## 1 Introduction  
The rapid development of innovative biomaterials in tissue engineering allows strong interactions and integration with cells; differentiation; and finally, three-dimensional (3D) tissue culturing [1]. Significant advancements in the field of tissue engineering (TE) have been accomplished over the past ten years thanks to the widespread application of additive manufacturing (AM) technologies [2]. Contrary to other manufacturing approaches, AM-based scaffold development enables precise and guided cell placement, highlighting its potential as a method for creating innovative, multifunctional, adaptable grafts for a variety of tissue types [3]. The lack of graft vascularization of the artificial tissue remains the main obstacle, discouraging the clinical application [4]. The directed vascularization of artificial tissue is the current major challenge for TE, whereas AM technologies are regarded as a crucial driver in addressing this bottleneck. Microchannels that resemble a vascular network are essential for cell survival and tissue functionality since they facilitate oxygen transport, nutrient delivery, and removal of metabolic waste [5]. High geometry fidelity during printing and maintenance of the structural integrity for an adequate--guided by the target tissue--time span post-printing is required when generating structures with embedded microchannels [6]. Extrusion-based 3D printing has, at the moment, made it possible to manufacture complicated structures due to low-cost customization and an expanding variety of materials [7]. When optimizing a number of process variables, especially the 3D printing of hydrogels, these capabilities have nonetheless additionally presented a substantial difficulty [8]. Additionally, a variety of factors, such as material characteristics and processing parameters, inhibit the processing of biomaterial inks and the post-process evaluation of manufactured structures (such as in vitro evaluation techniques). In accordance with this, selecting a material with extrusion AM processability, high printing accuracy, and desirable post-printing properties is of utmost importance in this method. Therefore, in order to create multilayer porous scaffolds, it is necessary to deeply investigate the AM process parameters, material characteristics, and system functionality, leading to higher manufacturing process efficacy [9]. A biomaterial requires the following properties in order to be used as an extrusion-based 3D printing ink: (i) relatively high viscosity at low shear rates, (ii) shear thinning fluid behavior, and (iii) quick crosslinking of polymer chains at the end of printing [10]. These characteristics define the polymer type referred to as hydrogels. Due to their great biocompatibility, biodegradability, hydrophilicity, and non-toxicity, hydrogels are among the most frequently utilized biomaterials for tissue engineering applications [11]. Additionally, they have a common use in extrusion-based AM due to their rheological behavior. However, there are two drawbacks that frequently occur when printing hydrogels: the challenge of modifying the printing behavior and the constrained mechanical properties of the printed scaffolds [12]. Due to its biocompatibility, a hydrogel that consists of gelatin and alginate, two natural biopolymers, has been widely used for bioprinting applications [13; 14]. Gelatin is typically obtained by jellyfish through the hydrolysis of collagen. It possesses emulsifying and foaming properties and thus is utilized in pharmaceutics, cosmetics, and biomedical applications [15]. Alginate, usually found in seaweeds, is a biopolymer used in food products and also in biomedicine (e.g., dentistry, etc.) [16]. Since the printed structure becomes stabilized simply and fast by cross-linking the polymer chains with the addition of calcium cations, alginate hydrogel is regarded as a highly promising hydrogel for bioprinting applications.