Human communication

Scientists make living human skin for robots

From action heroes to villainous assassins, biohybrid robots made of living and artificial materials have been the focus of many sci-fi fantasies, inspiring the robotic innovations of today. There’s still a long way to go before human-like robots walk among us in our daily lives, but Japanese scientists are bringing us one step closer by making living human skin on robots. The method developed, presented on June 9 in the journal QuestionNot only gave robotic finger skin-like texture, but also water-repellent and self-healing functions.

“The finger looks slightly ‘sweaty’ straight out of the grow medium,” says first author Shoji Takeuchi, a professor at the University of Tokyo, Japan. “Because the finger is driven by an electric motor, it’s also interesting to hear the clicks of the motor in harmony with a finger that looks like a real one.”

Looking “real” like a human is one of the top priorities for humanoid robots that are often tasked with interacting with humans in healthcare and service industries. A human appearance can improve communication efficiency and evoke sympathy. While current silicone skin designed for robots can mimic human appearance, it falls short when it comes to delicate textures like wrinkles and lacks skin-specific functions. Attempts to make sheets of living skin to cover robots have also had limited success, as it is difficult to conform them to dynamic objects with uneven surfaces.

“With this method, you need to have the hands of a skilled craftsman who can cut and fit the skin sheets,” says Takeuchi. “To effectively cover surfaces with skin cells, we established a tissue molding method to directly mold skin tissues around the robot, resulting in seamless skin coverage on a robotic finger.”

To make the skin, the team first immersed the robotic finger in a cylinder filled with a solution of collagen and human dermal fibroblasts, the two main components that make up the connective tissues of the skin. Takeuchi says the success of the study lay in the natural shrinking tendency of this mixture of collagen and fibroblasts, which shrunk and closely conformed to the finger. Like the paint primers, this layer provided an even base for the next layer of cells – human epidermal keratinocytes – to be bonded. These cells make up 90% of the outermost layer of skin, giving the robot a skin-like texture and moisture-retaining barrier properties.

The fabricated skin had enough strength and elasticity to support dynamic movements as the robotic finger curled and stretched. The outermost layer was thick enough to be lifted with tweezers and pushed back with water, which provides various advantages in performing specific tasks such as handling tiny electrostatically charged polystyrene foams, a material often used in the packages. When injured, the fabricated skin can even self-heal like that of humans with the help of a collagen bandage, which gradually turns into skin and resists repeated movement of the joints.

“We’re surprised at how well the skin tissue conforms to the surface of the robot,” says Takeuchi. “But this work is only the first step towards creating robots covered in living skin.” Developed skin is much more fragile than natural skin and cannot survive for long without a constant supply of nutrients and removal of waste. Next, Takeuchi and his team plan to solve these problems and incorporate more sophisticated functional structures into the skin, such as sensory neurons, hair follicles, nails and sweat glands.

“I think living skin is the ultimate solution for making robots look and feel like living creatures, because it’s the exact same material that covers animal bodies,” says Takeuchi.

This work was supported by funding from JSPS Grants-in-Aid for Scientific Research (KAKENHI) and JSPS Grant-in-Aid for Early-Career Scientists (KAKENHI).

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Material provided by Cell press. Note: Content may be edited for style and length.