A humanoid robot that has a skin that can detect its environment or a soldier with smart armour that harvests energy for anti-chemical weapon sensors are two possible applications for stretchable electronics.

The stretchable electronics consist of a thin polymer plastic sheet, a material known as PthTFB which can be very large, with polymer nanowires embedded in it and components printed on top. This electronic sandwich is then cut into the required shape with a laser. That shape could conform to a robot’s body as skin, be a bendable display, an electronic newspaper, or part of a soldier’s smart armour.

“We are exploring this now in a parallel project working on a smart armour system, so we can integrate the technology [for] for an electronic sensor device,” said one of the researchers, and a professor in the mechanical and aerospace engineering department of the University at Buffalo, Shenqiang Ren.

The stretchable electronics also have the ability to generate electricity from a person’s movement, soldier or robot, and this could power sensors on the smart armour, for example, for chemical weapon detection. Ren explained: “It can harvest energy using thermo-electrics or photovoltaics. The material will serve self-powered systems.” His team’s research is supported by the United States government’s Department of Energy. The stretchable electronics can also act as a sensor because its conductivity is sensitive to light or pressure or chemicals, allowing it to detect changes in its environment.

Nicholas Kotov, Joseph B. and Florence V. Cejka Professor of Chemical Engineering, shows one of the original paper models that served for inspiration for a stretchable conductor made out of mesh structure of carbon nanotubes in the North Campus Research Complex in Ann Arbor, MI on June 1, 2015. Image credit: Joseph Xu, Michigan Engineering.

Another of the stretchable electronics applications is smart clothing, using the textiles as a substrate upon which the electronic sandwich is attached. Ren said: “When we fabricate the sheet it can have good adhesion,” and this is how it can be attached to textiles or other materials. The flexible electronics could also be adhered to a flexible display for electronic paper or for a bendable screen.

Ren and his fellow researchers have used the principles of kirigami to design and produce elaborate shapes. Kirigami is the art of cutting paper, while origami the art of folding paper. The researchers have produced small examples of these kirigami inspired designs, but Ren told Electropages that the thin sheet produced could be very large, could be used for complex geometries, and its production automated.

This electronic sandwich is so flexible it can be stretched up to 2000%. For example, a centimetre of the material could be stretched to 20 metres. Such a characteristic is necessary for applications that will see the material subjected to substantial deformation during a machine, a robot for example, or other equipment’s operation. When stretched the material’s conductivity also improves by three orders of magnitude. The stretching aids the conductivity because it elongates the polymer’s structure of entangled strands and this elongation allows for improved conductivity.

Temple University in Philadelphia contributed to Ren’s team’s work with computational modelling on nanoconfinement engineering, which is the inclusion of the nanowires, and strain engineering, the stretching of the material. Ren’s team have put the material though 5,000 stretching cycles and found no degradation of its electronic performance.

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