Printability of pulp derived crystal, fibril and blend nanocellulose-alginate bioinks for extrusion 3D bioprinting

Background: One of themain challenges for extrusion 3Dbioprinting is the identification of nonsynthetic bioinks with suitable rheological properties and biocompatibility. Our aimwas to optimize and compare the printability of crystal, fibril and blend formulations of novel pulp derived nanocellulose bioinks and assess biocompatibility with human nasoseptal chondrocytes. Methods: The printability of crystalline, fibrillated and blend formulations of nanocellulose was determined by assessing resolution (grid-line assay), post-printing shape fidelity and rheology (elasticity, viscosity and shear thinning characteristics) and compared these to pure alginate bioinks. The optimized nanocellulose-alginate bioink was bioprintedwith human nasoseptal chondrocytes to determine cytotoxicity, metabolic activity and bioprinted construct topography. Results: All nanocellulose-alginate bioink combinations demonstrated a high degree of shear thinning with reversible stress softening behaviorwhich contributed to post-printing shape fidelity. The unique blend of crystal and fibril nanocellulose bioink exhibited nano-as well as micro-roughness for cellular survival and differentiation, aswell as maintaining themost stable construct volume in culture. Human nasoseptal chondrocytes demonstrated highmetabolic activity post printing and adopted a rounded chondrogenic phenotype after prolonged culture. Conclusions: This study highlights the favorable rheological, swelling and biocompatibility properties of nanocellulose-alginate bioinks for extrusion-based bioprinting.