In a previous experimental study using a chronic renal failure rat model, a dose-related multiphasic effect of strontium (Sr) on bone formation was found that could be reproduced in an in vitro set-up using primary rat osteoblasts. The results from the latter study allowed us to distinguish between a reduced nodule formation in the presence of an intact mineralization at low Sr-doses (1 microg/ml) and an interference of the element with the hydroxyapatite (HA) formation at high doses (20-100 microg/ml). To further investigate the latter effect of Sr on physicochemical bone mineral properties, an in vitro study was set up in which the UMR-106 rat osteosarcoma cell line was exposed to Sr, added to the cell culture medium in a concentration range varying between 0-100 microg/ml. Temporal growth and functionality of the culture was investigated by measurement of the alkaline phosphatase activity and calcium (Ca) concentration in the culture medium (used as an index of Ca-incorporation, i.e., HA formation) at various time points. At the end of the culture period (14 days post-confluence), samples of the mineralized cultures were taken for further analysis using X-ray diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FTIR). Synthetic HA doped with various Sr concentrations (based on the cell culture and previous experimental studies and yielding Sr/(Sr + Ca) ratios ranging from 0-60%), was prepared and examined for crystal growth and solubility. Crystal size was assessed using scanning electron microscopy (SEM). Ca incorporation indicated a reduced mineralization in the 20 and 100 microg/ml Sr groups vs. controls. Sr-doped synthetic HA showed a significant dose-dependent reduction in crystal growth, as assessed by SEM, and an increase in solubility, apparent from 12.7% Sr/(Sr + Ca) on. Moreover, in both mineralized cultures and synthetic HA, XRD and FTIR analysis showed a reduced crystallinity and altered crystal lattice at similar concentrations. These new data support our previous in vivo and in vitro findings and point to a potential physicochemical interference of Sr with HA formation and crystal properties in vivo.

These findings indicate that Sr accumulation in chronic renal failure rats resulted in the development of osteomalacic lesions, in contrast to the Al group where adynamic bone disease was induced in the present set-up. Further studies are required to define the mechanism by which way Sr causes osteomalacia in chronic renal failure rats.

Samples of petrified wood of different origins were analyzed by the use of the electron microprobe, capillary X-ray fluorescence microprobe, synchrotron capillary X-ray microprobe and optical microscope, applied in a microprobe manner. The main attention was given to the investigation of the ring structure of the petrified wood and the comparison of this with the ring structure of the living trees analyzed by much the same methods. The continuous X-radiation, applied in a microprobe manner, the distribution of the gray-scale representation of the secondary electron intensities and the characteristic X-ray signals, mainly from the light elements, were registered by the use of the electron microprobe method. The X-ray capillary microprobe detected the Rayleigh and Compton signals, scattered from microareas of the samples, and the characteristic X-ray signals, mainly from the heavier elements. In the synchrotron-based capillary microanalytical measurements, one of the most important results was achieved by the microprobe application of scattered synchrotron radiation. The emission and scattering results were supplemented by transmission measurements, where possible. All the methods proved to be complementary in the analysis of such periodic structures as tree rings. Both capillary microprobes were much more efficient in the detection of heavy elements and penetrated deeper than the traditional electron microprobe. Careful analysis of different signals indicated that some samples of petrified wood in the authors' possession, composed of silica of variable density, are the chemical negatives of the primordial living wood. This is the first such observation in the literature. Microdiffraction studies of the samples proved that polycrystalline a-quartz was the main matrix component of all these samples. The elemental analysis of the petrified wood gives important indications about the petrification processes. Comparison of the particular ring structure of the petrified wood with the ring structure of living trees shows great similarities. The widths of rings, density variations and density maxima are easily readable from the microanalysis of petrified wood. These parameters potentially can be exploited for the investigation of the biological, chemical, chronological and climatic information included in the fossilized tissues. image of the ring. Smaller steps allow penetration of the intra-†Presented at the Fifteenth International Congress on X-ray Optics and Microanalysis (ICXOM ),

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