In the pursuit of making human-like robots, sometimes it’s not enough to give them freaky yet believable facial expressions, or a killer sense of humor. Sometimes you have to give them actual human skin.
Engineers at the University of Tokyo have found a way to put human skin on a robotic finger that damn near feels like the real deal. In a paper published on Thursday in the journal Matter, the grafted skin—a mashup of collagen, precursor skin cells, and skin cells that produce keratin—kept the animatronic finger water-repellent and, creepily enough, self-healing. It could be a big step to building robots with living skin just as functional, sensing, and responsive as our own.
The skin of most humanoid robots is made with silicone, which looks human enough but isn’t capable of replicating real skin’s texture or functions. Scientists have attempted to fabricate living skin for our synthetic counterparts but it’s been a hard task to effectively drape biological materials around the hard contours of a robotic body.
“With that method, you have to have the hands of a skilled artisan who can cut and tailor the skin sheets,” Shoji Takeuchi, a mechanical engineer at the University of Tokyo and the paper’s co-author, said in a press release. “To efficiently cover surfaces with skin cells, we established a tissue molding method to directly mold skin tissue around the robot, which resulted in a seamless skin coverage on a robotic finger.”
This process involves dunking a three-jointed robotic finger into a pink solution eerily reminiscent of the Westworld robots submerged in white fluid vats. The solution contains collagen, a protein that provides structural support to skin and other tissues in the body, and human dermal fibroblasts, cells that produce collagen and repair skin cells. Over the course of seven days, the collagen and fibroblasts conform to the robotic finger, giving rise to the innermost layer of skin called the dermis.
To make the epidermis—the outermost layer of skin—the finger was submerged in a solution containing human epidermal keratinocytes. These cells make up 90 percent of the epidermis and produce keratin, a protein that sticks skin cells together allowing the epidermis to be a protective, waterproof barrier.
With its new skin, the motorized finger feels and looks nearly like a real digit. Its epidermis was thick enough to pinch with a pair of tweezers and repel water. When the researchers cut it to simulate a wound, the finger’s living skin healed itself much like human skin albeit with some help from a sheet of collagen much like a Band-Aid.
“The finger looks slightly ‘sweaty’ straight out of the culture medium,” said Takeuchi. “Since the finger is driven by an electric motor, it is also interesting to hear the clicking sounds of the motor in harmony with a finger that looks just like a real one.”
Sadly, because the skin is a living material, it cannot survive on the robotic finger for too long without a constant supply of nutrients and a method of waste removal. Takeuchi and his team are hoping to fix this issue by creating channels beneath the dermis that could provide water and nutrients, like blood vessels do in the human body. They also want to create a version of artificial sweat glands that could help keep the skin moist in dry environments. Down the road, the team is looking into adding other features like hair follicles and nails to make the skin more lifelike, and incorporate nerves that would allow a robot to sense and react to its environment.
“I think living skin is the ultimate solution to give robots the look and touch of living creatures since it is exactly the same material that covers animal bodies,” said Takeuchi.
The look and touch of living creatures—it can’t get more uncanny valley than that.