Page 32 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

cell attachment and proliferation [19,20]. Cell surface integrins, a group of cell surface proteins that mediate cell bonding to certain adhesion molecules, can recognize the RGD sequence on a substrate surface and facilitate attachment to the substrate [21,22]. The effect of these surface modifications on scaffold properties and cellular responses have been extensively studied [23,24]. However, these results are not generalizable for all types of scaffolds (i.e. film, electrospun mesh, spongy scaffold, 3D-printed scaffold). More importantly, it is currently unknown which of these surface modifications is more effective for pre-osteoblast proliferation and osteogenic activity in a 3D-structure. Therefore, in this study, we modified the surface of 3D-printed PCL scaffolds by alkaline treatment with NaOH for different time periods or by RGD immobilization, and investigated the response of MC3T3-E1 pre-osteoblasts to these surface modifications. Our objective was to determine which method is more effective in promoting MC3T3-E1 pre-osteoblast responses (i.e. seeding efficiency, proliferation, matrix production, ALP activity, and mineralization) in the whole 3D-printed structure for bone tissue engineering.
MATERIALS AND METHODS
Fabrication of scaffolds by 3D-printing
A 3D Discovery® bioprinter (RegenHU, Villaz-St-Pierre, Switzerland) was used to print the scaffolds. All scaffolds were printed using the HM-300H thermo polymer extruder (RegenHU Villaz-St-Pierre, Switzerland) at 25 revs/min, equipped with a needle with an inner diameter of 300 μm. Medical grade PCL (Purasorb® PC 12, Purac Biomaterials, the Netherlands) with inherent viscosity of 1.2 dl/g was melted at 85°C in the heating tank. The PCL was extruded through a pre-heated needle at 0.2 MPa (2 Bar), and the strands of PCL were plotted layer-by- layer with alternating 0°/90° lay-down pattern. Thirty six cubic scaffolds with dimensions of 0.8×0.8×0.8 cm (total volume 512×10-3 cm3) were produced.
Chemical surface modification by introduction of carboxyl and hydroxyl groups
To produce carboxyl and hydroxyl groups on the surface, PCL scaffolds were treated with NaOH solution (Merck, Darmstadt, Germany). The optimal NaOH concentration for cell proliferation and matrix deposition was determined prior to start of experiments as described below. PCL scaffolds were treated with 1, 3, or 5 M NaOH for 24 h. 3 M NaOH was chosen for treatment of PCL scaffolds since it resulted in higher cell proliferation and matrix deposition. PCL scaffolds were treated with 3 M NaOH for 24 or 72 h. Each scaffold was submerged in an individual tube
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