters (such as geometry, topology, density, coordination number, and complexity) to program system-level mechanics in a soft structure. Last, we demonstrated a tensegrity robot capable of walking in any direction and several tensegrity actuators by leveraging smart tendons with magnetic functionality and the programmed mechanics of tensegrity structures. The physical realization of complex tensegrity metamaterials with programmable mechanical components can pave the way toward more algorithmic designs of 3D soft machines.
Stimuli-responsive hydrogel actuators have promising applications in various fields. However, the typical hydrogel actuation relies on the swelling and de-swelling process caused by osmotic-pressure changes, which is slow and normally requires the presence of water environment. Herein, we report a light-powered in-air hydrogel actuator with remarkable performances, including ultrafast motion speed (up to 1.6 m/s), rapid response (as fast as 800 ms) and high jumping height (~15 cm). The hydrogel is operated based on a fundamentally different mechanism that harnesses the synergetic interactions between the binary constituent parts, i.e. the elasticity of the poly(sodium acrylate) hydrogel, and the bubble caused by the photothermal effect of the embedded magnetic iron oxide nanoparticles. The current hydrogel actuator exhibits controlled motion velocity and direction, making it promising for a wide range of mobile robotics, soft robotics, sensors, controlled drug delivery and other miniature device applications. Actuation of hydrogel actuators relies on slow swelling and de-swelling process which hampers its application in many fields. Here the authors report a light-powered in-air hydrogel actuator with remarkable performances including fast motion, speed and rapid response time.
Self-healing materials are indispensable for soft actuators and robots that operate in dynamic and real-world environments, as these machines are vulnerable to mechanical damage. However, current self-healing materials have shortcomings that limit their practical application, such as low healing strength (below a megapascal) and long healing times (hours). Here, we introduce high-strength synthetic proteins that self-heal micro- and macro-scale mechanical damage within a second by local heating. These materials are optimized systematically to improve their hydrogen-bonded nanostructure and network morphology, with programmable healing properties (2–23 MPa strength after 1 s of healing) that surpass by several orders of magnitude those of other natural and synthetic soft materials. Such healing performance creates new opportunities for bioinspired materials design, and addresses current limitations in self-healing materials for soft robotics and personal protective equipment. Protein-based materials for soft robotics that self-heal within a second while maintaining the high strength of the damaged area are reported.
The sense of touch is underused in today’s virtual reality systems due to lack of wearable, soft, mm‐scale transducers to generate dynamic mechanical stimulus on the skin. Extremely thin actuators combining both high force and large displacement are a long‐standing challenge in soft actuators. Sub‐mm thick flexible hydraulically amplified electrostatic actuators are reported here, capable of both out‐of‐plane and in‐plane motion, providing normal and shear forces to the user’s fingertip, hand, or arm. Each actuator consists of a fluid‐filled cavity whose shell is made of a metalized polyester boundary and a central elastomer region. When a voltage is applied to the annular electrodes, the fluid is rapidly forced into the stretchable region, forming a raised bump. A 6 mm × 6 mm × 0.8 mm actuator weighs 90 mg, and generates forces of over 300 mN, out‐of‐plane displacements of 500 µm (over 60% strain), and lateral motion of 760 µm. Response time is below 5 ms, for a specific power of 100 W kg⁻¹. In user tests, human subjects distinguished normal and different 2‐axis shear forces with over 80% accuracy. A flexible 5 × 5 array is demonstrated, integrated in a haptic sleeve.
Thermal perception is essential for the survival and daily activities of people. Thus, it is desirable to realize thermal feedback stimulation for improving the sense of realism in virtual reality (VR) for users. For thermal stimulus, conventional systems utilize liquid circulation with bulky external sources or thermoelectric devices (TEDs) on rigid structures. However, these systems are difficult to apply to compact wearable gear used for complex hand motions to interact with VR. Furthermore, generating a rapid temperature difference, especially cooling, in response to a thermal stimulus in real-time is challenging for the conventional systems. To overcome this challenge and enhance wearability, we developed an untethered real-time thermal display glove. This glove comprised piezoelectric sensors enabling hand motion sensing and flexible TEDs for bidirectional thermal stimulus on skin. The customized flexible TEDs can decrease the temperature by 10 °C at room temperature in less than 0.5 s. Moreover, they have sufficiently high durability to withstand over 5,000 bends and high flexibility under a bending radius of 20 mm. In a user test with 20 subjects, the correlation between thermal perception and the displayed object’s color was verified, and a survey result showed that the thermal display glove provided realistic and immersive experiences to users when interacting with VR.
