A group of researchers at Chalmers University of Technology in Sweden has managed to print and dry 3D objects made entirely by cellulose. The team also added carbon nanotubes to create electrically conductive material.
"Combining the use of cellulose with the technological development of 3D printing offers great environmental advantages," says Paul Gatenholm, professor of biopolymer technology at Chalmers. "Cellulose is an unlimited renewable commodity that is completely biodegradable and a means to bind carbon dioxide that would otherwise end up in the atmosphere."
The difficulty in using cellulose in additive manufacturing is that it doesn't melt when heated, meaning conventional 3D printers can't be used. The researchers solved this problem by mixing cellulose nanofibrils in a hydrogel consisting of up to 99% water. The gel could then be dispensed with high fidelity using a 3D bioprinter.
The next challenge was to dry the printed objects without them losing their shape. "The drying process is critical," Prof Gatenholm noted. "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 cellulose gel was also mixed with carbon nanotubes to create an electrically conductive ink. By using one conductive and one non conductive ink and controlling the drying process, the researchers produced 3D circuits, whose resolution was said to increase significantly upon drying.
The team says the two gels provide a basis for the possible development of a range of cellulose based products with integral circuits. "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 Prof Gatenholm.
