Antennal and cephalic organelles in the social wasp Paravespula germanica (Hymenoptera, Vespinae): form and possible function

This paper deals with hairs and organelles present on the head and antennae of the German wasp, Paravespula germanica, and their possible role in sensing the physical and chemical ambience, as well as in intercommunicating both while in flight outside or in the nest. Via scanning electron microscope photography, we detected on the frons plate of the wasp's head, hairs that were about 300 microm long and comprised the longest hairs on the body of the wasps. Additionally, the two antennae bore along their entire length photoreceptors, placoids, campaniforms, trichoids, and agmons. These organelles are located at high but variable density along the antennal segments. The paper provides the dimensions of each of the mentioned organelles, and discusses the possible functions of the organelles as well as of the hairs on the frons. Photographs taken via atomic force microscope reveal that the epicuticle of the antenna is of two typical shapes; one, bearing both longitudinal stripes as well as transverse bands that are about 1 mum in width, and a second granulated form. Conceivably, the wasp uses the various organelles mentioned to communicate with its mates that are some distance away, somewhat like the use of radar by humans.     

Imaging of the Surface of Human and Bovine Articular Cartilage with ESEM and AFM

The surface of human and bovine articular cartilage was imaged with environmental SEM and AFM. The effective modulus of the surface, from force--distance curves obtained with AFM, remained constant at 9±2 kPa in the presence of synovial fluid. Extensive washing of the cartilage surface with phosphate buffered saline (PBS) removed a superficial gel-like layer, leaving a granular layer intact. Force--distance curves showed that the chemical and mechanical properties of the gel exposed to PBS changed over time. The effective modulus at the surface dropped from 481 to 4 kPa over an hour. The results suggest that the gel-like layer, having partly lost water through evaporation on removal from the joint, absorbs water from PBS. It becomes softer and eventually begins to dissolve. The low effective modulus of the gel-like layer in synovial fluid indicates that it is too soft to influence the surface roughness. Imprints of the surface under pressure were taken using a low viscosity dental kit. Imaging of the imprint surface indicated that the topography of the cartilage under pressure was similar to that of the surface after removal of the gel-like layer. In conclusion, imaging of articular cartilage with ESEM and AFM revealed two distinct non-fibrous layers, which are granular and gel-like, and cover the fibrous collagen matrix.     

Mechanisms of detection and imaging in the ESEM

For proper understanding of image formation using charge carriers, it is shown that signal detection by means of induction must be considered. This explains the possibility of imaging insulators as well as other phenomena especially in the conditions of the environmental scanning electron microscope. In addition, a basic principle and method to separate the secondary and backscattered electrons is demonstrated.     

Morphology of polystyrene films deposited by RF plasma

A new plasma reactor, set up with a large planar inductively coupled source, is used for the first time to deposit a polymer coating (pPS) from a styrene monomer. This work is devoted to the relationship between external plasma parameters and substrate topography, and pPS coating morphology, which is investigated by scanning electron microscopy and atomic force microscopy. Stainless steel, gold and glass surfaces are used as substrates. It is clearly demonstrated that the film morphology can be controlled by adjustment of RF input power, pressure. The analysis performed further reveals that the pPS film's characteristics strongly depend on the substrate topography and its electrical potential during the discharge. Finally, the plasma duration also strongly influences the morphology of the films. The morphologies obtained include smooth films without any specific feature, worm‐like structures, particles (nanometer‐ and micrometer‐sized) associated along preferential directions and randomly distributed particles (micrometer‐sized). The intrinsic topography of the substrate influences the film structure in the case of thin films (thickness lower than about 100 nm). Polymerization is suggested to take place at the surface in contact with the discharge rather than in the gas phase. Nucleation and growth start preferentially on substrate defects such as polishing scratches.     

High resolution imaging of surface patterns of single bacterial cells

We systematically studied the origin of surface patterns observed on single Sinorhizobium meliloti bacterial cells by comparing the complementary techniques atomic force microscopy (AFM) and scanning electron microscopy (SEM). Conditions ranged from living bacteria in liquid to fixed bacteria in high vacuum. Stepwise, we applied different sample modifications (fixation, drying, metal coating, etc.) and characterized the observed surface patterns. A detailed analysis revealed that the surface structure with wrinkled protrusions in SEM images were not generated de novo but most likely evolved from similar and naturally present structures on the surface of living bacteria. The influence of osmotic stress to the surface structure of living cells was evaluated and also the contribution of exopolysaccharide and lipopolysaccharide (LPS) by imaging two mutant strains of the bacterium under native conditions. AFM images of living bacteria in culture medium exhibited surface structures of the size of single proteins emphasizing the usefulness of AFM for high resolution cell imaging.     

Steedman's polyester wax embedment and de-embedment for combined light and scanning electron microscopy

Steedman's polyester wax mixture is a good, general-purpose histological embedding medium that is suitable and convenient to use when it is desirable to combine light microscopy with scanning electron microscopy (SEM). A range of properties recommend this wax: it has a low melting temperature (37°C), is readily soluble in most dehydrating agents, results in negligible tissue shrinkage, preserves tissue antigenicity, and may even be used as a solvent for fixative agents. We prepare and embed tissues in polyester for light microscopy much as they would be for paraffin wax. For SEM, the block surface is micro- or ultraplaned, utilizing, respectively, a standard rotary microtome with razor blade knives or an ultramicrotome with glass knives. The block is de-waxed in absolute alcohol and then taken to critical point drying. Similarly, sections mounted on coverslips or glass slides may be brought to the SEM after removing the wax. This enables one to bring to the SEM relatively large block faces or sections with good control over orientation. We find the results to be superior to similar procedures employing paraffin. We believe it to be more versatile and equivalent or superior to a variety of other techniques designed to gain access to the interior of tissues with SEM.