Non-coating fixation techniques or redundancy of conductive coating, low kV FE-SEM operation and combined SEM/TEM of biological tissues

Non-coating fixation methods, in particular the tannic acid/arginine/osmium tetroxide procedure, are employed for a number of reasons on the guinea-pig organ of Corti hair cell stereocilia glycocalyx and the imprints of the stereocilia at the bottom side of the tectorial membrane, and on the rat and cat intestinal epithelial microvilli glycocalyx and mucus-producing goblet cells. These methods are used firstly to confirm that non-coating prepared specimens can be embedded for TEM observation at 60-100 kV without loss of detail information, and these images can be compared with cryo-FE-SEM images of the same structure/tissue. Secondly, they show that specimens treated according non-coating techniques become optimally preserved and electrically conductive, so that no external conductive coating is required. In this way a comparison of images of subsequent fresh fracture faces is possible without a decrease in information on detail, which otherwise could happen after subsequent coating layers required after standard fixation. Thirdly, they show that non-coating methods can be used quite well with low accelerating voltages because the osmium-tannic acid complex in the specimen surface produces a large number of backscattered and secondary electrons in the surface layer, showing in particular surface phenomena. Fourthly, they show that with an optimal non-coating preservation, in combination with a well-balanced pre-fixation mixture, preparation artefacts due to extraction and even dehydration and drying are minimized. This is compared with images of the organ of Corti hair cells treated with a so-called three-aldehyde pre-fixation mixture, which causes disrupted stereocilia to cling onto the bottom side of the tectorial membrane.

A micro-Raman spectroscopic study of hydrazine-treated human dental calculus

Hydrazine has been used to remove organic components and to isolate the mineral(s) from human calculus. Micro-Raman measurements were performed on the mineral phase. After the hydrazine-treatment, not only a large reduction in fluorescence but also an increase in Raman signal was observed. The treatment was essential in minimizing thermally-induced chemical changes which could otherwise occur to the original calculus mineral due to the intense laser light. The Raman spectral features of the mineral were nearly all identical among the Raman spectra obtained at many randomly-selected sites by the micro-Raman microbe with a lateral resolution of approximately 1 micron, and were consistent with those of impure hydroxyapatite containing CO3(2-) and HPO4(2-). The spectra contained typical hydroxyapatite bands including PO4(3-)bands of the v1, v2, v3 and v4 modes and one OH- stretch band. Other minor bands due to the CO3(2-) v1 and v3 modes and bands possibly due to the HPO4(2-) v1, v2 and v4 modes were observable by the technique despite the hydrazine-treatment that could in principle remove the HPO4 and CO3 ions from the mineral. In comparison with pure synthetic hydroxyapatite, the intensity of the OH- stretch band relative to that of the PO4(3-) v1 band was approximately 70% weaker, and the bandwidth of the phosphate v1 band was 200% broader, reflecting various crystal imperfections presumably present in the calculus mineral.

Demonstration of the fine structure of stereocilia in the organ of Corti of the guinea pig by field emission scanning electron microscopy

A combined perfusion- and immersion prefixation with glutaraldehyde followed by a tannic acid/arginine/osmium tetroxide (TAO) treatment of the guinea pig cochlea is described for field-emission gun scanning electron microscopy (FEG-SEM) observation of the fine structure of the stereocilia of the organ of Corti. Conventional osmium tetroxide postfixation methods in combination with a thin conductive coating failed to show the fine structure of the glycocalyx of the epithelial lining in the endolymphatic compartment of the cochlea, in particular, on the stereocilia surface. The antennulae-like glycocalyx covering of the stereocilia surface of the more pronounced rows of outer hair cells has been demonstrated only in ultrathin sections by means of cationic markers. The side- and tip-links connecting the stereocilia have been demonstrated both in scanning and transmission electron microscopy, although at that time these structures often were considered as artificial. However, they can be visualized with FEG-SEM at low accelerating voltage (2-3 kV), and at appropriate working distance and probe current, in combination with a glutaraldehyde perfusion/immersion prefixation and TAO postfixation. Stereo images enhance considerably the three-dimensional appreciation of the stereocilia with glycocalyx lining and side- and tip-links, proving that these connections are a structural part of the hair cell.

Micromorphology of the dorsal ocelli of the Oriental hornet

The development of vision in animals throughout evolution has been reviewed by Sir Stewart Duke-Elder, whose survey of the sense of sight ranges from lowly Crustaceans to mammals and man. According to Duke-Elder each ocellus is formed by the "fusion of two or more ocelli, each with its own retina and pigment cup". This process of 'ocellation' probably occurred independently in a number of phyla. So far as Hymenoptera are concerned, at least in Bombus, only the median ocellus has retained any evidence of its 'dual' origin. In hornets, there are three ocelli which are organized on the dorsal part of the head and receive their innervation from the optical lobes that are located in the protocerebrum. Proceeding from the exterior to the interior, the ocelli are generally composed of a cornea, followed by corneogenic cell layers and then by a layer of sensory cells from which emerges the ocellar nerve. Thus, in wasps and hornets the ocelli consist of a group of visual cells beneath a common lens and they possibly accentuate the response to light stimuli that are perceived by the compound eyes. Recently, the ocelli have been ascribed roles in orientation and navigation. In honeybees the sensitivity of the ocelli to light at various wavelengths was compared with that of the compound eyes, and was found to be different, to wit: in the ocellus there were two peaks--one of UV light at a wavelength of 335-340 nm and the other of green light at 490 nm, whereas in compound eye the peaks were at 350 nm and 540 nm. From all the foregoing, it would seem that the role of the ocelli in insects in general and in hornets in particular is not yet sufficiently clear. The present study was undertaken to elucidate the structure of the ocelli in the Oriental hornet and possibly also their function.

