Nanotechnology

3D printing biodegradable sensor and display with nano materials

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July 04, 2023

(Nanowerk News) Elastic material that changes color, conducts electricity, can be 3D printed and is also biodegradable? It wasn’t just wishful thinking: Empa researchers from the Cellulose & Wood Materials laboratory in Dübendorf have produced a material with these exact properties based on cellulose and carbon nanotubes. Colored cellulose Colorful cellulose: The 3D printed Empa logo of the new HPC blend changes color as it gets warmer. (Image: Empa)

The researchers started with hydroxypropyl cellulose (HPC), which is commonly used as an excipient in pharmaceuticals, cosmetics, and foodstuffs. When mixed with water HPC is known to form liquid crystals. These crystals have an amazing property: Depending on their structure – which depends partly on the HPC concentration – they glow in different colors, even though they themselves have no color or pigment. This phenomenon is called structural coloring and is known to occur in nature: Peacock feathers, butterfly wings and chameleon skin derive all or part of their brilliant coloring not from pigments, but from microscopic structures that “divide” daylight (white) into spectral colors. . and only reflects the wavelength for that particular color.

HPC structural coloring changes not only with concentration but also with temperature. To make better use of this property, the researchers, led by Gustav Nyström, added 0.1 weight percent carbon nanotubes to the HPC and water mixture. This makes the liquid electrically conductive and allows the temperature, and thus the color of the liquid crystals, to be controlled by applying a voltage. Added bonus: Carbon acts as a broadband absorber making colors deeper. By incorporating small amounts of cellulose nanofibers into the mix, Nyström’s team was also able to make them 3D printable without affecting structural coloring and electrical conductivity. display with electrically conductive segments that change color Biodegradable: The display consists of seven electrically conductive segments that change color when applied to a voltage. (Image: Empa)

Continuous sensors and displays

The researchers used the new cellulose blend to 3D print various potential applications of this new technology. These include a strain sensor that changes color in response to mechanical deformation and a simple seven-segment display. “Our laboratory has developed various disposable electronic components based on cellulose, such as batteries and sensors,” said Xavier Aeby, co-author of the study. “This is the first time we have been able to develop a cellulose-based display.”

In the future, cellulose-based inks could have more applications, such as temperature and strain sensors, in food quality control or biomedical diagnostics. “3D printable sustainable materials are in great demand, especially for biodegradable electronics and Internet of Things applications,” says Nyström, head of the laboratory. “There are still many open questions about how structural coloring is generated and how it changes with various additives and environmental conditions.” Nyström and his team aim to continue this work in hopes of discovering more interesting phenomena and potential applications.



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