Muscle tissues and 3D printing: a biohybrid robot that “walks” has been created in the laboratory

L'it was cyborgs not yet reality. But science fiction novels and the big screen have already given us a broad taste of it. Just think of the saga Terminators, the assassin cyborg played by Arnold Schwarzenegger. A cybernetic organism: living tissue on a metal endoskeleton. In a laboratory at the Center for International Research on Integrative Biomedical Systems (CIBiS) at the Institute of Industrial Sciences of the University of Tokyo, Professor Shoji Takeuchi and his research team have created a two-legged biohybrid robot by combining muscle tissue and artificial materials. Published on January 26 in the magazine Matterthis method allows the robot to walk and rotate.

What are biohybrid robots

Yes, but when can a robot be defined as biohybrid? Biohybrid robots are devices composed of a plastic frame (polymer matrices) and partly by biological elements of various types such as bacteria, small organisms or muscle cells – replies Guglielmo Lanzani, head of the Nanomaterials for Energy and Lifescience Laboratory of the Italian Institute of Technology, researcher in the field of biohybrid robotics -. The latter are grown and developed in contact with the polymeric part with which they integrate completely. The “living” component is the active element capable of deforming the polymer support, which, being elastic, returns to its original state after deformation, contributing to the overall movement of the device.

The advantages of grafting biological tissue onto a robot

What are the advantages of “grafting” biological tissues onto a robot? Biological tissues are the product of hundreds of millions of years of evolutionand in many aspects they are perfectly optimized – explains Lanzani – For example, the ability of cells to self-regenerate could be very advantageous, or the ability to conserve energy. Furthermore, they have an optimal weight-to-power ratio and are energetically sustainable (a man's heart consumes approximately 1 Watt of power). Finally the biocompatibility And biodegradability they are advantageous in certain applications from medicine to environmental monitoring.

How can they be useful to humans

Will biohybrid robots help us? Certainly. Devices of this type can have applications in various fields – explains Lanzani -. They can be used in medicine to simulate the functioning of muscle tissues and study associated pathologies, or to simulate the effect on them of new drugs. In robotics they can be used as actuators which set the components in motion, for example allowing the robot to move or carry out work. In a biological environment they could be completely bio-compatible and even biodegradable carriers, released by an intra-corporal probe to perform in situ operations. In the end, in the future they could be the first step towards the development of completely biocompatible prostheses made of muscle cells instead of metal.

This fusion of biology and technology aims to exploit the unique characteristics of biological materials together with the versatility and programmability of artificial components. The best biohybrid robots made so far include innovations such as combining muscle tissue with artificial materials to create more natural and flexible movements. Research on biohybrid robots, which are a fusion of biology and mechanics, is recently attracting attention as a new field of robotics with biological functions, underlines Professor Takeuchi, one of the leading experts in the field who has over 600 research works and over 15,000 citations to his credit. Professor Takeuchi also engaged in research to generate robots covered with skin obtained through tissue engineeringAnd.

How the Japanese biohybrid robot was made

Compared to robots, human bodies are flexible, capable of making fine movements and can efficiently convert energy into motion. Drawing inspiration from the human gait, Japanese researchers have created a more agile experimental model with fine and delicate movements. The bipedal robot consists of a foam float to maintain an upright posture in a growing medium; a polydimethylsiloxane (PDMS, silicone rubber that can bend and flex to conform to muscle movements) body that includes two flexible substrates, weighted 3D printed legs to help it stand upright underwater, and cultured skeletal muscle tissue.

The movement

The researchers then attached strips of skeletal muscle tissue grown in the laboratory, to the silicone rubber and each leg. When researchers stimulated muscle tissue with electricity, the muscle contracted, lifting the leg. The heel of the leg then landed forward as the electricity dissipated. By alternating electrical stimulation between the left and right legs every 5 seconds, the biohybrid robot successfully walked at speed of 5.4 mm/min (0.002 mph). To turn, the researchers repeatedly stimulated the right leg every 5 seconds, while the left leg served as an anchor. The robot made a 90-degree left turn in 62 seconds.

The results

The results showed that the muscle-driven bipedal robot can walk, stop and make optimized rotation movements. Currently, we are manually moving a pair of electrodes to apply an electric field individually to the legs, which takes time, Takeuchi says. In the future, integrating the electrodes into the robot, We plan to increase speed more efficiently. The team also plans to equip the bipedal robot with thicker joints and muscle tissue to enable more sophisticated and powerful movements.

But before upgrading the robot with more biological components, Takeuchi notes that the team will have to integrate a nutrient supply system to support living tissues and the device structures that allow the robot to operate in the air. Applause erupted during our regular lab meeting when we saw the robot successfully walk in the video, Takeuchi says. While they might seem like small steps, they are actually giant leaps for biohybrid robots.

very interesting the refined control on the movement of the actuator – comments the head of the Nanomaterials for Energy and Lifescience Laboratory of the Italian Institute of Technology -. In fact, precise control of the device is crucial for future use. Unlike most biorobots reported so far, this manages to maintain an upright position but not suspended, which imitates the behavior of two limbs. The reported mechanical study, also based on simulations, can be very useful for taking a further step towards the creation of a biohybrid robot capable of moving autonomously.

What is the state of the art of research

At what point is research in the sector? a still young research, but which has been growing a lot in recent years – underlines Lanzani -. For example, the studies in which they are tested are multiplying new techniques to stimulate muscle cells in hybrid robots. Among the problems to be solved, the dimensions of these actuators are still too small, millimeters or centimeters at most. This obviously makes their applications limited. The biological part cannot be exposed to the air for now.

The developments

When can we imagine we will arrive at a complete biohybrid robot? In reality they already exist for example a fish made by Kit Parker's group at Harvard University or a race, able to swim but with the aforementioned limitations, size, need to be in a liquid. My research group itself took part in a collaborative study with Harvard to create a hybrid actuator. Considering the growing interest in the community, I expect that in about ten years there will be biorobots that move autonomouslynot only in hyper-controlled environments, and capable of interacting with the outside world, concludes Lanzani.

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