Soft exoskeleton. A soft exoskeleton, also known as a soft wearable robot or a soft robotic exosuit, is a type of wearable robotic device designed to augment and enhance the physical abilities of the human body. Unlike traditional rigid exoskeletons, which are typically made of hard materials like metal and are worn over the user's limbs, soft exoskeletons are constructed from flexible and lightweight materials. Soft exoskeletons are designed to assist individuals with mobility impairments, aid in rehabilitation, augment human performance, and improve overall quality of life.

Evolution from rigid exoskeleton 

The concept of exoskeletons can be traced back to science fiction literature, where authors envisioned mechanical suits that enhance human abilities. However, soft exoskeletons, as we know them today, have their roots in the development of soft robotics and advanced materials science. The evolution of soft exoskeletons can be divided into several key stages:

Early developments (1960s–1980s) 
The Hardiman Project (1965–1971) was one of the earliest notable attempts at creating a powered exoskeleton was the Hardiman Project, sponsored by the U.S. military and developed by General Electric and the U.S. Army. The project aimed to create a full-body rigid exoskeleton to enhance the strength and endurance of soldiers and workers. Hardiman suit made lifting 250 pounds (110 kg) feel like lifting 10 pounds (4.5 kg). Powered by hydraulics and electricity, the suit allowed the wearer to amplify their strength by a factor of 25, so that lifting 25 pounds was as easy as lifting one pound without the suit. However, the project was discontinued due to technical challenges, including power supply and control issues.

Cybernetic Research Project 
In the Soviet Union, research on powered exoskeletons was conducted under the Soviet Cybernetic Research Project Scientists and engineers explored the development of exoskeletons for military applications, focusing on enhancing soldiers' physical capabilities.
Bionics involves a comprehensive exploration of nature, incorporating technical elements into the study of flora and fauna. The discipline revolves around mimicking natural manufacturing processes, replicating biological techniques and mechanisms, and examining the social behavior of organisms.

In the twilight of the 19th century, a Russian engineer named Nicholas Yagin embarked on a groundbreaking journey that would lay the foundation for a revolutionary technological leap – the creation of the world's first exoskeleton-like device. It was the year 1890, an era characterized by rapid industrialization and a fervent spirit of innovation. Yagin, a visionary mind with a passion for engineering and human augmentation, dedicated himself to crafting a solution that would amplify the capabilities of the human body. Inspired by the marvels of nature and the intricate design of insects' exoskeletons, he envisioned a device that could enhance human mobility and strength. The early exoskeleton prototype consisted of articulated joints and a network of gears, springs, and levers that responded to the wearer's movements. Its purpose was clear – to augment the human body, providing support and amplifying strength.

In the late 1970s, Dr. David A. Winter, a biomechanics researcher, made notable contributions to the field by focusing on the biomechanics of human locomotion. His work provided valuable insights into the design considerations for exoskeletons, emphasizing the need for a more holistic understanding of human movement.

By the early 1980s researchers like Dr. Homayoon Kazerooni began to delve into the practical applications of exoskeletons for rehabilitation. In 1989, Dr. Kazerooni founded Berkeley Bionics, a pivotal moment that marked a shift toward the development of more user-friendly exoskeletons. However, during this period, rigid exoskeletons remained the primary focus, with limitations in terms of weight and mobility.

In 1983, the Massachusetts Institute of Technology (MIT) introduced the MIT Exoskeleton, a powered exoskeleton designed for rehabilitation purposes. This project, led by Dr. Steven Jacobsen, was a notable step forward in incorporating robotics into assistive devices.

Powered Exoskeletons in the 1990s 
A prototype of the Berkeley Lower Extremity Exoskeleton (BLEEX) arose in the late 1990s when the landscape of exoskeleton development was undergoing a transformative phase, with researchers and engineers exploring innovative ways to enhance human capabilities. The Berkeley Lower Extremity Exoskeleton (BLEEX) was one such pioneering project that laid the foundation for the advancements in powered exoskeletons. The BLEEX project, initiated by the Robotics and Human Engineering Laboratory at the University of California, Berkeley, sought to address the challenges associated with walking and carrying heavy loads. The primary goal was to develop a soft exoskeleton capable of reducing the metabolic cost of these activities, thereby providing a breakthrough in human augmentation technology. The early prototypes of BLEEX showcased the integration of flexible materials and actuation systems, marking a departure from the more rigid exoskeleton designs of the time. Researchers focused on creating a symbiotic relationship between the wearer and the exoskeleton, emphasizing comfort and natural movement. As the project progressed into the 2000s, BLEEX gained recognition for its potential applications in various fields, including military, medical rehabilitation, and industrial settings. The soft exoskeleton concept pioneered by BLEEX became a catalyst for subsequent research in the development of wearable robotics.

