3D Printer Inks from the Woods Can Even Print Jawbones
Empa researchers have succeeded in developing an environmentally friendly ink for 3D printing based on cellulose nanocrystals. This technology can be used to fabricate microstructures with outstanding mechanical properties, which have promising potential uses in implants and other biomedical applications.
In order to produce 3D microstructured materials for automobile components, for instance, Empa researchers have been using a 3D printing method called “Direct Ink Writing” for the past year. During this process, a viscous substance – the printing ink – is squeezed out of the printing nozzles and deposited onto a surface, pretty much like a pasta machine.
The big advantage of “Direct Ink Writing” (DIW) lies in the almost unlimited selection of materials available for inks. The cartridges can be filled with any kind of ink with differing compositions and these can then be printed directly and alternately. The printer has one high and one low temperature cartridge. This means that if certain polymers need to be melted, this can be done directly in the printer. The temperature can also be set for the substrate to be printed on, so that the hot liquid will, for example, immediately cool as soon as it hits the substrate. This offers a large degree of freedom in the development of new kinds of inks with tailor-made properties.
Credit: Empa
Cellulose, along with lignin and hemicellulose, is one of the main constituents of wood. The biopolymer consists of glucose chains organized in long fibrous structures. In some places the cellulose fibrils exhibit a more ordered structure.
“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.
Bringing things together despite resistance
What sounds quite simple in retrospect caused the Empa team a great deal of head-scratching. Siqueira: “Most polymers are water-repellent or hydrophobic, whereas cellulose attracts water – it is hydrophilic. As a result they are not very compatible.” So the researchers first of all had to chemically modify the CNC surface.
After the first attempts at printing and X-ray analysis of the obtained microstructures, the researchers noticed that the CNC in the printed object had aligned itself almost perfectly in the direction it was printed in. They concluded that the mechanical strength used to push the ink through the printing nozzle was sufficient to align it. “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”, says Siqueira.
Lots and lots of possibilities
These outstanding mechanical properties represent a decisive advantage compared to other materials such as carbon fibers, which are also used in DIW inks. In addition, the new kind of ink from the Empa lab 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.
These possibilities are currently being investigated further at Empa. A PhD student is currently focusing on the further development of the materials and the printing method for other applications. In addition, a Master’s student intends to develop other “biological” inks. “Research in this field is only just beginning”, says Gilberto Siqueira. “Printing with biopolymers is currently a very hot topic.”
Contacts and sources:
Dr. Gilberto de Freitas Siqueira
Applied Wood Materials
Citation: Cellulose Nanocrystal Inks for 3D Printing of Textured Cellular Architectures, G. Siqueira, D. Kokkinis, R. Libanori, M.K. Hausmann, A.S. Gladman, A. Neels, P. Tingaut, T. Zimmermann, J.A. Lewis, A.R. Studart, Advanced Functional Materials, DOI: 10.1002/adfm.201604619
Source: http://www.ineffableisland.com/2017/05/3d-printer-inks-from-woods-can-even.html
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