Humans have been crafting objects from wood for millennia. But never like this.
Researchers at Chalmers University of Technology in Sweden have created an ink for use in 3D bioprinters made entirely from cellulose — the primary component of wood. A cellulose-based ink for 3D printing is itself desirable for the potential environmental benefits. By incorporating carbon nanotubes, the researchers were also able to provide the ink with the very useful property of electrical conductivity. The researchers presented their work at the New Materials From Trees conference in Stockholm, Sweden.
"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 lead researcher Paul Gatenholm in a statement.
So far, Gatenholm and his colleagues have demonstrated that it is possible to use the carbon nanotube-infused cellulose ink to print a three-dimensional circuit.
Creating a cellulose-based ink for 3D printing has proved to be problematic in the past, because many 3D printers are only designed for printing with plastics and metals — materials that become malleable with heat. As cellulose does not melt when heated, the researchers had to come up with a way to make cellulose ink that is pliable enough to be extruded from a 3D printer, but could solidify its three-dimensional structure once it dries.
The researchers contend that going through the trouble of solving these problems is worthwhile, because cellulose is an environmentally friendly material.
"Combing the use of cellulose to the fast technological development of 3D printing offers great environmental advantages," Gatenholm explained in the statement. "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."
To create cellulose ink with the right properties, the researchers mixed nanoscale fibers of cellulose into a hydrogel that was over 95 percent water. All hydrogels are extremely absorbent, and companies such as Miracle-Gro sell a kind of hydrogel that you can stick in your potted plants so you don't need to water them so often. This hydrogel mixture made it possible to dispense the cellulose-based ink from 3D bioprinters — the kind used for printing human organs, for example.
Once the objects are printed with this ink, they still contain a bunch of unwanted water from the hydrogel. So the researchers had to find a way to dry it out.
"The drying process is critical," Paul Gatenholm explained. "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."
In future work, the researchers hope to incorporate all of the chemical compounds found in wood into their ink.