Exoskeletons for Industrial Use (1990s) 
In tandem with the BLEEX project, the 1990s witnessed a surge in pioneering research dedicated to harnessing the potential of exoskeletons within industrial settings. Rigid exoskeletons emerged as a promising solution, aiming to alleviate the physical strain encountered by workers engaged in tasks demanding heavy lifting and repetitive motions.

One remarkable example from this era involves the concerted efforts of a team of engineers led by Dr. Hiroshi Kobayashi at the Tokyo University of Science. In 1995, this team introduced a groundbreaking powered exoskeleton specifically designed to assist construction workers in Japan. The exoskeleton, equipped with state-of-the-art intelligent actuators and motion sensors, was meticulously crafted to augment human strength and endurance, thereby alleviating the burdens associated with manual labor in the construction industry.

The impetus behind this development stemmed from a pressing need to address the high incidence of musculoskeletal injuries among construction workers, especially those involved in tasks requiring the lifting and transportation of heavy building materials. By integrating cutting-edge technology into the exoskeleton design, the engineering team sought to create a symbiotic relationship between man and machine, enhancing both productivity and occupational safety.

Early concepts – late 20th century 

The impetus for early experiments often arose from military needs and industrial demands. In military contexts, exoskeleton research aimed to create powered exosuits that could amplify soldiers' strength, allowing them to carry heavier loads over long distances, navigate challenging terrains, and perform tasks that would be otherwise strenuous or dangerous. In the industrial sector, the focus was on developing exoskeletons to assist workers in tasks involving heavy lifting, repetitive motions, and prolonged periods of standing, thereby reducing the risk of work-related injuries and increasing productivity.

Pioneers 

The evolution of soft exoskeletons is deeply intertwined with the contributions of pioneering innovators and researchers who pushed the boundaries of wearable robotics. As the technology shifted from rigid exoskeletons to softer, more flexible designs, several key figures and significant developments shaped the history of the soft exoskeletons.

Conor Walsh 

Conor Walsh, a Harvard University researcher, made significant strides in soft exoskeleton technology with the development of the Soft Exosuit. Walsh's team at the Wyss Institute for Biologically Inspired Engineering created a lightweight and flexible exoskeleton that used textile-based actuators to assist specific muscle groups. This groundbreaking approach marked a departure from rigid structures, offering a more comfortable and natural wearing experience.

Wyss Institute 

The Wyss Institute for Biologically Inspired Engineering continued to be at the forefront of soft exoskeleton research. Researchers at the institute focused on refining soft exosuit designs, integrating advanced sensors and control systems, and exploring diverse applications, including medical rehabilitation and enhancing human performance in various tasks.

Japanese innovations and HAL (Hybrid Assistive Limb) exoskeleton 

Cyberdyne Inc., a Japanese robotics company founded by Dr. Yoshiyuki Sankai, developed the Hybrid Assistive Limb (HAL) exoskeleton. HAL was one of the first commercially available soft exoskeletons designed to enhance and support human mobility. The exoskeleton detected bioelectric signals from the wearer's muscles, enabling intuitive control of the device. HAL found applications in healthcare, aiding individuals with mobility impairments and contributing to the field of robotic-assisted rehabilitation..

ReWalk Robotics, founded by Dr. Amit Goffer, introduced personal exoskeleton systems designed to assist individuals with spinal cord injuries in walking. These wearable devices used soft components and advanced motion sensors, allowing users to stand, walk, and climb stairs independently. ReWalk's exoskeletons represented a significant leap in assistive technology, enhancing the mobility and autonomy of individuals with paralysis.

Outcomes and challenges 
The outcomes of these early experiments were groundbreaking in concept, yet they faced formidable challenges. Rigid exoskeletons, although promising, often proved cumbersome and impractical for extended use. They limited natural movements, causing discomfort and hindering the wearer's agility. Moreover, power supply, control mechanisms, and the overall weight of these exoskeletons posed significant hurdles to their widespread adoption.

Despite these challenges, the early experiments with rigid exoskeletons marked a crucial step in the evolution of wearable robotics. They demonstrated the potential of augmenting human abilities through external systems, sparking curiosity and driving researchers to explore alternative approaches. It was from these challenges and insights that the shift toward soft materials and pneumatic actuators began, laying the groundwork for the development of soft exoskeletons in the subsequent decades.

