A flexible needle navigates inside the human body. Dodge structures that do not interest you on the way to your goal: a liver tumor. When located, its tip generates heat to remove the tumor with a single incision. It is a soft, tiny, mechanically designed robot to take advantage of the interaction with tissues and access tumors that are in very dense organs, such as the liver. This orientable needle is the result of the research of Allison Okamura, professor of mechanical engineering and director of CHARM laboratory at Stanford University. It is based on the idea that soft endoscopes, capable of lengthening their tentacles like an octopus, could make better diagnoses as they thoroughly investigate the human body and enter places that no rigid machine can reach.
In this technique rigid elements are combined, which provide precision; and soft, which facilitate reaching previously inaccessible places by functioning as tentacles. In fact, the development of flexible robots, which can be stretched, folded or twisted, is inspired by the way octopus and sepias move. These animals have no bones (just like soft robots have no rigid elements) and are able to adapt to their surroundings. Octobot, the first soft and autonomous robot created, was shaped like an octopus. It was developed by Harvard University in 2016 and, according to the magazine Nature, which then published the research, manufactured the elastomer body using a mold and printed all internal circuits in 3D, which were also flexible. Octobot laid the first stone for the creation of autonomous machines made of completely soft materials.
"The materials with which flexible robots are manufactured are usually polymers, silicone or compounds whose mechanical properties allow them to reach very large deformations," explains Giada Gerbani, a biomedical engineer at Stanford University and supervisor of Okamura airship needles research. While in rigid robotics the flexibility of the material is reduced so that they are more precise and powerful, in soft robotics a safer interaction with the environment is favored.
With this composition, soft robots are very useful to perform any activity that has to do with interacting with humans, remotely accessing places where other robots do not reach or adapting to the surfaces of objects to be able to manipulate them delicately. "In this case, claws constructed with inflatable fingers are used, which when pressurized acquire a certain stiffness while adapting to the surface of the object, but without the risks that the use of rigid claws would entail," says Alicia Casals, Professor and Coordinator from the robotics group of the Biomedical Engineering Research Center of the Polytechnic University of Catalonia.
The rigidity of traditional robots, with plastic and metal plates, copper wire joints, batteries and electric motors, makes your body not adapt to the interaction with the world. They are harder than everything around them. That's why experts anticipate that soft robots have a promising future in human interaction. “They are especially useful in the healthcare field,” explains Casals. "The person-robot interaction is more attractive if the contact is soft perception." They can be useful in industrial environments, both in situations where they have to cooperate with people and when handling very fragile objects. Inspired by the Octobot, "others have also been developed that, by means of suction cups, can reach a great capacity to hold delicate objects, however heavy they may be."
Robots with flexible bodies can move in an almost infinite number of ways, making it difficult to program their movements. “The manufacturer must face the challenges that cause interaction and adaptation with the environment,” explains Casals. This happens because, according to Gerbani, most of the traditional control strategies are not applicable in soft robots. However, the fact that they are soft makes them able to interact more safely with the environment, so they do not need to be so precise in their movements. "Even so, there is a need to develop new control algorithms," according to Gerbani.
Another puzzle to solve when creating a flexible robot is the source of energy. If everything in it must be malleable, what material are the electronic components? What do we do with the screws and batteries? "The simplest robots may lack internal wiring or electronic circuits," explains Casals. In these cases, they can obtain the energy they need to function from microfluids, as in the case of the Octobot, which is driven by transforming a liquid into a gas with which the arms are pneumatically activated. "Another option is to provide them with photovoltaic cells, when possible." They also work with waves or pressurized air. But the most widespread practice involves using more traditional power supplies (such as cables or batteries) but integrated with the flexible material. “When the robot is autonomous, the energy in general comes from the batteries they are equipped with. If the robot is a fixed base, the most common is the connection to the power grid, ”explains Casals.
"It seems that several groups have already begun to address some of the challenges facing flexible robots and are combining rigid and soft parts in the same robotic framework," Gerbani says. "It's a difficult, but also exciting, challenge to make soft robots efficient and useful as rigid ones are." Both experts agree that their applications are very promising, "but with a pace of development that will surely be much slower than predicted," says Casals.