(B-45) Engineering porosity as a bioactive cue in gelatin methacryloyl (GelMA) granular hydrogel scaffolds

Introduction:: Over the past few years, granular hydrogel scaffolds (GHS) have been used for various biomedical applications. GHS are fabricated by placing hydrogel microparticles (HMP) in close contact, followed by physical and/or chemical interparticle bond formation. Various techniques have been used for confining the HMP in close-packed conditions, including centrifugation and compression. Studies have shown the effect of centrifugal speed on the porosity of GHS with different HMP sizes and/or stiffness. However, the effect of HMP deformation using external forces on the porosity of photocrosslinkable, physically crosslinked soft gelatin methacryloyl (GelMA) GHS is unexplored.


Materials and Methods:: GelMA, synthesized by methacrylate modification of gelatin, was used to fabricate uniformly sized HMP via a step-emulsification microfluidic device (Fig. 1a). To investigate the effect of packing on GelMA GHS porosity, mechanical properties, in vitro cell viability and migration, and in vivo response, GelMA HMP were packed at different centrifugal forces and durations. Fluorescence microscopy was used to analyze the void fraction and the median pore equivalent diameter of GHS (Fig. 1b). In addition, mechanical characterization of the GHS was conducted via compression and frequency sweep tests. GHS was cultured with NIH/3T3 fibroblast cells or subcutaneously implanted in mice for in vitro or in vivo characterizations, respectively.


Results, Conclusions, and Discussions:: Increasing centrifugation time resulted in a higher degree of HMP packing, leading to a decrease in the void fraction and median pore diameter and an increase in compressive and storage moduli (Fig. 1c). The Cell viability and the metabolic activity of GelMA GHS was analyzed for 7 days, where a decrease in metabolic activity was observed on day 7 as the packing increased (Fig. 1d). Cell migration was analyzed over the period of 3 days and increasing the packing led to a lower cell migration within the GHS (Fig. 1e). In vivo subcutaneous implantation will be conducted on the two extreme conditions with the highest and lowest packing density to study the effect of packing on endogenous cell migration and tissue integration. In conclusion, we engineered GelMA GHS porosity by applying centrifugal force to induce HMP deformation and showed how mechanical and biological responses are affected by the packing. This research is a step forward in engineering GelMA GHS via external stimuli for tissue engineering.


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