## 3 Results and Discussion
### Some More Simulation Results
Figure 6: Effect of pore size on the elastic modulus (pattern fill column bars show experimental results for bioplotted scaffolds with (\(P_{x,z}=0\)), (\(P_{x}=470\) and \(P_{z}=390\)), and (\(P_{x}=551\) and \(P_{z}=487\))). A strong congruity was observed between experimental and numerically predicted values of elastic modulus. Although the model was developed based on the assumption of a symmetric structure, bioplotted scaffolds might be asymmetric in different directions due to random variables that affect extrusion. This asymmetry might cause an increase in the error between predicted and real values because of numerous variables associated with the 3D biofabrication regulate the structural uniformity and geometry of the scaffold. Fluid viscosity, temperature, dispensing pressure, needle speed, and crosslinker concentration have a profound effect on the strand diameter, porosity, and pore size distribution [24]. In this study, the scaffolds were printed in a static volume of the crosslinking solution of 1 mL and 50 mM CaCl\({}_{2}\), the number of available Ca\({}^{2+}\) ions in the crosslinking media decreases gradually with the fabrication of successive layers. Such a variable concentration of Ca\({}^{2+}\) ions can affect the structure and thus the mechanical properties of the printed scaffolds [32]. As such, the effect of the crosslinker mechanism can be taken into consideration for improving the accuracy of model prediction. Also, fluid viscosity is temperature-dependent and therefore temperature, changing during the printing process, can affect the fluid flow, which is also responsible for degraded structures in the bioplotted scaffolds. Another important factor influencing the mechanical behavior of porous scaffolds is microstructure degradation from the designed one [33; 34; 35; 36]. Thus, in order to enhance the accuracy of numerical models, one way is to identify these changes and degradations and specify them or their effects in the model. Moreover, it was reported that pore distribution and orientation of strands are not stable throughout the printed scaffold and it can influence the mechanical properties of scaffolds [37]. All of these can result in the degradation of the structure of scaffolds, thus affecting the error between the predicted and real values of scaffolds mechanical properties. According to the results obtained from the developed model, Equation (4) was derived by fitting a linear regression model (R\({}^{2}\) = 99.61%) to quantitatively specify the effect of each term on the elastic modulus. For this purpose, the degree of penetration, strand diameter, pore size, and extra materials in X and Z directions, and the number of layers in Y direction were considered in the model. The number of layers in X and Z directions were assumed as five. In addition, considering the effect of major factors (\(\Delta_{0}\), \(D\), \(P_{z}\), \(P_{x}\), \(E_{z}\), \(E_{x}\), and \(N_{y}\)), all the interactions amongst the aforementioned factors were considered in the model. Accordingly, with respect to the \(p\)-value, some parameters were not appeared to be significant. However, regarding the interaction between various terms, these factors  
Figure 7: Effect of the number of layers on the elastic modulus (pattern fill column bars show experimental results for bioplotted scaffolds with 16 (24.25 \(\pm\) 0.64 KPa), 24 (26.85 \(\pm\) 0.92 KPa), and 31 layers (32.1 \(\pm\) 0.60 KPa)). showed a significant effect Significant interactions were identified amongst many factors including penetration*\(N_{y}\), \(D^{\bullet}N_{y}\), \(D^{\bullet}P_{z}\), \(D^{\bullet}P_{x}\), \(N_{y}{}^{\bullet}P_{z}\), and \(N_{y}{}^{\bullet}P_{x}\). Figure 8 shows the effect of each factor on the elastic modulus demonstrating the significant effect of different terms on the elastic modulus. \[