Research and development 
The field of soft exoskeletons has witnessed rapid advancements in research and development, driven by the collaboration between experts in various disciplines such as engineering, biomechanics, materials science, and computer science.

Material innovation and flexibility 
Researchers have focused on developing advanced materials that strike a balance between flexibility, durability, and strength. Smart materials, including shape-memory alloys, flexible polymers, and lightweight composites, have been explored to create soft exoskeleton components. These materials enable the exoskeletons to conform to the wearer's body, ensuring a comfortable fit while providing the necessary support and assistance.
 A study published in the Journal of NeuroEngineering and Rehabilitation showcased a soft robotic exosuit made from lightweight, flexible materials, significantly improving gait efficiency in stroke survivors by 20%.
 In a groundbreaking research study highlighted in Advanced Materials, the integration of shape-memory polymers into soft exoskeletons has ushered in a new era of wearable technology. This innovative approach allows these devices to dynamically alter their shape in response to body temperature, a feature that has proven to be a game-changer in terms of wearer comfort and mobility.  Soft exoskeletons, equipped with shape-memory polymers, now possess the ability to seamlessly conform to the wearer's body, ensuring a personalized and comfortable fit. This adaptive quality not only revolutionizes the user experience but also facilitates a harmonious interaction between the exoskeleton and the natural motions of the wearer. Particularly beneficial for elderly users, this technological advancement marks a significant stride forward in enhancing overall mobility and ease of movement.
 The collaborative efforts between engineers at leading exoskeleton companies and biomedical researchers at universities, such as ETH Zurich and Imperial College London, have played a pivotal role in advancing the field of wearable assistive devices. The research focused on the arm therapy exoskeleton ARMin IV+, and the improvement of mechanics, sensorics, kinematics, and controllers to enhance the transparency of exoskeletons during human-robot interaction. The study's emphasis on avoiding unwanted forces during training with rehabilitation robots and comparing different control approaches, including the use of disturbance observers, demonstrates the integration of engineering expertise and biomedical research.

Soft Actuators and Sensing Systems 
The use of soft actuators, such as pneumatic artificial muscles and soft electroactive polymers, has changed the way soft exoskeletons operate. These actuators mimic natural muscle movements, allowing for smooth and precise assistance. Coupled with sensing technologies, such as flexible strain sensors and inertial measurement units, soft exoskeletons can detect the wearer's movements and intentions, enabling real-time adjustments and personalized support.
 The research titled "Effects of Two Passive Back-Support Exoskeletons on Muscle Activity, Energy Expenditure, and Subjective Assessments During Repetitive Lifting" aimed to investigate the efficacy of two passive back-support exoskeleton (BSE) designs in different postures during repetitive lifting tasks. The study, involving eighteen gender-balanced participants, employed lab-based simulations with 12 different conditions, including two BSEs, a control condition, symmetric and asymmetric lifting, and standing or kneeling postures. The results showed that both BSEs significantly reduced peak activity of trunk extensor muscles (10%–28%) and energy expenditure (4%–13%) across all conditions. However, the extent of reduction varied between BSEs and was task-dependent.
 The Rehabilitation Institute of Chicago (now known as the Shirley Ryan AbilityLab) conducted a clinical trial involving stroke survivors using soft exoskeletons with integrated inertial measurement units (IMUs). This study addresses the prevalent issue of gait deficits in stroke survivors, affecting up to 80% of patients despite current rehabilitation efforts. The research emphasizes the necessity for user-friendly rehabilitation technologies, introducing a soft wearable robot (exosuit) from Harvard's Wyss Institute for Biologically Inspired Engineering.  The soft exosuit, designed within the 2018–2023 funding cycle, employs compliant materials and features force-transmitting conformal textiles, proximally-mounted cable-based actuation systems, and adaptive control algorithms. Worn discreetly under clothing, the exosuit aims to enhance stability and dynamic control during gait and functional training, facilitating higher intensity and variable functional mobility levels in acute rehabilitation. The study's objectives include developing individualized adaptive controller parameters and progression strategies for inpatient stroke rehabilitation using the exosuit. The research also seeks to evaluate the exosuit's impact on functional recovery when used in conjunction with conventional rehabilitation, comparing outcomes to conventional rehabilitation alone. The observational study at the Shirley Ryan AbilityLab confirmed the exosuit's effectiveness in improving gait and functional mobility among stroke patients.
 Collaborative research from a team spanning multiple disciplines, including engineering, haptic feedback, and neuroscience, from Asia, Australia, the US, and the UK, has led to the creation of a hand rehabilitation system. Detailed in their publication, "Attention Enhancement for Exoskeleton-Assisted Hand Rehabilitation Using Fingertip Haptic Stimulation", the system combines an exoskeleton for hand movements with fingertip haptic stimulation to improve engagement and motor function recovery in stroke patients. The system's key features include 3D-printed pneumatic actuators for haptic stimulation, a rigid-soft combined mechanism in the hand exoskeleton, and a stimulation method simulating the contact force of grasping a glass. The research presents notable contributions such as the simultaneous provision of sensorimotor and cutaneous haptic feedback, the use of cost-effective 3D printing for soft pneumatic actuators, and experimental validation of the hypothesis that adding cutaneous haptic stimulation enhances user training involvement.
 A study conducted by researchers at Stanford University used soft actuators equipped with proprioceptive sensors, enabling the exoskeleton to respond to the user's movements intuitively. Users experienced a 35% reduction in muscle fatigue during prolonged walking sessions, demonstrating the efficiency of soft actuators combined with proprioceptive feedback.
 The research "Quantitative assessment of training effects using EksoGT® exoskeleton in Parkinson's disease patients: A randomized single-blind clinical trial" explores the quantitative assessment of training effects using the EksoGT, made by Ekso Bionics exoskeleton in patients with Parkinson's disease (PD) through a randomized single-blind clinical trial. The exoskeletons provided real-time gait analysis, leading to a 25% improvement in walking stability and reduced instances of freezing of gait, significantly enhancing the quality of life for Parkinson's patients.
 Soft exoskeletons equipped with electromyographic (EMG) sensors were employed in a rehabilitation program for patients recovering from spinal cord injuries . The EMG sensors detected subtle muscle signals, enabling users to regain 70% of their pre-injury motor functions, showcasing the potential of soft exoskeletons in neurorehabilitation.

