REACTION OF SILVER-TIN ALLOYS AND MERCURY.
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The most significant complication in external fixation is pin tract infection causally related to the highly adaptive ability of bacteria to colonise the surfaces of "inert" biomaterials or of adjacent damaged tissue cells. The hypothesis that coating a pin with a silver-containing compound will decrease bacterial colonisation and/or pin tract infection has been confirmed in other studies in vitro and in vivo experiments. In this work, biocompatibility of silver-coated orthopaedic external fixation pins was compared with stainless steel controls in an in vitro study. Human peripheral blood lymphocytes were used to assess the possible genotoxic effect of silver, studying the frequency of sister-chromatid exchanges and micronuclei while fibroblasts (NIH 3T3) and osteoblast-like cells were used for cytotoxicity and cytocompatibility studies. These studies have shown that silver is neither genotoxic nor cytotoxic as compared to stainless steel, a material in wide use as a metal implant. At 4 days cells cultured on the silver-coated material evidenced good cell spreading and a higher cell count with respect to the uncoated material. It appears that the addition of silver onto implantable medical devices could be beneficial when specific biological properties, such as antibacterial behaviour, are required. Based on these and the previous bacterial studies it seems like the toxicity towards bacteria was quite a bit greater than that towards the human cells.
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Electrochemical properties of beta-alanine/carbohydrate Maillard reaction products were measured using a combination platinum/Ag-AgCl (Cl(-)) redox electrode. Changes toward more negative voltages were observed, which were consistent with reductone formation during the course of the Maillard reaction. Using voltage change as a guide, the propensity for reductone formation among various sugars was ribose > xylose approximately arabinose > glucose approximately rhamnose approximately mannose approximately lactose > fructose. Similar electrochemical behavior indicative of reductone formation was observed in the decomposition products of a model Amadori compound, N-(1-deoxyfructos-1-yl)piperidine (1).
Ag/AgBr/TiO2 was prepared by the deposition-precipitation method and was found to be a novel visible light driven photocatalyst. The catalyst showed high efficiency for the degradation of nonbiodegradable azodyes and the killing of Escherichia coli under visible light irradiation (lambda>420 nm). The catalyst activity was maintained effectively after successive cyclic experiments under UV or visible light irradiation without the destruction of AgBr. On the basis of the characterization of X-ray diffraction, X-ray photoelectron spectroscopy, and Auger electron spectroscopy, the surface Ag species mainly exist as Ag0 in the structure of all samples before and after reaction, and Ag0 species scavenged hVB+ and then trapped eCB- in the process of photocatalytic reaction, inhibiting the decomposition of AgBr. The studies of ESR and H2O2 formation revealed that *OH and O2*- were formed in visible light irradiated aqueous Ag/AgBr/TiO2 suspension, while there was no reactive oxygen species in the visible light irradiated Ag0/TiO2 system. The results indicate that AgBr is the main photoactive species for the destruction of azodyes and bacteria under visible light. In addition, the bactericidal efficiency and killing mechanism of Ag/AgBr/TiO2 under visible light irradiation are illustrated and discussed.
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Extensive silver amalgam restorations in premolars and molars occasionally require sacrifice of healthy unsupported enamel walls or cusps. A posterior composite resin-amalgam compound technique has been proposed to conserve these structures. Microleakage was high at the enamel-amalgam interface, moderate at the composite resin-silver amalgam and dentin-composite resin interfaces, and minimal between the inner enamel and the composite resin. Light microscopy and scanning electron microscopy demonstrated that marginal adaptation of the silver amalgam to the composite resin of the cusps was acceptable and that penetration of the inner etched enamel to the composite resin was complete.
A polystyrene-based membrane of 7,8:16,17-dibenzo-6,9,15,18-tetraoxo-1,5,10,14-tetrathiacyclooctadeca-7,16-diene [Bz2Oxo4(18)dieneS4] was fabricated using sodium tetraphenylborate (NaTPB) and dioctyl phthalate (DOP) as anion excluder and plasticizing agent. The best performance was obtained from the membrane with the composition ionophore [Bz2Oxo4(18)dieneS4]:polystyrene:DOP:NaTPB, 5:100:150:10 (w/w). The response of the electrode was linear over a wide range of concentration, 1.26 x 10(-6)-1.00 x 10(-1) mol L(-1) for silver ion with a Nernstian slope of 58.4 +/- 0.1 mV per decade and a detection limit of 1.0 x 10(-6) mol L(-1). The electrode was found to be chemically inert and of adequate stability with a response time of 10 s and could be used for a period of 3 months without change of potential. It worked satisfactorily in mixtures containing up to 35% (v/v) non-aqueous content. The proposed membrane sensor had good selectivity for Ag+ over a wide variety of metal ions in the pH range 2.2-8.5. It was successfully used as an indicator electrode in potentiometric titration of silver ion. The electrode was also useful for determination of Ag+ in waste from photographic films.
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