Effects of the fibrous topography-mediated macrophage phenotype transition on the recruitment of mesenchymal stem cells: An in vivo study.

Host responses to a biomaterial critically influence its in vivo performance. Biomaterial architectures that can recruit endogenous host stem cells could be beneficial in tissue regeneration or integration. Here, we report that the fibrous topography of biomaterials promotes the recruitment of host mesenchymal stem cells (MSCs) by facilitating the macrophage phenotype transition from M1-to-M2. Electrospun poly (ε-caprolactone) fiber (PCL-fiber) films were implanted into the subcutaneous tissues of rats, and the response of host cells to the PCL-fiber was evaluated and compared with those of solid ones (PCL-solid). During the initial post-implantation period, greater numbers of cells were recruited and adhered to the PCL-fiber compared to the PCL-solid, and the cells exhibited the M1 phenotype, which was supported by the enhanced adsorption of complement C3a to the implanted PCL-fiber. Subsequently, the PCL-fiber supported the macrophage phenotype transition from M1-to-M2, which was confirmed by the ratio of M2/M1 marker (CD163/CCR7)-positive cells and by the expression of M2/M1 markers (arginase-1/iNOS). The PCL-fiber also reduced the formation of foreign body giant cells. MSC marker (CD29, CD44, and CD90)-positive cells began to appear as early as day 4 on the PCL-fiber, while few MSCs were observed on the PCL-solid. The MSCs migration ex vivo assay showed that MSCs substantially migrated across the trans-wells toward the implanted PCL-fiber. The cells on the implanted PCL-fiber expressed and secreted substantial levels of SDF-1 (CXCL-12), while anti-SDF-1 neutralizing antibody abrogated the MSCs migration. Taken together, these results provide evidence that the fibrous topography of biomaterials enhances the recruitment of MSCs by promoting macrophage recruitment, facilitating M1-to-M2 transition, and enhancing SDF-1 secretion.