Evaluation of the Ca/P concentration ratio in hydroxyapatite by STEM-EDXS:influence of the electron irradiation dose and temperature processing

Biomaterials used in dental and orthopaedic surgery to fill bony loss and t o coat prostheses are either of natural or synthetic origin. Amongst these biomaterials, hydroxyapatites (HA) offer good properties of biocompatibilit y and bioactivity when they interact with bone. This interaction depends ma inly on the physico-chemical properties of HA particles. In this work, usin g a scanning transmission electronic microscope equipped with an Si(Li) det ector for x-ray analysis, we analysed three kinds of hydroxyapatite: non-si ntered particles, 600 degreesC sintered particles and 1180 degreesC sintere d particles. Then, we determined the Ca/P concentration ratio in order to o bserve the influence of the temperature processing on this ratio. Concurren tly, we carried out measurements on the HA powders by varying the electron irradiation dose either with the current density or with irradiation time. When the electron irradiation dose varied with the current density (at cons tant and short irradiation time), the Ca/P concentration ratio did not vary . But, at fixed current density and increasing irradiation time, the calciu m and phosphorus intensities decreased, leading to an increase of the Ca/P concentration ratio at high electron irradiation dose. This phenomenon repr esents a mass loss of the specimen during electronic bombardment. We propos e an experimental procedure to avoid all these problems.