The effect... chameleon of biodegradable 3D sensors and displays

A mixture of hydroxypropyl cellulose with water, carbon nanotubes and cellulose nanofibrils changes color when heated or stretched

Biodegradable sensors and displays: Structural coloration due to HPC (hydroxypropyl cellulose)
Colored cellulose: EMPA's logo 3D printed from new HPC blend changes color when heated (Photo: EMPA)

Is it possible to 3D print biodegradable sensors and displays? Researchers from the Cellulose & Wood Materials laboratory at EMPA in Switzerland have developed a material that allows just this result.

A mixture of hydroxypropyl cellulose with water, carbon nanotubes and cellulose nanofibrils changes color when heated or stretched, without the addition of any pigments.

Circuits from renewable raw materials for "green" electronics
An innovative 3D aortic simulator for endovascular access

Biodegradable sensors and displays: the skin of chameleons
The skin of chameleons, like the wings of butterflies and the feathers of peacocks, gets all or part of its brilliant color not from pigments, but from microscopic structures that "split" daylight (white) into spectral colors and reflect only the wavelengths for specific colors

The useful and known characteristics of HPC of pharmaceutical, cosmetic and food origin

The question of scholars and the business world was the following: an elastic material that changes color, conducts electricity, can be printed in three dimensions and be biodegradable at the same time? He's not just a pious scientific desire.

In Dübendorf, researchers from the Swiss Federal Laboratory for Materials Science and Technology have in fact produced a material with these exact properties based on cellulose and carbon nanotubes.

The scientists svizzeria they started with hydroxypropyl cellulose (HPC), which among other things is commonly used as an excipient in pharmaceutical, cosmetic and food products.

When mixed with thewater, HPC is known to form liquid crystals. And these crystals have a remarkable property.

Depending on their structure, which depends, among other things, on the concentration of hydroxypropyl cellulose, they shimmer in different shades, even though they themselves have no color or pigment.

3D printed insoles to sense forces exerted in shoes
Thus a human brain affected by tumor was reproduced in 3D

Biodegradable sensors and displays: Structural coloration due to HPC (hydroxypropyl cellulose)
Biodegradable: A hydroxypropyl cellulose display composed of seven electrically conductive segments that change color when a voltage is applied
(Photo: EMPA)

No pigments, but a division of light, in the feathers of peacocks and the wings of butterflies

This phenomenon is called structural staining and is known to occur in nature.

The feathers of peacocks, the wings of butterflies and the skin of chameleons get all or part of their shine coloration not by pigments, but by microscopic structures that 'split' (white) daylight into spectral colors and only reflect the wavelengths for specific colors.

The structural coloration of HPC changes not only with concentration, but also with la temperature.

To make better use of this property, the researchers, led by Gustav Nyström, added 0,1 percent by weight of carbon nanotubes to the mixture of hydroxypropylcellulose and water.

This makes the liquid electrically conductive and allows for check the temperature, and therefore the color of the liquid crystals, by applying a voltage.

If in Switzerland the packaging of vegetables is the vegetable itself
A 3D model to measure Leonardo's "vital parameters".

Biodegradable sensors and displays: Structural coloration due to HPC (hydroxypropyl cellulose)
Colored cellulose: EMPA logo 3D printed from new HPC blend changes color when heated
(Photo: EMPA)

The added carbon acts as a broadband absorber and makes the colors more intense

An additional advantage: the carbon acts as a broadband absorber and makes the colors more intense.

By incorporating a small amount of cellulose nanofibers into the blend, the Swiss team he also managed to make it 3D printable without affecting the structural coloration and electrical conductivity.

Researchers have used the new cellulose blend to 3D print several potential applications of the new technology.

These include a strain sensor that changes color in response to mechanical strain and a simple seven-segment display.

A new process will make cotton flame retardant and comfortable
In 3D the technological glove that will make Virtual Reality tangible

Biodegradable sensors and displays: peacock feathers
Peacock feathers, as well as butterfly wings and chameleon skin, get all or part of their brilliant coloration not from pigments, but from microscopic structures that "split" (white) daylight into spectral colors and reflect only the wavelengths for specific colors

Future development: towards food quality control or biomedical diagnostics

“Our lab has already developed several cellulose-based disposable electronics, such as batteries and sensors”, explains Xavier Aeby, co-author of the study.

“This is the first time we have succeeded in developing a cellulose-based display.”

In the future, cellulose-based ink could have many other applications, such as temperature and strain sensors, in food quality control or in the biomedical diagnostics.

“Sustainable materials that can be 3D printed are of great interest, especially for applications in biodegradable electronics and the Internet of Things”, he claims Gustav Nystromlaboratory manager.

“There are still many open questions about how structural coloration is generated and how it changes with different additives and environmental conditions”.

The Swedish scientist and his team plan to continue this line of work in hopes of discovering many more interesting phenomena and potential applications.

The first… biodegradable battery is already a reality in Switzerland
Reproduced (and restored) in 3D the Bull that made Santo Antonio

The effect... chameleon: an iridescent 3D ink made from cellulose (in English)

The effect... chameleon: an iridescent 3D ink made from cellulose (in German)

Biodegradable sensors and displays: Structural coloration due to HPC (hydroxypropyl cellulose)
Colored cellulose: EMPA's logo 3D printed from new HPC blend changes color when heated (Photo: EMPA)