The 3D-Printed Ordered Bredigite Scaffold Promotes Pro-Healing of Critical-Sized Bone Defects by Regulating Macrophage Polarization

Abstract

Background: Repairing critical-sized bone defects secondary to traumatic or tumorous damage is a complex conundrum in clinical practice; in this case, artificial scaffolds exhibited preferable outcomes. Bredigite (BRT, Ca 7 MgSi 4 O 16 ) bioceramic possesses excellent physicochemical properties and biological activity as a promising candidate for bone tissue engineering. Methods: Structurally ordered BRT (BRT-O) scaffolds were fabricated by a three-dimensional (3D) printing technique, and the random BRT (BRT-R) scaffolds and clinically available β-tricalcium phosphate (β-TCP) scaffolds were compared as control groups. Their physicochemical properties were characterized, and RAW 264.7 cells, bone marrow mesenchymal stem cells (BMSCs), and rat cranial critical-sized bone defect models were utilized for evaluating macrophage polarization and bone regeneration. Results:The BRT-O scaffolds exhibited regular morphology and homogeneous porosity. In addition, the BRT-O scaffolds released higher concentrations of ionic products based on coordinated biodegradability than the β-TCP scaffolds. In vitro, the BRT-O scaffolds facilitated RWA264.7 cells polarization to pro-healing M2 macrophage phenotype, whereas the BRT-R and β-TCP scaffolds stimulated more pro-inflammatory M1-type macrophages. A conditioned medium derived from macrophages seeding on the BRT-O scaffolds notably promoted the osteogenic lineage differentiation of BMSCs in vitro. The cell migration ability of BMSCs was significantly enhanced under the BRT-O-induced immune microenvironment. Moreover, in rat cranial critical-sized bone defect models, the BRT-O scaffolds group promoted new bone formation with a higher proportion of M2-type macrophage infiltration and expression of osteogenesis-related markers. Therefore, in vivo, BRT-O scaffolds play immunomodulatory roles in promoting critical-sized bone defects by enhancing the polarization of M2 macrophages. Conclusion: 3D-printed BRT-O scaffolds can be a promising option for bone tissue engineering, at least partly through macrophage polarization and osteoimmunomodulation.

3D-printed bredigite scaffolds with ordered arrangement structures promote bone regeneration by inducing macrophage polarization in onlay grafts

“…Previous investigations have indicated that the phenotype of macrophages can affect the outcomes of bone regeneration after grafting bone scaffolds. Tuning macrophages toward the pro-regenerative M2 phenotype can evidently facilitate bone regeneration, which is consistent with the findings of the present study [ 25 , 32 – 34 ]. Future investigations should focus on the underlying mechanisms of macrophage regulation for designing bone scaffolds with immunomodulation strategies in the field of regenerative medicine.…”

“…Recently, researchers have focused more on the osteoimmunomodulatory properties of bone scaffold biomaterials, aiming to regulate immune reactions, and promote bone regeneration [ 20 , 29 – 31 ]. After biomaterials grafting in vivo, macrophages are the earliest cells recruited at the grafting site [ 25 , 32 ]. Furthermore, macrophages predominantly determine the long-term immune reactions to biomaterials [ 32 – 34 ].…”

“…In order to evaluate the macrophages in response to the scaffold’s impact on BMSCSs, supernatant samples were collected from wells that contained RAW264.7 cells seeded on scaffolds after three days of culture, in order to prepare a conditioned medium (CM). Then, the BMSCSs from the femurs and tibias of male C57BL/6 N mice (aged 6–8 weeks) were isolated, cultured and identified using a well-established technique, as previously described [ 25 ]. Briefly, BMSCSs were cultured in 96-well plates, and treated with a mixture of DMEM and CM, at a ratio of 1:1.…”

MicroRNA-21a-5p-modified macrophage exosomes as natural nanocarriers promote bone regeneration by targeting GATA2

“…In addition, the M1-Exos-miR-21a-5p group had significantly higher BV/TV and bonemineraldensity (BMD). Furthermore, M1 exosomes overexpressing miR-21a-5p composited with hydrogel showed excellent osteogenic potentiality [ 12 ].…”

“…Macrophage-derived exosomes were extracted as previously described [ 12 ]. The HyStem-HP Hydrogel Kit (Advanced BioMatrix) was opened in an ultra-clean table and the mixture of hydrogel and exosomes was prepared according to the instructions.…”