Phenotyping and Immune Signaling of Monocytes and Macrophages in Porous Precision-Templated Scaffolds

Abstract

Porous precision-templated scaffolds (PTS) are three-dimensional biomaterial constructs where the pore size and pore interconnects can be precisely controlled, allowing for the creation of scaffolds with tunable characteristics and implant outcomes. Regardless of the polymer used in construction and without the use of any signaling/stimulating molecules, PTS with uniform, interconnected, 40 μm pores have shown a remarkable ability in immunomodulating resident cells for tissue regeneration. In contrast, PTS with smaller or larger pores result in a pro-inflammatory and pro-fibrotic foreign body reaction. The mechanism behind the pore-size-mediated phenomenon remains unclear; however, monocyte and macrophage phenotypes have been identified as key mediators in regulating the implant outcome within the PTS. Here, we quantify the infiltration kinetics and functional response of circulating monocytes to subcutaneously implanted PTS. We then identify the regulatory roles of MyD88-dependent signaling downstream of Toll-like receptors (TLRs) that drive the regenerative, pro-healing response in 40 μm PTS. Finally, we demonstrate a synergetic relationship between TLR signaling and macrophage receptor with collagenous structure (MARCO), an innate activation marker of monocytes and macrophages, in modulating macrophage phenotype. Overall, these findings further our understanding of the molecular mechanisms underlying cell behavior and tissue regeneration in PTS and implantable biomaterials.