الفهرس 
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Abstract
In this study, chitosan/alginate hydrogel scaffolds were prepared, and they were loaded by nano hydroxyapatite, nano tricalcium phosphate and nano graphene oxide. These nanocomposite hydrogels were 3D printed by extrusion layer by layer technique.
The four hydrogel groups were characterized by tests such as cytotoxicity, scanning electron microscope, swelling kinetic, hydrolytic degradation, viscosity, FTIR and thermal analysis. All hydrogel scaffolds were implanted in rabbit’s skull (calvaria) and left for 8 weeks to evaluate bone regeneration.
The four groups showed enhanced and sustained cell proliferation. SEM images revealed that the surface morphology of the 4 groups seemed to be porous polyhedral structure. However, the addition of HAP lead to the formation of spherical shaped structure. The addition of TCP led to the formation of rounded structure. While the addition of graphe+*ne oxide led to the formation of many stacks indicating that graphite has a layered structure. The graphene nano sheets had a rippled surface.
The addition of hydroxyapatite, tricalcium phosphate and graphene oxide particles to chitosan/alginate hydrogel decreased swelling and degradation rate which affect the bone formation. Viscosity results showed that (CS/ALG/TCP) group was the most viscous group, while (CS/ALG) group was the least viscous group.
Histological observations and histomorphometric analysis results revealed that (CS/ALG/TCP) group showed the highest bone formation followed by (CS/ALG/GO) group then (CS/ALG) group and finally (CS/ALG/HAP) group which showed the least bone formation due to slow degradation rate of hydroxyapatite.