Flesh and Metal: Robot with 3D Printed Face and Living Skin

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In an exciting leap for robotics, researchers at the University of Tokyo invented a way to attach living skin to robots. This technique, involving 3D printing and inspired by human skin ligaments, promises to elevate the lifelike appearance and functionality of robots.

The Challenge of Robotic Skin

Robots designed to interact with humans often require skin-like coverings that can mimic the appearance and functionalities of human skin. Traditional materials have fallen short in achieving this, particularly in providing features like self-healing and realistic tactile feedback. Using cultured skin, made of living cells and extracellular matrix, is very promising because of its natural functions. But attaching this living skin firmly to robots has been a bit challenging.

Binding skin tissue to robots

Enter Perforation-Type Anchors

To address this challenge, a research team led by Professor Shoji Takeuchi of the University of Tokyo developed “perforation-type anchors” inspired by skin ligaments. These anchors are small, V-shaped holes designed into the robot’s surface using 3D printing. The idea is to fill these holes with a collagen gel that contains skin-forming cells, creating a secure attachment for the skin.

The anchors are created using an AGILISTA-3100 high-precision 3D printer from Keyence, an Osaka, Japan-based company. This printer uses material jetting technology, where UV-cured resin produces detailed and accurate parts. It is known for its ability to create high-resolution prototypes and functional parts with a layer thickness as fine as 15 micrometers. The device is particularly suited for applications that require precise and reliable 3D printing, making it an excellent choice for creating complex structures such as those needed in this study.

To ensure the collagen gel penetrates and adheres well inside the anchors, the surface of the 3D printed device is treated with plasma. This treatment makes the device more hydrophilic, enhancing the gel’s ability to spread and stick within the holes. The collagen gel is then introduced into the anchors and allowed to gelate, forming a stable attachment point for the skin.

The engineered skin tissue and its adhesion to the underlying complex structure of the robot’s features were inspired by skin ligaments in human tissues.

Testing the Method

The team tested the effectiveness of this method by creating a 3D facial mold covered with a skin equivalent using the perforation-type anchors. They even constructed a robotic face capable of smiling. The results were promising, showing that the plasma treatment significantly improved the gel’s penetration into the anchors, leading to a more secure attachment of the skin.

According to a study published in the Cell Reports Physical Science journal, “plasma-treated anchors showed better wettability,” allowing the collagen gel to infiltrate the anchors more effectively. This led to a stronger and more stable attachment of the skin. The method was successfully applied to complex 3D shapes, such as a facial mold, and demonstrated the ability to create lifelike expressions on a robotic face.

The new anchoring method allows flexible skin tissue to conform to a relatively flat robotic face made to smile, showing that the skin deforms without constraining the robot and returns to its original shape afterward.

“Being able to recreate wrinkle formation on a palm-sized laboratory chip can simultaneously be used to test new cosmetics and skincare products that aim to prevent, delay or improve wrinkle formation,” says Michio Kawai, a Harvard University bioengineering graduate student who worked on the project while at the University of Tokyo, where he had already published a paper called “Living skin on a robot” in 2022, also with Takeuchi.

This earlier work laid the groundwork for this new study. Back then, Kawai and fellow researchers created a controllable robotic finger covered with living skin tissue. The robotic digit had living cells and supporting organic material grown on top of it for ideal shaping and strength. Like with his latest study, the soft skin that can heal itself made the robotic finger useful for applications that require a gentle touch but also robustness. At the time, the team shared their desire to add other cells into future iterations, “giving devices the ability to sense like humans do.”

Biohybrid Robotics

Although many online are sharing their worries about this type of “realistic” advances, even comparing the robotic face to that of the fictional bioengineered humanoid replicants from the sci-fi film Blade Runner, this innovation has significant implications for the field of biohybrid robotics. Relatively new and emerging, biohybrid robotics integrates biological materials with robotic systems to create more lifelike and functional robots.

Takeuchi is a pioneer in the field 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 by using specially made V-shaped perforations in solid materials, we found a way to bind 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.”

By providing a reliable method to attach living skin to robots, this new technique could lead to progress in several areas. For example, using living skin with self-healing capabilities could extend the lifespan of robots and reduce maintenance costs. More lifelike robots could improve interactions in social and healthcare settings, where a realistic appearance is essential.

We are already seeing robots in action in these fields, such as the Da Vinci Surgical System for precision surgeries, the bear-shaped nursing robot Robear for patient care, and Pepper for providing information and entertainment in hospitals. In companionship, robots like Paro, the therapeutic seal; Jibo, the social robot; and Sony’s Aibo, a robotic pet dog, provide comfort and interaction in homes and care facilities. The versatility of the 3D printed perforation-type anchors and their potential to customize fit any robotic design could make this a sought-after commodity in a niche industry.

Professor Shoji Takeuchi of the University of Tokyo.

Although these breakthroughs also bring ethical considerations, such as the treatment and welfare of biological components and the societal impact of lifelike robots, the field of biohybrid robotics continues to evolve. Innovations like this could be key to bridging the gap between biological and mechanical systems, paving the way for the next generation of robots that look, feel, and function more like living beings.

All images courtesy of Takeuchi et al. CC-BY-ND/University of Tokyo.

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