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The effect of single-step and two-step aging treatments on the tensile properties of an Al-6 wt. % Ag alloy and an Al-14 wt. % Ag alloy has been investigated. Results show that the tensile properties of these alloys were approximately the same whether they were given single or two-step aging treatments. Reversion treatments applied to the fully age-hardened Al-14 % Ag alloy after 15 minutes at various temperatures between 200 and 350 °C showed two maxima in the ultimate tensile strength and the yield strength. It is believed that this result was caused by two transformation processes occurring simultaneously: i.e., (1) the coarsening and dissolution of G.P. zones and (2) the growth of the intermediate precipitate, γ'.

The underlying problems associated with the development of the biotic ligand model (BLM) for prediction of silver toxicity, and its associated physiological and toxicological endpoints, were investigated at a mechanistic, physiological level in juvenile rainbow trout. An equilibrium level of silver accumulation at the gills is achieved over time during flow-through exposures. The pattern of peak and decline in accumulation during static exposures is due to a decrease in the bioavailability of Ag⁺ because of complexation by organic carbon produced by the fish, a consequence of the use of a static exposure system. The decrease in bioavailability leads to a decline in apical silver uptake and together with constant basolateral silver export, a peak and decline in gill silver accumulation. Inhibition of carbonic anhydrase (CA) by silver is responsible for the early decline in active Na⁺ uptake at the gills during flow-through silver exposure, while Na⁺K⁺-ATPase inhibition is associated with the later decline in uptake. CA activity is inhibited early during silver exposure when Na⁺ and Cl⁻ uptake are decreasing but Na⁺ K⁺ ATPase activity is not inhibited until later. The implication of the data that the rate limiting step in the movement of Na⁺ and Cl⁻ across the gill epithelium is the movement across the apical membrane, as well as the identical time course and degree of Cl⁻ and Na⁺ uptake inhibition provide additional evidence for a role of CA inhibition in the early decline in Na⁺ uptake. A relationship exists between short-term gill silver accumulation and inhibition of Na⁺ uptake. There is also a relationship between silver accumulation on the gills after 3 h, as well as after 24 h, and 96 h mortality. Together, the results of this thesis indicate that short-term gill silver accumulation is an appropriate endpoint for the prediction of acute silver toxicity in freshwater fish, lending support to the current toxicological version of the silver BLM. These results also indicate that the predictive capabilities of the current physiological BLM may be improved by using Na⁺ uptake inhibition rather than Na⁺K⁺-ATPase inhibition as an endpoint to predict acute silver toxicity. / Thesis / Master of Science (MS)

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<p>Silver was used for its antimicrobial effect by the ancient Greeks, long before the existence of microorganisms were first suspected. Nowadays a wide range of antimicrobial dressings containing silver, either incorporated within or applied on the dressings, are available for clinical use. This type of dressings is designed to provide the antimicrobial activity of silver in a more convenient application.</p><p>The aim with this master thesis was to evaluate if silver release and antimicrobial effect of nine silver containing dressings are dependent on the test medium and if there is any relation between silver release and antimicrobial effect.</p><p>Release of silver and antimicrobial effect was evaluated by using a 6-well co-culture system, with inoculated test medium in the wells and dressing pieces in the culture well inserts. Three different test media with increased complexity and nutrient value were inoculated with either</p><p>Results show that release of silver depends on the test fluid used; for phosphate buffered saline (PBS), the silver concentration was as most 1.2 ppm, but for a complex media containing calf serum (SWF), it varied from 9 ppm to 134 ppm. The viable counts in PBS were reduced by at least 3 log units for all dressings and bacteria, whereas in SWF there were no reduction and instead growth was observed. In general, a high release resulted in less bacterial growth. Results also indicated that kinetics of silver release affect the antimicrobial effect. It is likely to assume that it is important for a dressing to release silver quickly.</p><p>It has previously not been possible to correlate silver release of wound care dressings and antimicrobial effect, since the two factors have been measured in different test systems and in different media. Since both factors depend on test medium and method used, it is shown in the present study that it is important to use relevant test medium for in-vitro evaluation. When measuring silver release and antimicrobial effect in the same test system, a relation is found.</p>

Silver was used for its antimicrobial effect by the ancient Greeks, long before the existence of microorganisms were first suspected. Nowadays a wide range of antimicrobial dressings containing silver, either incorporated within or applied on the dressings, are available for clinical use. This type of dressings is designed to provide the antimicrobial activity of silver in a more convenient application. The aim with this master thesis was to evaluate if silver release and antimicrobial effect of nine silver containing dressings are dependent on the test medium and if there is any relation between silver release and antimicrobial effect. Release of silver and antimicrobial effect was evaluated by using a 6-well co-culture system, with inoculated test medium in the wells and dressing pieces in the culture well inserts. Three different test media with increased complexity and nutrient value were inoculated with either Results show that release of silver depends on the test fluid used; for phosphate buffered saline (PBS), the silver concentration was as most 1.2 ppm, but for a complex media containing calf serum (SWF), it varied from 9 ppm to 134 ppm. The viable counts in PBS were reduced by at least 3 log units for all dressings and bacteria, whereas in SWF there were no reduction and instead growth was observed. In general, a high release resulted in less bacterial growth. Results also indicated that kinetics of silver release affect the antimicrobial effect. It is likely to assume that it is important for a dressing to release silver quickly. It has previously not been possible to correlate silver release of wound care dressings and antimicrobial effect, since the two factors have been measured in different test systems and in different media. Since both factors depend on test medium and method used, it is shown in the present study that it is important to use relevant test medium for in-vitro evaluation. When measuring silver release and antimicrobial effect in the same test system, a relation is found.