Tanshinone IIA-loaded aligned microfibers facilitate stem cell recruitment and capillary formation by inducing M2 macrophage polarization

Direct implantation of cell-free scaffolds capable of promoting tissue regeneration by manipulating immune responses has proven to be a promising therapeutic strategy for regenerative medicine. Here, we developed aligned microfiber scaffolds with sustained release of tanshinone ⅡA (Tan ⅡA) to modulate macrophages phenotypic transition, which subsequently promoted stem cell recruitment and capillary formation. Aligned microfibers scaffolds loaded with 1μM Tan ⅡA (AF-1) significantly down-regulated the expression of proinflammatory genes and proteins, while they upregulated anti-inflammatory genes and proteins, in RAW 264.7 macrophages. Conditioned medium collected from macrophages cultured on AF-1 scaffolds enhanced bone marrow-derived mesenchymal stem cell (BMSC) proliferation and migration, and also regulated their multiple biological functions as evidenced by RNA-Seq assays. Moreover, the conditioned medium also promoted human umbilical vein endothelial cell (HUVEC) proliferation, migration, and tube formation. Enhancement of endogenous stem cell recruitment and vascularization by regulating macrophage phenotype transition was further confirmed by utilizing rat subcutaneous implantation of the scaffolds. These results support the use of drug-loaded aligned microfiber scaffolds to enable immune modulation to stimulate stem cell recruitment and vascularization, which could potentially result in successful cell-free, scaffold-guided tissue regeneration.