Are ciliary hair cells and photoreceptors components of a gravitic system of the hornet Vespa orientalis?

Social wasps, including the sub-family Vespinae, are social insects that build combs beneath the ground which are directed towards the gravitic pull of the earth, and this in dim light or complete darkness. On the inner side of the frons plate in social wasps there is a gravity sensing apparatus composed of static and dynamic nerve fibers, some of which connect between the frons plate and the brain. It is highly probable that the interaction between the fibers and the various structures in the head is responsible for the proprioceptive ability of hornets, including gravity detection. Ishay et al called the apparatus involved, the "Ishay Organ", and also reported the presence of (stereo) cilia on the inner side of the frons plate. The frons plate which bears the gravity organs functions as a photovoltaic system. Additionally there are throughout the cuticle, at intervals of several micrometers apart, distinct pores which are the outlets of peripheral photoreceptors. In the past various investigators have studied the ciliar structures of different insects mainly by TEM, but we have now studied the hair cells in hornets by FE-SEM, to obtain a complete 3-dimensional image of the various hair cell structures involved.

Low-voltage field-emission scanning electron microscopy of non-coated guinea-pig hair cell stereocilia

The stereociliar structures of the guinea-pig cochlear organ of Corti were studied at low-voltage (1-5 kV) with field-emission scanning electron microscope (SEM) using various pre- and post-fixation methods, such as OTOTO (OsO4/thiocrbohydrazide/OsO4/thiocarbohydrazide/OsO4) and TAO (tannic acid/arginine/OsO4), and different dissection procedures of the cochlea. A perfusion and immersion pre-fixation with glutaraldehyde, in combination with removal of the bony wall and stria vascularis from the cochlea, followed by the TAO non-coating treatment gave the best result at 2 kV acceleration voltage. Due to these new technique, several interesting delicate structures of the stereocilia, in particular fine surface structures, were detected for the first time using SEM. These findings include the different types of cross-links and tip links, i.e., the fine surface morphology of the stereocilia and their attachments and imprints in the tectorial membrane (TM). One of the most interesting findings in this study is a network of long filamentous structures, which has been identified mainly at the top of the longest stereocilia and the undersurface of the TM and which may represent the glycocalyx. These findings and their possible implications in the process of mechanoelectrical transduction will be discussed.

New material for low-cost intraocular lenses

A UV-hardening lacquer material based on polyurethane, used in Philips compact disc lens systems, was tested as suitable material for low-cost intraocular lenses (IOLs). A slightly changed composition (code number I-0.5A) came out as the best and was subsequently tested, with reference to poly(methyl methacrylate) (PMMA), as a 'lobster-claw' lens in Hollander rabbit eyes for a period of 24 wk. No carcinogenic effects were found, while only minor vascularization of the cornea at the incision area occurred. The in vitro biocompatibility tests of the material were positive. Scanning electron microscopy images of the IOLs at 2, 6, 12 and 24 wk postoperative showed portions of an acellular membrane, multinuclear giant cells which hyalinize and stay as pigmented plaques, microphages and fibroblasts with fibrillar strands, long pseudopodia, and broad microplicea. The chosen UV lacquer showed a foreign body reaction and properties comparable with PMMA, and is suitable for manufacturing low-cost IOLs.

Closing of dentinal tubules by glutardialdehyde treatment, a scanning electron microscopy study

The properties of dentin are strongly influenced by the so-called smear layer. This layer is always present on the dentin surface after cutting, drilling, sawing, etc. The smear layer can be removed by various chemical treatments, such as those of acid etching or ethylenediaminetetraacetic acid (EDTA). These treatments remove the smear layer and open the tubules. In this paper, the effect on the smear layer of human dentin of treatment with a 2% glutardialdehyde (GDA) solution at pH 3.5 for 2 min and a 0.5-M EDTA solution at pH 7.4 for 4 min was investigated by scanning electron microscope (SEM). The dentin samples were dried by air or critical-point drying before SEM photography was employed. The number of open dentin tubules was quantified on micrographs of EDTA- and GDA+EDTA-treated dentin. The results show that the GDA treatment fixed part of the smear layer and the superficial dentin surface in such a way that at least 50% of the tubules remained closed after EDTA treatment. By closing the dentinal tubules, the GDA-fixed layer might have a positive effect on dentin hypersensitivity, root caries, and bonding of composite to dentin.

Natural and induced radiation caries: A SEM study

Radiation caries is a well-known indirect side effect of head and neck radiotherapy. The initiation and progression of radiation caries were studied using an in situ model. The morphology of induced carious lesions was compared with that of natural radiation caries. Both natural and induced radiation caries showed the same patterns of decay; widespread areas with porosity of enamel, crater formation with exposure of subsurface enamel, preferential dissolution of prisms with hollowing out of prism cores, loss of large parts of surface enamel and loss of full enamel coverage exposing the underlying dentin. In irradiated patients most enamel slabs were severely demineralized within 6 weeks whereas in control subject the slabs showed no significant demineralization after 12 weeks. The model may offer an excellent opportunity to study preventive fluoride regimens because of the rapid induction of radiation caries and its similarity with natural lesions.