Interaction and control systems 
Intelligent control algorithms, often based on artificial intelligence and machine learning, enable the exoskeletons to adapt to the user's gait, posture, and terrain. These algorithms analyze sensor data and optimize assistance in realtime, providing a seamless and natural walking experience for users with mobility impairments. Significant strides have been made in enhancing the interaction between humans and soft exoskeletons through the implementation of intelligent control algorithms. These algorithms, often rooted in artificial intelligence and machine learning, have transformed the way soft exoskeletons respond to users' movements, leading to more intuitive and efficient assistive devices.

Development of adaptive control algorithms (2018–2019) 
Researchers at Carnegie Mellon University, in collaboration with exoskeleton companies, pioneered the development of adaptive control algorithms for soft exoskeletons. A groundbreaking study concerning human-in-the-loop optimization of exoskeleton assistance while walking, published in Science, demonstrated the effectiveness of these algorithms in a real-time adjustment of exoskeleton assistance. Users with spinal cord injuries experienced a 30% improvement in walking efficiency, as the algorithms seamlessly adapted to changes in terrain and user posture.

Integration of deep learning models (2020–2021) 

Scientists at ETH Zurich delved into the application of deep learning models in soft exoskeleton control. A research paper published in 2020 8th IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob) outlined the integration of convolutional neural networks (CNNs) to analyze sensor data from wearable exoskeletons. The study showcased a 25% reduction in energy expenditure for users navigating varied terrains, emphasizing the role of deep learning in optimizing gait assistance.

User-Centric Control System Trials (2019–2020) 

The Rehabilitation Engineering Research Center (RERC) on Wearable Robotics conducted user-centric trials involving individuals with muscular dystrophy. Engineers at RERC developed a personalized control system based on reinforcement learning algorithms. The trials, spanning a year, revealed a 35% improvement in user-reported comfort and ease of use. The results were published in the Journal of NeuroEngineering and Rehabilitation, underscoring the significance of user-centered approaches in control algorithm development.

Soft exoskeleton usage 
Soft exoskeletons, with their advanced technology and innovative designs, have found widespread applications across various industries, transforming the way people work, move, and live. As the field of soft exoskeletons continues to advance, several key industries have embraced this technology, leading to significant improvements in efficiency, safety, and quality of life.

Healthcare and Rehabilitation 

Soft exoskeletons have revolutionized the field of healthcare and rehabilitation, offering hope and mobility to individuals with spinal cord injuries, stroke survivors, and neurological disorders. Companies like Ekso Bionics and ReWalk Robotics have developed soft exoskeletons specifically designed for rehabilitation purposes. EksoGT, introduced in 2016, has been widely adopted in rehabilitation centers globally, assisting patients in regaining mobility and independence. ReWalk's ReStore Exo-Suit, launched in 2019, has seen remarkable success in aiding stroke survivors during their recovery process, enhancing walking abilities and balance.

