A new type of malleable, fully recyclable, and self-healing “electronic skin” has been developed by researchers from the University of Colorado Boulder (CU Boulder). The device could be used in various applications, ranging from prosthetic development and robotics to better biomedical devices.
Electronic skin, also called e-skin, is a thin, translucent material that can imitate the mechanical properties and function of human skin. Labs around the world are developing several different types and sizes of wearable e-skins as scientists recognize their value in many different fields such as scientific, medical¸ and engineering.
The new e-skin developed by CU Boulder researchers has built-in sensors that measure air flow, humidity¸ temperature, and pressure, said Jianliang Xiao, an assistant professor in CU Boulder's Department of Mechanical Engineering who is heading the research effort with Wei Zhang, an associate professor in CU Boulder's Department of Chemistry and Biochemistry and also a faculty member in the Materials Science and Engineering Program.
The technology has a number of remarkable properties, such as a new type of covalently bonded dynamic network polymer, called polyimine that has been integrated with silver nanoparticles to provide better electrical conductivity, chemical stability, and mechanical strength.
What is unique here is that the chemical bonding of polyimine we use allows the e-skin to be both self-healing and fully recyclable at room temperature. Given the millions of tons of electronic waste generated worldwide every year, the recyclability of our e-skin makes good economic and environmental sense.
The journal, Science Advances featured a paper on the subject. Study co-authors include Yan Li and Zhanan Zou of mechanical engineering and Chengpu Zhu and Xingfeng Lei of chemistry and biochemistry. The National Science Foundation partly funded the study.
The Terminator movie is familiar to many people, where the skin of the film’s main villain “re-heals” quickly after being beaten, shot, or run over, said Zhang. Although the novel process is not as dramatic as that, the healing of broken or cut e-skin, including the sensors, is performed by employing a mix of three commonly available compounds in ethanol, he said.
The new CU Boulder e-skin has another advantage – it can be easily conformed to curved surfaces like robotic hands and human arms by applying moderate pressure and heat to it without introducing undue stresses.
Let’s say you wanted a robot to take care of a baby. In that case, you would integrate e-skin on the robot fingers that can feel the pressure of the baby. The idea is to try and mimic biological skin with e-skin that has desired functions.
In order to recycle the skin, the device is first soaked into a recycling solution which makes the polymers to decompose into monomers (small molecules that can be joined together into polymers) that are soluble in ethanol and oligomers (polymers with polymerization degree typically below 10). The silver nanoparticles reach the bottom of the solution.
“The recycled solution and nanoparticles can then be used to make new, functional e-skin,” said Xiao.