(602c) Engineering Mechanical and Biological Properties of Biomacromolecular Granular Hydrogel Scaffolds Via Microgel Packing

Granular hydrogel scaffolds (GHS) have been developed to overcome the structural limitations of bulk (nanoporous) hydrogels in tissue engineering and regeneration. GHS are fabricated by placing hydrogel microparticles (HMP) in close contact (packing), 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 effects of packing on the physical and biological properties of gelatin methacryloyl (GelMA) GHS are unexplored. In this work, GelMA HMP were packed at different centrifugal forces and durations (loosely packed: 3000 ×g-15 s and highly packed: 16000 ×g-300 s) to investigate the effect of packing on GelMA GHS porosity, mechanical properties, in vitro cell viability and migration, and in vivo response. Increasing centrifugation time/force resulted in a high degree of HMP packing, decreasing the void fraction and median pore diameter. Increased HMP contact area at the highly packed condition resulted in higher compressive and storage moduli. The cell viability and metabolic activity in GelMA GHS were analyzed for 7 days. Metabolic activity decreased on day 7 as the packing increased, as a result of higher cell density per volume when pore diameter and void fraction decreased. The migration length of cells within GHS was analyzed three days post-culture, and a decrease in migration length was observed by increasing the packing. Additionally, NIH/3T3 fibroblast cells spread more on the surface of HMP in loosely packed GHS compared with the highly packed counterpart. In vivo subcutaneous implantation conducted on the GHS showed a lower cell migration and tissue integration within the highly packed GHS. Harvested tissue was stained with a cluster of differentiation 31 (CD31), CD68, CD86, CD206, and α-smooth muscle actin (α-SMA) markers for analyzing the effect of packing on the invasion of endogenous cells and vessels within GHS. A lower cell coverage was observed in the highly packed GHS compared with the loosely packed one. In conclusion, we engineered GelMA GHS porosity by applying a centrifugal force to induce HMP deformation and showed how mechanical and biological responses were affected by the packing. This research is a step forward in engineering GelMA GHS via external stimuli for tissue engineering.