Manufacturing and Industrial Applications 

Soft exoskeletons have found a home in manufacturing and industrial settings, where they assist workers in lifting heavy loads and reduce the risk of musculoskeletal injuries. Hyundai Motor Company's wearable robot, the Hyundai Vest Exoskeleton (H-VEX), introduced in 2018, has been used in their assembly lines, improving productivity and reducing physical strain on workers. Ford Motor Company, in collaboration with Ekso Bionics, implemented the EksoVest (now it is the next evolution Ekso EVO) in 15 of its plants across the globe, supporting workers during overhead tasks and repetitive movements since 2017.

Defense and Military 

Soft exoskeletons have made significant strides in military applications, enhancing soldiers' endurance and reducing fatigue during long missions. The Tactical Assault Light Operator Suit (TALOS), developed by the United States Special Operations Command, incorporates soft exoskeleton components to augment soldiers' strength and agility. While still in the research and development phase, TALOS represents a pioneering effort in integrating soft exoskeletons into military operations, aiming to enhance soldiers' capabilities on the battlefield.

Construction and Heavy Machinery 

Construction workers and heavy machinery operators often face physically demanding tasks, and soft exoskeletons have proven to be invaluable in these environments. Launched in 2019, the Levitate AIRFRAME by Levitate Technologies is worn by construction workers to reduce fatigue and minimize the strain on the lower back and shoulders, allowing them to work more comfortably and efficiently. Additionally, companies like Sarcos Robotics have developed soft exoskeletons for industrial applications, including construction and infrastructure maintenance, enhancing workers' safety and productivity

Assistive Devices for Elderly and Mobility Impaired 

Soft exoskeletons have shown promise in improving the quality of life for the elderly and individuals with mobility impairments. The MyoSuit, developed by MyoSwiss AG, is a wearable exoskeleton that provides support to the lower body, aiding individuals with mobility challenges. MyoSuit has gained recognition for its user-friendly design and effectiveness in enabling natural movements. In Japan, the Hybrid Assistive Limb (HAL), developed by Cyberdyne Inc., has been used in rehabilitation centers to assist patients with mobility impairments, offering them the ability to stand, walk, and regain independence.

Logistics and Warehousing 

In 2018, companies like SuitX  introduced exoskeleton solutions, such as MAX, specifically designed for workers in logistics and warehousing. MAX exoskeletons assist with lifting and carrying heavy loads, reducing the risk of injuries. The MAX exoskeleton integrates the backX, shoulderX, and legX systems, forming a comprehensive full-body exoskeleton designed for diverse industrial settings. Its purpose is to minimize the stress on the knees, back, and shoulders, allowing users to extend their work duration with less fatigue and a decreased likelihood of injuries.

Hunic,  a notable player in the field (IFOY award winner), has developed a patent-pending soft exoskeleton named SoftExo, known for its lightweight wearability, high performance, and ergonomic design. The SoftExo offers advancements in exoskeleton technology, contributing to the evolution of solutions aimed at enhancing the well-being and capabilities of workers in various industries

Emergency Response and Disaster Relief 

Soft exoskeletons have been integrated into emergency response protocols, especially in disaster-prone regions. The XOS 2 exoskeleton, developed by Sarcos Robotics, has been used by emergency responders since 2016. By augmenting the wearers' strength, XOS 2 assists in lifting heavy debris and carrying essential equipment during rescue missions. This technology has been deployed in various disaster-stricken areas, enhancing the effectiveness of search and rescue operations

Education and Research 

Soft exoskeletons, like the MyoSuit developed by MyoSwiss AG, have been employed in educational institutions and research laboratories since 2019. Researchers and students use MyoSuit to study human movement patterns, rehabilitation techniques, and biomechanics. This wearable exoskeleton provides valuable insights into assistive technologies, shaping the future of rehabilitation practices and human-machine interaction research.

Entertainment and Media 

In the entertainment industry, the Teslasuit, introduced in 2017, integrates soft exoskeleton technology with haptic feedback systems. This suit provides users with immersive experiences in virtual and augmented reality environments. By delivering realistic sensations of touch and movement, the Teslasuit enhances gaming, simulations, and virtual experiences in entertainment attractions, making virtual worlds more engaging and interactive

These notable soft exoskeleton solutions and their implementations in various industries underscore the significance of this technology in enhancing efficiency, safety, and user experience. As these innovations continue to evolve, they hold the promise of reshaping industries and improving the lives of individuals across diverse sectors.

References 

Robotics