As the largest organ in the human body, skin plays an important role in our daily interaction with the environment. Skin not only protects the internal tissues and organs but also provides sensation of temperature, pressure, vibration, and haptics. It has been of great interest to the research community to design and fabricate electronic skins (e-skins) with functionalities and mechanical properties comparable to natural skin because of their great potential in robotics, prosthetics, health care, and human-computer interface.
Different sensing capabilities of e-skins have been realized by integrating tactile/pressure sensors, temperature sensors, strain sensors, humidity sensors, and chemical sensors. To obtain good compliance and conformability, design principles developed in flexible and stretchable electronics were introduced to create flexible and stretchable e-skins.
Serpentine and mesh structures were adopted to achieve very high stretchability and softness comparable to natural skin. Off-the-shelf chips were successfully integrated with stretchable networks to realize high-performance, multifunctional e-skins with acquisition, filtering, amplification, and communication capabilities. Advanced materials—including single-crystal silicon, organic semiconductors, nanoparticles, nanowires, nanotubes, and graphene—were used to realize superior sensing performances of e-skins.
Inspired by the wound healing capability of natural skin, rehealable e-skins have also been developed.Researchers have created an electronic skin that can be completely recycled. The e-skin can also heal itself if it’s torn apart.
The device, described today in the journal Science Advances, is basically a thin film equipped with sensors that can measure pressure, temperature, humidity, and air flow. The film is made of three commercially available compounds mixed together in a matrix and laced with silver nanoparticles: when the e-skin is cut in two, adding the three compounds to the “wound” allows the e-skin to heal itself by recreating chemical bonds between the two sides. That way, the matrix is restored and the e-skin is as good as new. If the e-skin is broken beyond repair, it can just be soaked in a solution that “liquefies” it so that the materials can be reused to make new e-skin. One day, this electronic skin could be used in prosthetics, robots, or smart textiles.
“This particular device … won’t produce any waste,” says study co-author Jianliang Xiao, an assistant professor of mechanical engineering at University of Colorado Boulder. “We want to make electronics to be environmentally friendly.”
So if the e-skin is severely damaged, or you’re just done with it, it can be recycled using a “recycling solution.” This solution dissolves the matrix into small molecules, allowing the silver nanoparticle to sink to the bottom. All materials can then be reused to create another patch of functioning e-skin. The whole recycling takes about 30 minutes at 140 degrees Fahrenheit (60 degrees Celsius) or 10 hours at room temperature. The healing happens even faster: within a half hour at room temperature, or within a few minutes at 140 degrees Fahrenheit (60 degrees Celsius), according to Xiao.
The e-skin isn’t perfect. It’s soft, but not as stretchy as human skin. Xiao says he and his colleagues are also working to make the device more scalable, so that it’ll be easier to manufacture and embed in prosthetics or robots. But it’s the fact that the e-skin can be recycled that gets Xiao excited.
“We are facing pollution issues every day,” he says. “It’s important to preserve our environment and make sure that nature can be very safe for ourselves and for our kids.”