Synthesis Of Modified Hydroxyapatite Via Incorporating Inorganic Trace Elements And The Related Biological Evaluation

Hydroxyapatite?HA?has been widely used by bone repair materials due to its chemical composition,which are similar with natural bone mineral,and superior bioadaptivity.However,as the complexity of the bone tissue system,stoichiometric HA has been unable to meet the current clinical needs.Therefore,nowadays,the modification of HA has gradually become a hot spot in HA research.Modification methods can be divided into chemical composition modification?chemical factor?and special shape structure?physical factor?.Among them,trace element doping and surface micro/nano-structure construction are the most common strategies,which have become the focus in recent years.Trace element doping can adjust the physical properties of HA?grain size,crystallinity,solubility,etc.?and impart excellent biological effects?promoting cell proliferation,differentiation,proangiogenesis,antibacterial,antitumor,etc.?.The micro/nano-structure of HA can promote the ability of controlled drug load/release of HA,which is beneficial to build excellent drug loading systems.On the other hand,as a membrane or coating material,it can be used to promote proteins and celladhesion,targeted osteogenic differentiation and inhibitory on osteoclast.Therefore,the formation of modified HA synergistically containing element doping and micro/nano-structure can give HA more superior functions,which have prominent research values.In this study,magnesium?Magnesim,Mg?and zinc?Zinc,Zn?have excellent biological functions,and few researches have been reported on Mg/Zn dication doping HA.Therefore,Mg²⁺and Zn²⁺are used to blend HA.This project plans to add Mg and Zn as doping elements and urea as a precipitant to build doped HA bio-ceramics with micro/nano morphology by hydrothermal system.The main research contents are as follows:Firstly,based on the hydrothermal method,monolithic Zn-doped HA with different doping rates?0%,1%,3%,5%,7%,10%?,Zn-doped HA in different doping rates with the addition of small molecule template agent H₆L and Mg/Zn doped HA with different doping amounts were prepared and used to investigate the morphology,crystal growth,chemical composition,ion release tendency and protein adsorption/release performance.The results showed that,with the increase of Zn doping rates,the Zn-HA morphology changed from strip-like to spherical-like and then to petal-like shape.When the template H₆L was added,the morphology of Zn-HA-H₆L stared to turned into microspheres with micro/nano morphological structure.Under the same condition,the Zn doping rates had little effect on changing HA-H₆L morphology.Mg/Zn-HA exhibited in spherical shapes and their morphology tended to alter into regular microspheres,which was similar to Zn-HA-H₆L,with the increase of Mg and Zn doping rates?Up to 10%?.Mg and Zn could be detected in modified HA in Energy Disperse Spectrascopy?EDS?and no other non-HA phase existed?X-ray Diffraction,XRD?.The presence of Mg²⁺and Zn²⁺could also be observed in X-ray Photoelectron Energy Spectroscopy?XPS?.It was speculated that Mg²⁺and Zn²⁺,to some extent,were doped into the HA lattice and replaced Ca²⁺location.The doping efficiency test results showed that,the Zn²⁺doping efficiency was higher than that of Mg;the Zn²⁺doping efficiency decreased with the increase of Zn theoretical doping amount,and Mg²⁺showed in a slightly increase.The release amount of element in modified HA increased with the increase of doping rate.Besides,Mg/Zn-HA could release both elements at the same time,and the release efficiency of Zn was slightly lower than that of Mg.What's more,the release tendency of element was slower,which was beneficial to sustained release in vivo.In the protein adsorption/release test,Zn-HA-H₆L and 10Mg10Zn-HA could adsorb/release proteins?bovine serum albumin,lysozyme protein?more efficiently by virtue of the excellent surface structure.Mg/Zn doped HA microspheres?Mg/Zn-HA?could release chemical signals(Mg²⁺and Zn²⁺).The ion-releasing extracts were evaluated for osteoblast-related properties such as cell viability and osteogenic differentiation.The results showed that,when the concentration was in 50 mg/mL,the extract had significant cell proliferation and differentiation.Significant cell proliferation and differentiation were observed.Those results showed that Mg²⁺could not only promote osteoblast?OBs?proliferation,but also promote alkaline phosphatase?ALP?activity of bone stem cells?BMSCs?and up-regulate osteogenic genes.Zn²⁺could also promote ALP activity of BMSCs and up-regulate osteogenic gene expression,but the effect of cell proliferation of it was not significant.Mg/Zn doped HA microspheres?Mg/Zn-HA?,via using special morphological structure,could affect the growth state of bone-related cells,thereby influencing the activity of osteogenic differentiation.The results showed that the modified HA membrane material had no obvious effect on promoting cell proliferation,and Mg/Zn-HA showed more significant in promoting on ALP activity of stem cell and up-regulation of osteogenic genes due to its special morphological structure.In summary,Mg²⁺and Zn²⁺were successfully doped into HA as trace elements.By this synthesis method,the morphology of modified HA in different elements varied.Modified Mg/Zn-HA not only have properties of ion release,high-efficiency protein adsorption,and controlled protein release,but also could promote cell proliferation through ion releasing,which could upgrade the expression of osteogenic genes.In addition,as a membrane layer materials,the surface micro-nanotopography can also be used to influence the cell adhesion morphology of osteoblast,and to facilitate the differentiation of stem cells into bone cells.In short,the results of this study provided an experimental basis for the researches of HA modification,which provide new ideas for the development of new HA materials.