Hydrogel materials based on sodium alginate find versatile applications in regenerative medicine and tissue engineering due to their unique properties, such as biocompatibility and biodegradability, and the possibility of the customization of their mechanical properties, such as in terms of the individual requirements of separate clinical applications. These materials, however, have numerous limitations in the area of biological activity. In order to eliminate their limitations, sodium alginate is popularly applied in combination with added gelatin, which represents a product of collagen hydrolysis. Despite numerous beneficial biological properties, matrix materials based on gelatin have poor mechanical properties and are characterized by their ability for rapid degradation in an aqueous environment, particularly at the physiological temperature of the body, which significantly limits the independent application opportunities of this type of composition in the range of scaffolding production dedicated for tissue engineering. Collagen hydrogels, unlike gelatin, are characterized by higher bioactivity, dictated by a greater number of ligands that allow for cell adhesion, as well as better stability under physiological conditions. Fish-derived collagen provides a material that may be efficiently extracted without the risk of mammalian prion infection and can be used in all patients without religious restrictions. Considering the numerous advantages of collagen indicating its superiority over gelatin, within the framework of this study, the compositions of hydrogel materials based on sodium alginate and fish collagen in different concentrations were developed. Prepared hydrogel materials were compared with the properties of a typical composition of alginate with the addition of gelatin. The rheological, mechanical, and physicochemical properties of the developed polymer compositions were evaluated. The first trials of 3D printing by extrusion technique using the analyzed polymer solutions were also conducted. The results obtained indicate that replacing gelatin with fish collagen at an analogous concentration leads to obtaining materials with a lower swelling degree, better mechanical properties, higher stability, limited release kinetics of calcium ions cross-linking the alginate matrix, a slowed process of protein release under physiological conditions, and the possibility of extrusion 3D printing. The conducted analysis highlights that the optimization of the applied concentrations of fish collagen additives to composition based on sodium alginate creates the possibility of designing materials with appropriate mechanical and rheological properties and degradation kinetics adjusted to the requirements of specific applications, leading to the prospective opportunity to produce materials capable of mimicking the properties of relevant soft tissues. Thanks to its excellent bioactivity and lower-than-gelatin viscosity of the polymer solution, fish collagen also provides a prospective solution for applications in the field of 3D bioprinting.

Hydrogel materials provide an extremely promising group of materials that can find an increasingly wide range of use in treating urinary system conditions due to their unique properties. The present review describes achievements to date in terms of the use and development prospects of hydrogel materials applications in the treatment and reconstruction of the urinary system organs, which among others include: hydrogel systems of intravesical drug delivery, ureteral stents design, treatment of vesicoureteral reflux, urinary bladder and urethral defects reconstruction, design of modern urinary catheters and also solutions applied in urinary incontinence therapy (Figure 4). In addition, hydrogel materials find increasingly growing applications in the construction of educational simulation models of organs and specific conditions of the urinary system, which enable the education of medical personnel. Numerous research efforts are underway to expand the existing treatment methods and reconstruction of the urinary system based on hydrogel materials. After conducting the further necessary research, many of the innovative solutions developed to date have high application potential.

Alginate‐gelatin hydrogels are the most commonly used materials for 3D bioprinting. Their printability depends on their properties, and these derive from the way they are prepared and their very composition. Therefore, the aim of the study was to investigate the type of solvent (deionized water, phosphate buffer, and culture medium) and contents of gelatin in the composition of hydrogel (2% wt/vol alginate, 6% and 9% wt/vol of gelatin) on their biological, physicochemical, and mechanical properties, as well as printability and the ability of cells to proliferate in the printed structures. The results obtained revealed that all the manufactured hydrogel materials are biocompatible. The use of deionized water as a solvent results in the highest degree of cross‐linking of hydrogels, thus obtaining a polymer with the highest rigidity. Moreover, an increase in gelatin content leads to an increase in the Young's modulus value, irrespectively of the solvent in which the hydrogels were prepared. Based on the chemical structure, it is more reasonable to use a culture medium for bioink preparation due to free NH and NH₂ groups being present, which are ligands for cell attachment and their proliferation. For the selected material (2A9GM), the printability and high viability of the cells after printing were confirmed. In this case, the concentration of the cross‐linking agent influences gelatin amount release and calcium ions release, and these two processes determine the change in the viability of the cells encapsulated in the bioink.

