Introduction: abstract
although the researches about nanocellulose have improved these years, 3D Bioprinting nanocellulose and its biomedical improvements are still in basic levels. We try to reviewed of challenges and developments in nanocellulose 3D Bioprinting as biomedical materials in a brief way.
Introduction
Hydrogels are crosslinked hydrophilic polymer chains to fabricate of three-dimensional (3D) networks with imbibing large quantities of water efficiency. abundance and low cost make cellulose as a proper polysaccharide to polymer manufacturing.
Methods: Synthesis and Mechanical Properties
Plants and trees are main sources for CNCs and CNFs whereas BNCs are sourced from Gluconacetobacter xylinus[5]. CNCs are mostly generated under strong acid hydrolysis on native cellulose fibers, as well as nowadays The method(TEMPO) is getting popular to CNFs manufacturing [9, 10].
Nanocrystalline cellulose gives us good properties as high tensile strength, elastic modulus and reactive surface.it also has been known as reinforcing agents [3,11,13].
The well-known biodegradation of nanocellulose has performed by cellulolytic microorganism’s enzyme and environmentally-relevant consortia, in which each of the methods has different pathways[14,17].
The hydrogels have made preparations for biomedical application by homogenization, cyclic freeze-thaw, free radical polymerization, UV/ion mediated cross-linking and 3D printing approaches [18].
Results: 3D bioprinting approaches
3D printing is a kind of rapid prototyping in which 3D physical construction manufactured from different materials. two regular methods in 3D printing are stereolithography (SLA), which have used liquid and ink to make solid part by polymerization, and fused deposition modeling (FDM), which produced hardened continuous layers from continuous filament of thermoplastic [19,20].
Four main areas include 3D printing applications in biomedical engineering: 1) manufacturing of local bioactive and biodegradable scaffolds, 2) fabrication of permanent non-bioactive implants, 3) manufacturing pathological organ models, 4) direct 3D printing of tissues and organs with complete life functions which recently using biocompatible inks (commonly called bio-inks) [ 20,21,22]. also hydrogels 3D bioprinting has three steps: 1) model designing or creation, 2) printing by bio-inks, 3) printed structures stabilization by in-situ and/or post-printing cross-linking process [23].stability after drying is a nanocellulose hydrogel challenge for 3D printing[25]. CNFs in low concentrations have been entangled to form hydrogels networks.in addition, the charged functional group makes it more stable and makes the ink more viable[25,28].also, in the absence of physical captivity, having viscosity and proper modulus is important for semi-crystalline CNFs which get prepare by CNC-reinforced inks [29]. Molino et al, (2018) have applied a two steps 3D printing which has used TEMPO-oxidized CNF hydrogel scaffolds [26]. also there are some auxiliary materials that includes naturally-derived polymers ( alginates, hyaluronic acid, gelatin, etc ) which improved the nanocellulose-based inks functions[25,30].one of the most applied axillary material is alginate, which has shown proper biocompatibility, printability[32]. the reports have announced about human ear, sheep meniscus shaped structures and human nasal chondrocytes or rabbit auricular chondrocytes manufacturing by CNFalginate as bio ink[33,34]. also there are some reports about alginate sulfate which have been demonstrated the improvement while maintaining the expression of chondrogenic markers by promoting the chondrocyte proliferation[36].
An anionic, nonsulfated glycosaminoglycan and extra-cellular matrix (ECM) is Hyaluronic acid (HA) or hyaluronan which has applied in engineering hydrogel designing .an study reports that CNF/HA which has used H2O2 as crosslinked showed proper cell viability(95%)[38,39].
Conductive CNF/carbon nanotube is another 3D printing ink which has applied as neural tissue
Because of its electrical conductivity [27].
In 2019 two article reports about UV cross-linking of methacrylate derivative-based from CNF-based ink group [42, 43].they used photoinitiator and Irgacure 2959 in companion of CNF/gelatin methacrylate (GelMA) and CNF/galactoglucomannan methacrylate (GGM) systems as crosslinked,which showed successful result in mouse fibroblast cell proliferation and viability and human dermal fibroblast and pancreatic tumor cell viability respectively [42]. the CNCs hydrogel preparation in compare of CNFs may lead us to have fewer CNCs composites than the CNCs [44]. recently researchers reported a novel blend including CNFs, CNCs and alginated which used CaCl2 as its crosslinked[46].
Conclusion: Conclusion
Proper biodegradability, biocompatibility, strength, surface area and chemistry, cellular interactions and tissue development make the Nanocellulose material famous as a good biomedical hydrogel.
The 3D bioprinting hydrogel processes involve bio-ink printing and in-situ cross-linking/post-stabilization structure or the geometrics stabilization printing and post-cell seeding. with, these achievements we expect advances in animal and human tissue engineering and wound healing by nanocellulose-based hydrogel will be expected.
Keywords: nano-cellulose; 3D printing; hydrogels; tissue engineering