Preparation And Bioactivity Of Hydroxyapatite-based Composite Ceramics

Background and objective:The bone tissue has excellent regeneration capability but areas beyond the critical defect without reconstruction spontaneously.Autologous bone grafts are considered the gold standard for the treatment of bone defects,but autologous bone transplantation often causes secondary damage and infection in the donor site.And allogeneic bone transplantation has risks of immune rejection and infection,so finding new bone replacement materials to solve the above problems is the research focus currently.Hydroxyapatite(HA)is chemically similar to the calcium phosphate in human bone tissue and can promote the formation of new bone.However,it has lower fracture toughness,and its biological activity is harmed by the addition of toughening phases,which limits its clinical application.Therefore,the columnar β-Si3N4 as the toughening phase with excellent mechanical properties and good biological activity and La3+ sintering additive as active ions are used in this study to prepare β-Si3N4/HA composite biomaterials.The mechanical properties,micromorphology and compositional changes of the composites under different sintering conditions and their effects on bioactivity are also investigated.Materials and methods:(1)Preparation of β-Si3N4/HA composite ceramics:The composition of composite ceramics was HA as the main body,adding different proportions of β-Si3N4.In composite ceramics,the sintering additives lanthanum oxide(La2O3)and yttrium oxide(Y2O3)accounted for 12wt%of β-Si3N4,respectively.The materials were ultrasonically dispersed,mechanically stirred,vacuum dried,cold-pressed,and sintered at high temperatures to obtain β-Si3N4/HA composite ceramics.(2)Characterization of ceramics:The densities of the ceramics were tested using the drainage method;their hardness and fracture toughness were measured by a Vickers hardness tester;their micromorphology and physical and chemical properties were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD)and energy spectroscopy(EDS).The surface roughness and wettability of composite ceramics were measured by atomic force microscopy(AFM)and contact angle meter.(3)Evaluation of ion release and protein adsorption capacity of the ceramics:The ceramics were immersed in simulated body fluid(SBF),and then the concentration of bioactive ions was measured using an inductively coupled plasma emission spectrometer.The bovine serum albumin model was employed to analyze the protein adsorption capacity of the ceramics.(4)The biocompatibility and osteogenic capacity of ceramics:The MC3T3-E1 mouse embryonic osteoblasts were used to evaluate cell bioactivity including cell adhesion,spreading and metabolic activity.The influences of ceramics on osteogenic differentiation of MC3T3-E1 mouse embryonic osteoblasts were examined by alkaline phosphatase(ALP)staining and semiquantification and Alizarin Red S staining.Results:(1)As the sintering temperature rose,an increase was observed in the density,microhardness,and fracture toughness of HA and composite ceramics.In the presence of the sintering additives,the hardness and toughness of 10wt%β-Si3N4/HA composite prepared by press sintering at 1300℃ were 6.44 GPa and 1.69 MPa·m1/2,respectively,being 110%and 140%higher than those of pure HA.(2)The composite ceramics containing sintered additives could significantly improve their surface roughness and exhibited a better protein adsorption capacity.(3)The concentrations of silicon and lanthanum ions released by composite ceramics were within the physiological range.The release of bioactive ions synergized with the physicochemical properties of the composite ceramics significantly promoted cell adhesion,proliferation and osteogenic differentiation.Conclusions:In this study,the β-Si3N4/HA composite can maintain the biological activity of HA and significantly enhance its mechanical properties.This composite system will provide a material basis for preparing bone tissue engineering scaffolds with excellent bioactivity and mechanical properties.Background and objective:In the field of bone tissue engineering,porous hydroxyapatite(HA)bone repair scaffolds with controlled architecture are challenging to manufacture and lack sufficient osteoinductive activity.The ceramic 3D printing method based on the digital light processing(DLP)process has the advantages of high forming accuracy,low consumption of consumables and high mechanical properties.Studies have shown that graphene oxide(GO)has excellent mechanical strength and can also promote the osteogenic differentiation of stem cells.Therefore,this study aims to develop GO/HA composite ceramic photosensitive slurries suitable for DLP 3D printing and to guarantee the molding quality of scaffolds by investigating the photosensitive parameters of the composite ceramic slurry and optimizing the DLP printing degreasingsintering process.And to observe the effects of GO content on the mechanical properties and bioactivity of composite ceramics.Our ultimate goal is to fabricate GO/HA porous ceramic scaffolds with good mechanical properties and enhanced bioactivity.Materials and methods:(1)Preparation of GO/HA composite ceramics:The GO/HA composite photosensitive slurries with GO mass fractions of 0%,0.1%,0.2%,0.4%and 0.6%were prepared;the viscosity of each formulation was evaluated by a rotational rheometer;the photosensitive parameters of HA slurry with different GO content were optimized by investigating the critical exposure energy and single layer curing thickness.The GO/HA ceramic green bodies were printed by a DLP 3D printer.(2)Degreasing and sintering of composite ceramics:To investigate the effect of the amount of oxygen introduced on the removal of pyrolytic free carbon by establishing degreasing and sintering process curves based on thermogravimetric analysis.And to explore the influence of the decarbonization process on the micromorphology of GO.(3)Characterization of composite ceramics:the mechanical properties such as density and hardness of composite ceramics were tested;the physicochemical properties and micromorphology of the raw material and the sintered ceramic body were analyzed by XRD and SEM;the pore size and overall dimensions of scaffolds were measured using a digital electron microscope and then the shrinkage was calculated.(4)Evaluation of the bioactivity of composite ceramics:the cytotoxicity and cell proliferation were detected by CCK-8 assay;the adhesion and growth of rat bone marrow mesenchymal stem cells(rBMSCs)were observed by confocal laser scanning microscopy(CLSM).The expression of osteogenesis-related genes in rBMSCs was detected by qRT-PCR assay and the osteogenic activity was investigated by ALP staining and semi-quantification,and Alizarin Red S staining.Results:(1)Adding an appropriate amount of GO(0.1-0.4%)can ensure the forming accuracy of the scaffolds.With the increase of GO content,the critical exposure energy of GO/HA composite slurry increased,and the maximum curing layer thickness decreased.GO could absorb part of the UV light,which was just enough to weaken the scattering effect of the ceramic particles and keep the shape of predesigned pores unchanged even under high or prolonged exposure.(2)During the degreasing and sintering process,the organic residual free carbon can be removed by introducing air at a rate of 0.32 L/min for 7.5 min at 800℃,which also can protect the integrity of the GO.(3)GO can significantly improve the mechanical properties of 3D-printed composite ceramics.The density,hardness,and fracture toughness of the 0.4GO/HA composite ceramics were 92.7%,5.72 GPa,and 1.55 MPa·m1/2,respectively.(4)The GO/HA composite ceramic scaffolds significantly promoted the adhesion,proliferation and osteogenic differentiation of rBMSCs,exhibiting enhanced osteoinductivity.Conclusions:GO can enhance both the mechanical properties and the osteogenic activity of HA.The 0.1-0.2wt%GO/HA composite ceramic scaffolds constructed by DLP 3D printing exhibited precise porous morphology and excellent osteogenic activities.The GO/HA composite will provide the material basis for preparing high-performance HA-based ceramic scaffolds for repairing bone defects.