Modulation of macrophage polarization by mixed hydroxyapatite and polycaprolactone scaffolds

Studies on the immunomodulatory properties of 3D printed HA/PCL scaffolds with different proportions of hydroxyapatite (HA) are limited. In this study, 3D printing technology was used to prepare PCL scaffolds with different HA contents: P, HP (2:10), and HP (3:10), and to ensure that the porosity of the scaffold fibers was basically the same. The results showed that the introduction of HA significantly enhanced the osteogenic differentiation ability of rat bone marrow mesenchymal stem cells (BMSCs) induced by PCL scaffolds. However, the bioactivity of scaffolds did not continuously increase with the increase of HA content. Through transcriptome sequencing analysis, we found that HP (2:10) scaffold was particularly prominent in immune regulation, which significantly promoted the polarization of macrophages (RAW264.7 cells) to M2 phenotype through MAPK, IL-17, Toll-like receptors and other signaling pathways. The polarization of M2 macrophages plays a key role in the construction of immune microenvironment conducive to bone regeneration and provides important support for osteogenic differentiation and tissue repair. Animal experiments further verified that HP (2:10) scaffold not only effectively guided new bone tissue to grow into the pores of the scaffold, but also significantly enhanced the deposition of vascular growth factor (VEGF) and M2 macrophage phenotype protein (CD163), which promoted angiogenesis and bone regeneration. This study revealed the molecular mechanism of M2 polarization of macrophages through transcriptome sequencing, highlighted the central role of M2 macrophages in bone regeneration, and provided an important theoretical basis for optimizing the immunomodulatory properties of 3D printed HA/PCL scaffolds.