Preparation And Properties Of Selenium And Strontium Doped Hydroxyapatite Powders And Ceramics

Hydroxyapatite（HA）doped with different elements is a research hotspot in bone repair field.The human body trace element selenium（Se）has anticancer effect,and strontium（Sr）also has promoting effects on the osteogenesis.However,a few studies have focusd on the effect of selenium doping on the HA,the study on Se/Sr co-doped hydroxyapatite is much less.Therefore,this paper revolves around selenium-doped hydroxyapatite（Se-HA）and selenium and strontium co-doped hydroxyapatite（Se-Sr-HA）.The substitution mechanism,fine structure and the thermal stability were comprehensively investigated by X-ray fluorescence spectroscopy,X-ray diffraction,Rietveld refinement and so on.Cell biology evaluation was also discussed.On this basis,the particle size of doped hydroxcapatite was controlled.In a word,a safe and multi-functional HA biomaterial with the ability of anti-tumor and bone repair are expected to be synthesized,which is of great significance to promote the development of HA biomaterial.Se-HA with different Se/P ratios were synthesized by the chemical precipitation method.The results showed Se incorporated into the HA lattice in the form of SeO₃^2-by substituting for PO₄^3-,but the amount of incorporated selenite is limited.When the ratio of Se/P was higher than 0.08,SeO₃^2-could not completely incorporate in the HA structure.When HA was doped with selenite,the lattice parameter a increased and c decreased.It also resulted in the increase of cell volume and mean microstrain,and the decrease of density and average grain size of Se-HA crystal.The decomposition of SeO₃^2-at high temperature affected the thermal stability of HA.The Se-HA samples with small amount of Se/P doping（Se/P≤0.05）were more stable after heat treatment without any impurities,contrarily,the calcium oxide phase appeared in the sample.Cell behavior was related to the concentration of SeO₃^2-.When the ratio of Se/P=0.05 and the concentration of powders≤0.2 mg/ml,samples had no influence on normal cells,but the proliferation of osteosarcoma cells was inhibited.This condition is considered to be an ideal amount of Se doping.Se-Sr-HA were synthesized by the chemical precipitation method.SeO₃^2-and Sr²⁺could be successfully substituted into the HA lattice,resulting in the increase of lattice parameter a and c,the expansion of the cell volume and the decrease of density.The occupancy displaied a slight preference for the CaⅡsites at low Sr²⁺concentrations.With the increase of Sr²⁺,the occupancy of CaⅠsites increased,which affected the stability of the crystal structure.When the Sr content was greater than 5 mol%,the thermal decomposition temperature of Se-Sr-HA was increased.Conversely,the thermal stability of HA decreased,and theβ-TCP phase appeared when the Sr content was less than 5 mol%.Se-Sr-HA samples had inhibitory effect on osteosarcoma cells.The release of Sr²⁺had no effect on cancer cells,the inhibiting effect mainly caused by the SeO₃^2-.The incorporation of Sr²⁺promoted the releasing of SeO₃^2-.In this paper,element-doped HA nanopowders were prepared by chemical precipitation and hydrothermal method.Accordingly,appropriate experimental conditions were obtained.Cell viability evaluation showed that the HA nanoparticles obtained by two kinds of synthetic methods had no influence on proliferation of normal cells,but HA nanoparticles obtained by precipitation method had stronger inhibitory effect on osteosarcoma cells than hydrothermal method.At the same time,Se-HA nanoparticles with small particle size could further enhance the inhibitory effect of osteosarcoma cells.Finally,selenium and strontium doped HA ceramics could be obtained by secondary molding and high-temperature sintering process.The incorporation of Se promoted the densification of HA ceramics,but the incorporation of Sr was not.The co-doping of Sr/Se decreased the sintering temperature of HA ceramics,which conducived to obtaine the dense HA ceramics.The HA ceramics doped with different elements all had mineralization ability.