## 1 Introduction
The interaction between multivalent cations and the glucuronic blocks in alginate causes the ionic cross-linking of the alginate beads, resulting in the development of a 3D network and improving the mechanical properties of the thus generated scaffold [17]. The fact that this hydrogel hinders cell adhesion and growth is a significant drawback. However, the addition of gelatin improves cell survival and attachment while also enabling the blend's viscosity to satisfy the extrusion criterion. Additionally, the alginate-gelatin hydrogel is a well-studied biomaterial with a wide range of uses and is employed in the printing of scaffolds for tissue regeneration as well as scaffolds with integrated vascular networks due to its biocompatibility [18; 19]. Regarding the printability of hydrogels, the created hydrogel blend must adhere to the biofabrication window's requirements, which attempt to outline the trade-offs that must be made in order to achieve the best printability without sacrificing the ability of the printed material to function as a scaffold for cell growth [20]. The hardware being used and the print settings, like temperature, printing speed, or layer height, impact this window. Due to the widespread use of this biomaterial, the optimization of its processability as an ink for extrusion-based AM is selected. Therefore, in order to design and evaluate the AM-processability of an alginate-gelatin hydrogel for extrusion in Direct Ink Writing (DIW), an in-depth study of its rheological behavior is required [21]. Despite efforts to improve this hydrogel's printability, little has been accomplished in terms of relating printability with significant rheological material features and printing parameters. The focus to date has been on the relationship between the viscosity of the material at printing temperature and printing accuracy, as well as the elastic modulus and loss tangent of the material in connection to extrusion quality [22]. However, a more thorough investigation should identify the rheological characteristics that most impact the material's printing behavior. In an attempt to classify the printing behavior of various biomaterials based on their rheological properties, Principal Component Analysis (PCA) might ensure their printability. This approach could be improved by decreasing the number of printing trials by a Design of Experiments (DoE) that takes into consideration the significance of each printing parameter [23]. Concerning the optimization of AM technologies, until present, the main emphasis in this field has been given to 3D printing of thermoplastics (Fused Deposition Modeling (FDM)) [24; 25; 26; 27], and ceramics (Screw Type Extrusion (STE)) [28] as various studies have attempted to investigate how process factors affect 3D printing quality. In contrast, extrusion-based 3D printing of biomaterials has not yet been thoroughly studied regarding the correlation between the printing settings and inks' composition. Some studies focused on defining the best levels for pressure and head speed [25]. It is well established that changing the pressure had the strongest effect on shape fidelity [25], based on the fact that extrusion rate and pressure are directly correlated. Therefore, finer pressure setting adjustment would be the most effective approach to improve print quality [29]. However, a complete examination of other parameters, such as nozzle diameter and temperature, could enhance the printing's accuracy and resolution [30]. Even, [PERSON] et al., who studied the contribution of more printing settings to the final printing object, did not take into account the material's properties for tailoring hydrogels' printability [30]. Thus, DIW might be enhanced by first revealing the most crucial factors and their interactions and then defining the optimal levels by applying the Taguchi method for both line and layer printing [30].