The purpose of this work was to find and investigate a correlation between the carbonate ion content in crystalline lattice and defect structure, and solubility of the materials; finally, to prepare the materials under study for in vitro tests. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca-ionometry, microvolumetric analysis of evolved CO2, BET adsorption, were applied to determine the efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution,. It was shown that AB-type substitution prevails over other types with the carbonate content increase. According to in vitro tests, the bioactivity of the samples is correlated with the carbonate content in carbonate-doped hydroxyapatite due to accumulation of defects in carbonated hydroxyapatite nanocrystals.
Incorporation of carbonate ions to the crystal structure of carbonated hydroxyapatite (CHAp) leads to the formation of point defects (vacancies) in Ca-and OH-sublattices as well as to microstrains revealed in CHAp nanocrystals. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca-ionometry, microvolumetric analysis of evolved CO 2 , BET adsorption, were applied to determine an efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution. It was shown that there is insignificant incorporation of Na into the crystal structure of HAp. Over the range of 0 -4 % wt. (x<0.25), the substitution of OH-by CO 3 2-takes place leading to A-Type of CHAp, further increase of CO 3 2--content enhances PO 4 3--substitution giving AB-type of CHAp. According to in vitro test, the bioactivity of the samples is increasing with the growth of carbonate content due to accumulation of the defects in CHAp nanocrystals.
It is established that the two dimensional crystallization of sodium chloride on the surface of a biopolymer film (film of a glycoprotein, mucin), which is used as a template, gives rise to the formation of crystals with unusual morphology-in particular, dendrites. This type of crystallization is observed in two cases-namely, when drying a film formed from a salt containing mucin dispersion and when drying a salt solution droplet on the surface of a dry mucin film obtained from a salt free mucin dispersion. Mechanisms leading to unusual salt crystallization are discussed, and the role of specific interactions of sodium chloride with mucin is shown.
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