Effect Of Fibronectin On Growth Of Apatite Mineralized Layer On Strontium-doped Calcium Phosphate Prepared By Wet Chemical Method

The interaction between biomedical materials and proteins is a hot spot in the forefront of biological materials research.This paper aims to investigate the adsorption behavior of protein on biological calcium phosphate materials' surface and study its mineralization processs.Element doping is an effective way to improve the performance of hydroxyapatite(HA).Strontium(Sr)doping could change the crystallinity,solubility and crystal structure of HA,then affecting the mechanical property and mineralization performance of HA ceramic.Sr ion is participated in human bone metabolism and has an impact on bone mineralization process.The common way to study the materials in vitro activity of mineralization is to characterize the thickness and composition of mineralized layer formed on materials' surface in stimulate body fluid(SBF).However,this method cannot monitor the mineralization process in real-time.Proteins play an important role in biological mineralization,which affect the nucleation,growth and morphology of apatite crystal.A quartz crystal microbalance with the dissipation method(QCM-D)has been widely developed for in situ and real-time detection of micro-variation in the nanogram range.In this paper,Sr-doped hydroxyapatite(SrHA)were synthesised by wet chemical method.The adsorption behavior of fibronectin(Fn)on Sr-doped hydroxyapatite and the effect of Fn adsorbed layer on growth of mineralized layer on SrHA surface were studied by QCM-D technology.Nano rob-like Sr-doped HA precursor powders with varying strontium contents,were successfully prepared by wet chemical method.The effect of Sr doping on the phase transformation of HA powders was investigated.It was found that Sr doping could decrease the crystalline of HA and facilitate the phase transformation from HA to beta-tricalcium phosphate(?-TCP)at 1000 °C.The ?-TCP content increased with increasing Sr amount,causing a decline in the ratio of HA to ?-TCP.With Sr contents of ? 5 mol%,HA remained the major phase in the biphasic mixtures;in contrast,with Sr contents of ? 15 mol%,the mass fraction of ?-TCP exceeded 50%.The incorporation of Sr2+ into HA and ?-TCP cause the lattice parameters(a,c,and V)of both phase to increase.Modulating the amount of Sr doping could be obtained Sr-doped calcium phosphate with different phase fractions of HA and ?-TCP.The effect of strontium contents on mechanical and mineralization performances of calcium phosphate ceramic was studied.The results showed that 5 mol% Sr doping was beneficial to improve the mechanical property of ceramics.The compressive strength and elasticity modulus of various Sr-doped calcium phosphate ceramics were in the range of 138.3~264.9 M Pa and 10.35~15.46 G Pa respectively,closed to human cortical bone.Sr-doped calcium phosphate ceramics with different biphase proportion of HA and ?-TCP had good mineralization performance.QCM-D technology was employed to in situ study the adsorption behavior of Fn on SrHA coating.It was found the Sr doping affected the adsorption amount and viscoelasticity of Fn protein.The adsorption capacity of Fn on SrHA surfaces was in the order of 15 SrHA > 5SrHA ~ HA > 21 SrHA.The effect of concentration gradient on Fn adsorption property on Au and HA surfaces was also discussed.The results showed that the capacity and viscoelastic of Fn adsorbed on Au surface increased with the increasing of protein concentration.However,the amount of Fn adsorbed on HA surface was in the order of HA-Fn100 > HA-Fn200 > HA-Fn50.The effect of Fn adsorbed layer on the mineralization process of different substrates' surfaces(Au,HA and SrHA)was investigated by QCM-D method.The results showed that Fn adsorbed layer could induce the nucleation and growth of apatite crystal on Au surface,reduced the growth rate of mineralization crystal on HA surface,and promoted the nucleation and inhibited the growth of apatite crystal on SrHA surface.The mineralization capacity of Fn adsorbed layer on different substrates' surface was in the order of HA-Fn50 > 5Sr HA-Fn50 > 21SrHA-Fn50 > 15SrHA-Fn50.In addition,the effect of Fn adsorption on the mineralization morphology was also studied.Different substrate surfaces had different morphology,such as sphere-shape layer on Au-Fn50 surface,random-network structure on HA-Fn50 and 5SrHA-Fn50 surfaces,and flake-shape layer on 15SrHA-Fn50 and 21SrHA-Fn50 surfaces.