Page 125 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

longitudinally, the structured pore scaffolds show uniform cell distribution throughout, whereas the random pore scaffolds have a very low number of cells distributed in the central region [14]. These results are clearly in agreement with our data showing slightly lower cell proliferation, but more homogeneous cell dispersion in the 3D-printed PLGA/β-TCP scaffolds compared with the porous scaffolds.
Since cells have to be encapsulated in a hydrogel in the bioprinting process (i.e. simultaneous printing of cells and biomaterials), most studies have focused on the bioprinting of cell-laden hydrogels (bioinks) and optimization of cellular responses in these constructs [15-18]. One of the major limitations of using hydrogel-based bioinks is that they are often mechanically weak. Hydrogel-based bioinks alone are not capable of supporting loading for applications such as bone and osteochondral tissue engineering. To overcome this limitation, composite-reinforced scaffolds have been developed where a soft bioink can be reinforced with stiffer biocompatible and biodegradable polymer. This approach has been developed first by Schuurman et al. who successfully fabricated composite-reinforced constructs by bioprinting chondrocyte-laden alginate between PCL struts [19]. They demonstrated that the viability of the cells in the composite- reinforced constructs is within the same range as those of non-printed constructs consisting of hydrogel only [19]. Other studies also developed bioprinted constructs consisting of cell-laden alginate reinforced with different thermoplastic polymers, mostly PCL [20-25]. However, no study evaluated the osteogenic differentiation of pre-osteoblasts encapsulated in alginate, and 3D- printed with PLGA/β-TCP struts compared to cells seeded on 3D-printed PLGA/β-TCP scaffolds. Therefore, our results are rather unique and difficult to compare with other studies.
We conclude that both RGD immobilization (0.011 μg/mg scaffold) on the surface and 24 h NaOH treatment of the surface of 3D-printed PCL scaffolds enhanced pre-osteoblasts proliferation and matrix deposition, while only 24 h NaOH treatment resulted in increased osteogenic activity, making it the treatment of choice to promote bone formation by osteogenic cells. We tailored the mechanical properties of 3D-printed PCL scaffolds based on the predicted forces on mandibular symphysis during normal functions. Moreover, we showed that the mechanical properties of the 3D-printed PCL scaffolds were different in scaffold-building direction compared with the side direction which should be taken into account when placing the scaffold in the defect site. Porous and 3D-printed PLGA/β-TCP scaffolds equally supported the pre- osteoblasts proliferation and matrix deposition while only 3D-printed scaffolds showed enhanced mechanical properties and osteogenic differentiation potential in vitro. Encapsulation of MC3T3- E1 pre-osteoblasts in alginate and printing inside PLGA/β-TCP scaffolds enhanced cell retention, but impaired cell proliferation and osteogenic differentiation compared to seeding the cells on the
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