3D printing is a modern breakthrough but it may surprise you that engineers and designers have been using the technology for nearly three decades making progress in aerospace, defence and automotive companies. Nevertheless, as the process improves, 3D printing is likely to become a big part of our future advancement. In preparation for this, researchers have been developing an environmentally friendly ink for 3D printing based on one of the main constituents of wood – cellulose. This technology has great potential to be used in implants and other biomedical applications.
The biopolymer consists of glucose chains organised in long fibrous structures. In some places the cellulose fibrils exhibit 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", explains Empa ( @Empa_CH ) researcher Gilberto Siqueira.
The final product is cellulose nanocrystals that researchers wanted to use to create a new type of environmentally friendly 3D printing ink. Previous inks contained a rather small proportion of 'biological' materials, with a maximum of 2.5 percent CNC. The Empa team wished to increase this proportion, as they have now succeeded in doing – their new inks contain a full 20 percent CNC.
"The biggest challenge was in attaining a viscous elastic consistency that could also be squeezed through the 3D printer nozzles", says Siqueira.
The ink must be “thick” enough so that the printed material stays “in shape” before drying or hardening, and doesn't immediately melt out of shape again. The first CNC mixtures were water-based. This did work in principle, but yielded a very brittle material. Therefore, Siqueira and his colleagues developed a second, polymer-based recipe that had a decisive advantage: after printing and hardening using UV radiation, the CNC cross-linked with polymer building blocks, which gave the composite material a significantly higher degree of mechanical rigidity.
These outstanding mechanical properties represent a decisive advantage compared to other materials such as carbon fibres, which are also used in DIW inks. In addition, the new kind of ink from the Empa laboratory is made from a renewable material – cellulose. "Cellulose is the most frequently occurring natural polymer on Earth", says Siqueira. It is not just found in trees, but also in other plants and even in bacteria. The crystals, which are isolated from various cellulose sources, are morphologically different from each other and differ in size, but not in their properties. And they may also be of interest to, for example, the automobile industry or for packaging of any kind.
However, the most important area of application has to be biomedicine to create implants or prostheses. Researchers at Empa are convinced that the CNC materials is suitable for a wide range of applications due to its mechanical properties, as well as the possibility of chemical modification and alignment during printing.
These possibilities are currently being investigated further at Empa. "Research in this field is only just beginning", says Gilberto Siqueira. "Printing with biopolymers is currently a very hot topic."
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