Page 60 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani
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generate a symphyseal region, the reconstructed mandible was split midsagittally (details provided in Supplementary information; [23-25]).
Simulations
From a closed jaw position, jaw open-close cycles were simulated. Jaw-opening started with activation of the jaw-opening muscles simultaneously. Then they were deactivated with a simultaneous activation of the jaw-closing muscles [21]. Activation and deactivation of the muscles included ramps of 45 ms and 75 ms, respectively, to incorporate activation dynamics [26]. All activation patterns were symmetrical. To obtain a maximum possible jaw opening (30 mm inter-incisal distance, 23 degrees jaw angle) the jaw openers were activated to 100% of their capacity. A jaw-closer activation of 10% was sufficient to close the jaw about as fast as it had been opened. Output predictions included tri-axial forces and torques passing the symphysis that were time-related dynamic measurements.
To calculate the force induced on any point around the symphysis during jaw opening and closing, forces and torques in the relevant directions were summed and the net compressive or tensile force was calculated. We calculated the transverse force induced on top-to-bottom of a cubic rectangular (1×1×2 cm; length×width×height) scaffold in the symphysis by summing the force along the transverse y-axis and torque around the anteroposterior x-axis.
Scaffold design and fabrication
Cubic rectangular scaffolds (1×1×2 cm) with 5 different internal structures were designed using BioCADTM software (RegenHU, Villaz-St-Pierre, Switzerland). Three designs had a homogeneous internal structure and two designs had a gradient internal structure. In the homogeneous designs, the distance between two PCL struts (void size) was 0.3, 0.6, or 0.9 mm. In the first gradient design, the void size was 0.3 mm in the upper half and 0.6 mm in the lower half of the scaffold. In the second gradient design, the void size was 0.3 mm in the upper third, 0.6 mm in the middle third, and 0.9 mm in the lower third of the scaffold (Fig. 1b). The gradient designs were based on the modeled forces on the mandibular symphysis during a cycle of jaw opening and closing. A 3D-Discovery® bioprinter (RegenHU, Villaz-St-Pierre, Switzerland) was used to print the scaffolds. All scaffolds were printed using the HM-300H thermos polymer extruder (RegenHU) at 25 revs/meter, equipped with a needle with an inner diameter of 300 μm. Medical grade PCL (Purasorb, Purac Biomaterials, The Netherlands) was melted at 85°C in a heating tank. The PCL was extruded through the pre-heated needle at 0.2 MPa (2 Bar), and the struts of PCL were plotted layer-by-layer on the platform until the desired height was achieved (Fig. 1c). The
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