Preparation And Properties Research Of Sr-doped Hydroxyapatite Composites (Chitosan And Graphene Oxide)

Hydroxyapatite(HA,Ca₁₀?PO₄?₆?OH?₂)is widely applied for skeletal repair and regeneration due to its component and structure closing to natural human bone.As good bone substitute material,HA possesses various excellent performances such as bioactivity,biocompatibility,osteoconductivity,and is of the commendable non-toxicity and nonimmunogenicity,which can be combined with bone tissue without rejection.Nevertheless,the use of HA as a scaffold material encounters some difficulties since HA has poor mechanical properties and adhesion.Therefore,it is necessary to combine a second phase or polyphase with HA to enhance mechanical properties.In this paper,Sr was used to modify HA as it can promote the growth of osteoblasts.The preparation of SrHA composite with chitosan?CS?or graphene oxide?GO?were investigated.The obtained products were characterized by means of X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?energy-dispersive X-ray spectroscopy?EDX?,X-ray photoelectron spectroscopy?XPS?and Raman spectroscopy.The first chapter reviews the application prospect of HA in biomedicine field.The preparation methods of HA and HA coatings are introduced in detail.Besides,the research background and innovation of this experiment are also introduced.The second chapter mainly introduces the raw materials and equipments used in the experiment,as well as the experimental scheme.In the third chapter,based on chemical precipitation method,the HA powders were prepared with Na₂HPO₄ and Ca?NO₃?₂·4H₂O as raw materials.The powders were dispersed into chitosan-acetic acid solution with the aid of continuous ultrasonic agitation to prepare HA/CS suspension via solution blending and magnetic stirring.HA/CS composite coatings were fabricated on 304-type stainless steel substrates by spin-coating technique,then dried at 25?and 37?for 12h respectively.The results indicate the tensile strength of HA/CS composites reached up to 69.02MPa.Adhesion strength of the coatings was 12.61MPa.And the coatings display good crystallinity,good adhesion,high purity and little decomposition.In addition,by means of spin-coating technique,HA could be evenly dispersed in CS and there is no aggregated or free HA particles present in the coatings.The HA/CS composite coatings show better performance when drying at 37?comparing to 25?,which is more conducive to combining interaction between HA and CS.In the fourth chapter,a series of HA samples doped with Sr molar fractions?0?pure HA?,0.5%,1%,2%,4%?were synthesized using chemical precipitation method.And then Sr-doped hydroxyapatite/chitosan?HA/CS?composite coatings were fabricated for the first time on stainless steel substrates by a spin-coating technique.The effects of drying at 37?on the composition and morphology of the composite coatings were investigated.The results showed that Sr²⁺ions had replaced the partial Ca²⁺ions and were doped into HA lattice successfully.The synthetic HA nanoparticles exhibited spherical morphology,while the substitution of the Sr ions promoted the growth of Sr-doped HA crystal and increased its size.Furthermore,Sr-doping made up the apatite with calcium deficiency.As the molar fraction of Sr is increased up to 4%,the ratio of[?Sr+Ca?/P]gets up to 1.68,which is theoretically close to the Ca/P molar ratio 1.67.And the adhesion strength was 13.33MPa as the Sr content was 4%.By means of spin-coating technique,HA could be evenly dispersed into CS so that the synthetic composite coatings were dense and uniform,there didn't exist destruction or cracks on the coating surface.In addition,the results of cell experiment showed that all composite coatings held good biocompatibility.And4SrHA/CS composit coating contributed to proliferation,adhesion and differentiation of cell.In the fifth chapter,the SrHA/GO composites with different GO contents?GO has few cytotoxicity when the concentration is under 100?g/ml?were successfully synthesized by hydrothermal method.The prepared SrHA particles were rod-like and arranged in order.The length of SrHA grain was about 80nm,and had the diameter of30nm.SrHA particles were deposited on the GO surface to form microgaps with biological characteristics.The increase of GO concentration promoted a benign reaction between SrHA and GO as well as improved the combination effect of the SrHA/GO composites.Because of the addition of GO,the mechanical properties of composites were improved.And all prepared samples showed few cytotoxicity.The sixth chapter is the summary and prospect of this research.