Study on 3D-Printed Emodin/Nano-Hydroxyapatite Scaffolds Promoting Bone Regeneration by Supporting Osteoblast Proliferation and Macrophage M2 Polarization

The treatment of bone defects caused by diseases, trauma,or tumorhas always been a great clinical challenge. Implantation of bone biomaterialsinto bone defect areas is an effective method for bone injury repair.In this study, we used three-dimensional (3D) printing technologyto prepare nano-hydroxyapatite (nHA)/sodium alginate (SA)/gelatin(Gel) hydrogel scaffolds loaded with different ratios (0, 0.13, 0.26,0.39, 0.53, and 0.79 parts per thousand) of emodin (EM) (EM/nHA/SA/Gel). Scanningelectron microscopy showed that the scaffolds had a smooth surfacewithout fracture and nHA was evenly distributed on the surface. Thecell proliferation and migration results showed that the 0.39 parts per thousand EM group, in particular, could significantly promote the proliferationand migration of mouse embryonic osteoblast precursor (MC3T3-E1) cellsand significantly increase the mRNA expression of osteogenic differentiation-relatedgenes (bone morphogenetic protein/BMP-2, BMP-9, osteocalcin). In addition,the 0.39 parts per thousand EM group exhibited the best effect on osteogenicdifferentiation-related proteins (alkaline phosphatase, Runx 2, OSX).The expression of M2 polarization-related genes (arginase-1, CD206)also significantly increased after the treatment with the 0.39 parts per thousand EM group. Micro-CT showed that in the rat skull defect model, theEM/nHA/SA/Gel scaffold group significantly promoted bone regenerationafter being implanted into the skull for 30 days. Our results indicatethat the EM/nHA/SA/Gel hydrogel scaffolds can not only directly promotethe proliferation and differentiation of osteoblasts but also indirectlypromote osteogenic differentiation by supporting M2 polarization ofmacrophages. EM/nHA/SA/Gel hydrogel scaffolds are potential bone tissueengineering materials for bone regeneration.