REVIEW www.advmat.de Functional Fibers and Fabrics for Soft Robotics, Wearables, and Human–Robot Interface Jiaqing Xiong, Jian Chen, and Pooi See Lee* excellent mechanical adaptability to enable Soft robotics inspired by the movement of living organisms, with excellent safe and friendly interactions with human. adaptability and accuracy for accomplishing tasks, are highly desirable for Fiber that has been known for thousands efficient operations and safe interactions with human. With the emerging of years for textile engineering, is a kind of wearable electronics, higher tactility and skin affinity are pursued for safe thin 1D material with large length–diam- eter ratio and softness. Fiber can be fur- and user-friendly human–robot interactions. Fabrics interlocked by fibers ther processed into 1D or 3D yarns and 2D perform traditional static functions such as warming, protection, and or 3D fabrics and can be subjected to well- fashion. Recently, dynamic fibers and fabrics are favorable to deliver active established textile manufacturing tech- stimulus responses such as sensing and actuating abilities for soft-robots niques, such as dyeing, twisting, sewing, [1] and wearables. First, the responsive mechanisms of fiber/fabric actuators and knitting, weaving, braiding, etc. As com- mercially available material, fabric has their performances under various external stimuli are reviewed. Fiber/yarn- been widely used for clothing, bedding, based artificial muscles for soft-robots manipulation and assistance in human or furniture. Such wide-adoption dem- motion are discussed, as well as smart clothes for improving human percep- onstrates fabrics/textiles to be important tion. Second, the geometric designs, fabrications, mechanisms, and functions and adaptable as daily useable material of fibers/fabrics for sensing and energy harvesting from the human body and due to their merits of protection, breatha- [2] environments are summarized. Effective integration between the electronic bility, comfort, and durability. In recent years, novel smart responsive functions components with garments, human skin, and living organisms is illustrated, are desirable to be implemented on fibers presenting multifunctional platforms with self-powered potential for human– and fabrics for seamless integrations of robot interactions and biomedicine. Lastly, the relationships between robotic/ actuators, sensors, power sources, etc., wearable fibers/fabrics and the external stimuli, together with the challenges to realize the robotic fibers/fabric-based and possible routes for revolutionizing the robotic fibers/fabrics and weara- manipulators and human–robot inter- faces. These emerging responsive fibers/ bles in this new era are proposed. fabrics are desirable to offer program- mable functions, actuations, perception and capable of building an intuitive and 1. Introduction dynamic collaborative scenarios with human, promising in ena- bling applications such as remote operation, human motion Human–robot interface (HRI) is an emerging smart interface assistance, human perception, health monitoring and biomed- that allows operations, interactions and collaborations between ical detection and therapy.[3–5] It is an attractive concept that the human and robots/machines in a colocated or coordinated future human–robot interfaces could be embodied in familiar way, fulfilling works with higher efficiency or addressing some forms for humans such as textiles or clothes. Compared with complicated/dangerous tasks. Soft robotics, often inspired by the polymeric and elastomeric soft robotics,[6–9] fibers and fab- the adaptability of living organisms, are capable of delivering rics are advantageous in applications of soft robotics and weara- bles for human. The devices could be programmable to have accurate designs in configuration and high performance by Dr. J. Xiong, Dr. J. Chen, Prof. P. S. Lee School of Materials Science and Engineering traditional manufacturing processes of textile, applying twist to Nanyang Technological University transform fibers into coils, yarns with hierarchical structures, Singapore 639798, Singapore which could be further fabricated into fabrics or textiles by E-mail: [email protected] sewing, weaving, knitting, etc., techniques (Figure 1), guaran- The ORCID identification number(s) for the author(s) of this article teeing good wearability, skin affinity, washability, and durability, can be found under https://doi.org/10.1002/adma.202002640. which are intriguing and necessary for friendly robotics interac- © 2020 The Authors. Published by Wiley-VCH GmbH. This is an open tions with human. access article under the terms of the Creative Commons Attribution- Soft robotics include three main components of actuators, NonCommercial License, which permits use, distribution and reproduc- sensors, and control modules with power sources.