The team rendered their creations electrically conductive by adding carbon nanotubes, a development that could see cellulose and other raw material based on wood competing with fossil-based plastics and metals in additive manufacturing.
“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.
The breakthrough was accomplished at Wallenberg Wood Science Center, a research centre aimed at developing new materials from wood, at Chalmers University of Technology.
The difficulty using cellulose in additive manufacturing is that cellulose does not melt when heated so the 3D printers and processes designed for printing plastics and metals cannot be used for materials like cellulose.
The Chalmers researchers is said to have solved this problem by mixing cellulose nanofibrils in a hydrogel consisting of 95-99 percent 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 in a statement. “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.”
Furthermore, the cellulose gel was mixed with carbon nanotubes to create electrically conductive ink after drying. Carbon nanotubes conduct electricity, and another project at Wallenberg Wood Science Center aims at developing carbon nanotubes using wood.
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. “Our research group now moves on with the next challenge, to use all wood biopolymers, besides cellulose.”
The research findings were presented this week at the “New Materials From Trees” conference that took in Stockholm, Sweden, between June 15-17.