3D Printing Of Nano Hydroxyapatite With Tunable Morphology/Sodium Alginate Composite

Hydroxyapatite(Hydroxyapatite,HA)has become one of the most important materials for bone grafts owing to its excellent biological activity,biocompatibility and bone conductibility.Advances in nanotechnology have led to the development of hydroxyapatite nanoparticles(nano-HA).The preparation and application of nano-HA have drawn great attention.The morphologies of nano-HA can have significant effects on its surface property,biological activity and biocompatibility.Therefore,tuable morphologies of the nano-HA,such as needle,rod,ball and flake like,will further expand application of nano-HA in biomedical field.3D printing has recently gained much attention in manufacturing,and has been perceived as a flexible alternative tool to fabricate reproducible and highly-organized microarchitecture with patient-specific geometry through precise control over scaffold porosity,pore size,and interconnectivity.However,HA particles with micro size have unsatisfied flowing and setting properties for 3D printing.Mechanical activation has been used as a powerful tool for prepararation of new materials or modification of materials,due to mechanical energy can induce the chemical reaction and the change of material organization,structure and performance.In this study,in order to prepare nano-HA at a high-scale yield to satisfy the amount of nano-HA in 3D printing,the precipitate of nano-HA synthesized by a wet chemical method was directly treated by mechanical activation.Sodium alginate,an organic and natural polymer,was combined with nano-HA to give consideration to flowing and setting properties of nano-HA in 3D printing.The rheological,swelling,mechanical properties and biocompatibility of composite were characterized.In this paper,polyethylene glycol(PEG)with non-toxic,non-stimulating and biocompatibility was used as one of the soft template.The size of HA particle can be modulated by controlling the concentration of PEG.The morphologies of the nano-HA can be tuned by different synthetic methods(titration and diffusion).Rod like and sphere of nano-HA were obtained by titration and diffusion,respectively.The 4.0 mM of PEG concentrations is the optimal concentration of template.Mechanical force of mechanical activation resulted in crystal defects,lattice distortion,decrease of the crystallinity,and grain refinement.A large amount of nano-HA precipitate synthesized by wet method was directly treated by mechanical activation,which could produce hige-scale yield rod like and spherical nano-HA without hard agglomeration after final drying.Alendronate sodium(ALN),one of the third generation of bisphosphonates for anti-osteoporotic,has a strong affinity to Ca2+,which inhibits the crystal growth and agglomeration of nano-HA.ALN as a dispersant was added in mechanical activation can achieve nano-HA with lower crystallinity and better dispersion in this study.ALN was used as an alternative soft template to modulate the synthesis of nano-HA.The present study used remarkably higher concentrations of reactants,in mole(M),to synthesize nano-HA.A large amount of nano-HA precipitate synthesized by wet method was directly treated by mechanical activation combined with the chemical dispersion of ALN,which could produce powers without hard agglomeration after final drying.TEM revealed that nano-HA with size less than 100 nm appeared as single particle after being treated by mechanical activation combined with the dispersion of ALN(AMA-HA and MA-HA).HRTEM and X-ray diffraction(XRD)confirmed that as-prepared nanoparticles were HA with low crystallinity and crystallite size.The present approach makes it feasible to produce nano-HA at high-scale yield,which provide the possibility to construct bone graft.ALN acted not only as a chemical dispersant but also as an orthopedic drug.In vitro release of ALN showd three stages:the initial burst release,the following rapid release.Fitting results of software show that the curve of ALN release conform to the Logistic model.Nano-HA through mechanical activation and sodium alginate were used as the printed materials to construct bone repair scaffold with similar composition and structure of natural bone by 3D printing,due to the flowing and crosslink properties of sodium alginate and improved mechinal property of scaffolds through nano-HA.Rheometer test characterizes the hydrogel composite as a shear thinning material.Swelling experiments showd that hydrogel 15%HA swlled least compared to other three samples under the six conditions and was applied in 3 D printing.Mechanical performance test demonstrated the higher proportion of the nano-HA,the larger young’s modulus and stiffness of hydrogel.The microstructure of scaffolds illustrated the higher proportion of the nano-HA induced the reduce of porosity and size of pores.The elements distribution scan of scaffolds showed that nano-HA was uniformly distributed in the hydrogel composite.Four different morphologies of the nano-HA(needle,sphere,rod and irregular shape)was cultured with bone sarcoma cells(MG-63).Cytotoxicity test demonstrated that the cytotoxicity of sample through treatment of adding ALN in mechanical activation(MA-HA)reduced to a level 0 after 5 days compared to other samples,and the RGR(%)of MA-HA was also higher than the other samples.Therefor,MA-HA was used as raw material for 3D printing of hydrogel 15%HA.The hydrogel 15%HA showed that RGR(%)was 110.4±5.2%to MG-63 after 5 days,and was observed the promotion on the proliferation of MG-63.MG-63 cells were observed on the surface of hydrogel 15%HA with variety of morphologies(fusiform,triangular or polygonal cells)according to fluorescent staining and SEM,and parapodiums of cells stetched to spread out on the materials surface,indicating the beneficial biocompatibility.This study prepared large-scale yield nano-HA with different sizes and morphologies through combination of different organic templates and synthesized methods with mechanical activation for 3D printing.Sodium alginate was combined with nano-HA to give consideration to flowing and setting properties of nano-HA in 3D printing.In vitro cell evalution demonstrates that the composite scaffold through 3D printing possesses good celluar compatibility and expected to be applied to repairation of complex bone defect in clinical.