Synthesis,Characterization And Performance Study Of Ag-doped Hydroxyapatite Composite Materials

Hydroxyapatite(Ca₁₀?PO₄?₆?OH?₂,HA)is the main content of human skeleton.Man-made HA has great bioactivity while this material needs to be modified by variety ways to improve its clinical applications.Modifying HA by doping mantal ions is widely studied so that Ag doped HA?AgHA?is popular for its unique antibacterial property.What's more,man-made HA gains poor mechanical property.In order to improve the property,it's necessary to add second phase into HA as supporting phase.This paper synthesized AgHA first and then chose polylactic acid?PLA?and graphene oxide?GO?as supporting phases to produce AgHA/PLA and AgHA/GO composites,then AgHA/GO/PLA three-phase composite coatings were obtained.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?were used to characterize the obtained samples.Escherichia coli?E.coli?was used to evaluate the antibacterial properties of all samples and the mechanical properties were also studied.AgHA powders with different initial[Ag]/[Ca]molar ratios were synthesized through chemical precipitation method and then sintered under high-temperature condition.What would happen to the powders'property while the initial Ag concentration changed was studied.The research showed that Ag ions had entered the crystal lattice of HA by taking place of Ca ions.The lattice of HA crystal would be distorted while more Ag ions entered which could lead to the change of crystal form of the powders.Some Ag ions that couldn't enter the crystal lattice might form silver phosphate.The silver phosphate then could react with itself and be reduced to metallic Ag phase during sintering process under high temperature condition.The synergistic effect between Ag⁰ particles and Ag⁺ions greatly enhanced the antibacterial activity of AgHA powders.The prepared AgHA powders were used to form AgHA/PLA composite coatings on 304-type stainless steel substrates.The results showed that there were both Ag⁰and Ag⁺existed in composite coatings with high Ag concentration.The synergistic effect between Ag⁰ and Ag⁺increased the antibacterial property of composite coatings prominently.The present of PLA lead to an increase of amorphous phase which results in the agglomeration on the coatings.But on the other hand,PLA can also improve the adhesion property and tensile strength of composite coatings.AgHA/GO composite materials were synthesized by hydrothermal method.The result indicated that AgHA powders with good crystallinity could be produced by hydrothermal method and the AgHA powders were attached to the GO surface in the composite materials.More amorphous phases appeared in the materials and agglomeration happened on GO surface while the initial Ag concentration increased.The antibacterial property of composite materials was also enhanced as the initial Ag concentration increased.There were no Ag⁰ particles as the result of the lack of sintering process.It was ineffective to improve the antibacterial property of the composite materials by increasing initial Ag concentration as there was no synergetic effect between Ag⁰ and Ag⁺.On the contrary,higher initial Ag concentration would cause more agglomerations which would affect the release of Ag⁺from crystal lattice and further influence the antibacterial property of AgHA/GO composite materials.The AgHA/GO/PLA three-phase composite coatings were obtained by spin coating technique on 304 stainless steel substrates based on the prepared AgHA/GO powders.PLA covered all phases and the AgHA particles were still attached to GO surfaces and the particles started clustering while the Ag ratio increased.The content of Ag showed little influence on the mechanical properties.But the interaction between GO and PLA led to the decrease in adhesion property and elongation at break of AgHA/GO/PLA while the tensile strength of AgHA/GO/PLA was strengthened by it.