Three-Dimensional Bioprinting of GelMA Hydrogels with Culture Medium: Balancing Printability, Rheology and Cell Viability for Tissue Regeneration.

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.

Fabrication and characterisation of bioglass and hydroxyapatite-filled scaffolds.

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.

Comparison of the potential for bioprinting of different 3D printing technologies.

26Additive 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.

Methodology for characterizing the printability of hydrogels.

280Currently, 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.

Relationship between shear-thinning rheological properties of bioinks and bioprinting parameters.

Three-dimensional bioprinting is a technology in constant development, mainly due to its extraordinary potential to revolutionize regenerative medicine. It allows fabrication through the additive deposition of biochemical products, biological materials, and living cells for the generation of structures in bioengineering. There are various techniques and biomaterials or bioinks that are suitable for bioprinting. Their rheological properties are directly related to the quality of these processes. In this study, alginate-based hydrogels were prepared using CaCl2 as ionic crosslinking agent. Their rheological behavior was studied, and simulations of the bioprinting processes under predetermined conditions were carried out, looking for possible relationships between the rheological parameters and the variables used in the bioprinting processes. A clear linear relationship was found between the extrusion pressure and the flow consistency index rheological parameter, k, and between the extrusion time and the flow behavior index rheological parameter, n. This would allow simplification of the repetitive processes currently applied to optimize the extrusion pressure and dispensing head displacement speed, thereby helping to reduce the time and material used as well as to optimize the required bioprinting results.