The Morgagnian and Brunescens cataract morphology studied with with SEM and TEM

The Morgagnian cataract lenses--pre-fixed with GA for SEM & TEM and post-fixed with tannic-acid-arginine-OsO4 for SEM and OsO4/K4Fe(CN)6 for TEM after staining with Ur-acetate/Pb-citrate--showed areas in the cortex with radial instead of concentric running lens fibres, degeneration of lens fibres with vacuoles and defected "ball & socket" connections. The presence of oval/spherical bodies of 0.5-20 microns was acknowledged, the largest of them having a golf-ball appearance and originating from the cytoplasm of the degenerating lens fibres; the smallest of them with an approximate size of 0.2-0.5 micron seemed to be formed by budding off from the microvilli of the furrowed lens epithelium. The Brunescens cataract lenses showed at low magnification no difference between lens fibres from the cortical area and the nucleus. The disintegration process of the lens fibres was observable as degradation of the ball & socket system and the existence of holes in the lens fibre body and emerging of spherical bodies from the cytoplasm. The globular structures seemed to be covered with a thin coating and were partly filled with a low density membranous-like material. In TEM-sections of the cataractous lens aterial vacuoles were visible consisting of a large number of smaller globules with a contents of low contrast low density membranous-like material, comparable with the globular structures seen in SEM.

Healing of microvenous PTFE prostheses implanted into the rat femoral vein

44 PTFE prostheses (Gore-Tex; ID 1 mm) were implanted into rats' femoral veins by means of the sleeve anastomotic technique and were evaluated at regular intervals from 1 h up till 24 weeks after implantation by means of light and electron microscopy to study in detail their healing process. All prostheses, except one at 1 week and one at 24 weeks after implantation, were patent at the time of removal. Upon implantation, the luminal surface of the prostheses became covered with a thin clot layer. From 1 week onwards, endothelial cells originating from the anastomotic sides grew in across the anastomoses. In addition, small capillary-like orifices were present at the anastomotic sites, from which endothelial cells also seemed to originate. At 2 weeks, in several areas in the mid-region of the prostheses, the fronts of regenerating endothelial cells had reached each other, and about 80% of the luminal surface was covered by endothelium and at 3 weeks, the prostheses were completely covered by an endothelial layer. These results demonstrate that PTFE microvenous prostheses heal exclusively by means of rapid ingrowth of endothelial cells originating from both sides at the anastomoses.

Human capsule epithelial cell degeneration, A LM, SEM and TEM investigation

The degeneration of the capsule epithelium of cataractous lenses has been studied with LM, SEM en TEM with emphasis on TEM. The observed degeneration of the epithelial cells can be described as follows: The cell nucleus becomes picnotic and disintegrates as result of change of the chromatin. Degeneration of the cytoplasm starts with swelling of the mitochondria, coming into existence of filamentous networks and balloon-like bulges of the nucleus. Repelling of the cell nucleus due to a porosity of the plasma membrane. Collapse of the cell due to degeneration of the cell and loss of the cytoplasmic contents, leaving finally only a swollen framework of cell walls.

Lensfibre degeneration at cataract lenses. A LM, SEM and TEM investigation

The degeneration process of lensfibres in a cataractous lens, described as the biochemical changes of a part of the lensproteins, can be characterised morphologically as follows: Emulsification of a part of the lensfibre-mass and the development of open spaces between the lensfibres with the formation of vacuoles (spherical structures) with a granular or a compact contents with high contrast, which is squeezed into the intercellular space. Degeneration of the ball & socket system interdigitation and microvilli domain system and the formation of almost empty rectangular structures in somewhat radial array. Balloon-like bulging of the cytoplasm of the lenscell, degeneration of the cytoplasm membrane and visualisation of a micro-filamentous network with enclosed cell organelles.

Microorganisms found in secondary cataract material of ECCE patients, a study with SEM and TEM

Globular secondary cataract material, removed from 24 patients with ECCE after ophthalmic cleaning of the anterior capsule, were investigated with SEM and TEM. Besides spherical, somewhat oval shaped bodies of various shape and size comparable with those found in cataractous lenses, (an)aerobic bacteria and yeast cells were found in approximately 70% of the cases, all of them in eyes without intra-ocular inflammation. Probably these bacteria have been transferred from the conjunctiva during IOL.-implantation and were encapsulated without starting an inflammation.

Combined Raman and SEM study on CaF2 formed on/in enamel by APF treatments

Raman spectra containing the distinct band at 322 cm-1 due to CaF2 or CaF2-like material formed in/on fluoridated bovine enamel were recorded using a micro-Raman spectrograph. Due to increasing levels of background fluorescence with increasing thickness of enamel, the Raman measurements were carried out on thin regions of wedged enamel sections. The distribution of the CaF2 or CaF2-like material was estimated using a simple model. The results indicate that 1/3 of the total CaF2 was concentrated within the narrow depth < 2 microns with high CaF2 concentrations (> 10 wt%), and that the majority of the CaF2 was distributed over the depths up to 26 microns (1 wt% CaF2). SEM observations on fractured fluoridated enamel confirmed that morphological changes were present in the depth range comparable to that of the high CaF2 concentration region expected from the Raman analysis. In deeper regions where lower concentration (< 10%) but a large amount of CaF2 was still expected, the SEM images failed to distinguish between the normal and fluoridated enamel. After KOH treatment, the Raman spectra did not show evidence of the CaF2 peak and the SEM micrographs also confirmed the removal of globules. The peak position of the Raman band of the CaF2 formed by the fluoridation was identical to that of pure CaF2. However, the linewidth was 23 cm-1 (FWHM) and a factor of 2 broader than that of pure CaF2 (12 cm-1). This implies that the lattice dynamics of the CaF2 formed by fluoridation is different from of pure CaF2, and that the material formed is 'CaF2-like' or 'disordered CaF2'.

