Engineers in Japan are trying to get robots to imitate that particularly human expression — the smile.

They have created a face mask from human skin cells and attached it to robots with a novel technique that conceals the binding and is flexible enough to turn down into a grimace or up into a squishy smile.

The effect is something between Hannibal Lecter’s terrifying mask and the Claymation figure Gumby. But scientists say the prototypes pave the way for more sophisticated robots, with an outward layer both elastic and durable enough to protect the machine while making it appear human.

Beyond expressiveness, the “skin equivalent”, as the researchers call it, which is made from living skin cells in a lab, can scar and burn and also self-heal, according to a study published in Cell Reports Physical Science.

“Human-like faces and expressions improve communication and empathy in human-robot interactions, making robots more effective in healthcare, service and companionship roles,” said Shoji Takeuchi, a professor at the University of Tokyo, Japan, and the study’s lead researcher.

The research comes as robots are becoming more ubiquitous on factory floors.

There were 3.9 million industrial robots working on auto and electronics assembly lines and other work settings in 2022, according to the International Federation of Robotics. A subset of the total robot stock includes so-called humanoids that were built for human workers, such as factories, but also in hospitality, health care and education. Carsten Heer, a federation spokesperson, said that humanoids were “an exciting area of development” but that mass market adoption would be complex, and could be constrained by cost.

Still, in October 2023, the Chinese government announced a goal of mass-producing humanoids by 2025, which it predicted would greatly increase its industrial productivity.

For decades, robotic engineers have experimented with materials, hoping to find something that could protect a robot’s complex machinery but be soft and light enough for a wide range of uses.

If the surface of a robot gets dinged or scratched, it can lead to machine malfunction, making the capacity for self-repair a “critical feature” for humanoid robots, the researchers said in the paper.

The skin attachment method advances the nascent field of “biohybrid” robotics, which integrates mechanical engineering with genetic and tissue engineering, said Kevin Lynch, director of the Center for Robotics and Biosystems at Northwestern University, US. For such robots, the materials challenge extends to verisimilitude — finding ways to imbue the machine with characteristics that make it appear and behave more like a human, such as the ability to smile. Scientists, including Takeuchi and his colleagues at the University of Tokyo, have been working with lab-made human skin for years.

In 2022, the research team developed a robotic finger covered in living skin, allowing the machine’s digit to bend like a human finger, giving it the tactility to potentially perform more precise tasks.

Takeuchi’s team had tried anchoring the skin with mini-hooks, but those caused tears as 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 into the robot and applied a gel containing collagen, which plugged the holes and tethered the artificial skin to the robot.

“This approach integrates traditional rigid robots with soft, biological skins, making them more ‘humanlike,’” 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 binding also gives a biohybrid robot the potential for sensation, taking science one step closer to sci-fi fantasy.

“This could create opportunities for the robot to sense, and safely interact with humans,” Wang said.

NYTNS