An international team of scientists from Yunnan University and the University of Colorado Boulder has developed a new type of malleable, self-healing and fully recyclable electronic skin (e-skin). Their work appears in the journal Science Advances.
The new e-skin can be conformally mounted onto a human arm; it can be rehealed when it is damaged and can be fully recycled at room temperature. Image credit: Jianliang Xiao, University of Colorado Boulder.
E-skin is a thin, translucent material that can mimic the function and mechanical properties of human skin.
A number of different types and sizes of wearable e-skins are now being developed in labs around the world as researchers recognize their value in diverse medical, scientific and engineering fields.
“The newly-developed e-skin has sensors embedded to measure pressure, temperature, humidity and air flow,” said lead co-author Dr. Jianliang Xiao, from the Department of Mechanical Engineering at the University of Colorado Boulder.
It has several distinctive properties, including a novel type of covalently bonded dynamic network polymer, known as polyimine that has been laced with silver nanoparticles to provide better mechanical strength, chemical stability and electrical conductivity.
“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,” Dr. Xiao said.
“Given the millions of tons of electronic waste generated worldwide every year, the recyclability of our e-skin makes good economic and environmental sense.”
“Many people are familiar with the movie The Terminator, in which the skin of film’s main villain is ‘re-healed’ just seconds after being shot, beaten or run over,” said lead co-author Dr. Wei Zhang, from the Department of Chemistry and Biochemistry at the University of Colorado Boulder.
“While the new process is not nearly as dramatic, the healing of cut or broken e-skin, including the sensors, is done by using a mix of three commercially available compounds in ethanol.”
Another benefit of the new e-skin is that it can be easily conformed to curved surfaces like human arms and robotic hands by applying moderate heat and pressure to it without introducing excessive 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,” Dr. Zhang said.
To recycle the skin, the device is soaked into recycling solution, making the polymers degrade into oligomers (polymers with polymerization degree usually below 10) and monomers (small molecules that can be joined together into polymers) that are soluble in ethanol. The silver nanoparticles sink to the bottom of the solution.
“The recycled solution and nanoparticles can then be used to make new, functional e-skin,” Dr. Xiao said.
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Zhanan Zou et al. 2018. Rehealable, fully recyclable, and malleable electronic skin enabled by dynamic covalent thermoset nanocomposite. Science Advances 4 (2): eaaq0508; doi: 10.1126/sciadv.aaq0508
