Page 131 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

compressive strength in the scaffold. Measuring the compressive strength in the upper and the lower half of the gradient scaffolds separately confirmed that the gradient scaffolds have higher compressive strength in the upper half compared with the lower half which matches the predicted forces induced on the symphysis. We also showed that the 3D-printed PCL scaffolds have higher compressive strength in the scaffold layer-by-layer building direction compared with the direction perpendicular to the building direction (side direction). Our result indicate that the directionality of melt extrusion-based 3D-printed PCL scaffolds is highly important and should be taken into account in the design process and when placing the scaffold in the defect site.
Scaffold internal architecture directly determines cellular microenvironment. Scaffold architecture can affect cell growth, signaling, and osteogenic differentiation. Scaffolds fabricated by conventional methods such as solvent casting-porogen leaching have a random porous internal structure while scaffolds fabricated by AM techniques such as 3D-printing have an ordered internal structure consisting of struts of the scaffold material. In Chapter 4, proliferation, matrix deposition, and differentiation of MC3T3-E1 pre-osteoblasts in porous or 3D-printed poly(lactic-co-glycolic) acid/β-tricalcium phosphate (PLGA/β-TCP) scaffolds were investigated. Our data demonstrate that the porous and the 3D-printed scaffolds equally support the pre- osteoblasts proliferation and matrix deposition, while only the 3D-printed scaffolds show enhanced mechanical properties and osteogenic differentiation potential in vitro. This suggests that the 3D-printed PLGA/β-TCP scaffolds may be more promising for in vivo bone formation than the porous PLGA/β-TCP scaffolds.
Effective incorporation of cells in 3D scaffolds remains a challenge. Conventional cell seeding may result in inhomogeneous distribution of cells in the scaffold and low seeding efficiency. With further development of the 3D-printing technology, it is now possible to print cells encapsulated in a hydrogel or “cell-ink” simultaneously with the scaffold material referred to as “3D-bioprinting”. However, some cell functions might be affected by the hydrogel properties. Moreover, during the bioprinting process, cells might experience unintended shear stress that may adversely affect their function. In Chapter 5, we incorporated MC3T3-E1 pre-osteoblasts in PLGA/β-TCP scaffolds by either seeding the cells post scaffold printing or by bioprinting the cells encapsulated in alginate layer-by-layer between the PLGA/β-TCP struts and investigated whether differences exist in the response of pre-osteoblasts to these two cell/scaffold constructs. We found that encapsulation of MC3T3-E1 pre-osteoblasts in alginate and printing inside PLGA/β-TCP scaffold enhances cell retention, but impairs cell proliferation and osteogenic differentiation compared to seeding the cells on PLGA/β-TCP scaffolds post-printing. These results, together with new insights in the effects of scaffold architecture and surface modifications on increasing
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