The common use of hydrogel materials in 3D bioprinting techniques is dictated by the unique properties of hydrogel bioinks, among which some of the most important in terms of sustaining vital cell functions in vitro in 3D cultures are the ability to retain large amounts of liquid and the ability to modify rigidity and mechanical properties to reproduce the structure of the natural extracellular matrix. Due to their high biocompatibility, non-immunogenicity, and the possibility of optimizing rheological properties and bioactivity at the same time, one of the most commonly used hydrogel bioink compositions are polymer solutions based on sodium alginate and gelatin. In 3D bioprinting techniques, it is necessary for hydrogel printouts to feature an appropriate geometry to ensure proper metabolic activity of the cells contained inside the printouts. The desired solution is to obtain a thin-walled printout geometry, ensuring uniform nutrient availability and gas exchange during cultivation. Within this study’s framework, tubular bioprinted structures were developed based on sodium alginate and gelatin, containing cells of the immortalized fibroblast line NIH/3T3 in their structure. Directly after the 3D printing process, such structures are characterized by extremely low mechanical strength. The purpose of this study was to perform a comparative analysis of the viability and spreading ability of the biological material contained in the printouts during their incubation for a period of 8 weeks while monitoring the effect of cellular growth on changes in the mechanical properties of the tubular structures. The observations demonstrated that the cells contained in the 3D printouts reach the ability to grow and spread in the polymer matrix after 4 weeks of cultivation, leading to obtaining a homogeneous, interconnected cell network inside the hydrogel after 6 weeks of incubation. Analysis of the mechanical properties of the printouts indicates that with the increasing time of cultivation of the structures, the degree of their overgrowth by the biological material contained inside, and the progressive degradation of the polymer matrix process, the tensile strength of tubular 3D printouts varies.

3D bioprinting processes show great potential in the context of repair, regeneration, and substituting damaged tissues. Incorporating biomaterials of natural origin into the structure of sodium alginate through adhesive peptides and cellular ligands effectively improves its bioactivity. Despite the advantages and common use of gelatin-based hydrogel materials, their application carries limitations. The possibility of replacing gelatin with collagen during the production of bioinks is becoming promising. Marine organisms are safe, attractive sources from the point of view of ethical restrictions, as well as abundant due to the amount of waste from collagen sources. This work focuses on analyzing the effect of different concentrations of 50-50 mixture of cold and warm water fish collagen in polymer solutions on the physicochemical and mechanical properties of the developed materials, emphasizing their significant impact on cell proliferation in bioprinted constructs. The obtained results demonstrate that increasing the concentration of fish collagen increases the system’s viscosity; at the same time, in the case of the final hydrogel materials, a higher swelling degree and improved mechanical properties can be obtained. Furthermore, the use of 1.5% (w/v) fish collagen in sodium alginate-based bioinks (2A1.5ColF) promotes proliferation and the organization of cells into extensive cellular networks, leading to the formation of tissue structures.

This study presents the design and validation of a modular, multi-head 3D bioprinter developed for the fabrication of single- and multilayer tubular constructs. The system integrates two extrusion heads for hydrogels or cell-laden bioinks with a direct-feed head for thermoplastic polymers, thereby enabling materials with markedly different processing requirements to be deposited within a single manufacturing platform.,The hydrogel-printing modules provide independent material delivery and temperature control, allowing different hydrogel formulations or cell-laden bioinks to be processed. The thermoplastic module produces a mechanically supportive outer framework intended to improve the handling and structural stability of the hydrogel component. Tubular constructs were fabricated on a rotating, multi-diameter mandrel using a PCL/PLGA thermoplastic blend and an alginate-gelatin bioink containing NIH/3T3 mouse fibroblasts.,Device performance was evaluated through chamber decontamination tests, fabrication of multimaterial tubular constructs, extract-based cytotoxicity testing of the thermoplastic material, and Live/Dead assessment of cells encapsulated in the hydrogel phase. No microbial growth was detected in the tested media after chamber treatment. Cell viability exceeded the 70% cytotoxicity threshold for both filament and printed thermoplastic extracts, while fibroblast viability in the bioprinted hydrogel was 90.2 ± 1.3% immediately after printing and remained 83.7 ± 2.1% after 9 days. These findings demonstrate the feasibility of integrating thermoplastic printing and extrusion bioprinting for the manufacture of tubular tissue-engineering constructs.