in 2009 have shown [83]. However the preference coordination site of Zn, the Ca2 site of the HA crystal, would allow the uptake

and release of Zn as the Ca2 site framework of the structure is not disrupted [83]. Zn2 + is not simply incorporated by ion exchange processes, but Ca2 + vacancy-defects can act as plausible sites for Zn2 + substitution [84]. As said above, Zn is essential for bone metabolism, as it is part of enzymes important for the remodeling mechanisms of bone and the Zn released during bone remodeling is incorporated back into the bone [46], [50] and [52]. GDC-0449 The matching of qBEI images with μ-XRF obtained elemental maps could not be perfectly performed. The different lateral resolutions of SR μ-XRF (~ 10–20 μm) and of qBEI (1–2 μm) make an exact overlay of both maps impossible. Thin features (e.g. cement lines) in the qBEI are blurred in the μ-XRF maps. Furthermore the larger information depth of SR μ-XRF (~ 20 μm for Ca-Kα) compared to qBEI (~ 1 μm) contributes to further blurring. Features close below the surface (e.g. cement lines, or cavities/voids) are not detected by qBEI but might be visible in the corresponding μ-XRF maps. However, superimposing the corresponding SR μ-XRF elemental maps and BE images was found to be very useful in linking bone morphology with X-ray intensities. An underestimation of Zn and Pb

signal intensities in the cement lines is introduced due to the fact that the cement lines are much thinner (in the range of 2 μm) Akt tumor than the focused X-ray beam width. The XRF signal is averaged over a larger matrix volume than the true cement line feature occupies. Hence the obtained Suplatast tosilate data shows a lower limit for the real relative elemental concentration. Assuming a SR μ-XRF voxel size of 12 × 13 × 17 μm3 and a cement line of width of 1 μm a 2-fold increase in Pb level in the cement line as measured by μ-XRF might be the result of an actual 34-fold

increase. To determine the signal intensity ratios of Zn and Pb between cement lines and mineralized bone matrix and to further investigate their spatial distribution within the cement line scans or even mappings at nano focus beam lines such as P06 at PETRA III (DESY, Hamburg, Germany) are planned for the future. No absolute values (wt.%) of Zn, Pb and Sr can be given. Thus, only relative differences between the elements could be reported. Since bone is a complex and highly heterogeneous organic mineral compound, there is no suitable reference material yet for calibration of the experimental setup available, which would have allowed obtaining the absolute concentrations of trace elements corresponding to each measured X-ray count rates. The incorporated Pb, Zn and Sr ions in HA will most likely distort the crystal lattice of the mineral due to the different atomic sizes compared to Ca. This might have negative effects on the stability and strength of the mineral.