HA/PCL scaffolds regulate bone regeneration by stimulating macrophage M2 phlarization

Given that there are few reports on the immune modulation properties of 3D printed HA/PCL scaffolds with different hydroxyapatite(HA) ratios. Here, we applied 3D printing to prepare PCL scaffolds with different HA contents: P, HP (2:10), HP (3:10), and kept the fiber porosity of the scaffolds essentially the same. It was found that HA significantly enhanced the osteogenic differentiation performance of PCL-promoted rat bone marrow mesenchymal stem cells (BMSCs). Particularly, the bioactivity of the scaffolds did not consistently increase with the increase of HA content. Compared to other groups, HP (2:10) may maximally induce macrophage (raw 264.7 cells) polarization towards the M2 phenotype through multiple signaling pathways, including MAPK, IL-17 and Toll-like receptor, to form an immune microenvironment conducive to osteogenesis. Animal experiments showed that HP (2:10) was able to now direct the growth of newborn bone tissue toward the scaffold holes, along with stronger induction of vascular growth factor (VEGF) and macrophage M2 phenotypic protein (CD163) deposition. This study can make up for the deficiency of HA/PCL-based bone filling materials in immunomodulation of osteogenesis to a certain extent. Meanwhile, it provides a suitable mixing ratio of HA and PCL, which is an important reference value for subsequent studies.