Macrophage Polarization in Response to Varying Pore Sizes of 3D Polyurethane Scaffolds

Activated macrophages dominate the progression of foreign-body response (FBR) and may be in a bimodal state, which determines the fate of biomaterials postimplantation. The purpose of this study was to investigate the phenotypic profile of macrophages polarized by waterborne biodegradable polyurethane (WBPU) scaffolds with different pore diameters (PU8, PU12, and PU16) both in vitro and in vivo. The results demonstrated that WBPU scaffolds with smaller pore sizes promoted the polarization of RAW 264.7 cells towards an M1 phenotypic profile at the early stage (24 and 48 h of in vitro cultivation), indicating a pro-inflammatory response. After being implanted subcutaneously, however, the WBPU scaffolds recruited more macrophages over time and polarized them towards an M2 phenotype on Day 3 and 14, presenting an anti-inflammatory response and tissue repair. When the internal pores were filled up (on Day 30 of implantation), the interaction between the scaffolds and macrophages decreased, indicating an endpoint of tissue repair. In general, WBPU scaffolds with tunable internal pore sizes have potential application prospects in the field of tissue engineering.