1 of 9) 1600096 wileyonlinelibrary.com bio-based materials instead of fossil oil based plastics is key. A tremendous drawback of biomaterials such as biopolymers (cellulose, hemicelluloses, and lignin) from wood is that they do not melt, which is a huge obstacle also for the 3D printing process. Here, instead of a melt we used a hydrogel ink consisting of 2 wt% cellulose nanofi brils (CNF) and 98 wt% water to produce 3D structures with a 3D bioprinter. [ 4 ] Thereafter, the structures were dried and by controlling the solidifi cation process, the structure could either be kept intact or collapse in a controlled manner. We foresee a huge potential in using hydrogels and controlled collapse, as presented here, since it can increase the resolution of the print by 14 times after water evaporation. Increasing the resolution by modifying the ink, instead of making the printer head smaller, [ 6 ] could take the miniaturization of 3D printing to the next level.The CNF can be extracted from trees by a chemical pretreatment followed by a homogenization process, [ 7 ] where after the CNF form a stable hydrogel dispersion with more than 98% water. [ 8 ] Recently, CNF have been evaluated as a building block for nanopaper, [ 9 ] fl exible electronics, [10][11][12][13] capacitors, [ 14,15 ] magnetic paper, [ 16 ] and batteries. [17][18][19] However, the resulting structures have always been 1D, 2D or very simple 3D in case of foams. One of the big challenges with the CNF hydrogels is the difficulty to produce 3D shapes due to the lack of suitable processes and, not to be neglected, the collapse upon drying, resulting in 2D fi lms or 1D fi laments. [ 20 ] Other efforts, toward increasing the processability, have combined the CNF with thermoplastics to fabricate nanocomposites, [ 21,22 ] which indeed makes the composite processable but no longer a fully sustainable material.Working with CNF hydrogels enables the incorporation of functional components such as carbon nanotubes, [ 23,24 ] graphene, [ 15 ] polypyrrole, [ 25 ] or magnetic nanoparticles. [ 16 ] However, it is not until now that the 3D shapes and structures can be fully used, with the introduction of our 3D printing and drying methods. Furthermore, we demonstrate the use of the 3D bioprinting technology for biomaterials beyond the biomedical fi eld, which opens up a new door for the materials from plants to new applications such as functional packaging, textiles, health care products, and even furniture.In order for a fl uid (liquid, solution, melt, hydrogel, etc.) to be printable in a 3D printer, the fl uid needs to fl ow in the printer and have the ability to become solid like on a substrate after Cellulose nanofi brils isolated from trees have the potential to be used as raw material for future sustainable products within the areas of packaging, textiles, biomedical devices, and furniture. However, one unsolved problem has been to convert the nanofi bril-hydrogel into a dry 3D structure. In this study, 3D printing is used to convert a cellulose nanofi bril hydrogel ...

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