Nowadays, bioprinting is rapidly evolving and hydrogels are a key component for its success. In this sense, synthesis of hydrogels, as well as bioprinting process, and cross-linking of bioinks represent different challenges for the scientific community. A set of unified criteria and a common framework are missing, so multidisciplinary research teams might not efficiently share the advances and limitations of bioprinting. Although multiple combinations of materials and proportions have been used for several applications, it is still unclear the relationship between good printability of hydrogels and better medical/clinical behavior of bioprinted structures. For this reason, a PRISMA methodology was conducted in this review. Thus, 1,774 papers were retrieved from PUBMED, WOS, and SCOPUS databases. After selection, 118 papers were analyzed to extract information about materials, hydrogel synthesis, bioprinting process, and tests performed on bioprinted structures. The aim of this systematic review is to analyze materials used and their influence on the bioprinting parameters that ultimately generate tridimensional structures. Furthermore, a comparison of mechanical and cellular behavior of those bioprinted structures is presented. Finally, some conclusions and recommendations are exposed to improve reproducibility and facilitate a fair comparison of results.

Bioinks are usually cell-laden hydrogels widely studied in bioprinting performing experimental tests to tune their rheological properties, thus increasing research time and development costs. Computational Fluids Dynamics (CFD) is a powerful tool that can minimize iterations and costs simulating the material behavior using parametric changes in rheological properties under testing. Additionally, most bioinks have specific functionalities and their properties might widely change with temperature. Therefore, commercial bioinks are an excellent way to standardize bioprinting process, but they are not analyzed in detail. Therefore, the objective of this work is to study how three temperatures of the Cellink Bioink influence shear stress pressure and velocity through computational simulation. A comparison of three conical nozzles (20, 22, and 25G) for each temperature has been performed. The results show that shear stress, pressure, and velocity vary in negligible ranges for all combinations. Although these ranges are small and define a good thermo-responsive bioink, they do not generate a filament on the air and make drops during extrusion. In conclusion, this bioink provides a very stable behavior with low shear stress, but other bioprinting parameters must be set up to get a stable filament width.

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The brittle behavior of amorphous soda-lime glasses has been a major setback for the widespread use of this material in many industrial applications. Due to the low energy barrier of the matrix, the arrest of propagating cracks in such amorphous material is poor and often results in low energy toughness and strength. Glass is more susceptible to heat treatment and its hardness is slightly affected by use reinforcement. In the present work, the effects of reinforcing soda-lime glass with CuO and ZrO 2 particles were investigated. Fracture toughness was measured using the indentation technique. It was found that the fracture toughness increased by 17.4% and 29.5% for glass samples reinforced with CuO and ZrO 2 , respectively. The distribution of the reinforcement particles was strongly affected by their average size and degree of wetting. In particular, ZrO 2 particles having sizes in the nano-range are more uniformly distributed when compared to micron-range particles, which have the tendency to form isolated clusters in the glass matrix. AFM analysis performed on some samples showed evidence of particle distribution in the surroundings of indentations.

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