[10,11] Of which, tion in any medium, provided the original work is properly cited and is not used for commercial purposes. actuators, sensors and power sources all could be designed in the form of fibers or fabrics, rendering facile assembly, and DOI: 10.1002/adma.202002640 integration by interlocking.[12] Common actuations can be Adv. Mater. 2020, 2002640 2002640 (1 of 43) © 2020 The Authors. Published by Wiley-VCH GmbH www.advancedsciencenews.com www.advmat.de Figure 1. The available forms of fibers in 1D, 3D, and 2D configurations include yarns and fabric/textile for application in actuators, sensors, and power sources. achieved under external stimuli such as electricity, light, heat, In recent years, increasing efforts are dedicated to develop magnetic field, solvent, and vapor conditions, realizing various power-fibers/fabrics for self-powered wearables and intelli- displacements in 1D, 2D, or 3D directions. For example, fiber gent robotic systems. It has been proven that thermal energy, actuators could deliver linear motion, enabling important mechanical energy, water energy, solar irradiance energy, etc., applications in some special 1D or space-limited scenarios, can be harvested and stored individually or simultaneously by such as biomedical targeted delivery and therapy in vessels.[13] fibers/yarns or fabrics/textiles-based devices, such as thermoe- Twisting manipulation through internal contraction or relaxa- lectric generator, piezo-/triboelectric nano generators, and solar tion forces could be realized using the yarn-based actuators, cells.[25–27] These devices can power traditional devices, or serve capable of simulating the motions such as contraction, relaxa- as self-powered sensors and functional components, enabling tion, and expansion, alike of artificial muscles for operating seamless integrations with actuators and sensors to simplify the robots and assisting the human motions especially the the robotic fiber/fabric systems, which are especially effective disabled.[14] Besides, weaving or knitting the actuation fibers for wearables power sources or sensors to bridge the connec- and yarns could be further fabricated into fabric actuators, tions for more-friendly human–robot interactions. In addi- attaining higher actuation displacement and force, with the tion, efforts were also made to integrate other functions such potential to produce smart garments that have active responses, as color changing and data storage/processing for applications such as thermal-regulation under the stimuli from solvent/vapor, of fibers/fabrics in camouflage, displays, memories, artificial heat, light, electricity, magnetic field, etc., and self-protection synapses and information communications, assisting to con- actions against mechanical attacks or invasions.[15] These smart struct more intelligent interfaces for robots–environments and responsive clothes are significant for improving the human human–machines.[28–36] perception and quality of life. Herein, we summarize the progress of fibers/yarns and Sensors are essential for feedback-control of the soft robots. fabrics/textiles for soft robots, wearables, and human–robot Fiber/fabric-based sensors possess intrinsic merits for wear- interface. First, mechanisms of fiber/fabric-based actua- able applications and human–robot interactions, providing tors responding to various stimuli were introduced, the latest good skin affinity and safer interactive platforms for users.[16] achievements of each kind of actuators were reviewed with In terms of fabrication, fibers, yarns, and fabrics/textiles are all classifications to figure out the device designs and working pro- feasible to be designed as sensors, such as mechanical sensor cesses. Combining various responsive mechanisms, we sum- (strain sensor, pressure sensor), thermal sensor, humidity marize the types of artificial muscles assembled by fibers and sensor, electrochemical sensor, etc.[17] They can perceive and yarns, presenting attractive functions for soft-robots manipula- convert various mechanical motions, temperature/humidity tion, human motions, and the disabled assistance, furthermore, changes, metabolite, and various bio/chemical inputs into we show the smart responsive clothes for human perception electricity signals, detecting the actuation displacement/force, and smart actuation. Secondly, we summarize the fiber/fabric- human motions, and environmental conditions, enabling pre- based wearable sensors for detection of mechanical motions, cise feedback-controls for actuators/robots. Besides, the fiber/ temperature, humidity, metabolite, etc., and power fibers/fab- fabric-based sensors are also compatible