## 2 Three-Dimensional Printing Parameters  
Three-dimensional printing parameters can be categorized into two groups, as shown in Figure 3. The first group includes topological parameters that can be adjusted via the slicing software, referred to as \"layering parameters\". The second group, i.e., \"device parameters\", are those directly related to the 3D printing device. According to a study conducted by [PERSON] et al. [24], the main parameters affecting the fatigue strength of FFF prints include build orientation, infill density, number of shells, raster angle, nozzle temperature, platform temperature, printing speed, layer height, and nozzle diameter. Layering and device parameters are shown in Figure 4. Figure 4a illustrates the extrusion width, infill pattern, infill density, and perimeter (shell). The extrusion width is the width of the extruded filament. This parameter is adjusted by the nozzle pressure and normally can be from 90% to 250% of the nozzle diameter. Extruded filaments in each layer are laid in a configuration called \"infill pattern\", determining the internal structure of the print. In this regard, different infill patterns, including rectilinear, grid, and honeycomb, can be used, as indicated by Figure 4a. In this study, patterns such as grid and honeycombs are referred to as \"cross-over\" patterns since the extruded filaments of each layer or successive layers cross each other with an angle larger than zero. The fraction of the solid volume within the printed object is termed \"infill density\", which is a determining factor for the mechanical properties of the print. The infill density can range from 0% to 100%, with 0% being an empty volume and 100% showing a fully solid object. In addition, to maintain the structural integrity of the 3D-printed object, perimeter/shell layers are used to enclose the internal structure. Perimeters are fully dense layers that can have a different width from the as-extruded filaments inside the part. Some solid layers (with 100% infill density) may be positioned at the bottom or top of the object to strengthen it and avoid the pillowing effect. Pillowing occurs at the top layer of prints, appearing as irregular bumps and undesired holes. Pillowing is caused by improper cooling of the top layers and can be avoided by using solid layers at the top [25]. Figure 3: The 3D printing parameters influencing the mechanical properties of FFF prints. Other parameters include the build orientation, layer height, and nozzle diameter, as illustrated in Figure 4b. The build orientation determines the positioning of the object of interest in the 3D printer chamber. In other words, the build orientation denotes the direction of the specimen with respect to the build platform. Figure 4b shows the build platform and tensile specimens fabricated at three orthogonal build orientations, i.e., X, Y, and Z, denoting the perpendicularity of the build platform to the sample's thickness (shortest length), width (medium length), and height (highest length), respectively. This definition applies to all samples discussed in this study. Finally, the height of each layer can be adjusted in the slicing software. As depicted in Figure 4b, the smaller the layer thickness, the larger the number of required layers. Raster orientation denotes the direction of extruded filaments in the build platform. This study defines the raster angle as the angle between the raster orientation and the stress direction when they are at the same plane. This definition has been derived according to various works studied in this review. Although some studies define the raster angle as the angle of the raster orientation with respect to the x-axis of the build table [26], the  
Figure 4: Schematic illustration of 3D printing parameters: (**a**) infill density, infill pattern, perimeters, and raster orientation, and (**b**) different build orientations, layer height, and nozzle diameter.