Search

Elemental silver nanoparticles are an effective antibacterial substance and are found as additive in various medical applications. Gold nanoparticles are used due to their optical properties in microscopy and cancer therapy. These advantages might be combined within alloyed nanoparticles of both elements and thereby open new fields of interest in research and medical treatment. In this context, laser ablation of solid alloys in liquid gives access to colloidal silver-gold alloy nanoparticles with a homogeneous ultrastructure. Elemental and alloy silver-gold nanoparticles with increasing molar fractions of silver (50, 80, and 100%) were produced and stabilized with citrate or albumin (BSA). Particles were embedded in agar at concentrations of 3-100 [micro]g [cm.sup.-3] and tested on clinical relevant Staphylococcus aureus regarding their antibacterial properties. Cytotoxic effects were measured within the same particle concentration range using human gingival fibroblasts (HGFib). As expected, a reduced fraction of silver in the nanoalloys decreased the antibacterial effect on S. aureus according to the evaluated minimal inhibitory concentrations. However, this decrease turned out stronger than expected by its relative mass per particle, due to the electrochemical, disproportionally high effect of gold on the bioresponse to silver within silver-gold nanoalloy particles. BSA was able to stabilize all colloids and maintain antibacterial activity, whereas sodium citrate reduced antibacterial effects and cytotoxicity even at high nanoparticle concentrations. The alloying of silver with gold by laser ablation in liquid produced nanoparticles with both reduced antibacterial and cytotoxic properties in comparison to silver nanoparticles but still retains the application spectrum of both elements combined in one colloid. In particular, alloying with gold may render silver nanoparticles more biocompatible, and allows bioconjugation via established thiol chemistry. Keywords AgAu * nanotoxicology * antibacterial * nanocolloids, Introduction Alloying of metals has been established for centuries in material science and metallurgy, aiming at the optimization of material properties and functionality. Multifunctional materials attract a lot of attention [...]

Objectives: To investigate the formation of oral biofilm on various dental ceramics in vivo. Method and Materials: Five different ceramic materials were included: a veneering glass- ceramic, a lithium disilicate glass-ceramic, a yttrium-stabilized zirconia (Y-TZP), a hot isostatically pressed (HIP) Y-TZP ceramic, and an HIP Y-TZP ceramic with 25% alumina. Test specimens were attached to individually designed acrylic appliances; five volunteers wore these appliances for 24 hours in the maxillary arch. After intraoral exposure, the samples were removed from the appliances and the adhering biofilms vitally stained. Then, the two-dimensional surface coating and thickness of the adhering biofilm were determined by confocal laser scanning microscopy. Statistical analysis was performed using one-way ANOVA with the level of significance set at .05. Results: Significant differences (P < .001) in the bacterial surface coating and in the thickness of the biofilm were found between the various ceramic materials. The lowest surface coating (19.0%) and biofilm thickness (1.9 μm) were determined on the HIP Y-TZP ceramic; the highest mean values were identified with the lithium disilicate glass-ceramic (46.8%, 12.6 μm). Conclusion: Biofilm formation on various types of dental ceramics differed significantly; in particular, zirconia exhibited low plaque accumulation. In addition to its high strength, low plaque accumulation makes zirconia a promising material for various indications (including implant abutments and telescopic crowns) that previously were met only with metal-based materials. [ABSTRACT FROM AUTHOR]