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

BACKGROUND: One of the main challenges for extrusion 3D bioprinting is the identification of non-synthetic bioinks with suitable rheological properties and biocompatibility. Our aim was to optimise and compare the printability of crystal, fibril and blend formulations of novel pulp derived nanocellulose bioinks and assess biocompatibility with human nasoseptal chondrocytes for cartilage bioprinting. 
 
 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 optimised nanocellulose-alginate bioink was bioprinted with 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 behaviour which 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, as well as maintaining the most stable construct volume in culture. Human nasoseptal chondrocytes demonstrated high metabolic activity post printing and adopted a rounded chondrogenic phenotype after prolonged culture.
 
 Conclusions: This study highlights the favourable rheological, swelling and biocompatibility properties of nanocellulose-alginate bioinks for extrusion-based bioprinting.