TEM study of the morphology of Mn2+ -doped calcium hydroxyapatite and beta-tricalcium phosphate

Mn-doped carbonated hydroxyapatites (HA) were prepared by precipitation method. Ca-deficient HA samples were obtained by this method with the characteristic hexagonal apatite structure. Scanning transmission electron microscopy (STEM) of two HA samples with two different Mn content has shown that their morphology depends on their Mn content. In case of relatively low (0.73%) Mn content (HAMn1), platelet crystals about micron size and needle-like crystals up to 100 nm were observed, while with 1.23% Mn (HAMn2) crystals were smaller, needle-like and with sizes up to 400 nm only. Mn-doped TCP samples were prepared by two methods. In one case it was obtained by direct solid-state reaction with the characteristic rhombohedral structure of beta-TCP and with composition of Ca(2.7)Mn(0.3)(PO(4))(2). TEM pictures of crystals of this sample were tens of micron and submicron size with visible faces. Crystals of beta-TCP obtained by high temperature partial transformation of sample HAMn2 to beta-TCP were found by TEM to be smaller, micron sized, drop-like shaped, sensitive to beam radiation. These results indicate that the morphology of Mn doped beta-tricalcium phosphate samples depends on the method of their preparation. Morphological properties of HA and TCP are discussed and it is suggested that the smaller and less perfect HA crystals with the higher Mn-content as well as the less perfect TCP crystals obtained by transformation of HA to TCP might be of more biocompatible character.