[Xerostomia-related dental caries]

The initiation and prevention of xerostomia-related dental caries were studied using an in situ model. The morphology of induced carious lesions was compared with that of natural xerostomia-related dental caries. Both natural and induced xerostomia-related dental caries showed the same patterns of decay. Using the in situ model three preventive procedures were tested: neutral F gel applied every second day or weekly, and a daily rinse with a fluoride mouthwash for a period of six weeks. Application of fluoride gel or the use of the fluoride mouthrinse resulted in significant inhibition of the demineralization process. Of the procedures evaluated fluoride gel applied every second day was the most effective in preventing the onset of xerostomia-related dental caries.

Mersilene (polyester), a new suture for penetrating keratoplasty

Mersilene (polyester monofilament) seems to be suitable for penetrating keratoplasty because it is strong, shows no degradation by ultraviolet light, is insoluble, so that it can be left in situ, and offers the possibility of regulating postoperative astigmatism by suture adjustment. In 12 patients penetrating keratoplasty was performed with the combined interrupted/running suturing technique, using eight interrupted nylon 10-0 sutures and one running Mersilene 11-0 suture. The results were compared with those of 25 patients in whom eight interrupted nylon 10-0 sutures and one running nylon 11-0 suture were used. Six months after penetrating keratoplasty, no differences could be found between the two groups in keratometric astigmatism, visual acuity or slitlamp findings. In three patients postoperative adjustment of the running Mersilene suture reduced astigmatism by 50, 90 and 100% respectively. In an animal study the behaviour of Mersilene in the cornea was evaluated by slitlamp examination, histology and electron-microscopy. The tissue response to Mersilene was minimal. Considering the resemblance to nylon in clinical findings, minimal tissue response, lack of biodegradation and possibility of regulating postoperative astigmatism by suture adjustment, Mersilene seems to be a suitable material for penetrating keratoplasty.

Secondary retention of permanent molars: an assessment of ankylosis by scanning electron and light microscopy

Secondary retention refers to the cessation of eruption of a tooth after emergence. This may be the result of pathological changes in the periodontal ligament. The aim of this study was to describe the morphological and histological aspects of the radicular surface of secondarily retained permanent molars. The roots of 12 secondarily retained molars and two control molars, were examined by means of scanning electron microscopy (SEM) and light microscopy (LM) in order to analyse the occurrence and localisation of ankylosis. With SEM it was observed that the root surface of retained molars showed local areas covered with bonelike tissue. LM of these areas showed that this tissue was bone in direct contact with the root surface (ankylosis). In 11 cases, the areas of ankylosis were observed in the bifurcation area and at the interradicular root surface. In the remaining case, ankylosis was located at the outer root surface. The results of this study endorse the assumption that focal ankylosis is an important factor in secondary retention. Treatment recommendations must be based on this fundamental principle, because orthodontic movement of ankylotic molars is not possible.

(An)aerobic bacteria found in secondary-cataract material. A SEM/TEM study

Twenty four patients, who had marked reduction of vision due to secondary-cataract developed after an ECCE, were treated by surgical cleaning of the posterior lens capsule. During this procedure globular secondary-cataract material was removed and collected for morphological examination by SEM and TEM. Fragments of various sizes and shapes, including some with a 'golf ball' structure, were seen; these closely resembled particles frequently found in cataractous lenses. In addition, in 18 patients micro-organisms were found: rod-shaped bacteria, cocci, and in 2 cases yeasts. These findings were the more remarkable because these were clinically quiet eyes with no signs of intra-ocular inflammation and cultures have been persistently negative. We imagine that these bacteria must have entered the eye during the cataract extraction and have settled there without causing an infection.

Study of the substructure of the Morgagni and Brunescens cataract with the TAO non-coating technique. Part 1: Morgagni cataract

Lens tissue from a Morgagni cataract was examined by SEM and TEM. For SEM, after prefixation with glutaraldehyde and postfixation with the tannic acid/arginine/OsO4 non-coating (TAO) technique, and for TEM, after prefixation with glutaraldehyde, postfixation with OsO4/K4Fe(CN)6 and poststaining with uranyl acetate/lead citrate. The TAO technique seems to be a particularly suitable postfixation method for the SEM investigation of cataract tissue because of the presence of the protein structures present. The cortical region showed areas of radially, instead of concentrically, arranged lens fibres, degenerated lens fibres with holes (vacuoles), broken ball and socket connections between the lens fibres, and oval or spherical structures varying in size from 0.5-20 microns, the largest resembling a golfball, arising from the cytoplasm of degenerating lens fibres. The smallest, 0.2-0.5 microns, appear to have been expelled from the furrowed lens epithelium.

Rate and mechanism of enamel demineralization in situ

In this paper, data are presented on the in situ demineralization of human enamel as a function of the demineralization period. To quantify the mineral loss parameters versus time, it is important to obtain information on the kinetics, and thus on the mechanism of dental caries. The results show that for in situ enamel demineralization, the lesion depth as well as the mineral loss parameter both vary linearly with the demineralization time. This is in contrast to in vitro lesion formation where the third power, or the square power of the lesion depth is linearly related to the demineralization time. In in situ demineralization, the rate-determining step of the demineralization process is the inhibitor-controlled dissolution process at the enamel crystallite surfaces, while the inhibitor content (F-, proteins etc.) in the lesion originating from the plaque, saliva and enamel is high. Furthermore, the study indicates that in in situ demineralization, interprismatic mineral loss is very important.

Study of the substructure of the Morgagni and Brunescens cataract with the TAO non-coating technique. Part 2: Brunescens cataract

Lens tissue from a Brunescens cataract was prepared for SEM study by prefixation with glutaraldehyde and postfixation with the tannic acid/arginine/OsO4 combination; for TEM study the material was prefixed with glutaraldehyde, postfixed with OsO4/K4Fe(CN)6 and poststained with uranyl acetate/lead citrate. At low magnification, in contrast to the Morgagni cataract, no difference could be seen between the lens fibres in the cortical and nuclear areas. Morphologically, the destruction of the ball and socket system and the development of holes and spherical structures was striking. The latter appeared to have a thin coating and, after fracture, were either empty or showed remnants of material resembling membranes. In sections of the cataractous material, larger vacuoles containing smaller spheres were indistinctly visible.

