Antimicrobial activity of transition metal acid MoO(3) prevents microbial growth on material surfaces

Serious infectious complications of patients in healthcare settings are often transmitted by materials and devices colonised by microorganisms (nosocomial infections). Current strategies to generate material surfaces with an antimicrobial activity suffer from the consumption of the antimicrobial agent and emerging multidrug-resistant pathogens amongst others. Consequently, materials surfaces exhibiting a permanent antimicrobial activity without the risk of generating resistant microorganisms are desirable. This publication reports on the extraordinary efficient antimicrobial properties of transition metal acids such as molybdic acid (H(2)MoO(4)), which is based on molybdenum trioxide (MoO(3)). The modification of various materials (e.g. polymers, metals) with MoO(3) particles or sol-gel derived coatings showed that the modified materials surfaces were practically free of microorganisms six hours after contamination with infectious agents. The antimicrobial activity is based on the formation of an acidic surface deteriorating cell growth and proliferation. The application of transition metal acids as antimicrobial surface agents is an innovative approach to prevent the dissemination of microorganisms in healthcare units and public environments.

Micromechanics and ultrastructure of pyrolysed softwood cell walls

Pyrolytic conversion causes severe changes in the microstructure of the wood cell wall. Pine wood pyrolysed up to 325 °C was investigated by transmission electron microscopy, atomic force microscopy and nanoindentation measurements to monitor changes in structure and mechanical properties. Latewood cell walls were tested in the axial, radial and tangential directions at different temperatures of pyrolysis. A strong anisotropy of elastic properties in the native cell wall was found. Loss of the hierarchical structure of the cell wall due to pyrolysis resulted in elastic isotropy at 300 °C. The development of the mechanical properties with increasing temperature can be explained by alterations in the structure and it was found that the elastic properties were clearly related to length and orientation of the microfibrils.

Origin of broad NIR photoluminescence in bismuthate glass and Bi-doped glasses at room temperature

Bi-doped glasses with broadband photoluminescence in the near-infrared (NIR) spectral range are presently receiving significant consideration for potential applications in telecommunications, widely tunable fiber lasers and spectral converters. However, the origin of NIR emission remains disputed. Here, we report on NIR absorption and emission properties of bismuthate glass and their dependence on the melting temperature. Results clarify that NIR emission occurs from the same centers as it does in Bi-doped glasses. The dependence of absorption and NIR emission of bismuthate glasses on the melting temperature is interpreted as thermal dissociation of Bi(2)O(3) into elementary Bi. Darkening of bismuthate glass melted at 1300 °C is due to the agglomeration of Bi atoms. The presence of Bi nanoparticles is confirmed by transmission electron microscopy, high-resolution energy dispersive x-ray spectroscopy and element distribution mapping. By adding antimony oxide as an oxidation agent to the glass, NIR emission centers can be eliminated and Bi(3+) is formed. By comparing with atomic spectral data, absorption bands at ∼320 , ∼500 , 700 , 800 and 1000 nm observed in Bi-doped glasses are assigned to Bi(0) transitions [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], respectively, and broadband NIR emission is assigned to the transition [Formula: see text].

Enzyme-catalysed synthesis of calcium phosphates

A biomimetic method is described for the precipitation of nanosized calcium phosphates using the alkaline phosphatase (EC 3.1.3.1), which is responsible for hydrolysis of organic and inorganic phosphates in vivo. Buffered solutions containing glycerol-2-phosphate and CaCl(2) in addition to MgCl(2) and the respective enzyme were prepared for calcium phosphate precipitation. The phosphate group of glycerol-2-phosphate was cleaved through enzymatic hydrolysis. The local inorganic phosphate concentration increased resulting in the precipitation of nanosized calcium phosphates phases (Ca-P phase) composed of calcium deficient hydroxyapatite (CDHA) and hydroxyapatite (HA). At high Ca(2+)-concentration and large enzyme amounts mixed phases of HA/CDHA with an increasing quantity of HA were favoured. Under basic conditions (pH > 9) formation of HA was observed, whereas at neutral pH of 7.5 CDHA was primarily formed. The assignment of Ca-P phases was accomplished by FT-IR and Raman-spectroscopy in addition to X-ray diffractometry. The Ca-P materials exhibited BET surface areas of 173 m(2)/g. SEM-micrographs of the Ca-P powders showed globular-shaped agglomerates of Ca-P particles. The size of the Ca-P crystallite ranged from 9 nm to 25 nm according to transmission electron microscopy (TEM), where round-shaped, platelike and fibrelike crystallites were found. All crystallites showed diffuse ring patterns in electron diffraction confirming the nanosize of the precipitate. Using the developed technique, it was possible to synthesise 100 g of bonelike Ca-P materials in 1 day using 15 L batches with optimised parameters.

Photoluminescence of annealed biomimetic apatites

Biomimetic apatite coatings are widely used in orthopaedic applications to provide bioinert material surfaces with bioactive behaviour by means of initiating bone growth at the implant surface. In this study we manufactured biomimetic calcium phosphate coatings consisting of a calcium deficient carbonated apatite by immersing activated titanium platelets into simulated body fluid. The development of the crystal phases was monitored by X-ray diffractometry in addition to Fourier-transform infrared spectroscopy. The microstructure of the biomimetic apatites and phase composition was analysed using scanning and transmission electron microscopy as well as attached energy dispersive X-ray spectrometry. The samples were annealed in air yielding in an inherent luminescence of the biomimetic apatite up to temperatures of 600 degrees C. The photo-induced emission spectra were recorded in the range from 400 to 750 nm at excitation wavelengths ranging 310-450 nm. A blue (437 nm) and a green (561 nm) emission were found between 200 and 600 degrees C visually appearing white. Photoluminescence of annealed biomimetic apatites might be of interest for histological probing and monitoring of bone re-modelling. The results are discussed in terms of chemical and crystallographic changes in the calcium phosphate layer during heat treatment.