Page 76 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

and shear stress between the layers resulted in scaffold fracture (Fig. 10b). These data show that the directionality of the layer-by-layer 3D-printed scaffolds in the defect site is extremely important. If a tensile force is induced on the defect site during normal functions, the 3D-printed scaffold should be placed in the defect site in such a way that scaffold layer-by-layer building direction is not in the direction of the tensile force. Based on our findings, when the layer-by-layer 3D-printed PCL scaffold is used for the replacement of a defect in mandibular symphysis, the scaffold building direction should be in the symphysis anteroposterior x direction to reduce the risk of failure against the tensile force.
Fluid flow dynamics affects cell proliferation, distribution, and activity within 3D-scaffolds [51-53]. A fluid shear stress of 0.002-0.4 mPa increases osteoblast proliferation and differentiation [54]. Using FE modeling, we found that the average shear stress in both the homogeneous and gradient-structured scaffolds was between 0.03-0.06 mPa, which falls in the range for enhanced osteoblast proliferation and differentiation. However, we observed an inhomogeneous fluid shear stress and fluid pressure distribution in the 0.3 mm void size scaffold. This indicates that cells attached to the struts of the 0.3 mm void size scaffold are exposed to different shear stress at various locations in the scaffold, which affects their behavior. Fluid shear stress and fluid pressure in the gradient-structured scaffolds was rather homogeneous despite the graded void size, which might favor homogeneous cell growth and differentiation in the gradient-structured scaffolds.
Figure 10. Schematic illustration of the deformation mechanisms for building and side direction tests under compression and tension. (a) When compressive force was applied in the scaffold building direction, struts were compressed against each other in their contact points. When compressive force was applied from the two sides, strut buckling occurred and shear stress was formed between the layers. (b) When tensile force was applied in the scaffold building direction, the main mechanism of deformation was delamination of the layers. When tensile force was applied from the two sides, tensile stress on the struts aligned in the direction of the force and shear stress between the layers resulted in scaffold fracture.
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