‘Terminator’-Style Robots Could Become Reality Thanks To This Realistic, Self-Healing Skin
Scientists at Stanford University have developed a self-healing, multi-layered electronic skin. The researchers achieved this significant advance in synthetic skin technology by drawing inspiration from the remarkable natural healing abilities of human skin.
“We have achieved what we believe to be the first demonstration of a multilayer thin-film sensor that automatically realigns itself during cure. This is a crucial step in mimicking human skin, which has multiple layers that are properly reassembled during the healing process,” explains Chris Cooper, lead author of the achievement. “It’s soft and stretchable. But if you pierce, slice or cut them, each layer will selectively heal to restore overall function,” adds Sam Root, another of the authors. “Just like real skin,” he compares.
Root says the research group could create a multi-layered synthetic skin with individual functional layers so thin that a stack of 10 or more layers is no thicker than a sheet of paper. Thanks to this concept, each layer can be designed to detect various changes. “One layer can feel pressure, another temperature and another tension”, he details it.
The engineers note that existing self-healing synthetic skins need to be manually realigned, but a slight misalignment in the layers could compromise functional recovery. The current result is distinctive in that layers recognize themselves and align with similar layers during the healing process, restoring functionality layer by layer as they heal.
What is the secret of this novel result?
The secret is in the materials used: PPG (polypropylene glycol) and PDMS (polydimethylsiloxane, better known as silicone). Both are biologically compatible and have electrical and mechanical properties similar to those of rubber. By mixing them with nanoparticles or microparticles, their electrical conductivity is increased. When heated, they soften and flow, but solidify when cooled. Although these polymers do not mix, due to the hydrogen bonds they form, they strongly adhere to each other to create a durable multilayer material.
By heating the synthetic skin, the researchers were able to speed up the healing process. At room temperature, curing can take up to a week, but when heated to just 70°C, self-aligning and curing occurs in approximately 24 hours. The two materials were carefully designed to have similar viscous and elastic responses to external stress over an appropriate temperature range.
“The skin also takes time to heal. I cut my finger the other day and it was still healing four or five days later,” Cooper says. “For us, the most important part is that it heals to regain function without our input or effort,” he adds.
More properties and perspectives
Engineers added magnetic materials to its polymer layers to allow the faux leather to not only heal, but also self-assemble from separate pieces. “Combining with magnetic field guided navigation and induction heating, we can build reconfigurable soft robots that can change shape and detect their deformation on demand,” explains Renee Zhao, a mechanical engineer participating in the project.
“Our long-term vision is to create devices that can recover from extreme damage. For example, imagine a device that when broken into pieces and torn apart could autonomously rebuild itself,” says Cooper.
The breakthrough heralds a new era of robots and prosthetics wrapped in self-healing synthetic materials imbued with a human-like sense of touch. He also envisions robots that could be swallowed in pieces and then self-assemble inside the body to perform non-invasive medical treatments. The results of the study were published this Thursday in Science.
