Gelatin and hydroxyapatite concentration improves rheological properties of 3D-printed HA/Gel/CMC bone scaffolds

This study investigates the rheological properties and stability of hydroxyapatite (HA)/gelatin (Gel)/carboxymethyl cellulose (CMC) hydrogel inks to establish ideal printing conditions for 3D printing of bone scaffolds. The effects of 10 and 20 wt% of HA and 7.5 and 15 w v^-1% Gel on viscosity, storage modulus, loss modulus and printability of hydrogel inks were analyzed. Rheological properties showed that all hydrogel inks exhibited shear-thinning behavior and that higher Gel concentration (w/v%) resulted in increased gelation temperature. This is due to the increase in viscosity and gel strength with higher Gel concentration. Moreover, the printability test demonstrated that the hydrogel inks with higher concentrations of HA and Gel required higher printing temperature and extrusion pressure due to enhanced intermolecular interactions within the hydrogel matrix. Gel7.5 compositions were preferred over Gel15 due to better printability near body temperature which is preferable for bioprinting cell-laden constructs. The stability and integrity of the printed struts were investigated to achieve high shape fidelity through the filament fusion test and the ideal printing speed was determined to be 6 mm/s. These findings contribute to advancing hydrogel-based 3D printing strategies for bone tissue engineering.