Macroporous ZnO foams by high internal phase emulsion technique: synthesis and catalytic activity.

Zinc(II) oxide nanoparticles were used for the stabilization of dicyclopentadiene (DCPD)-water-based high internal phase emulsions (HIPEs), which were subsequently cured using ring-opening metathesis polymerization (ROMP). The morphology of the resulting ZnO-pDCPD nanocomposite foams was investigated in correlation to the nanoparticle loading and nanoparticle surface chemistry. While hydrophilic ZnO nanoparticles were found to be unsuitable for stabilizing the HIPE, oleic acid coated, yet hydrophobic ZnO nanoparticles were effective HIPE stabilizers, yielding polymer foams with ZnO nanoparticles located predominately at their surface. These inorganic/organic hybrid foam-materials were subsequently calcined at 550 °C for 15 min to obtain inorganic macroporous ZnO foams with a morphology reminiscent to the original hybrid foam, and a specific surface area of 1.5 m(2) g(-1). Longer calcination time (550 °C, 15 h) resulted in a sea urchin like morphology of the ZnO foams, characterized by higher specific surface area of 5.5 m(2) g(-1). The latter foam type showed an appealing catalytic performance in the catalytic wet air oxidation (CWAO) process for the destruction of bisphenol A.

In situ determination and imaging of physical properties of soft organic materials by analytical transmission electron microscopy.

Analytical transmission electron microscopy (ATEM) offers great flexibility in identification of the structural-chemical organization of soft materials at the level of individual macromolecules. However, the determination of mechanical characteristics such as hardness/elasticity of the amorphous and polycrystalline organic substances by ATEM has been problematic so far. Here, we show that energy filtered TEM (EFTEM) measurements enable direct identification and study of mechanical properties in complex (bio-)polymer systems of relevance for different industrial and (bio-)medical applications. We experimentally demonstrate strong correlations between hardness/elasticity of different polymers (polycaprolactone, polylactid, polyethelene, etc.) and their volume plasmon energy. Thickness and anisotropy effects, which substantially mask the material contrast in EFTEM bulk plasmon images, can be adequately removed by normalizing the latter by carbon elemental map. EFTEM data has been validated using atomic force microscopy phase images, where phase shift related to the hardness and elastic modulus of the materials.

Nanocomposite foams from iron oxide stabilized dicyclopentadiene high internal phase emulsions: preparation and bromination.

Nanocomposite polyHIPE foams with open-cellular morphology were obtained using nanoparticles (γFe2O3/Fe3O4), surfactant (Pluronic L121) or nanoparticle/surfactant stabilized dicyclopentadiene high internal phase emulsions (DCPD HIPEs). Upon curing, cavity sizes were found to vary drastically between 950 ± 360 µm down to 7 ±3 µm depending on the HIPE formulations. As-obtained nanocomposite polyHIPE foams were functionalized using elemental bromine in THF. Upon bromination the nanoparticles are moved from the cavities surfaces into the bulk phase of the polymer scaffold, which affects the inductive-heating capability of the magnetic nanocomposite foams decreasing it by the factor of 2.

Analytical electron microscopy for characterization of fluid or semi-solid multiphase systems containing nanoparticulate material.

The analysis of nanomaterials in pharmaceutical or cosmetic preparations is an important aspect both in formulation development and quality control of marketed products. Despite the increased popularity of nanoparticulate compounds especially in dermal preparations such as emulsions, methods and protocols of analysis for the characterization of such systems are scarce. This work combines an original sample preparation procedure along with different methods of analytical electron microscopy for the comprehensive analysis of fluid or semi-solid dermal preparations containing nanoparticulate material. Energy-filtered transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy and high resolution imaging were performed on model emulsions and a marketed product to reveal different structural aspects of both the emulsion bulk phase and incorporated nanosized material. An innovative analytical approach for the determination of the physical stability of the emulsion under investigation is presented. Advantages and limitations of the employed analytical imaging techniques are highlighted.

An analytical technique to extract surface information of negatively stained or heavy-metal shadowed organic materials within the TEM.

Using a series of uranyl acetate stained or platinum-palladium shadowed organic samples, an empirical analytical method to extract surface information from energy-filtered transmission electron microscopy (EFTEM) images is described. The distribution of uranium or platinum-palladium atoms, which replicate the sample surface topography, have been mathematically extracted by dividing the image acquired in the valence bulk plasmon energy region (between 20 and 30 eV) by the image acquired at the carbon K ionization edge (between 284 and 300 eV). The resulting plasmon-to-carbon ratio (PCR) image may be interpreted as a precise metal replica of the sample surface. In contrast to conventional EFTEM elemental mapping, including an absolute quantification approach, this technique can be applied to 200-600 nm thick organic samples. A combination of conventional TEM and PCR imaging allows one to detect complementary transmission and topographical information with nanometer precision of the same area of carbon-based samples. The advantages and limitations of PCR imaging are highlighted.

Electron microscopy of pharmaceutical systems.

