## 1 Introduction  
Three dimensional (3D) printing enables fabrication of complex structures [1; 2; 3]. Among the established 3D printing techniques, material extrusion is a prevailing technique due to facile process implementation under relatively moderate ambient conditions and a diverse material palette [4]. As a result of these materials processing characteristics, microextrusion-based bioprinting (micro-EBB) of cell-laden biopolymer materials has been advanced to fabricate analog tissue constructs towards targeted cell-based models and therapeutic applications [5; 6; 7; 8; 9]. The micro-EBB materials fabrication process extrudes suspensions of live cells within hydrogels, enabling tissue scale constructs with high flexural and mechanical strength and cell proliferation rates [10]. The operating principle behind the micro-EBB techniques is one that combines a fluid-dispensing system with an automated robotic system for precision printing. During printing, computer-controlled deposition of cells within continuous filament structures results in rapid fabrication of the desired 3D customized structures with adequate mechanical stiffness [11; 12; 13]. Various bioprinting process innovation strategies have recently been developed, including single axis printing and co-axial printing. Moreover, beyond the traditional implementation of bioprinting in an air medium, emerging techniques have implemented printing in a liquid bath or hydrogel support bath medium. Among the various bioprinting techniques, extrusion within a support bath medium is a burgeoning technique that enables complex 3D structured materials processing of low viscosity liquid hydrogel precursors [14; 15; 16; 17]. By depositing structural filaments within a support bath, the limitations of conventional printing in air processing configurations can be mitigated, including clogging [18; 19], gravity-induced structural collapse with weak interfacial strength [20], and the absence of a support structure [21; 22]. Specifically, bioprinting within a support bath enables low viscosity materials processing to minimize the extent of the material occlusion of the extruding nozzle. Also, the layer-to-layer interfacial strength can be maintained due to the characteristically low surface tension of the bio-ink within a liquid medium [15]. Also, the bath material serves as a provisional frame for the in-process support of the printed bio-ink towards an integrated 3D structure with high shape fidelity upon post-process material gelation. To better understand bioprinting performance outcomes within a support bath material, the key consideration is how to confer and maintain the complex structural properties, including construct shape fidelity and mechanical stiffness, in the context of low viscosity prints. Related work includes studies in which the printability of gelatin-alginate hydrogel blends within a yield stress bath has been demonstrated to yield complex 3D structures [10]. Moreover, print feasibility studies with various materials, including PDMS and agarose hydrogels, have been reported for hydrophilic support baths such as Carbopol gel and perfluorotributylamine [17; 23]. Supermolecular hydrogels have also been printed in self-healing hydrogels to achieve fine, multi-material structures [24]. Developing a support bath material is critical for the printing of liquid hydrogel precursors. Currently, gelatin microparticles, Carbopol microgels, nanoclay, and pluronic F127 represent some of the most promising candidate support bath materials. Gelatin is a thermosensitive material that can serve as a support bath in gel form at a relatively low working temperature (<25 \({}^{\circ}\)C), which can be removed by increasing the temperature. In this paper, gelatin is selected as a component of the bio-ink, thereby limiting the use of gelatin as the prescribed support bath material. The ion-sensitive Carbopol can be used to print hydrogels without an ionic cross-linking post-processing step.