Page 116 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani
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Cell retention refers to the ratio of cells that remained in the scaffold after cell incorporation, to the total number of cells seeded on or printed in the scaffold. Cell retention was lower in the cell-seeded scaffold compared with the bioprinted scaffold. When cells are seeded on a 3D-printed scaffold, a fraction of cells go through the scaffold voids and adhere to the plate instead of attaching to the scaffold struts. The percentage of cell attachment to the scaffold depends on several factors such as scaffold surface hydrophilicity and roughness [30, 31]. On the other hand, when cells are encapsulated in a hydrogel and deposited layer-by-layer between the scaffold struts, it is more difficult for cells to leave the scaffold and attach to the plate. Therefore, a higher percentage of cells remain in the scaffold. The live/dead staining images confirmed these results as lower cellular density was observed in the cell-seeded scaffold compared to the bioprinted scaffold.
Cell viability which is the ratio of live cells to the entire cells in the scaffold was slightly higher in the cell-seeded scaffold (87 ± 2%) compared with the bioprinted scaffold (78 ± 4%). This might be due to the harsh conditions that cells undergo during printing. In the process of cell printing, different parameters such as extrusion pressure, needle diameter, needle height, and needle head speed affect cell viability [32]. The extrusion pressure has been shown to have the most significant effect due to the exposed shear stress on the cells [33]. On the contrary, cells do not experience such harsh conditions when seeded on the scaffold which could be the reason for higher cell viability on the cell-seeded scaffold compared with the bioprinted scaffold. These findings are in agreement with data by others who showed that despite high cellular density in the bioprinted scaffold, cell viability is reduced due to the shear stress [32].
Proliferation of MC3T3-E1 pre-osteoblasts was higher in the cell-seeded scaffold compared with the bioprinted PLGA/β-TCP scaffold. This is probably due to encapsulation of cells in the alginate in the bioprinting process. Although alginate is known to be a suitable hydrogel for encapsulation of cells and can act as a template to permit cell localization [22], it is a relatively biologically inert material and provides cells with a non-interactive encapsulation matrix [34, 35]. This results in weaker interaction between the cells that is essential for cellular functions such as proliferation and differentiation [36]. Nevertheless, cells could deposit collagenous matrix in both scaffolds by day 21, i.e. in both scaffolds, the voids between the PLGA/β-TCP struts were filled with collagenous matrix indicating the presence of viable functioning cells in both scaffold types by day 21.
We found higher ALP activity, indicating enhanced osteogenic differentiation in the cell- seeded scaffold compared with the bioprinted scaffold. Cell-material interaction is a key factor for cell survival and determines the majority of cellular functions such as cell migration, proliferation,
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