Poster N7 - Increasing void volume fraction and cell infiltration in granular hydrogel scaffolds through porous microgels

Introduction: Hydrogels have been explored as acellular matrices to facilitate endogenous tissue repair by leveraging the regenerative capacity of the body. Nevertheless, bulk (nanoporous) hydrogels lack interconnected cell-scale pores, impeding the process of cell infiltration necessary for tissue regeneration. Granular hydrogel scaffolds (GHS), formed through the assembly of hydrogel microparticles (microgels), tackle this limitation by creating microscale void spaces among the microgels, facilitating nutrient diffusion and cell infiltration/migration. However, the prevalent use of spherical microgels in GHS fabrication limits void fraction, a critical factor in enabling nutrient diffusion and cell infiltration. In this study, we engineered porous spherical microgels through the thermally induced phase separation of composite gelatin methacryloyl (GelMA) polymers, then assembled them into GHS, enabling hierarchical porosity at particle and scaffold levels.

Materials and

Methods: GelMA solution (14% w/v) was prepared by dissolving GelMA in DPBS containing photoinitiator (PI). Additionally, PEG solutions with various concentrations (3, 4, and 5% w/v) were prepared by dissolving PEG in DPBS with 0.1% w/v PI. The final precursor polymer solution was created by mixing equal volumes of the GelMA and PEG solutions. The GelMA or GelMA/PEG mixture formed the dispersed phase, while the continuous phase comprised Novec oil supplemented with Pico-Surf (0.5% v/v). The two phases were introduced into a step-emulsification microfluidic device. The resulting droplets were collected and placed in a water bath set at different temperatures to induce phase separation. Subsequently, the droplet suspension was stored at 4 °C overnight, leading to the formation of physically crosslinked microgels. Microgels were then used for scaffold fabrication, followed by pore characterization to examine the impact of porous microgels on void volume fraction. Subsequently, in vitro and in vivo studies were conducted to evaluate the influence of porous microgels on cell migration and infiltration into the scaffolds.

Results, Conclusions, and Discussions: Void volume fraction significantly increased in GHS incorporating porous microgels as opposed to their nonporous counterparts. In vitro cell infiltration into porous microgels was higher in microgels containing larger pores, as indicated by the total infiltrated cell volume in individually crosslinked microgels. In vivo, cell infiltration was significantly higher in subcutaneously implanted GHS made up of porous microgels, which facilitated the host tissue integration. This research highlights the potential of porous microgels in developing the next generation of GHS with hierarchical porosity for tissue engineering and regeneration.

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