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Macrophages are essential in the initiation, maintenance, and transition of inflammatory processes like foreign body response and wound healing. Mounting evidence suggests that physical factors also modulate macrophage activation in vitro and in vivo. 2D in vitro systems have demonstrated that constraining macrophages to small areas or channels modulates their phenotypes and changes their responses to known inflammatory agents such as lipopolysaccharide. However, how dimensionality and pore size affect macrophage phenotype is less explored. In this work, we studied the change in M1/M2 polarization when macrophages were confined in microporous annealed particle scaffolds (MAP), which are granular hydrogels generated from annealed spherical microgels. We engineered three types of MAP gels comprising 40, 70, and 130 μm diameter particle sizes, respectively. Particles sizes were selected using outputs from software LOVAMAP that analyzes the characteristics of 3-D pores in MAP gels. Since the size of building block particle correlates with pore size inside the final scaffolds, our three scaffold types allowed us to study how the degree of spatial confinement modulated the behavior of embedded macrophages. Spatially confining macrophages in scaffolds with pore size on the scale of cells led to a reduced level of the inflammatory response, which was correlated with a change in cell morphology and motility.

Liu Y, Suarez-Arnedo A, Riley L, Miley T, Xia J, Segura T