Control Assembly Of Selenium Doped Hydroxyapatite Nanorods And Their Osteogenesis Influence

Bone,as physical support and mineral storage of human body,has excellent mechanical properties and a highly anisotropic structure.The complexity of bone comes from the fact that bone is a tissue containing nanocomposites in which the inorganic hydroxyapatite [HA,Ca10(PO4)6(OH)2] nanophase is regularly dispersed within collagen fibers.HA used in the preparation of bioceramics has good biological activity and bone conductivity.In order to meet the clinical needs in the field of surgery,some researchers have turned their attention to the research direction of doping the structure of HA with trace elements.It has been reported that a variety of trace elements such as magnesium,strontium,silicon and zinc have been doped with HA,showing good osteogenic stimulation and inflammatory inhibition.As one of the most important trace elements for human health,selenium helps certain enzymes to function and performs other essential biochemical duties in organisms.In order to enhance the potential application value of HA,HA nanorods(HAN)and selenium doped HAN(Se HAN)were synthesized and characterized by two-step method in this dissertation;the mechanism of nanorods synthesis was studied,and the potential bone repair ability was evaluated in vivo and in vitro.The main research content of this dissertation includes the following parts:1)Selenium doped HAN were synthesized by two steps.The first step was to synthesize the precursors of Se HAN by wet chemistry,and the second part was to convert the precursors to Se HAN under high temperature and pressure via the alcohol thermal method.Through a series of characterization,the result showed that the product was hydroxyapatite single crystal nanorods with length of about 2 μm.When the doping amount of selenium is lower,the particle is wider and when the doping amount of selenium is higher,the particle is narrower,and the variation range is between 50–200 nm.2)As studying the morphology of HA nanorods at various stages of synthesis,it was found that the growth mechanism of HA nanorods was the way of the control assembly of nanocrystal,and its basic process was as follows: in the first step,the Ca salt in the solution could react with the P salt and formed small size amorphous calcium phosphate particles,which was transferred to the reaction kettle in the ethanol system for high temperature reaction;if the first step reaction time was suitable,the particles could crystallize and form nano crystalline particles which can aggregate and form a larger size nanorods via the control assembly method,in which nano crystalline particles fusion via oriented attachment(OA)method or contacting with each other and recrystallize in the contact area.The final product was single-crystal nanorods.3)The biocompatibility of the nanorods and the effect of Se doping HAN on bone mesenchymal stem cell(BMSC)differentiation were evaluated by the method of the materials and cells co-culture.The synthesized HAN and Se HAN had good cellular compatibility,and Se HAN had better effects on BMSC proliferation than the HAN.After the nanorods entered BMSC,their localization was correlated with the distribution of lysosomes,which indicated the nanorods were probably metabolized by lysosomes.Se HAN could promote BMSC’s differentiation towards osteoblast and have good cellular compatibility and could promote BMSC to osteogenic differentiation,which had potential application in the field of hard tissue repair.4)The prepared scaffolds were made with gelatin and HAN/Se HAN,8 mm in diameter,0.78 mm in thickness,50-100 mm in internal holes,and 75% to 85% in porosity.The subcutaneous implantation experiment of the scaffolds proved that they had good biocompatibility and degradation performance with the skin tissues,and was suitable for tissue growth.The skull repair experiment in rats further proved that the selenium doped HAN scaffold had the best skull repair effect and showed a better repair effect.5)A certain concentration of Se HAN were injected into mice to study their system toxic effects through testing the animal body weight,blood biochemical indices and organs analysis,showing there was no difference between Se HAN and the control group.In general,HAN and Se HAN,highly crystalline nanorods with length of 2 μm and width of 50-200 nm,were synthesized by a two-step method.The synthesis mechanism was firstly shown by direct evidence.We found that the reaction time of wet chemical synthesis and the doping amount of selenium are the two key factors which determined the morphology and size of HAN/Se HAN.Thus,it is simple and effective for us to synthesize desired HAN in a controllable way.Further,the influence of Se HAN on differentiation of BMSC was also depended on selenium concentration wherein high selenium concentration facilitated osteogenic differentiation of BMSC and inhibited the abiogenesis differentiation.This work provides new perspectives for Se HAN,not only in controllable synthesis,but also in the applications of Se HAN.