Carbonated hydroxyapatite nanopowders for preparation of bioresorbable materials

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 CO2, 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 CO3 2- -content enhances PO4 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.