Programmable Granular Hydrogel Inks for 3D Bioprinting Applications

Granular inks comprising jammed hydrogel unit building blocks are emerging as multiprogramable precursors for 3D/4D printing nonbulk hydrogel constructs. In addition to their injectability, they also exhibit high porosity when compared to bulk hydrogels, allowing more efficient nutrient transport and cell migration through the scaffold structure. Herein, the key steps in the production of these inks, from the fabrication of the microgels, the jamming process, and how fabrication affects final material properties, such as porosity, resolution, and fidelity is reviewed. In addition, the main techniques used for the stabilization of scaffolds after the printing process and the assessment of cell viability, in the case of bioinks, are meticulously discussed. Finally, the most recent studies in the application of granular hydrogels for different biomedical applications are highlighted. All in all, it is envisioned that 3D-printed granular constructs will continue to evolve towards increasingly stimuli-responsive platforms that may respond in a spatiotemporally controlled manner that matches that of user-defined or biologically encoded processes.

Automated summary

Granular inks composed of jammed hydrogel unit building blocks have become a versatile precursor for 3D/4D printing of nonbulk hydrogel constructs. These inks, along with their injectability, possess high porosity compared to bulk hydrogels, allowing efficient nutrient transport and cell migration. This review illustrates the key steps in the ink production, from microgel fabrication, jamming process, to the influence of fabrication on material properties. It also discusses the techniques for scaffold stabilization and cell viability assessment. Furthermore, recent studies on the biomedical applications of granular hydrogels are highlighted, indicating their potential as stimuli-responsive platforms.