Research On Biomimetic Mineralization Of Apatite And Precursor Phase Regulated By Various Organic Biomolecules

Biomineralization is a formation process of mineral in vivo,one of its important characteristics is that inorganic minerals can nuclear and grow to form bio-mineralization materials which have special ordered and multi-level structure under the regulation of organic matrix. Biomimetic mineralization is a process for preparing the organic/inorganic composite with organic assembly as a template to control the formation of inorganic materials according to the mechanism of biological mineralization. Thus it is an important significance for exploring the mechanism of the formation of inorganic minerals under the regulation of the organic matrix.In this study,the biomimetic mineralization of apatite and precursor phase was regulated through four types of biomolecules(Citrate、Glutamate、Aspartate and Lysine).The effect of each biomolecule can be observed at different time points(2min、10min、30min、60min).The type、size and morphology of the formed mineral was investigated via changing the type and concentrate of biomolecules and the p H of reaction solution. The composition and structure of apatite and precursor phase was characterized by XRD、FTIR、Zeta potential、SEM、TEM、electron probe and BET to compare and analysis the apatite state under the regulation of various organic biomolecules at different time and to explore the regulation mechanism about these biomolecules for the formation of apatite and precursor phase.The results indicated that compared Lys,the organic biomolecules having more carboxyl groups would have more significant inhibition to the nucleation and growth of apatite,which partly depended on the binding capacity of organic biomolecules and Ca2+,and ionization capacity of the biomolecules. When the –COOH/Ca2+ in Citrate、Glu、Asp and Lys were respectively higher than the ratios of 0.267、8.93、11.9、12.0,the solution became clear and no apatite formation,we can infer that the binding capacity of organic biomolecules’ carboxyl groups and Ca2+ was Citrate>Glu>Lys>Asp. Moreover,the charge of various minerals is different. After the addition of organic biomolecules,the negatively charge of the minerals was Citrate>Glu>Asp>Lys.The morphologies of apatite regulated by various organic biomolecules with kinds of concentration were different significantly at different time points. When the concentration of Citrate was from 0.0125 M to 0.015 M,the mineral kept the amorphous state and held the spherical particles state. When Glu≥0.1M,Asp≥0.4M,Lys≥0.2M,the minerals can maintain the state of spherical particles,delay the transformation of precursor phase and generate the poorly crystalline hydroxyapatite crystals at the middle reaction time(30min).When Glu>0.4M,Asp>0.5M,Lys>0.2M,they can stabilize the precursor phase all the time. It demonstrates that when the concentration of biomolecules were from 0M to 0.1M,their stabilization was Citrate>Glu>Lys>Asp. However,as the concentration of biomolecules were more than 0.1M,their stabilization and the inhibition to the growth of minerals was Citrate>Lys>Glu>Asp. When the concentration of Glu and Asp were from 0.05 M to 0.4M and the concentration of Lys was from 0.05 M to 0.2M,the change trend of apatite morphologies was from spherical particles to spherical particles with needle-like cluster,then from needle-like aggregates to sheet aggregates at the whole reaction stage. Meanwhile,they can get the complex apatite nanocrystals which contain some organic biomolecules.For the nucleation and growth of apatite,various organic biomolecules with different concentration would have different effect. As to 0.05 M Glu、Asp and Lys,they would promote the nucleation and growth of apatite. However,when Glu>0.05M、Asp>0.2M,Lys>0.1M,they would show the inhibitional action. The inhibitional effect of Citrate and its stabilization for precursor phase were most significant.The results also revealed the various organic biomolecules would regulate the surface areas,pore sizes and contact angles of apatite,they would make the contact angles and pore sizes of the apatite more small relatively and make their surface areas larger relatively.