Research Of Nucleation Growth Of Calcium Phosphate On Mixed Self-Assembled Monolayer

Biomineralization is the basic process in nature,and can form a complex and sophisticated multi-level organization and structure under the regulation of organic matric,and endow these organizations unparalleled performance,such as human bones and teeth,which have a high strength and toughness.The organic matrix regulating biomineralization reaction proceeds at the interface,The physical and chemical properties of the interface have a crucial impact on mineral crystal form,size,shape,etc.,so the study on crystallization mechanism of hydroxyapatite under the regulation of a variety of different interfaces in the biomineralization process can not only help us learn more about the mineral formation process in vivo,but also be able to provide a theoretical basis for development and improvement of new biomedical materials.In this study,self-assembled monolayers（SAMs）technology was used to construct surfaces with single chemical functional groups（-OH,-COOH,-NH₂,-CH₃）and surfaces with mixed chemical functional groups（-OH/-CH₃,-COOH/-NH₂）on gold substrates,then soaked in 2× simulated physiological body fluid（SBF）to proceed biomimetic mineralization.Water contact angle measurements,XPS,AFM,SKPM,Zeta potentials was used to measure wettability,electronegativity,surface density,surface distribution and relative amounts on substrates;Calcium phosphate crystal formed on surfaces and the change of ions in solution was characterized by the using of AFM,SEM,Raman,ICP-OES techniques,and further deducing the induction mechanism.Experimental results show that four kinds of thiol molecules can be successfully grafted on the surface with similar grafting density and the same structure unit.The-COOH Surface with low isoelectric point can strongly promotes crystallization of calcium phosphate in early period,initially forming a network structure,and finally appeared hierarchy,while promoting effect of-NH₂ surface with high isoelectric point of was not obvious,and spherical calcium phosphate crystals formed on this surface.spherical calcium phosphate was induced on –OH surface,which is hydrophilic,While the –CH₃ surface with highly hydrophobic ability could inhibite the crystallization of calcium phosphate.As to-COOH /-NH₂ mixed surface chemical functional groups,the experimental results show that the surfaces have similar grafting density and the same structure unit,and the isoelectric point and water contact angle on surfaces gradually increases with the increasing of –NH₂ ratio.In the course of mineralization experiment,we can make a conclusion as follow: the charge distribution on the surface decide the crystallization manner of calcium phosphate,when the surface gathered a large number of negative charge,which can be used as crystallization sites,initially,adsorption of Ca²⁺ ions from solution occurred,then PO₄^3-ions were adsorbed onto surfaces.which promote non-spontaneous crystallization of calcium phosphate,The ability of promoting crystallization weaken with the reduction of negative charge,when the surface only possess a small number of negative charge,can absorb calcium phosphate particles formed in solution by spontaneous crystallization,and calcium phosphate in this way can continue to grow on the surface.For surface-OH /-CH₃ mixed SAMs functional group,the experimental results show that the surfaces also have similar grafting density and the same structure unit,and water contact angle increases from 21.5 ° to 114.7 ° with the increasing proportion of-CH₃ ratio.The fact of various hydrophobic and hydrophilic also affect crystallization of calcium phosphate was testified.when water contact angle is less than 72 °,the surface negative charge can be used as crystalline sites to promote non-spontaneous crystallization of calcium phosphate,the smaller water contact angle is,the stronger ability of promoting crystallization of calcium phosphate is.When the water contact angle is greater than 97 °,strong hydrophobic will restrict Ca²⁺,PO₄^3-and calcium phosphate micro grain formed by spontaneous nucleation from solution contact with surfaces,ultimately inhibiting calcium phosphate crystals on the surface.