Tailored order: the mesocrystalline nature of sea urchin teeth.

We investigated the pattern of crystal co-orientation at different length scales, together with variations in chemical composition and nanomechanical properties in the teeth of the modern sea urchin Paracentrotus lividus with electron backscatter diffraction (EBSD), electron probe microanalysis, energy-dispersive X-ray spectroscopy and nanoindentation testing. Modern sea urchin teeth are Mg-dominated calcite composite materials. They are distinctly harder than inorganically precipitated calcite. Some parts exceed even the hardness of dolomite. The teeth show a structuring of their mechanical properties that can be correlated to variations in major element chemical composition, such that their hardness is positively correlated to their magnesium contents. Mg/Ca ratio in Paracentrotus lividus varies between 10 and 26mol.%. Nanohardness of the tooth scatters between 3.5 and >8GPa compared to values of 3.0±0.2, 7.3±0.1 and 9.2±0.9GPa measured on the (104) planes of inorganic calcite, dolomite and magnesite, respectively. High-resolution EBSD shows that major structural units and subunits of the tooth of Paracentrotus lividus are tilted to each other by ∼3-5° and 1-2°, respectively. This indicates that the tooth is not a single crystal. With EBSD we can show that the tooth of the sea urchin Paracentrotus lividus is a hierarchically assembled biological mesocrystal with a mosaic texture. In comparison to the misorientation spread of 0.5° of calcite grown from solution, misorientation in the tooth varies between 2° and 4°. Thus, the self-sharpening feature of the tooth is enabled by a close interplay of its highly evolved micro- to nanostructure, structural unit size variations with a varying degree of crystal orientation, chemical structuring of the mineral component and a gradation of incorporated organic polymers.

Time course of serial cystatin C levels in comparison with serum creatinine after application of radiocontrast media.

BACKGROUND: The delayed increase of creatinine after radiocontrast application is a potential reason for overlooking radiocontrast nephrotoxicity. Cystatin C may be more useful to rapidly assess a decrease in glomerular filtration rate (GFR). We compared cystatin C and creatinine to examine their kinetics after application of radiocontrast media. PATIENTS AND METHODS: Forty-one patients (60.8 +/- 8.8 years, 68% males) with normal to subnormal GFR scheduled for coronary angiography (27% with angioplasty), were studied for serum cystatin C and creatinine levels before, 5 h, 24 h and 48 h after angiography. Furthermore, alpha1-microglobulin was checked for evidence of tubular damage. RESULTS: At 5 hours after angiography, there was no significant change compared to baseline in either serum creatinine nor cystatin C. In comparison with the value immediately before coronary angiography, the increase of cystatin C achieved a maximum at 24 h after the application of the contrast agent (+7.2%). Within 48 h, cystatin C decreased to the level before angiography. Serum creatinine increased at 24 h (+7.7%) and continued to increase at 48 h (+11.3%). CONCLUSION: Cystatin C increases earlier after radiocontrast application compared with creatinine. Therefore, cystatin C needs to be investigated as a potential early marker for nephrotoxicity, especially in the upcoming setting of short-time hospitalizations for coronary angiographies and interventions. Thus, further studies in patients with renal failure undergoing radiocontrast application are warranted to assess the usefulness of cystatin C in respect of an earlier detection of radiocontrast nephrotoxicity.