Page 99 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani
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DISCUSSION
It is generally accepted that 3D-structure and internal architecture of bone tissue engineering scaffolds play key roles in improving the performance of the scaffolds since the formation of new tissue is greatly influenced by the porosity, pore size, and 3D-structure of the scaffolds [18,19]. In this study, we assessed the scaffold characteristics and the proliferation and osteogenic differentiation potential of porous versus 3D-printed PLGA/β-TCP scaffolds containing MC3T3- E1 pre-osteoblasts. We found that compared to the porous scaffolds (i) the 3D-printed scaffolds had a relatively smooth surface with more regular structure; (ii) β-TCP particles were more homogeneously dispersed on the 3D-printed scaffolds surface; (iii) the surface of the 3D-printed scaffolds was more hydrophilic; (iv) compressive strength of the 3D-printed scaffolds was significantly higher; (v) a more dense cellular network was formed on and between the struts of the 3D-printed scaffolds; (vi) seeding efficiency and cell proliferation were similar; (vii) cells deposited comparable amounts of collagenous matrix; and (viii) ALP activity was significantly higher on the 3D-printed scaffolds.
Calcium phosphates such as hydroxyapatite and β-TCP are well known for their osteoconductive properties [20]. Some reports also claim osteoinductivity for these materials [21,22]. In this study, β-TCP particles were more homogeneously dispersed on the surface of the 3D-printed scaffolds than on the surface of the porous scaffolds. Moreover, aggregations of β- TCP particles were visible on the surface of the porous scaffolds which is not favorable for homogeneous osteogenesis by pre-osteoblasts. The inhomogeneous dispersion of the β-TCP particles in the porous scaffolds was due to low viscosity of the PLGA/DMSO solution, causing premature gravity precipitation during the solidification step after casting the mixture over the fused sugar mold. On the other hand, the molten PLGA/β-TCP mixture used for 3D-printing was far more viscous, thus allowing a more homogeneous distribution of β-TCP particles in the PLGA matrix after 3D-printing. This represents an important advantage of the 3D-printed scaffolds in this study.
Scaffold surface roughness is known as an important factor influencing cellular functions especially osteogenesis [23,24]. This may occur through topography-induced modulation of the cell mechanotransduction [25]. Surfaces with relatively high roughness (high Ra values) as well as smooth surfaces (low Ra values) are neither suitable for cell activities [26,27]. For example, surfaces with micrometer-sized roughness may prevent cells to establish effective cell-cell and/or cell-matrix interactions due to difficult-to-bridge surface irregularities [28]. Moreover, on more hydrophilic surfaces, cells generally show good spreading, proliferation and differentiation which
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