## 4 Discussion
These results were interpreted as meaning that changing the needle direction by having a sharp angle of more than 90\({}^{\circ}\) may lead to poor angle printability due to a sudden change of the direction of the nozzle. Such a change in direction may cause stretching of the strands and results in modulating the strand diameter. In agreement with the 2D printability results, 3D printability studies showed that all printed scaffolds had acceptable pore printability while strand printability was not acceptable (most values were more than \(1\pm 0.1\)). As mentioned, the criteria used only accounted for pore shape. Hence, both pore and strand printability should be considered. Surprisingly, strand printability has been neglected in the literature and our results showed that while having acceptable pore printability, scaffolds can also have poor strand printability. One possible solution to address poor strand printability is to modulate the nozzle speed at constant pressures to get closer to the theoretical values. However, using such an approach, other interrelated factors, such as poor printability, can be affected. Except for Group 4, all the groups showed less than 10 percent irregularity in the \(X\) and \(Y\) directions. For Groups 1 and 2, scaffoldswith 15 layers were printed but Groups 3 and 4 showed poor printability for scaffolds made from more than five layers. Referring back to Section 3.2, Groups 3 and 4 with relatively lower viscosities showed poor printability while other groups showed better printability. The viscosity of biomaterials can significantly influence the printability of the bioplotted scaffolds, such that high viscosity biomaterials need higher pressure and low viscous materials require less pressure to be extruded. Overall, many factors are causing a deviancy between experimental and theoretical values, including pressure, nozzle speed, and offset. These are interrelated elements from a printability perspective and, thus, modulating one of them can affect the other elements. That said, all elements should be selected carefully to avoid, on the one hand, any strand coiling owing to over-extrusion of an extruded strand, and on the other hand, using a low pressure that cannot dominate the surface tension of the biomaterial. To create a clear picture of printability and significantly effective elements, we developed the following linear regression models (R\({}^{2}\) more than 85%) to map the relationship between the studied parameters including nozzle speed, pore, and strand printability for 2D printing (Table 4), based on the results presented in Table 2.  
It is worthwhile to cite the fact that a high concentration of alginate is not an appropriate environment for cells [37]. High concentrations of alginate can interrupt diffusion mass transfer mechanisms and lead to low cell viability. Inhabitation of cell migration/proliferation is another reason to avoid high concentration alginate. That being said, the present study showed that we could mix other cell-friendly hydrogels such as gelatin to have a low concentration of alginate along with improving the printability of such low concentration alginate. It should be noted that this study investigated factors that affected printability. However, it should be noted that cell viability is a vital factor to be considered alongside other mentioned factors. It means that factors affecting printability such as pressure can directly affect cell viability and that is why it is important to consider cell viability. Readers are encouraged to check a recent study on printability and cell viability for more information [29].