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Researchers devise method to 3D print wood cellulose

17 June 2015

A group of Swedish researchers has managed to print and dry three-dimensional objects made entirely from wood cellulose using a 3D-bioprinter.

This tiny chair made of cellulose demonstrates how objects can be printed using a 3D bioprinter (photo: Peter Widing)

The researchers, based at Chalmers University of Technology, also added carbon nanotubes to create electrically conductive material. They believe 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.

“Combining the use of cellulose with the fast technological development of 3D printing offers great environmental advantages,” says 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; manufacture using raw material from wood, in essence, means to bind carbon dioxide that would otherwise end up in the atmosphere."

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

The Chalmers researchers solved this problem by mixing cellulose nanofibrils in a hydrogel consisting of 95-99 percent water. The gel is carefully dispensed into a 3D bioprinter, which was earlier used to produce scaffolds for growing cells, where the end application is patient-specific implants.

The circuit in the form of a tree is made up of cellulose, which has been made electrically conductive by means of carbon nanotubes, and printed using a 3D bioprinter (photo: Peter Widing)

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

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

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.

“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,” says Gatenholm. “Our research group is now moving on with the next challenge, to use all wood biopolymers, besides cellulose."

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