3D printing has become more environmentally friendly with a demonstration by Swedish researchers of a technique that uses additive manufacturing to create objects from plant-based cellulose.
In what is claimed to be a world first, researchers from Sweden’s Chalmers University of Technology printed a series of small objects from plant-based material with a special bio-printer that doesn’t melt the cellulose in the same way that plastic and metal processes do.
“Combing the use of cellulose with the fast technological development of 3D printing offers great environmental advantages,” said Paul Gatenholm, professor of biopolymer technology at Chalmers and the leader of the research group. “Cellulose is an unlimited renewable commodity that is completely biodegradable, and manufacturing using raw material from wood, in essence, means binding carbon dioxide that would otherwise end up in the atmosphere.”
To make the printed objects electrically conductive and therefore capable of competing with plastic and metal-based 3D-printed structures, the researchers added carbon nanotubes into the cellulose.
The whole process, however, required a rather complex approach.
The main hurdle the researchers needed to overcome was to create a liquid form of cellulose. This polysaccharide doesn’t melt when heated up, which means the conventional 3D-printing technique wouldn't work.
The Chalmers researchers solved the problem by mixing miniature fibres of cellulose in a hydrogel consisting mostly of water. The gel was subsequently filled into the bio-printer – a modified version of a device used previously to print scaffolds for growing patient-specific implants.
To make it conductive, the researchers mixed the cellulose gel with a carbon nanotube gel before loading it into the printer.
The next step was to find how to dry the 3D-printed object without damaging its shape.
“The drying process is critical,” Gatenholm explained. “We have developed a process in which we freeze the objects and remove the water by different means to control the shape of the dry objects. It is also possible to let the structure collapse in one direction, creating thin films.”
The electrically conductive 3D-printed cellulose-based objects could be used as sensors with integrated packaging, textiles that convert body heat to electricity or bandages that communicate with healthcare workers, the researchers envision.
“Our research group now moves on with the next challenge, to use all wood biopolymers, besides cellulose,” said Gatenholm.