Acute irradiation effects on morphology and function of rat submandibular glands

In this study the morphologic and functional changes were compared after irradiation (single dose, 15 Gy) of rat submandibular salivary glands. Before and 1-10 days after local irradiation of the gland region, samples of submandibular saliva were collected after stimulation by pilocarpine. At the same time-points and also 3 h postirradiation submandibular glands were carefully extirpated and prepared for histocytologic examination (LM, TEM). Maximal increase of the lag phase and decrease of the flow rate were observed 3 days after irradiation, while [K+] and [Na+] increased and decreased, respectively, from days 1 and 3 after irradiation. Morphologic changes were observed from the third hour after irradiation, were maximal 3 days after irradiation and had partially recovered by day 10. Three hours and 1 day after irradiation degranulation of convoluted granulated tubes (CGT) was observed. Three days after irradiation the most striking morphologic changes in serous and mucous cells were distension of the cisternae of the RER, degeneration of mitochondria and vacuolization of the cytoplasm. Fibril-like condensations of electron dense material in the mucous granules were observed 3 h, 1 and 6 days after irradiation. Regranulation of CGT cells was observed from day 6. From this study it is concluded that changes in salivary gland function can be observed before major morphologic changes occur. Functional changes persist after the morphologic changes seem to have virtually returned to normal.

A combined scanning and transmission electronmicroscopic investigation of human (secondary) cataract material

Cataract lenses from patients of advanced age were processed for SEM by standard pre-fixation followed by treatment by the Tannin-Arginine-Osmium-tetroxide (TAO) method and critical point drying, and for TEM by standard pre-fixation followed by vibratomation, standard post-fixation, ultramicrotome sectioning and staining with uranyl acetate/lead citrate. Secondary cataract material was brought onto a Millipore filter, fixed by standard methods, dried in air and sputter-coated with Au. Both SEM and TEM images revealed degeneration processes in lensfibre material, such as swelling of the lensfibre, protrusion of the cytoplasm, fibrillation of the cell membrane, loss of the nucleus, spherical bodies of various sizes between 0.5-1.5 microns, sometimes surrounded by a (double) membrane with different contrast but without cellular evidence, and small and large vacuoles partly filled with granular material both in and at the periphery of the lensfibre-body. The secondary cataract material on the Millipore filter revealed erythrocytes and more or less spherical bodies with high contrast, measuring between 0.5-1.5 microns, often referred to as Elschnig's pearls, besides non-definable organic material. The SEM and TEM micrographs of the cataract lens material strongly suggest that the spherical bodies with sizes of approximately 0.5-1.5 micrometer and high contrast without cellular evidence, are similar to the more or less spherical bodies found in the secondary cataract material on the filter, referred to as Elschnig's pearls.

Morphological aspects of human lens capsules. A comparative LM, SEM and TEM examination

Lens capsules of patients of advanced age, obtained after extracapsular cataract surgery, were carefully prepared for a combined LM, TEM and SEM investigation, after preliminary washing and mounting onto a holder in a buffer solution. After pre-fixation with GA, samples were postfixed for LM/TEM and OsO4/K4Fe)CN)6 and stained with toluidine-blue/basic fuchsin for LM and with uranyl acetate/lead citrate for TEM; for SEM the GA-pre-fixed samples were post-fixed by the Tannin Arginine-OsO4 non-coating technique. At LM-level discrimination between healthy and degenerating cells was possible after toluidine staining. At SEM-level protrusion of the cell nucleus and fibrillation and blebbing of the cell membrane as the result of capsular degeneration could be observed with the TAO-method. At TEM-level protrusion of the cell nucleus, degeneration of the cytoplasm, ballooning of the mitochondria, the presence of microfilaments and the occurrence of vacuoles were visible as the result of capsular degeneration on cataract formation.

Cell-ingrowth in a silicone plombe. Interactions between biomaterial and scleral tissue after 8 years in situ: a SEM and TEM investigation

A male patients (42 years) who had been treated for retinal detachment by the implantation of a silicone plombe into the sclera, returned to the clinic 8 years after implantation because of inflammation of the tissue and partial protrusion from the sclera. After removal of the plombe this was processed for TEM and SEM and examination of the plombe material after 8 years in situ could be carried out in order to get information about the cell-biomaterial interface. A large proportion of the silicone pores was filled with cellular material, including macrophages, giant cells and erythrocytes thus indicating a foreign body granuloma. The external surface of the pores showed a granular osmiophilic dense amorphous layer including extracellular debris. Engulfing of silicone particles by macrophages and the evidence of long-term tissue response suggest partial biodegradation of the silicone and certainly not complete inertness as was formerly claimed.

Amount and surface structure of albumin adsorbed to solid substrata with different wettabilities in a parallel plate flow cell

In this article we studied the adsorption of serum albumin to substrata with a broad range of wettabilities from solutions with protein concentrations between 0.03 and 3.00 mg.mL-1 in a parallel-plate flow cell. Wall shear rates were varied between 20 and 2000 s-1. The amount of albumin adsorbed in a stationary state was always highest on PTFE, the most hydrophobic material employed and decreased with increasing wettability of the substrata. Increasing stationary amounts of adsorbed albumin were observed with increasing wall shear rates at the lowest protein concentration. Inverse observations were made at the highest protein concentration. Transmission electron micrographs of replicas from the albumin-coated substrata showed that proteins were mostly adsorbed in islandlike structures on the hydrophobic substrata. The tendency to form islandlike structures was shear rate- and concentration-dependent and disappeared gradually going to more hydrophilic substrata. On glass, the most hydrophilic material employed, a homogeneous, well distributed, fine knotted, reticulated structure was found. In conclusion, this study demonstrates that both the amount of adsorbed albumin as well as the surface structure of the adsorbed proteins are regulated by the substratum wettability. This observation may well account for the fact that substratum properties can be transferred by an adsorbed protein film to the interface with adhering cells or microorganisms.

