Page 73 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

DISCUSSION
In the case of bone loss that requires replacement by a scaffold, understanding the force regime on the defect site can help the design and fabrication of the proper scaffold [14]. It is highly important that the mechanical properties of bone tissue engineering scaffolds are proportional to the forces exerted on the defect site during normal functions, since a mismatch of the mechanical properties can result in scaffold failure [31]. In this study, we predicted the forces induced on the mandibular symphysis during opening and closing of the jaw and developed homogeneous and gradient-structured scaffolds accordingly. We found that (i) during opening and closing of the jaw, the highest force on the symphysis was along the transverse y-axis, while forces along the anteroposterior x-axis and superoinferior z-axis were negligible, (ii) during opening of the jaw, the upper parts of the symphysis experienced more compression compared with the lower parts, (iii) during opening of the jaw, a small tensile force was induced to the lower parts of the symphysis in the transverse direction, (iv) compressive and tensile strength of the 3D-printed homogeneous PCL scaffolds decreased with increasing scaffold void size, (v) both gradient scaffolds had higher compressive strength in the upper half compared with the lower half of the scaffold, (vi) 3D-printed PCL scaffolds had higher compressive strength in scaffold layer-by-layer building direction compared with the side direction, (vii) 3D-printed PCL scaffolds had a very low tensile strength in scaffold layer-by-layer building direction, (viii) fluid shear stress and fluid pressure distribution in the gradient scaffolds were more homogeneous than in the 0.3 mm void size scaffold and similar to the 0.6 mm and 0.9 mm void size scaffolds.
Our finite element modeling results showed that during opening and closing of the jaw, the highest force induced to the symphysis was in the transverse (y) direction. Additionally, using our model we found that during jaw opening, a compressive force was induced throughout the symphyseal line that reduced from top-to-bottom, while a small tensile force was induced only to the lower parts of the symphysis. This is in agreement with data by others who showed that in a dynamic pig jaw model, the highest force on the symphysis is in the transverse direction during jaw opening [32]. However, these results are only related to the function of jaw opening and closing, and it can be expected that during other functions, such as mastication, the vertical force on the symphysis along its superoinferior z-axis would increase.
Based on our modeling results showing that during opening and closing of the jaw, different force regimes are induced on the mandibular symphysis from top-to-bottom, we aimed to develop scaffolds with tailored mechanical properties from top-to-bottom according to the predicted forces. Therefore, we designed and 3D-printed scaffolds with uniform or varying
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