Page 123 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

inside PLGA/β-TCP scaffolds, the osteogenic activity of the cells was lower compared to that when cells were seeded onto the scaffolds in the absence of alginate, and thus were in direct contact with PLGA/β-TCP struts with suitable surface roughness. These results collectively provided a better insight regarding the interaction of pre-osteoblasts with 3D-(bio)printed polymer and polymer/calcium phosphate composite scaffolds.
LIMITATIONS OF THE CURRENT STUDIES
Several limitations were identified in the studies described in this thesis. Firstly, during surface modification of 3D-printed PCL scaffolds with NaOH, we observed that the topography created on the surface was not homogeneous at some locations of the scaffold surface. It is possible that the solution was not in contact with the interior surfaces of the scaffolds as much as it was in contact with the exterior surfaces of the scaffolds while the scaffolds were immersed in NaOH solution. Another explanation might be that the dissolved PCL at the outer surface of the scaffolds leaks away more easily, thus forming a concentration gradient with higher PCL loss at the outer surface and less PCL loss in the inner surface of the scaffolds.
Secondly, the pore size of the porous scaffolds was higher than the void size of the 3D- printed scaffolds. We were unable to create equal-sized pores and voids in the porous and in the 3D-printed scaffolds, since upon increasing the void size of the 3D-printed scaffolds, the cells could not bridge the voids. Another contributing effect was the difference in surface roughness of the two scaffold types. Inhomogeneous distribution of β-TCP particles in the PLGA solution resulted in inhomogeneous distribution of β-TCP particles on the surface of the porous scaffolds after solvent casting-porogen leaching, leading to inhomogeneous surface roughness in the porous scaffolds. It is possible that different cellular responses would have been obtained if the porous and 3D-printed scaffolds had equal pore size and surface roughness.
Thirdly, the high temperature (110°C) used for melting PLGA/β-TCP mixture in the bioprinting process might have had adverse effects on the viability of alginate-encapsulated cells printed between the PLGA/β-TCP struts. In addition, the change of different printer heads occasionally caused start-and-stop ink flow, introducing defects into the printed construct. These issues were the major limitations faced in the studies presented in this thesis.
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