Large-scale additive manufacturing with bioinspired cellulosic materials

www.nature.com/scientificreports OPEN Large-scale additive manufacturing with bioinspired cellulosic materials Naresh D. Sanandiya, Yadunund Vijay , Marina Dimopoulou, Stylianos Dritsas & Javier G. Fernandez Received: 17 April 2018 Accepted: 23 May 2018 Published: xx xx xxxx Cellulose is the most abundant and broadly distributed organic compound and industrial by-product on Earth. However, despite decades of extensive research, the bottom-up use of cellulose to fabricate 3D objects is still plagued with problems that restrict its practical applications: derivatives with vast polluting effects, use in combination with plastics, lack of scalability and high production cost. Here we demonstrate the general use of cellulose to manufacture large 3D objects. Our approach diverges from the common association of cellulose with green plants and it is inspired by the wall of the fungus-like oomycetes, which is reproduced introducing small amounts of chitin between cellulose fibers. The resulting fungal-like adhesive material(s) (FLAM) are strong, lightweight and inexpensive, and can be molded or processed using woodworking techniques. We believe this first large-scale additive manufacture with ubiquitous biological polymers will be the catalyst for the transition to environmentally benign and circular manufacturing models. Cellulose and chitin are the first and second most abundant polymers on the surface of the Earth1, and consequently a recurrent topic of research for their potential utilization in manufacture2,3. Typically, cellulose is associated with plants and chitin with arthropods, however the natural occurrence of both biopolymers as structural components broadens to most kingdoms of eukaryota and bacteria1. Despite their abundance, they rarely coappear in the same organism. One exception of this are certain species of oomycetes4, a large class of eukaryotic organisms. Oomycetes grow in a mycelial form as fungi. However, in contrast to fungi which are characterized by a chitinous wall, oomycetes’ cell walls, and those of their close relative hyphochytrids, are predominately based on cellulose4,5. In the last few years, the pathogenic nature of some oomycetes has motivated a meticulous characterization of their wall singularities, as possible targets for disease control6. Those studies have also shed some light on the characteristics of natural structures made of chitin and cellulose. This knowledge has direct application on the development of bioinspired materials. We now know oomycetes are not a homogeneous population but a combination of members with at least three distinctive cell wall types7. While those walls are mostly composed of cellulose, they also contain low concentrations of chitinous polymers, comprising up to a 10% of the cellulose content8. Inspired by this idea we studied the effects on manufacturability of cellulose by the addition of small amounts (<15%) of highly deacetylated chitin (i.e. chitosan) and the influence of the chitinous polymer in the ability of the composite to form three-dimensional structures. The objective of our research is to apply the principles of the cell wall of fungi and oomycetes to produce a general manufacture system based on three premises: (i) The resulting bioinspired composite must be made by its natural constituents; (ii) Components must be available and abundant in every habitat on earth; (iii) Cost, environmental impact, and scalability must enable generalized use. Due to recent research on the oomycetal walls we know that chitin and cellulose produce structural composites in their natural form6, without being regenerated, and therefore our criteria (i) and (ii) are theoretically possible. Additionally, both molecules are common industrial byproducts with a combined cost in the range of commodity plastic9–12, being exceptional, and probably unique, biological candidates to fulfill criterion (iii). Our research focuses on the reproduction of the synergies between molecules in biological composites, and we approach this by artificially associating structural biomolecules in their organization in living systems13. This differs from the two predominant approaches to bioinspired materials, based on the reproduction of natural composites with synthetic materials of known manufacturability, and from transforming natural components to fit in already existing manufacture techniques14. The later, has given rise to cellulose modified to form thermoplastic polymers (celluloid), and regenerated to form films (cellophane) or fibers (rayon). These chemical Singapore University of Technology & Design, 8 Somapah Road, 487372, Singapore, Singapore. Correspondence and requests for materials should be addressed to J.G.F. (email: ) Scientific REportS | (2018) 8:8642 | DOI:10.1038/s41598-018-26985-2 1 www.nature.com/scientificreports/ Figure 1. Supramolecular organization of fungus-like mimetic materials. (a) Cellulose fibers from plant origin are dispersed in chitosan solution. After removal of the water, chitosan crystallize in between fibers. In the process the sterically available amino groups in chitosan not involved in the crystal conformation react with the free hydroxyl groups on the surface of the cellulose fiber. As the chitosan losses intermolecular water, the polymer crystal reduced volume brings together the cellulosic fibers into a solid composite. (b) Scanning electron microscopic images of the cellulose fibers (left) and their structure in the chitinous composite (12.5% chitosan concentration). (c) X-ray diffraction pattern of the composite and their constituents. The data shows a cellulose I polymorph unaltered during the formation of the composite. A relaxation on the crystal structure, reflected in a shift of the 002 reflection, could be caused for the hydrogen bond of the cellulosic hydroxyl groups with chitosan, reducing the amount of cellulose-cellulose intermolecular hydrogen bonds. (d) FTIR fingerprint of the Chitosan-cellulose composite. The amino groups of the chitosan shifted from 1538 to 1556 cm−1 and the band associated with the hydroxyl groups of the cellulose shifted from 1640 to 1648 cm−1 indicated the interaction between amino groups of chitosan and hydroxyl groups of the cellulose. transformations and dissolutions require strong organic solvents and hazardous pollutants such as acetone, carbon disulfide, and sulfuric acid15. As a result, while some of those variants of cellulose were very popular in the 1970′s, their current use has declined to small niche markets16. In contrast with the chemical stability of cellulose, chitin with low degree of acetylation (i.e. chitosan) contains enough protonatable groups to enable its dispersion in low concentrations (i.e. 1% v/v) of acetic acid17 (e.g. table vinegar 4–10%). Chitosan in solution is driven into a liquid crystal by partial removal of the intermolecular water18 and in that state we used it as external phase to form colloidal dispersions of cell (...truncated)