Soft robots of the future will be fully flexible, much like the tentacles of an octopus

Soft robots: merging nature and the future

Advanced robots with pressure-sensitive surfaces, flexible joints and novel actuators could help people overcome their physical limitations.

“Look deep into nature and then you will understand everything better,” said Albert Einstein. He probably wasn’t thinking about robots, but his maxim is particularly apt for an exciting, cutting-edge blend of engineering, technology and the natural world – soft robotics.

Taking ideas from biological systems, soft robots are made of deformable structures that can deal with uncertain and dynamic tasks, offering benefits over the rigid, linear and constraining motions and abilities of traditional robots. They are brought to life thanks to recent developments in materials science, sensor technology and biologically-inspired actuators. Controlling them are innovative systems and algorithms that make these soft robots aware of and responsive to their environment.

Creating new and useful applications for soft-robot technologies is challenging researchers, businesses and governments across the world. From mobility to medicine and the military, soft robotics offers a potential revolution in the way we live our lives.

“We want to replace rigid robots that we see in the films and in science fiction with soft robots that interact with, and take their inspiration from, nature,” says Jonathan Rossiter of the Bristol Robotics Laboratory in the UK, one of the leading soft robotics institutions in Europe. “Our research seeks to create and exploit new materials with specific, beneficial properties.”

In one human hand, there are 29 major and minor bones and the same number of major joints, 123 named ligaments, 34 muscles and 48 named nerves. When you consider the biomechanics at work, nature’s engineering is even more impressive. Our hands are soft enough to lift the most fragile of items, and strong enough to support our own weight – sometimes with just a few fingers. The force generated by the muscles that bend the fingertips must be at least four times the pressure which is produced at the fingertips.

Recreating such a complex system incorporates all three aspects of soft robotics development: biosensors, bioactuators and biomaterials. It sounds a tough challenge, but in 2015 a group of students from Harvard University and the Indian Institute of Science created a soft robotic prosthetic hand as part of Harvard’s Global Immersion summer programme.

With the help of fibre-reinforced bending actuators to mimic the movements of the fingers and a pneumatically actuated artificial thumb, the students made a functioning prototype. Controlled by an open-?source and freely available Soft Robotics Toolkit control board, the prosthetic hand demonstrates essential functions, including pinching, open palm, the ability to point, and a grip with some power.

Creating such a complex mechanism was achieved by students working with cheap, readily available and open-source materials and software. But what about the work of the leading soft robotics experts?

The ‘right’ trousers

Around the world, there are people with some form of mobility impairment, from difficulties lifting or carrying to problems with coordination, and more severe disabilities. In early 2015, the Engineering and Physical Sciences Research Council (EPSRC), the UK’s main agency for funding research in these areas, allocated almost £5 million of funding for soft robotic projects. Led by Rossiter at the Bristol Robotics Lab the ‘Wearable soft robotics for independent living’ project is using its £2m grant from the EPSRC to develop a soft robotic ‘second skin’ that would provide support and aid for those with mobility impairments.

This intelligent clothing uses artificial ‘muscles’ made from smart materials and reactive polymers to help the wearers and give them extra propulsion. The soft polymers are coated with compliant electrodes that flex with the underlying surface, with the actuation provided by placing an electrical current across them. “The trousers are loose when they are off, but once on, they automatically add support to the user,” Rossiter says. “There’s a lot of power needed to lift someone from a chair, for instance, so the engineering challenge is significant.”

The trousers are currently still on the drawing board, but when built they will incorporate not only soft robotics but also nanoscience, functional electrical stimulation and even 3D printing. Controlling it all will be a full-body monitoring system, working in harmony with the user’s body. “The trousers themselves will respond to the wearer’s environment. They can calculate, for instance, when the wearer is climbing stairs,” says Rossiter.

Together with researchers from the Universities of Leeds, Loughborough, Nottingham, Strathclyde and the West of England, Rossiter and his team aim to develop a wearable prototype in three years. And the scientists are already involving potential patients in the design process. “We are developing the technology in partnership with patients and are currently seeking applications from potential users of these trousers,” says Rossiter.

Transatlantic competition

Another lab working on soft robotics projects aimed at enhancing mobility is Harvard University’s Wyss Institute for Biologically Inspired Engineering. “The basic premise is that small levels of assistance, delivered with a lightweight and non-restrictive system, can have a significant impact on a person’s mobility,” says Conor J Walsh, a roboticist at Wyss Institute.

