The cellulose biopolymer consists of glucose chains organized in long, fibrous structures. In certain places, the cellulose fibrils show a more ordered structure.
“The places with a higher degree of order appear in a more crystalline form. And it is these sections, which we can purify with acid, that we require for our research,” said Siqueira.
“The biggest challenge was in attaining a viscous elastic consistency that could also be squeezed through the 3D printer nozzles,” said Siqueira.
The first formulations the researchers tried were water-based, but they produced a very brittle material, so they tried a new polymer-based formula. Once it was 3D printed and cured with UV light, the CNC cross-linked with polymer building blocks, which gave the material a higher level of mechanical rigidity. It wasn’t easy to get to that point, though.
“Most polymers are water-repellent or hydrophobic, whereas cellulose attracts water — it is hydrophilic,” Siqueira explained. “As a result they are not very compatible.”
“It is pretty interesting that one can so easily control the direction of the nanocrystals, for example, if you want to print something that should have a specific mechanical rigidity in a certain direction,” said Siqueira.
The mechanical properties of the material, in addition to its natural base, make it highly appealing for a number of applications. The cellulose crystals, which can be obtained from numerous different sources including plants and bacteria, differ from each other morphologically and in size, but not in their properties, so they’re an abundant resource. The automobile and packaging industries could benefit from using the material, which is versatile and can be chemically modified if necessary during the 3D printing process. In Siqueira’s opinion, however, the most important applications are biomedical ones such as implants or prostheses.
Empa is further investigating the potential applications of cellulose 3D printing ink, as well as other biologically-based inks. The researchers are using a 3D-Bioplotter system from EnvisionTEC in their work on this front.
“Research in this field is only just beginning,” said Siqueira. “Printing with biopolymers is currently a very hot topic.”
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[Source/Images: Empa]