Material innovation: Swiss researchers develop bio-displays
Structural colouring. This phenomenon means nothing to you? Swiss researchers have developed a new type of material on this basis that enables special biodegradable displays.
Scientists at the Swiss Federal Laboratories for Materials Science and Technology (Empa) present an innovation: a biodegradable display that changes colour depending on stretching and temperature. It is elastic, conducts electricity and can be 3D printed. A potential milestone, but how does it work?
Components and how it works
The researchers use hydroxypropyl cellulose (HPC) as a starting material. This is used as an excipient in pharmaceuticals, cosmetics and food, among other things. The special thing about it is that when water is added, liquid crystals are formed that glow in a wide variety of colours depending on their structure. They are actually colourless or pigmentless. A structural colouration sets in.
Not only the concentration of the crystal structure, but also the temperature plays a role. The researchers therefore decided to add 0.1 per cent by mass of carbon nanotubes to the mixture of HPC and water. This makes the liquid electrically conductive. It also makes it possible to control the temperature and therefore the colour of the crystals by applying an electrical voltage. A small additional amount of cellulose nanofibres also makes it possible to 3D print the mixture. This does not impair the colouring and conductivity.
Application examples
"We have already developed various electronic components based on cellulose in our laboratory, such as batteries and sensors," says Xavier Aeby, one of the researchers. According to Empa, temperature and deformation sensors for monitoring food quality or for biomedical diagnostics are concrete examples of applications for cellulose-based ink. "This is the first time that we have been able to develop a cellulose-based display." The application examples were produced using 3D printing. "Sustainable materials that can be 3D printed are of great interest, including for applications in biodegradable electronics and for the Internet of Things," says laboratory manager Gustav Nyström.
In addition, there are still many unanswered questions to be clarified: the origin of the structural colouring, the effect of different additives or environmental influences on this phenomenon. Nyström's team will continue to investigate these topics in order to discover further interesting phenomena and possible applications.
Comparable research
In the past, a team from the Karlsruhe Institute of Technology (KIT) had already developed a biodegradable display. It consists of an organic polymer (PEDOT:PSS), gold and a gelatine-based electrolyte and can also change colour by applying a voltage. The display is produced using an inkjet printer and then coated with gelatine. This sealing makes it adhesive and customisable. It can also be worn directly on the skin on various parts of the body.
The researchers have presented their findings in more detail in the scientific journal Journal of Materials Chemistry.
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