Seminars Archive

X-ray and IR micro-analysis studies of biological samples -Focus on bone mineral-

Abstract
Commonly considered as inert, the mineral of hard tissues (bone, teeth) appears in fact as a very reactive and sophisticated material. The composition, the crystal size, the crystal orientation and the surface properties all contribute to adapting the tissue to its biological functions. The various existing types of biological mineralization are based on apatitic calcium compounds and, in the case of vertebrates, on apatitic calcium phosphate compounds (apatite biominerals). For bone, providing mechanical resistance and acting as a primitive ion reservoir are two crucial functions. They are obtained through a tissue organisation involving apatite nanocrystals with a very high specific surface area and a well-developed hydrated layer responsible for ion exchanges with body fluids. Maturation, ion exchange and absorption are involved in the dynamic behaviour of apatitic biominerals. Consequently, bone mineral presents a complex composition. In addition to calcium and phosphate, it contains numerous other ions (hydrogenophosphate, carbonate, magnesium, sodium…), metals and trace elements. All these compositions vary strongly in bone through and with time, but also depending on the diet, turn over rate of the mineral, medical treatments… The aim of this general presentation is to discuss the processes of maturation of bone mineral, but also to present some pathologies which perturb the natural bone turnover and maturation process, related proposed medical treatment, and biomaterials. New information obtained using a combination of synchrotron imaging techniques (X-ray microfluorescence, infrared microscopy, micro-diffraction) will be presented. Finally, other examples of microanalysis studies performed on biological specimens will be given.