Engineers in Japan are trying to get robots to imitate that particularly human expression: the smile.
They've created a face mask from human skin cells and attached it to robots using a novel technique that hides the seam and is flexible enough to twist down into a grimace or up into a soft smile.
The effect is something between the terrifying Hannibal Lecter mask and the Claymation Gumby figure.
But scientists say the prototypes paved the way for more sophisticated robots, with an outer shell stretchy and durable enough to protect the machine while making it look more human.
Beyond expressiveness, the “skin equivalent,” as researchers call it, which is made from living skin cells in a lab, can leave scars and burns and also self-heal, according to A study published on June 25 in the journal Cell Reports Physical Science.
“Human-like faces and expressions enhance communication and empathy in human-robot interactions, making robots more effective in healthcare, service and companionship roles,” Shoji Takeuchi, a professor at the University of Tokyo and lead researcher on the study, said in an email.
The research comes at a time when robots are increasingly ubiquitous in factories.
There was 3.9 million industrial robots working on automotive and electronics assembly lines and other work environments by 2022, according to the International Federation of Robotics.
A subset of the total stock of robots includes so-called humanoids, machines designed with two arms and two legs that allow them to work in environments built for human workers, such as factories, but also in hospitality, healthcare and education.
Carsten Heer, a spokesman for the federation, said humanoids were “an exciting area of development” but mass market adoption would be complex and could be limited by cost.
Still, in October 2023, the Chinese government announced the goal of mass production humanoids by 2025, which he predicted would greatly increase its industrial productivity.
For decades, robotics engineers have experimented with materials, hoping to find something that could protect a robot's complex machinery but was soft and light enough for a wide range of uses.
If a robot's surface is damaged or scratched, it can cause the machine to malfunction, making self-healing ability a “critical feature” for humanoid robots, the researchers said in the paper.
The novel skin-attachment method advances the nascent field of “biohybrid” robotics, which integrates mechanical engineering with genetic and tissue engineering, said Kevin Lynch, director of Northwestern University’s Center for Robotics and Biosystems.
“This study is a groundbreaking contribution to the problem of anchoring artificial skin to the underlying material,” said Professor Lynch, adding that “living skin can help us achieve the holy grail of self-healing skins in biohybrid robots.”
He added that the study does not address how the robots' skin will heal on its own without external support.
For these robots, the materials challenge extends to verisimilitude: finding ways to equip the machine with features that make it look and behave more like a human, such as the ability to smile.
Scientists, including Professor Takeuchi and his colleagues at the University of Tokyo, have been working with lab-created human skin for years.
In 2022, the research team developed a robotic finger covered in living skin, allowing the machine finger to bend like a human finger, giving it the tactile ability to perform potentially more precise tasks.
Professor Takeuchi's team had tried to secure the skin with mini hooks, but these caused tears when the robot moved. So the team decided to mimic ligaments, the tiny ropes of loose tissue that connect bones.
Team members drilled small V-shaped holes in the robot and applied a gel containing collagen, which plugged the holes and attached the artificial skin to the robot.
“This approach integrates traditional rigid robots with soft biological skins, making them more 'human-like,'” said Yifan Wang, an assistant professor at the School of Mechanical and Aerospace Engineering at Nanyang Technological University in Singapore who researches “soft robots” that mimic biological creatures.
The skin bonding also gives the biohybrid robot the potential to generate sensations, bringing science one step closer to sci-fi fantasy.
“This could create opportunities for the robot to safely sense and interact with humans,” Professor Wang said.
The faces of the artificial-skinned robots in Professor Takeuchi's lab do not have the ability to sense touch or changes in temperature or other external stimuli.
Professor Takeuchi said that is his next research goal.
“Our goal is to create skin that mimics the functionality of real skin as closely as possible by gradually building up essential components such as blood vessels, nerves, sweat glands, sebaceous glands and hair follicles,” he said.
Instead of neural systems transmitting sensations in a human body, a robot's electronics would need to feed a sensor signal, a development that Professor Wang says would require much more time and research.