The introduction of 3D bioprinting is expected to revolutionize the field of tissue engineering and regenerative medicine. The 3D bioprinter is able to dispense materials while moving in X, Y, and Z directions, which enables the engineering of complex structures from the bottom up. In this study, a bioink that combines the outstanding shear thinning properties of nanofibrillated cellulose (NFC) with the fast cross-linking ability of alginate was formulated for the 3D bioprinting of living soft tissue with cells. Printability was evaluated with concern to printer parameters and shape fidelity. The shear thinning behavior of the tested bioinks enabled printing of both 2D gridlike structures as well as 3D constructs. Furthermore, anatomically shaped cartilage structures, such as a human ear and sheep meniscus, were 3D printed using MRI and CT images as blueprints. Human chondrocytes bioprinted in the noncytotoxic, nanocellulose-based bioink exhibited a cell viability of 73% and 86% after 1 and 7 days of 3D culture, respectively. On the basis of these results, we can conclude that the nanocellulose-based bioink is a suitable hydrogel for 3D bioprinting with living cells. This study demonstrates the potential use of nanocellulose for 3D bioprinting of living tissues and organs.

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 ...

This paper presents a sustainable all-wood-based ink which can be used for 3D printing of constructs for a large variety of applications such as clothes, furniture, electronics, and health care products with a customized design and versatile gel properties. The 3D printing technologies where the material is dispensed in the form of liquids, so called inks, have proven suitable for 3D printing dispersions of cellulose nanofibrils (CNFs) because of their unique shear thinning properties. In this study, novel inks were developed with a biomimetic approach where the structural properties of cellulose and the cross-linking function of hemicelluloses that are found in the plant cell wall were utilized. The CNF was mixed with xylan, a hemicellulose extracted from spruce, to introduce cross-linking properties which are essential for the final stability of the printed ink. For xylan to be cross-linkable, it was functionalized with tyramine at different degrees. Evaluation of different ink compositions by rheology measurements and 3D printing tests showed that the degree of tyramine substitution and the ratio of CNFs to xylan-tyramine in the prepared inks influenced the printability and cross-linking density. Both two-layered gridded structures and more complex 3D constructs were printed. Similarly to conventional composites, the interactions between the components and their miscibility are important for the stability of the printed and cross-linked ink. Thus, the influence of tyramine on the adsorption of xylan to cellulose was studied with a quartz crystal microbalance to verify that the functionalization had little influence on xylan's adsorption to cellulose. Utilizing xylan-tyramine in the CNF dispersions resulted in all-wood-based inks which after 3D printing can be cross-linked to form freestanding gels while at the same time, the excellent printing properties of CNFs remain intact.