The Gonioseton, a surgical treatment for chronic glaucoma

A new and simple technique for glaucoma filtering surgery is presented. It is based on the introduction of a stainless steel microspiral or gonioseton into a goniopuncture by way of an ab interno procedure, minimising surgical trauma to the filtration area. Preliminary results are presented.

Morphology of donor lens-capsule material studied by SEM

The lens capsule of a 70-year-old male donor with a cataractous lens was carefully prepared for SEM by first washing the capsule with buffer solution to remove lens-fibres and subsequently attaching it to silicon rubber. During the fixation and drying stages of the preparation procedure the capsule stayed attached to the rubber substratum. In the equatorial zone germinating cells were found with knob-shaped microvilli, closely connected to lens-fibres. Large units of pathological capsule epithelial cells were found, only slightly inter connected by a few pseudopodia. In addition, single pathological epithelial cells with pseudopodia, arranged on top of the cell in a rosette-like configuration, were found at certain locations. Both types are probably related to the original lens-cataract.

Secondary cataract material collected with a glass cannula. A SEM study

Secondary cataract material from three patients, collected with a glass cannula approx. 18, 24 and 30 months respectively after operation, was prepared for SEM examination. For the soft samples this was done by filtration through a millipore filter followed by fixation and drying. The more solid material was suspended in a fixation solution, followed by centrifuging, suspension in 70% ethanol and drying on a specimen-holder. The short residence samples (18 months) showed mainly erythrocytes, some (inflammatory) cells and degenerated lens-fibre material. Most of the more solid material, which was collected more than 20 months after operation, showed fragments of (regenerated) capsule epithelium and pieces of solid lens-fibre material with fragments of capsule epithelium attached.

Reaction of the rabbit corneal endothelium to nylon sutures. A SEM study

Nylon and stainless steel sutures separately placed deeply into rabbit corneas by splitting the stroma for a few millimeters, without closing sutures, remained in the cornea for two, four and six weeks respectively. In contrast to the stainless steel sutures an extensive tissue reaction could be observed clinically around the nylon sutures within a few days and was still present after 4-6 weeks. On the endothelial side, covering of the nylon with fibroblast cells took place very slowly, this in contrast with stainless steel. Irritation of the tissue and an oedematous appearance of the endothelium around the nylon suture was the result. At first a kind of collagen network, often mixed with inflammatory cells, was deposited on the nylon material before fibroblast cells could grow in. Covering of the stainless steel started quite soon after implantation, without preliminary deposition of collagen material. The reason for this phenomenon must be sought in the high free surface energy of the stainless steel, which attracts cells, in contrast to nylon which has a very low free surface energy.

Remineralization of human dentine in vitro

In this paper the in vitro remineralization of human dentine with 0, 0.5, 2 and 10 ppm F in the remineralization solution is presented and analyzed by microradiography. Furthermore, the remineralization data of human and bovine dentine are quantitatively compared. The main results of this paper are: (1) the efficacy of human (and bovine) remineralization is about proportional to the square root of the F level in the remineralizing solution, and (2) the amount of mineral effectively deposited in the dentine is most likely controlled by the diffusion of fluoride into the tissue. This study shows furthermore that although numerical differences exist in the remineralization of human and bovine dentine, the general remineralization behaviour is quite similar. The presence of F- in the parts per million range is essential for the remineralization efficacy in vitro and also for the 'overremineralization' of the outer dentine surface.

Prosthetic microvenous grafting into the femoral vein of the rat; considerations concerning the anastomotic technique

The sequential thrombotic events which occur after implantation of microvenous prostheses prepared from a polyurethane-based material (I.D. 1 mm, length 5 mm, n = 36) into the rat femoral vein by means of the conventional end-to-end suture technique were evaluated by direct inspection and by scanning electron microscopy during the first 24 postoperative hours. Thrombus formation started at the anastomotic sites on the exposed collagenous vessel wall tissue and increased with increasing postoperative time intervals, leading to complete occlusion of the prostheses after 30 minutes of implantation. As a result of these findings, 8 more microvenous prosthetic implantations were performed with the sleeve anastomotic technique and evaluated after 24 hours. Six of these prostheses were patent with only minimal exposure of collagenous tissue at the anastomotic sites and subsequently minimal thrombus accumulation. Two prostheses left in situ and evaluated after 3 weeks were then still patent and completely endothelialised. Based upon the present study, we recommend the sleeve anastomotic technique for implanting synthetic microvenous prostheses because this technique prevents extensive exposure of collagenous vessel wall tissue at the anastomoses, thus leading to less thrombus accumulation and subsequently to a higher patency rate.

Keratoconus morphology and cell dystrophy: a SEM study

The SEM-pictures represent a keratoconus in a 59-year-old patient with a Descemet rupture, which had led to a so-called Kammerwassereinbruch, where the failure of the endothelial structure has become manifest in the epithelium. In the Descemet-rupture the onset of stromal pathology is observable, while outside the rupture severe degradation of endothelial cells is seen. This is manifested as cell-membrane perforation, loss of cell contents and oedema formation in general. On the epithelial side the pathology is expressed as cell-membrane degradation and the presence of very irregularly shaped, sometimes swollen and in other cases shrunken, epithelial cells, in particular in the areas of the surface depressions. The topographical correspondence of these pathological phenomena on the endothelial and the epithelial sides is stressed.