More specifically, he’s creating a flexible and supportive exoskeleton – a suit that resembles a scuba diver’s attire and could be like a second skin. “Compared to previous exoskeleton designs, these systems are significantly lighter as they do not contain any rigid structure, and they provide minimal restrictions to the wearer’s motion, avoiding problems relating to joint misalignment,” says Walsh.

“Our approach to interfacing with the human body is to use functional textiles that enable forces to be comfortably and effectively applied to the joints to augment the biological muscles.”

The exosuit’s actuator system gives assistance when needed: a nudge rather than a push. “The biologically-inspired architecture provides force transmission paths in a manner that is consistent with and does not impede normal human walking,” Walsh adds. The suit’s built-in sensors help to ensure that the support is provided at the right time, actively surveying the environment and responding to stimulus. Walsh estimates that the sensors can improve muscle power by up to 20 per cent, which could make the difference between leading an active or sedentary life.

One of the key challenges has been to reduce weight, says Walsh. The current suit weighs 6kg, with the battery pack needed to power it slotted onto the wearer’s hip. As the technology becomes more advanced, it should be possible to make the suit lighter, to ensure that it is indeed supportive and not restrictive.

Apart from people with disabilities, soldiers could benefit from soft robotics too. They may lug anywhere up to 50kg on their backs while marching long distances or patrolling difficult terrain. As a result, leg injuries are common.

The concept of a wearable exosuit has been part of the US development of military technology since the 1960s, and is only now – through the Darpa Warrior Web programme – coming to fruition. Walsh, whose work at the Wyss Institute has received almost $3m in funding to develop functional prototypes, says that the exosuits will reduce the stress on muscles and tendons, enabling soldiers to walk further with less effort and have a reduced risk of injury.

Walsh’s military exosuits are the technology of tomorrow, but soft robotics is already benefiting some patients, offering them a chance to walk again after injury, accident or illness.

Founded in 2005, Ekso Bionics has created assistive exosuit technologies that are now being used in hospitals across the US. “Our technology measures 500 times per second where the body is in space and uses a sophisticated algorithm to determine how much power and where to assist the foot on its gait trajectory,” explains Ekso Bionics spokeswoman Heidi Darling.

The suit mimics the action of the leg muscles and tendons when a person walks, and provides small but carefully timed assistance at the joints of the leg without restricting the wearer’s movement.

Working with real patients is helping the company refine and improve its technology. It’s also helping to break down the barriers between man and machine, pointing to a future where they may coexist invisibly. “As we exponentially improve upon these technologies, they will become less and less noticeable. We predict a day in the not too distant future where robotic legs could simply look like the clothing we wear today,” says Darling.

Surgical robots

Soft robotics aren’t just used to add capabilities to humans, though. They may also have a role in treating us. In just one of many hundreds of medical projects across Europe, STIFF-FLOP is a research venture using flexible robot technology to aid surgeons carrying out some of the most demanding keyhole operations. “The inspiration for our project comes from the octopus and how it can use its limbs,” says Kaspar Althoefer, STIFF-FLOP project coordinator and a roboticist at King’s College, London. “Octopuses are soft, with no skeleton, but if they want to, they can stiffen their limbs to do things like picking up stones, catching prey and even walking. It’s a fantastic role model for our design.”

When fully developed, STIFF-FLOP’s soft robotic arm will be capable of fitting through a 12mm gap – the width of a human finger. Once inside, its soft manipulator and gripper will be able to carry out surgical operations and procedures under human control.

The unit’s module base is made of silicone that can be pneumatically actuated. Its state can change from floppy to stiff through a process called granular jamming: by applying vacuum, the granules move, solidifying the unit. It’s a unique way to gain access to specific parts of the body, and the unit also uses distributed sensing and biologically-inspired actuation to give it an extra dimension of control.

“We need to integrate the technology with sensors. We don’t want just the hardware and the actuators, but a system that can feel its environment and understand where it is in the human body,” says Althoefer. “One day we can use these sensors to improve control, possibly automating certain tasks so the robot can avoid healthy organs, navigate to parts of the body and even carry out surgery.”

Using nature as its basis, soft robotics technologies continue to develop and evolve, with ever more exciting uses, and an ever greater potential for benefit.

Rossiter is keen to point out that the individual technologies at work – sensors, actuators and more – aren’t necessarily new, but they’re being combined in different and exciting ways. Likening it to the advances in 3D-printing technology over the past decade, he’s confident that soft robotics can add real benefit to the way we live our lives, augmenting and supporting human function.

So just how will people react to soft robots? Rossiter has an interesting take on this: “In the future, we won’t be talking about robots at all. They will – quite literally – be built into the fabric of our existence and our built environment. We don’t see them as separate things. They can and will coexist with humans.”

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