3D bioprinting has emerged as a key tool in tissue engineering by facilitating the creation of customized scaffolds with properties tailored to specific needs. Among the design parameters, porosity stands out as a determining factor, as it directly influences critical mechanical and biological properties such as nutrient diffusion, cell adhesion and structural integrity. This review comprehensively analyses the state of the art in scaffold design, emphasizing how porosity-related parameters such as pore size, geometry, distribution and interconnectivity affect cellular behavior and mechanical performance. It also addresses advances in manufacturing methods, such as additive manufacturing and computer-aided design (CAD), which allow the development of scaffolds with hierarchical structures and controlled porosity. In addition, the use of computational modelling, in particular finite element analysis (FEA), as an essential predictive tool to optimize the design of scaffolds under physiological conditions is highlighted. This narrative review analyzed 112 core articles retrieved primarily from Scopus (2014–2025) to provide a comprehensive and up-to-date synthesis. Despite recent progress, significant challenges persist, including the lack of standardized methodologies for characterizing and comparing porosity parameters across different studies. This review identifies these gaps and suggests future research directions, such as the development of unified characterization and classification systems and the enhancement of nanoscale resolution in bioprinting technologies. By integrating structural design with biological functionality, this review underscores the transformative potential of porosity research applied to 3D bioprinting, positioning it as a key strategy to meet current clinical needs in tissue engineering.

Currently, the characterization techniques for hydrogels used in bioprinting are extensive, and they could provide data on the physical, chemical, and mechanical properties of hydrogels. While characterizing the hydrogels, the analysis of their printing properties is of great importance in the determination of their potential for bioprinting. The study of printing properties provides data on their capacity to reproduce biomimetic structures and maintain their integrity after the process, as it also relates them to the possible cell viability after the generation of the structures. Current hydrogel characterization techniques require expensive measuring instrument that is not readily available in many research groups. Therefore, it would be interesting to propose a methodology to characterize and compare the printability of different hydrogels in a fast, simple, reliable, and inexpensive way. The aim of this work is to propose a methodology for extrusion-based bioprinters that allows determining the printability of hydrogels that are going to be loaded with cells, by analyzing cell viability with the sessile drop method, molecular cohesion with the filament collapse test, adequate gelation with the quantitative evaluation of the gelation state, and printing precision with the printing grid test. The data obtained after performing this work allow the comparison of different hydrogels or different concentrations of the same hydrogel to determine which one has the most favorable properties to carry out bioprinting studies.

Three-dimensional extrusion bioprinting technology aims to become a fundamental tool for tissue regeneration using cell-loaded hydrogels. These biomaterials must have highly specific mechanical and biological properties that allow them to generate biosimilar structures by successive layering of material while maintaining cell viability. The rheological properties of hydrogels used as bioinks are critical to their printability. Correct printability of hydrogels allows the replication of biomimetic structures, which are of great use in medicine, tissue engineering and other fields of study that require the three-dimensional replication of different tissues. When bioprinting cell-loaded hydrogels, a small amount of culture medium can be added to ensure adequate survival, which can modify the rheological properties of the hydrogels. GelMA is a hydrogel used in bioprinting, with very interesting properties and rheological parameters that have been studied and defined for its basic formulation. However, the changes that occur in its rheological parameters and therefore in its printability, when it is mixed with the culture medium necessary to house the cells inside, are unknown. Therefore, in this work, a comparative study of GelMA 100% and GelMA in the proportions 3:1 (GelMA 75%) and 1:1 (GelMA 50%) with culture medium was carried out to determine the printability of the gel (using a device of our own invention), its main rheological parameters and its toxicity after the addition of the medium and to observe whether significant differences in cell viability occur. This raises the possibility of its use in regenerative medicine using a 3D extrusion bioprinter.

3D bioprinting is a promising technique for creating artificial tissues and organs. One of the main challenges of bioprinting is cell damage, due to high pressures and tensions. During the biofabrication process, extrusion bioprinting usually results in low cell viability, typically ranging from 40% to 80%, although better printing performance with higher cell viability can be achieved by optimising the experimental design and operating conditions, with nozzle geometry being a key factor. This article presents a review of studies that have used computational fluid dynamics (CFD) to optimise nozzle geometry. They show that the optimal ranges for diameter and length are 0.2 mm to 1 mm and 8 mm to 10 mm, respectively. In addition, it is recommended that the nozzle should have an internal angle of 20 to 30 degrees, an internal coating of ethylenediaminetetraacetic acid (EDTA), and a shear stress of less than 10 kPa. In addition, a design of experiments technique to obtain an optimal 3D bioprinting configuration for a bioink is also presented. This experimental design would identify bioprinting conditions that minimise cell damage and improve the viability of the printed cells.

Additive manufacturing technologies offer a multitude of medical applications due to the advances in the development of the materials used to reproduce customized model products. The main problem with these technologies is obtaining the correct cell viability values, and it is where three-dimensional (3D) bioprinting emerges as a very interesting tool that should be studied extensively, as it has significant disadvantages with respect to printability. In this work, the comparison of 3D bioprinting technology in hydrogels and thermoplastics for the development of biomimetic parts is proposed. To this end, the study of the printability of different materials widely used in the literature is proposed, to subsequently test and analyze the parameters that indicate whether these materials could be used to obtain a biomimetic structure with structural guarantees. In order to analyze the materials studied, different tools have been designed to facilitate the quantitative characterization of their printability using 3D printing. For this purpose, different structures have been developed and a characterization methodology has been followed to quantify the printability value of each material in each test to subsequently discard the materials that do not obtain a minimum value in the result. After the study, it was found that only gelatin methacryloyl (GelMA) 5% could generate biomimetic structures faithful to the designed 3D model. Furthermore, by comparing the printing results of the different materials used in 3D bioprinting and consequently establishing the approach of different strategies, it is shown that hydrogels need to be further developed to match the results achieved by thermoplastic materials used for bioprinting.

Tissue engineering is a continuously evolving field. One of the main lines of research in this field focuses on the replacement of bone defects with materials designed to interact with the cells of a living organism in order to provide the body with a structure on which new tissues can easily grow. Among the most commonly used materials are bioglasses, which are frequently used due to their versatility and good properties. This article discusses the results of the production of an injectable paste of Bioglass® 45S5 and hydroxyapatite on a 3D printed porous structure by additive manufacturing, using a thermoplastic (PLA). The results were evaluated in a specific application of the paste, so the mechanical and bioactive properties were studied to show the multiple possibilities of using this combination for its application in regenerative medicine and more specifically in bone implants.