Lens-capsule material of human and animal origin, studied by SEM

Lens-capsule material from healthy and cataractous human lenses and from rabbits was collected with specially designed forceps. Subsequently the capsule fragments were fastened, after short pre-fixation, onto a rubber substrate with small stainless steel tacks, to prevent rolling-up of the fragments during the fixation and drying procedure for the SEM. Finally the capsule fragments were studied by SEM. Marked morphological changes, e.g., irregular swelling (like blebs) of the nuclei, formation of deep grooves at the cell borders and complete loss of epithelial cells, were found in the lens capsules obtained from certain cataractous lenses. Differences in capsule thickness were found in pathological capsule material. The imprints (attachment-lines) of the lens-fibres on the epithelial cells were often difficult to visualize.

Air-injection of the corneal stroma: a SEM study

The corneal stroma is supposed to be a homogeneous structure both from an optical and an anatomical point of view. Intrastromal injection of glutaraldehyde as a fixative causes local swelling and opacification of the corneal tissue. Local injections of small volumes of air superficially and more deeply into the corneal stroma produce similar swellings and formation of opaque areas. SEM investigation of these areas shows the existence of stromal canals, partly pre-existing, partly caused by the internal 'explosions' due to the air-injection. This suggests an anatomically non-homogeneous, although optically homogeneous, cornea.

Comparison of the reaction of the cornea to nylon and stainless steel sutures: an animal study

In 11 rabbits a comparison was made between the reactions of the cornea to nylon and to stainless steel sutures, macroscopically and by means of scanning electron-microscopy (SEM). Macroscopically, the wounds sutured with steel thread showed much less reaction than the wounds sutured with nylon. Vascularization was never encountered in the wounds sutured with steel thread. SEM examination also showed clear differences, which became noticeable within a short time. Both on the suture and round the opening in the cornea extensive deposits of material are seen within a short time (1 week) in the case of nylon, in the case of stainless steel this reaction is much less marked. A few weeks later deposits also appear on the steel thread, but these have a different composition and contain no material suggestive of an inflammatory reaction.

A transmission electron microscopy study of the adsorption patterns of early developing artificial pellicles on human enamel

Adsorption patterns of pellicles formed in a flow cell system under a moderate shear rate of 21 s-1, were studied with a replica technique. Characteristic features of the bare enamel surface disappeared within seconds after exposure to reconstituted saliva, indicating the adsorption of a homogeneous film. After that, three to four distinct homogeneous films were adsorbed on top of each other within 10 s and an uneven, knotted structure developed with stalky projections on the outer surface. This heterogeneous adsorption pattern determined the structure of the pellicle surface for at least 2 h.

Dentine caries in vivo. Combined scanning electron microscopic and microradiographic investigation

Dentine subjected to an in vivo demineralization challenge by plaque looses substantial amounts of mineral and is expected to change its ultrastructure. Results are presented of a combined microradiography and scanning electron microscopy (SEM) study on in vivo demineralized human dentine. The tissue was first demineralized in vivo under plaque for 3 weeks and subsequently analyzed by microradiography and SEM. In 6 participants dentine was positioned in a full prosthesis just under M2 in such a way that the outer surface of the tissue was 1.5 mm lower than the surface of the prosthesis; plaque accumulation takes place in the recessed area. A special technique allows SEM observations (at a given distance from the outer surface) on broken thin sections of demineralized dentine with a mineral content determined by microradiography. The results show that the ultrastructure of the dentine changes during severe demineralization. The main ultrastructural features are, however, still largely intact, even if half of the mineral originally present has been lost. In dentine with a mineral content of about 25 vol%, the dentinal tubules are enlarged by about 30%. In vivo demineralized dentine looses mineral in substantial amounts both from intertubular and from peritubular regions.

Remineralization of bovine dentine in vitro. The influence of the F content in solution on mineral distribution

In this paper remineralization of bovine dentine is reported. After demineralization of the dentine in an acidic gel system creating lesions of about 180 microns depth, the tissue was remineralized in a 1.5 mM Ca and 0.9 mM phosphate containing solution at pH 7 and 37 degrees C for 8 or 21 days. The F content in the remineralization solution was 0.02, 2, or 10 ppm as NaF. Samples were analyzed by means of microradiography and scanning electron microscopy. The results show that remineralization (without F added in solution) causes a decrease in mineral loss and in lesion depth. With 2 or 10 ppm in solution, however, a substantial mineral accumulation in the lesion, but particularly on the original dentine surface, was observed. During 3 weeks of remineralization, mineral accumulations of 67 and 70 vol% of mineral for 2 and 10 ppm F in solution, respectively, were found near the original outer surface, with the sound dentine mineral value being 48 vol%. The combined microradiography and scanning electron microscopy data show that the mineral accumulated is for a major part deposited on the dentine tissue and partly inside. The latter deposition occurred both inside the tubules as well as in the intertubular areas. Inside the tubules dense precipitates were observed. Because several differences exist between bovine and human dentine, an extrapolation to the human in vivo situation is speculative. The results indicate that the presence of fluoride in the parts per million range is important for dentine remineralization efficacy and that the outer surface area in dentine can be 'overremineralized'.

