3-D printer creates objects using wood cellulose

LONDON: In a breakthrough, scientists have used a 3D bioprinter to print three-dimensional objects made entirely from cellulose.
The researchers from Chalmers University of Technology in Sweden also added carbon nanotubes to create electrically conductive material.

The effect is that cellulose and other raw material based on wood will be able to compete with fossil-based plastics and metals in the on-going additive manufacturing revolution, which started with the introduction of the 3D-printer, researchers said.

"Combing the use of cellulose to 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 manufacture using raw material from wood, in essence, means to bind carbon dioxide that would otherwise end up in the atmosphere," Gatenholm said.

The difficulty using cellulose in additive manufacturing is that cellulose does not melt when heated. Therefore, the 3D printers and processes designed for printing plastics and metals cannot be used for materials like cellulose.

The Chalmers researchers solved this problem by mixing cellulose nanofibrils in a hydrogel consisting of 95-99 per cent water.

The gel could then in turn be dispensed with high fidelity into the researchers' 3D bioprinter, which was earlier used to produce scaffolds for growing cells, where the end application is patient-specific implants.

The next challenge was to dry the printed gel-like objects without them losing their three-dimensional shape.

"The drying process is critical," Gatenholm said. "We have developed a process in which we freeze the objects and remove the water by different means as to control the shape of the dry objects. It is also possible to let the structure collapse in one direction, creating thin films," Gatenholm said.

Furthermore, the cellulose gel was mixed with carbon nanotubes to create electrically conductive ink after drying.

Using the two gels together, one conductive and one non-conductive, and controlling the drying process, the researchers produced three-dimensional circuits, where the resolution increased significantly upon drying.

The two gels together provide a basis for the possible development of a wide range of products made by cellulose with in-built electric currents.

"Potential applications range from sensors integrated with packaging, to textiles that convert body heat to electricity, and wound dressings that can communicate with healthcare workers," said Gatenholm.