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Background: Low dietary calcium intake and bioavailability may adversely affect bone health. Reducing the size of calcium compounds increases their specific surface area (SSA, expressed as m 2 /g) and may increase calcium dissolution and bioavailability. Objective: We investigated the influence of SSA and chemical composition on the bioavailability of calcium and compared in vitro calcium dissolution with in vivo absorption. Methods: Calcium dissolution was measured in 0.1 M phosphoric acid, whereas color and pH changes of foods were assessed as indicators for potential sensory performance. Calcium absorption, retention, and fractional retention were measured over a 5-d balance study in growing Sprague-Dawley male rats after 21 d of feeding. Femoral and vertebral bone mineral density (BMD) and extensive tissue histology were assessed at study end. The influence of SSA on calcium bioavailability was assessed by comparing the groups fed pure calcium carbonate (CaCO 3 ) with increasing SSAs of 3, 36, and 64 m 2 /g (CaCO 3 _3, CaCO 3 _36 and CaCO 3 _64), whereas chemical composition was assessed by comparing the smallest CaCO 3 _64, a 50:50 wt:wt percent solution mixture of CaCO 3 and hydroxyapatite_94, and pure hydroxyapatite_100. Results: In vivo, fractional calcium retention from hydroxyapatite_100 (mean ± SEM: 54.86% ± 0.95%/5 d) was significantly greater than from CaCO 3 _64 (49.66% ± 1.15%/5 d) ( P = 0.044). Increasing SSA of the pure CaCO 3 did not significantly improve calcium retention. Across all 5 groups, there were no significant differences in BMD or tissue calcification by histology. In vitro calcium dissolution did not correlate with SSA or calcium absorption. In selected food matrixes, hydroxyapatite_100 caused less color change and/or smaller pH increase than did the other calcium compounds. Conclusions: Our findings suggest that chemical composition rather than SSA is a predictor of nanostructured calcium bioavailability and that in vitro dissolution of nanostructured calcium does not predict in vivo absorption. Although its phosphorus content may limit use in some populations, nanostructured hydroxyapatite may be a promising calcium compound for food fortification., (© 2017 American Society for Nutrition.)

Nanosilver is one of the first nanomaterials to be closely monitored by regulatory agencies worldwide motivating research to better understand the relationship between Ag characteristics and antibacterial activity. Nanosilver immobilized on nanostructured silica facilitates such investigations as the SiO 2 support hinders the growth of nanosilver during its synthesis and, most importantly, its flocculation in bacterial suspensions. Here, such composite Ag/silica nanoparticles were made by flame spray pyrolysis of appropriate solutions of Ag-acetate or Ag-nitrate and hexamethyldisiloxane or tetraethylorthosilicate in ethanol, propanol, diethylene glucolmonobutyl ether, acetonitrile or ethylhexanoic acid. The effect of solution composition on nanosilver characteristics and antibacterial activity against the Gram negative Escherichia coli was investigated by monitoring their recombinantly synthesized green fluorescent protein. Suspensions with identical Ag mass concentration exhibited drastically different antibacterial activity pointing out that the nanosilver surface area concentration rather than its mass or molar or number concentration determine best its antibacterial activity. Nanosilver made from Ag-acetate showed a unimodal size distribution, while that made from inexpensive Ag-nitrate exhibited a bimodal one. Regardless of precursor composition or nanosilver size distribution, the antibacterial activity of nanosilver was correlated best with its surface area concentration in solution.

Metal nanoparticles have distinctly different chemical and physical properties than currently investigated oxides. Since pure metallic nanoparticles are igniting at air, carbon stabilized copper nanoparticles were used as representative material for this class. Using copper as a representative example, we compare the cytotoxicity of copper metal nanoparticles stabilized by a carbon layer to copper oxide nanoparticles using two different cell lines. Keeping the copper exposure dose constant, the two forms of copper showed a distinctly different response. Whilst copper oxide had already been reported to be highly cytotoxic, carbon-coated copper nanoparticles were much less cytotoxic and more tolerated. Measuring the two material's intra- and extracellular solubility in model buffers explained this difference on the basis of altered copper release when supplying copper metal or the corresponding oxide particles to the cells. Control experiments using pure carbon nanoparticles were used to exclude significant surface effects. Reference experiments with ionic copper solutions confirmed a similar response of cultures if exposed to copper oxide nanoparticles or ionic copper. These observations are in line with a Trojan horse-type mechanism and illustrate the dominating influence of physico-chemical parameters on the cytotoxicity of a given metal., ((c) 2010 Elsevier Ireland Ltd. All rights reserved.)

The urgent need for toxicological studies on carbon nanotubes (CNTs) has arisen from the rapidly emerging applications of CNTs well beyond material science and engineering. In order to provide a basis for comparison to existing epidemiological data, we have investigated CNTs at various degrees of agglomeration using an in vitro cytotoxicity study with human MSTO-211H cells. Non-cytotoxic polyoxyethylene sorbitan monooleate was found to well-disperse CNT. In the present study, the cytotoxic effects of well-dispersed CNT were compared with that of conventionally purified rope-like agglomerated CNTs and asbestos as a reference. While suspended CNT-bundles were less cytotoxic than asbestos, rope-like agglomerates induced more pronounced cytotoxic effects than asbestos fibres at the same concentrations. The study underlines the need for thorough materials characterization prior to toxicological studies and corroborates the role of agglomeration in the cytotoxic effect of nanomaterials.

In order to observe anisotropically grown crystalline materials perpendicular to a certain preferred orientation, a standard cross-sectional TEM preparation method has been modified. The material is embedded in an organic epoxy resin between two Si-wafers. Plates, needles and tubes lay flat inside the resulting sandwich, which is then cut into slices perpendicular to the wafers. The slices are thinned by mechanical abrading and, finally, by ion milling. Crystals located near the central hole are electron-transparent, and their orientation often allows for an observation along the desired direction. The usefulness of this procedure is demonstrated on the examples of high-Tc superconductors and vanadium oxide nanotubes.