During the last decades, the focus of research in pharmaceutical technology has steadily shifted towards the development and optimisation of nano-scale drug delivery systems. As a result, electron microscopic methods are increasingly employed for the characterisation of pharmaceutical systems such as nanoparticles and microparticles, nanoemulsions, microemulsions, solid lipid nanoparticles, different types of vesicles, nanofibres and many more. Knowledge of the basic properties of these systems is essential for an adequate microscopic analysis. Classical transmission and scanning electron microscopic techniques frequently have to be adapted for an accurate analysis of formulation morphology, especially in case of hydrated colloidal systems. Specific techniques such as environmental scanning microscopy or cryo preparation are required for their investigation. Analytical electron microscopic techniques such as electron energy-loss spectroscopy or energy-dispersive X-ray spectroscopy are additional assets to determine the elemental composition of the systems, but are not yet standard tools in pharmaceutical research. This review provides an overview of pharmaceutical systems of interest in current research and strategies for their successful electron microscopic analysis. Advantages and limitations of the different methodological approaches are discussed and recent findings of interest are presented.

Microscopic analysis of the surface functionalization of polymer particles and subsequent grafting of polymer chains from the surface.

The characterization of the surface functionalization of polymer particles and subsequent grafting of hydrated polymer chains from their surface by microscopic techniques are essential to obtain reliable data about the actual morphology of the system. Since the size range of morphological features of functionalized polymer surfaces has long ago reached the lower end of the nanometer scale, classical light microscopy and dynamic light scattering have been replaced by electron and atomic force microscopy techniques which provide sufficient resolution for the visualization of nano-sized structures. Moreover, only polymer particle aggregates and fine organization of hydrated polymer chains which are not efficiently characterized by particle size measurements can be detected accurately with microscopy methods. Both solid and hydrated systems can be characterized by transmission electron microscopy and scanning electron microscopy (inc. cryo-electron microscopy (EM)) after appropriate sample preparation. Moreover, analytical EM methods allow not only for the size, shape and internal structure characterization, but also for the chemical composition with high spatial resolution.

Electron microscopy of nanoemulsions: an essential tool for characterisation and stability assessment.

The characterisation of pharmaceutical formulations by microscopic techniques is essential to obtain reliable data about the actual morphology of the system. Since the size range of colloidal drug delivery systems has long ago reached the lower end of the nanometer scale, classical light microscopy has been replaced by electron microscopy techniques which provide sufficient resolution for the visualisation of nano-sized structures. Indeed, the superior resolution and methodological versatility of electron microscopy has rendered this technique an indispensable tool for the analysis of nanoemulsions. Microscopic analysis of these lipid-based drug delivery systems with particle sizes in the lower submicron range provides critical information about the size, shape and internal structure of the emulsion droplets. Moreover, surfactant aggregates such as liposomes or multilamellar structures which remain unnoticed during particle size measurements can be detected in this fashion. This review provides a brief overview about both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques which have been employed to characterise nanoemulsions. Of special interest are sophisticated cryo techniques of sample preparation for both TEM and SEM which deliver high-quality images of nanoemulsions in their natural state. An overview about the instrumentation and sample preparation for all presented methods is given. Important practical aspects, sources of error and common artefacts as well as recent methodological advances are discussed. Selected examples of electron microscopic studies of nanoemulsions are presented to illustrate the potential of this technique to reveal detailed and specific information.

Decrease of liposomal size and retarding effect on fluconazole skin permeation by lysine derivatives.

Liposomes are ideal dermal drug delivery systems because of their ability to alter the biodistribution profile of incorporated drugs. In a novel approach to optimize the liposomal microstructure, lysine derivatives were employed. The effect of the oligopeptides Lys-5 and Lys-7 on the structure as well as on the skin permeation of the antimycotic drug fluconazole in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine vesicles was studied using a variety of techniques. It was demonstrated by addition of the shift reagent praseodymium(III)chloride and subsequent (31)P NMR measurements that the liposomes produced consisted mainly of unilamellar vesicles. This was confirmed by cryo-transmission electron microscopy. The addition of Lys-5 and Lys-7 induced a structural change resulting in a decrease in particle size between 10% and 40% and a retarding effect on fluconazole skin permeation.

Silicon: The key element in early stages of biocalcification.

Biocalcification is a widespread process of forming hard tissues like bone and teeth in vertebrates. It is also a topic connecting life sciences and earth sciences: calcified skeletons and shells deposited as sediments represent the earth's fossil record and are of paramount interest for biogeochemists trying to get an insight into the past of our planet. This study reports on the role of silicon in the early biocalcification steps, where silicon and calcium were detected on the surface of cyanobacteria (initial stage of lacustrine calcite precipitation) and in crustacean cuticles. By using innovative methodological approaches of correlative microscopy (AFM in combination with analytical TEM: EFTEM, EELS) the chemical form of silicon in biocalcifying matrices and organic-inorganic particles is determined. Previously, silicon was reported to be localized in active growth areas in the young bone of vertebrates. We have found evidence that biocalcification in evolutionarily distant organisms involves very similar initial phases with silicon as a key element at the organic-inorganic interface.

Atomic force microscopy applied to study macromolecular content of embedded biological material.

We demonstrate that atomic force microscopy represents a powerful tool for the estimation of structural preservation of biological samples embedded in epoxy resin, in terms of their macromolecular distribution and architecture. The comparison of atomic force microscopy (AFM) and transmission electron microscopy (TEM) images of a biosample (Caenorhabditis elegans) prepared following to different types of freeze-substitution protocols (conventional OsO4 fixation, epoxy fixation) led to the conclusion that high TEM stainability of the sample results from a low macromolecular density of the cellular matrix. We propose a novel procedure aimed to obtain AFM and TEM images of the same particular organelle, which strongly facilitates AFM image interpretation and reveals new ultrastructural aspects (mainly protein arrangement) of a biosample in addition to TEM data.