Glass-metal keratoprosthesis: light and electron microscopical evaluation of experimental surgery on rabbit eyes

A keratoprosthesis (KP) is the last and only surgical resort to regain some visual acuity in eyes with severely damaged corneae. Corneal blindness represents an important percentage of the blind in the economically poor countries. Commercially available KP's, e.g. those made of PMMA, which are difficult to sterilize and vulnerable to surface damage, are too expensive in these countries. To overcome these disadvantages, we developed a new KP, made of a glass core melted into a platinum cylinder with flange. They were implanted unilaterally in eyes of ten Hollander rabbits intralamellarly. They were fixated by two stainless steel traction threads passed around the whole eyeball. We investigated this type of KP in the rabbit cornea, its acceptance by stroma, epi- and endothelium, and its hydro-mechanical dynamics in situ. No signs of infection or extrusion were observed. No epithelial downgrowth, nor adverse tissue reaction could be detected. LM and SEM showed endothelialization of the newly formed stroma around the central column of the KP. We conclude that this type of KP (although optically still to be optimized) has been accepted by the rabbit cornea and a clinical trial on cornea-blind patients is justified.

Soemmering's ring, an aspect of secondary cataract: a morphological description by SEM

A Soemmering's ring attached to a patient's I.O.L. was removed and processed for SEM-examination. The enveloping structure of the Soemmering's ring was clearly of capsular origin, adherent along a single line and forming an envelope around the inner material. The envelope had a membranous character. The contents of the ring varied from the outside to the centre. Close to the capsule envelope a more or less amorphous material was found. Most of the contents of the ring was made up of lens-fibre material. Sometimes clear lens fibres were visible with densely packed lens-fibre proteins, sometimes with clusters of recrystallized proteins, rod-shaped or spherical, surrounded by what appeared to be amorphous material. The recrystallized and the amorphous lens-fibre material are similar to material found in cataractous lenses.

Stainless steel as suturing material in human- and rabbit corneas: a SEM-study

Stainless steel wire, dia. 50 microns, was used as suturing material in rabbit corneas for periods of 1.5, 3 and 7 months respectively, in order to test its inertness and acceptance by the corneal tissue. One clinical case of stainless steel wire used for fixation of an I.O.L.-implantation, after a 5-year residence in the eye, is reported as well. After 1.5 months' residence, the suture margins were well covered with tissue containing irregularly shaped endothelial cells, some fibroblastic-type cells and various kinds of collagenous fibre material. The buckled surface was partly covered with a very thin membrane of collagenous material, strands of collagenous fibres and a few fibroblastic-type cells. After 3 months' residence the buckle was almost completely covered with an endothelial cell layer. The individual cells had a somewhat irregular hexagonal shape. At a few local sites closure was still progressing, with filopodia and other collagenous matter generated by neighbouring cells on top of previously deposited Descemet's membrane. After 7 months' residence, the buckle was completely covered with normal endothelium. The fixation suture in the human case showed perfect acceptance by the corneal tissue.

Some aspects of cataract morphology: a SEM-study

Two lenses from patients of very advanced age with senile cataracts were processed for SEM, fractured equatorially, sputtered with Au and examined by SEM. In the cross-fracture various areas could be observed. Although the overall structure of the lens-fibres appeared to be intact, higher magnifications showed that the len-fibre material had changed into a brittle structure, with either a granular appearance or a fibrillar character. At other places clearly recrystallization of lens-fibre proteins had taken place, with the formation of finger-like substructures, sometimes organized into plate-like structures or running parallel to each other in a kind of undulating pattern. Between the various areas of chemically changed lens-fibre material certain 'canal-like' areas were found with cellular structures, the so-called 'waterclefts' or 'Wasserspalten'. Structures which, together with the chemical change in the lens proteins, account for the dramatic change in light dispersion.

A model to investigate xerostomia-related dental caries

The aim of this study was to develop an in vivo model in which onset, progression, and prevention of xerostomia-related dental caries can be studied. The progress of the caries process was investigated on ground and polished human enamel blocks placed in the lower denture of 7 edentulous subjects suffering from xerostomia. During a period of 6 weeks the samples were analyzed at weekly intervals by means of scanning optical monitoring, scanning longitudinal microradiography, scanning electron microscopy, and hardness measurements. Although the indentation length increased significantly within 2 weeks, no demineralization could be yet observed with scanning optical monitoring, longitudinal microradiography, and electron microscopy in most samples. Starting from the 3rd week a progressive demineralization could be observed by all methods. The mineral loss (hydroxyapatite) in the 3rd week was 0.0126 kg.m-2 (median) which increased to 0.0761 kg.m-2 after 6 weeks. Scanning electron microscopy showed a destruction which resembled that of natural xerostomia-related dental caries. From this study it may be concluded that the in vivo model developed is suitable for studying onset, progression, and prevention of xerostomia-related dental caries.

Fungal growth on soft contact lenses: a SEM-study

Three soft contact lenses of the HEMA type, discarded because of irritation of the cornea, were processed for and subsequently examined with the SEM, A large portion of the convex surface was covered with globular deposits of fungal spores. Cross-fractures of lenses showed penetration of the fungi into the matrix material of the lenses. The concave surface of the contact lenses showed at two points imprints of the epithelial cells of the cornea in the deposited material on that side of the lenses.

A morphological description of human cataractous lenses by SEM

Human cataractous lenses from patients of advanced age (101 & 85 year) were investigated by SEM. Various aspects of the cataract morphology could be observed. Even when the overall shape of the lens fibres had remained unchanged (although the typical ball and socket interconnections were barely visible) the homogeneous fibre content had changed into fibrillar and/or granular material, or the lens fibres had been (partly) hollowed out. Where there was shrinkage of the originally hexagonally-shaped lens fibres to a more or less rounded form with a wrinkled surface, the contents had changed into granular material with low density. Both granular and fibrillar material could account for a substantial increase in light scattering, resulting in a considerable decrease in vision through the lens.