Page 59 - Development of Functional Scaffolds for Bone Tissue Engineering Using 3D-Bioprinting of Cells and Biomaterials - Yasaman Zamani

properties of 3D-printed PCL scaffolds with different porous architectures have been studied by others [16].
The mandible is a unique structure since it supports several delicate functions in mastication and speech [1]. When designing a scaffold for the reconstruction of a mandibular bone defect, the type and magnitude of the forces induced on the defect site during normal functioning should be taken into consideration. Ingrowth of bone into the scaffold can occur more effectively if the mechanical properties throughout the scaffold match those of the surrounding bone. Ingrowth of bone into the scaffold leads to biological fixation of the scaffold in the defect site which in turn plays a critical role in the formation of new bone in the defect site [17].
Gradients can be found in the body tissues such as bone, in the form of physical and/or biochemical inhomogeneities. Long bones contain structural gradient in a radial direction and flat bones contain structural gradient in an axial direction, providing a variation in bone density [18]. Melt extrusion-based 3D-printing, a type of additive manufacturing (AM) is an attractive vehicle for the fabrication of tissue engineering scaffolds incorporating architectural and compositional gradients with high precision and reproducibility [19,20].
The aim of the present study was to customize the mechanical properties of the scaffold based on the forces induced on the mandibular symphysis during normal functioning. We used a previously developed model [21] to predict the forces and torques induced on the mandibular symphysis during opening and closing of the jaw. According to the modeling results, PCL scaffolds with uniform or varying mechanical properties were designed and 3D-printed. Compression and tensile strength of the scaffolds were measured in different parts of the scaffold and in different directions in order to evaluate their compatibility with the modeling results.
MATERIALS AND METHODS
The dynamic biomechanical model of the human masticatory system
A three-dimensional biomechanical model of the human masticatory system was constructed using MADYMO 7.4.2 (TASS International, Helmond, The Netherlands). It contains the skull and the mandible, which articulated at two six degree-of-freedom temporomandibular joints. Twelve pairs of Hill-type muscles are able to move the mandible with respect to the skull (Fig. 1a). Muscle attachment, maximum force, fiber length, and sarcomere length (for a complete overview see: Koolstra and van Eijden, 2005 [21]) had been obtained from eight human cadavers. The contractile characteristics had been shaped according to van Ruijven and Weijs 1990 [22]. To
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