| Bone defects caused by trauma,inflammation,tumor and other factors have caused great harm to human health and quality of life.However,the critical bone defect usually cannot heal spontaneously through the body’s own repair mechanism,and bone graft is often needed for treatment.Autogenous bone transplantation,as the "gold standard" for the treatment of bone defects,is limited in its application due to the limitation of the size of the available site,the long operation time and the complications at the donor site.Therefore,a lot of research in recent years has focused on developing new strategies for bone tissue engineering.The ideal bone tissue engineering material should have good biocompatibility,osteoinduction,osteoconduction,degradability,and meet the mechanical properties required by the bone tissue at the implant site,so as to provide adequate mechanical support.However,3D printed scaffolds can meet the above requirements,so it has attracted the attention of most researchers,and become a kind of bone tissue engineering materials with great potential.However,after implantation,foreign body reaction(FBR)will occur in the host body,which will affect the bone repair performance of the material.Macrophages play a key role in the process of foreign body reaction and bone regeneration,and especially the macrophage phenotype plays an important role in determining the local immune microenvironment.Therefore,how to regulate the macrophage phenotype has become a research focus of biomaterials.In this study,a flexible bioactive porous hydroxyapatite(HA)scaffold was constructed by 3D printed technology,and the effect and mechanism of the morphology(pore size and hydrophilicity)of the 3D-printed bioactive scaffold on the regulation of macrophage polarization was systematically studied.Then,their influence on the bone defect repair was systematically evaluated.In addition,two classic bioactive materials,BG and HA,were selected as the different components of 3D printed bioactive scaffolds.Subsequently,the differences in their effects on macrophage polarization and bone regeneration were systematically studied.The main research contents and results are as follows:(1)Three kinds of flexible PCL/PEG/HA scaffolds with different pore size(200μm,400 μm,600 μm)were prepared by 3D printed technology.The effects of pore size on material properties,FBR severity,macrophage polarization and bone regeneration and the mechanism of action were studied,and verified by in vitro and in vivo experiments.The results showed that compared with 200 μm and 400 μm scaffolds,600 μm scaffolds caused the least FBR after implantation,and promoted the macrophages polarization towards M2 phenotype and the growth of blood vessels,thus promoting bone regeneration.It was found that TLR/My D88 dependent pathway may be involved in the signal transduction of macrophage polarization regulated by pore size.However,with the increase of pore size,the mechanical properties of large pore size scaffolds decrease obviously,which limits the application of large pore size scaffolds in bone tissue engineering to a certain extent.Therefore,we need to make a compromise choice between mechanical properties and pore size.(2)The surface hydrophilicity of the 3D printed scaffold(pore size=600μm)was modified by alkali treatment with different concentrations of Na OH solution(2and 2.5 mol/L).The influence of hydrophilic factors on the macrophage polarization was detected through in vitro and in vivo experiments,and the effect of the scaffold on the bone defect repair was studied.The results showed that with the increase of alkali concentration,the hydrophilicity increased gradually and the mechanical properties decreased gradually.Compared with PCL/HA-AT-2.5 and PCL/HA,PCL/HA-AT-2scaffolds could significantly reduce FBR and promote the polarization of M2 macrophages,thus showing better osteogenic ability.PCL/HA-AT-2.5 scaffolds might cause heavier foreign body reaction and M1 macrophage polarization due to excessive hydrolysis of ester bond of PCL materials.The Wnt/β-catenin pathway might be involved in the signal transduction process of osteogenesis regulated by alkali-treated scaffolds.In conclusion,alkaline treatment with appropriate concentration can improve the surface hydrophilicity of 3D printed flexible PCL/PEG/HA bioactive scaffolds,further regulate macrophage polarization and promote bone regeneration.(3)3D-printed flexible PCL/PEG/BG scaffolds(0B,1B,2B,3B)and PCL/PEG/HA scaffolds were prepared.The effects of different active components on macrophage polarization and bone regeneration were studied in vitro and in vivo.The results showed that the 2B and HA scaffolds caused the least foreign body reaction,and the 2B scaffolds promoted more vascularization and M2 macrophage polarization.The2 B scaffold had better osteogenic performance than HA,and the 2B scaffold recruits more M2 macrophages in the process of bone repair.In conclusion,3D printed flexible2B-BG scaffolds have good biocompatibility,and can regulate macrophage polarization and promote bone regeneration.It is a bioactive scaffold material with great potential for bone defect repair.To sum up,this paper studied the influence and related regulatory mechanisms of morphology and components of 3D-printed flexible bioactive scaffolds on macrophage polarization and bone regeneration,and preliminarily explored its application in bone tissue engineering.It will provide some reference for the application of 3D printed bioactive scaffold with bone immune regulation in the field of bone defect repair in the future. |
