The present invention relates to preparation of bioink composed of 
cellulose nanofibril hydrogel with native or synthetic 
Calcium containing particles. The concentration of the 
calcium containing particles can be between 1% and 40% w / v. Such bioink can be 3D Bioprinted with or without human or animal cells. Coaxial needle can be used where 
cellulose nanofibril hydrogel filled with 
Calcium particles can be used as shell and another hydrogel based bioink mixed with cells can be used as core or opposite. Such 3D Bioprinted constructs exhibit high 
porosity due to 
shear thinning properties of 
cellulose nanofibrils which provides excellent printing fidelity. They also have excellent mechanical properties and are easily handled as large constructs for patient-specific bone cavities which need to be repaired. The 
porosity promotes vascularization which is crucial for 
oxygen and 
nutrient supply. The 
porosity also makes it possible for further recruitment of cells which accelerate 
bone healing process. 
Calcium containing particles can be isolated from 
autologous bone, allogenic bone or xenogeneic bone but can be also isolated from minerals or be prepared by synthesis. Preferable Calcium containing particles consist of β-
tricalcium phosphate which is resorbable or 
natural bone powder, preferably of human or porcine origin. The particles described in the present invention have particle size smaller than 400 microns, or more preferably smaller than 200 microns, to make it possible to 
handle in printing 
nozzle without clogging and to obtain a good resolution. 
Cellulose nanofibrils can be produced by 
bacteria orbe isolated from plants. They can be neutral, charged or oxidized to be biodegradable. The bioink can be additionally supplemented by other biopolymers which provide crosslinking. Such biopolymers can be alginates, chitosans, modified 
hyaluronic acid or modified collagen derived biopolymers.