Researchers have found a way to bind engineered skin tissue to the complex forms of humanoid robots. This brings potential benefits to robotic platforms such as increased mobility, self-healing abilities, embedded sensing capabilities, and an increasingly lifelike appearance. Taking inspiration from human skin ligaments, the team, led by Professor Shoji Takeuchi of the University of Tokyo, included special perforations in a robot face, which helped a layer of skin take hold. Their research could be useful in the cosmetics industry and help train plastic surgeons. 

Mimicking human skin structure 

Takeuchi is a pioneer in biohybrid robotics, where biology and mechanical engineering meet. So far, his lab, the Biohybrid Systems Laboratory, has created mini robots that walk using biological muscle tissue, 3D-printed lab-grown meat, engineered skin that can heal, and more. During research on the last of these items, Takeuchi felt the need to take the idea of robotic skin further to improve its properties and capabilities. 

“During previous research on a finger-shaped robot covered in engineered skin tissue we grew in our lab, I felt the need for better adhesion between the robotic features and the subcutaneous structure of the skin,” said Takeuchi. “By mimicking human skin-ligament structures and using specially made V-shaped perforations in solid materials, we found a way to bind the skin to complex structures. The natural flexibility of the skin and the strong method of adhesion mean the skin can move with the mechanical components of the robot without tearing or peeling away.” 

Overcoming adhesion challenges with innovative collagen gel technique 

Previous methods to attach skin tissue to solid surfaces involved mini anchors or hooks, but these limited the kinds of surfaces that could receive skin coatings and cause damage during motion. By carefully engineering small perforations instead, essentially, any shape of the surface can have skin applied to it. The team used a special collagen gel for adhesion, which is naturally viscous, so it is difficult to feed into the minuscule perforations. However, using a common technique for plastic adhesion called plasma treatment, they managed to coax the collagen into the fine structures of the perforations while also holding the skin close to the surface in question. 

“Manipulating soft, wet biological tissues during development is much harder than people outside the field might think. For instance, if sterility is not maintained, bacteria can enter, and the tissue will die,” said Takeuchi. “However, now that we can do this, living skin can bring a range of new abilities to robots. Self-healing is a big deal — some chemical-based materials can be made to heal themselves, but they require triggers such as heat, pressure or other signals, and they also do not increase like cells. Biological skin repairs minor lacerations as ours does, and nerves and other skin organs can be added for sensing and so on.” 

Unlocking the potential of biological skin in robotics 

This research was not just made to prove a point, though. Takeuchi and his lab have a goal in mind for this application that could help in several areas of medical research. The idea of an organ-on-a-chip is not especially new and finds use in things like drug development. Still, something like a face-on-a-chip could be useful in research into skin ageing, cosmetics, surgical procedures, plastic surgery and more. Also, if sensors can be embedded, robots may be endowed with better environmental awareness and improved interactive capabilities. 

“In this study, we managed to replicate human appearance to some extent by creating a face with the same surface material and structure as humans,” said Takeuchi. “Additionally, through this research, we identified new challenges, such as the necessity for surface wrinkles and a thicker epidermis to achieve a more human-like appearance. We believe that creating a thicker and more realistic skin can be achieved by incorporating sweat glands, sebaceous glands, pores, blood vessels, fat and nerves. Of course, movement is also a crucial factor, not just the material, so another important challenge is creating human-like expressions by integrating sophisticated actuators, or muscles, inside the robot. Creating robots that can heal themselves, sense their environment more accurately and perform tasks with human-like dexterity is incredibly motivating.” 

Source: University of Tokyo