A comparative study of softeners and catalyst systems upon dimensional changes and sectioning quality of glycol methacrylate sections

It is shown that softeners and temperature have an important influence upon the stretching parameters of glycol methacrylate sections. Also it is demonstrated that the catalyst system used may significantly interfere with section stretching.     

The influence of tissue processing on quantitative histopathology in breast cancer

Objective grading of breast cancer by morphometry has been suggested for improving the precision of the prognostic prediction. However, the tissue components evaluated might be influenced by variations in the processing, reducing the clinical value. In the present study, the impact of the period of fixation, of the acidity of the fixative and of the embedding medium was investigated by allocating tissue samples from 27 surgical breast cancer specimens systematically randomly to different modes of processing. The volume-weighted mean volume of cancer cell nuclei, v?_V(nuc), was estimated using the method of point-sampled intercepts on vertical sections. In addition, estimates of the mean nuclear profile area, ā_H(nuc), the nuclear volume fraction, V_V(nuc), the nuclear profile density, ND, and the mitotic profile frequency, MF, were obtained. The quantitative histopathological estimates were stable with respect to the investigated variables of the tissue processing. No significant differences were found when comparing the estimates obtained in samples from five tumours fixed in formalin at pH 5·0, 6·0, 7·0, 7·4 and 8·0, respectively. Similarly, no significant correlations between the estimates and the period of formalin fixation (24 h, 3 days and 3 months) were found in samples from five other tumours. However, the v?_V(nuc) was 13% larger (2p = 0·004) and the mean ND 17% smaller (2p = 0·04) in hydroxyethyl-methacrylate-embedded samples from 17 tumours as compared to paraffin-embedded samples. Thus, the shrinkage observed in paraffin seems to affect nuclei less than tissue.     

An experimental study of the scratch properties of poly(methyl methacrylate) as a function of the concentration of added slip agent

A scratch test was performed on poly(methyl methacrylate) (PMMA) material that had been optimised for electronic products. In this study, the scratch properties of PMMA containing various concentrations of slip agent were investigated by performing scratch tests under two different load conditions, i.e., a static normal load and a variable normal load. The effects of the concentration of slip agent on the scratch properties of PMMA were characterised by some key tribological parameters, based on a new standard test methodology. Additionally, the damaged surfaces of the specimens were investigated to understand the variations in scratch mechanisms.     

Staining sections of water-miscible resins 2. Effects of staining-reagent lipophilicity on the staining of glycol-methacrylate-embedded tissues

Glycol methacrylate (GMA) sections of animal tissues were stained with a group of twenty-seven reagents of very varied chemical characteristics. The artefactual background staining of the resin was found to be dependent on the hydrophilic/lipophilic character of the staining reagent, as estimated from the logarithm of its octanol-water partition coefficient (log P). Intense background staining occurred with lipophilic stains, whose log P>2. In keeping with this, use of GMA semi-permeable membranes for enzyme histochemistry failed to give staining when using a lipophilic substrate, probably because the substrate was trapped in the membrane. An analysis of other routine histochemical stains—in terms of the probable occurrence of high resin background staining and low tissue sensitivity—is made. A numerical guide is provided to help avoid artefacts resulting from hydrophobic and size effects. Note: small, hydrophilic reagents (log P <0; molecular weight < 550 Da) are least likely to show either type of artefact. Conversely, reagents which are lipophilic, or/and of intermediate size (log P > 2; 550 < ionic weight < 1000 Da), give strong background staining.     

The projection of a negatively-stained filamentous object down its central axis as revealed by image reconstruction from tilt series

Helical reconstructions of negatively stained biological objects contain distortions arising from filament flattening and the non-cylindrical profile of the stain envelope. Current methods of estimating flattening do not make full use of the information available in electron micrographs. We have applied the more rigorous approach of reconstructing the density profile from tilt series using digital image processing techniques. Tilt series were collected for tobacco mosaic viruses (TMV) and seven independent reconstructions were calculated using equatorial data out as far as ～1/9·3 nm^—1. They indicated that the filaments were flattened with an axial ratio of about 2·4:1, which was probably closer to 3:1 in the original specimen, because the limited resolution caused flattening to be underestimated. The stain envelope around TMV and some indication of the underlying carbon substrate were also observed. This information could enable correction factors for flattening to be developed, which could be useful when calculating helical reconstructions or indexing helical diffraction patterns. This method could also be extended to non-equatorial layer planes, which would provide three-dimensional information on a wide range of macromolecules that possess a one-dimensional repeat.