Preparation And Simulation Of Zinc-doped Hydroxyapatite Composites (polylactic Acid Or Graphene)

Zn-doped hydroxyapatite?ZnHA?,a man-made biomaterial analogous to mineral in human skeleton,has been widely used for bone substitute material due to high biocompatibility,biological activity and osteoconductivity.However,its inherent low fracture toughness,high brittleness and poor fatigue resistance limit its clinical application.Therefore,it is necessary to combine a second phase or polyphase with ZnHA to enhance mechanical properties.In this paper,the preparation of ZnHA composite with polylactic acid?PLA?or graphene?GP?was investigated,then Zn HA crystal structure and its elastic properties were studied.X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,field emission scanning electron microscopy?FESEM?,energy-dispersive X-ray spectroscopy?EDX?,transmission electron microscopy?TEM?,and X-ray photoelectron spectroscopy?XPS?and Raman spectroscopy?Raman?were used to characterize the obtained samples.ZnHA powder was synthesized by chemical precipitation method and then Zn-doped hydroxyapatite/polylactic acid?ZnHA/PLA?composite coatings were coated on stainless steel substrates?type 304?using the spin-coating technique for the first time.The effects of heat treatment in air at 600? on the composition and morphology of ZnHA/PLA composite coatings with a series of molar ratios of Zn were discussed.The results showed that Zn ions had replaced partial Ca ions and were doped into hydroxyapatite lattice successfully.The synthetic hydroxyapatite nanoparticles showed rod-like morphology,whereas the substitution of Zn ions restrained the growth of Zn-doped HA crystal and decreased its size.The surface morphology of ZnHA/PLA composite coatings after sintering at 600 ? for 1h exhibited a uniform,porous structure with a thickness of 60 ?m or so.The introduction of PLA in composite coatings could keep metal substrates from catalyzing the decomposition of HA caused by high temperature heat treatment.Zn-doped hydroxyapatite/graphene?ZnHA/GP?composites were successfully in situ synthesized by one-pot hydrothermal treatment for the first time.The effects of different Zn doping content on the microstructure of HA in the composites were studied.And the effects of the change of HA crystal structure due to introducing Zn ions on the interfacial interaction of the composites were discussed.The morphology of Zn HA/GP composite showed that ZnHA grains with molar fraction of 1 mol% Zn were intimately attached on the surface of graphene whereas the amounts of ZnHA attached on the GP surface reduced obviously and the interfacial interactions were weakened accordingly as the Zn doping amount increased from 5 to 20 mol%,which indicated that the low crystallinity of Zn-doped HA particles due to an increasing Zn content might have a negative effect on interfacial interactions between ZnHA and GP.The effects of Zn incorporation on the elastic properties and structure of HA crystals were analyzed by using the first principle combined with experimental data.The results showed that the incorporation of Zn would soften the overall structure of the HA crystals and decrease the elastic properties of HA.However,compared with the defect HA,ZnHA still possessed good stability and elastic properties.Density functional theory calculations combined with FTIR,XRD analysis of ZnHA showed that the replacement of Zn atoms in HA crystal lattice could cause the OH-group to move off the c axis toward the Zn atom and become closer to the PO₄^3-group,resulting in the formation of hydrogen-bond between OH-and PO₄^3-groups.