Analysis of living cells grown on different titanium surfaces by time-lapse confocal microscopy

In this study we have combined fluorescence- and reflection-confocal laser scanning microscopy for the simultaneous visualization of living cells and surface topography beneath them. To this purpose we have designed a specific flow chamber and we have tested it with osteoblasts grown on an opaque, thick support, made of smooth or sandblasted titanium. Cells were loaded with Calcein-AM or tetramethylrhodamine methyl ester (TMRM), two probes employed as indicators of cell viability/morphology and mitochondrial membrane potential, respectively. Besides the acquisition of stacks of confocal sections, the system allowed also vertical views and faithful three-dimensional reconstruction of the samples. Confocal microscope implemented with our flow chamber proved to be a promising tool for time-lapse investigation of cell-biomaterial interactions.

3D analysis of SEM images of corrosion casting using adaptive stereo matching

The corrosion casting method represents one of the most widely used technique to study the 3D microvascularization of many tissues, both in their normal and pathological conditions. For a long time this technique was used only to perform a qualitative evaluation of the images obtained by scanning electron microscopy (SEM). A quantitative evaluation of vascular parameters (e.g., interbranching and intervascular distances, angle measurements, lengths and diameters) was lacking, mainly because of the difficulties found in the measurement performed on 2D SEM images. Then, some authors reported a quantitative method based on the analyses of stereo-pair images that allowed precise morphometric measurements. To visualize the specimens in 3D, it was necessary to use red-green glasses. In this article we describe a new approach by which we can automatically obtain a 3D reconstruction of vascular cast specimen's surface directly from stereo-images. Moreover, we developed a software that performed micrometric measurements on the 3D construct generated from the stereo-pictures. In conclusion, implementing together these two softwares and applying them to corrosion casting samples made it possible to render in 3D the surface of corrosion cast as well as make quantitative measurements on the corrosion casts.

Plexiform vascular structures in the human digital dermal layer: A SEM – corrosion casting morphological study

This study aimed to describe the impressive diversity of vascular plexiform structures of the hypodermal layer of human skin. We chose the human body site with the highest concentration of dermal corpuscles, the human digit, and processed it with the corrosion casting technique and scanning electron microscopy analysis (SEM). This approach proved to be the best tool to study these microvascular architectures, free from any interference by surrounding tissues. We took high-definition pictures of the vascular network of sweat glands, thermoreceptorial and tactile corpuscles, the vessels constituting the glomic bodies and those feeding the hair follicles. We observed that the three-dimensional disposition of these vessels strictly depends on the shape of the corpuscles supplied. We could see the tubular vascularization of the excretory duct of sweat glands and the ovoid one feeding their bodies, sometimes made up of two lobes. In some cases, knowledge of these morphological data regarding the normal disposition in space and intrinsic vascularization structure of the dermal corpuscles can help to explain many of the physiopathological changes occurring during chronic microangiopathic diseases.

In situ hybridization by scanning electron microscopy for painting, centromeric, and YAC localization

The hybridization site of a DNA probe was detected using a scanning electron microscope (SEM), modifying the standard in situ hybridization (ISH) method. The experiments were performed on human metaphases obtained from lymphocyte cultures of human peripheral blood. The libraries and probes used were: 1-chromosome library for the painting of chromosome 1 (wcp 1), an alphoid centromere-specific probe of chromosome 8 (pZ8.4), and the yeast artificial chromosome (YAC) 964-C10 mapped at band p13 on chromosome 12. These probes were labeled by nick translation with biotin and displayed with a gold-conjugated anti biotin goat antibody. The gold signal was amplified by silver enhancement. The chromatides appeared as packages of thin filaments 120 nm high; some of them collapsed, probably due to ISH procedures. All the probes were clearly detected as small gold particles grouped on the surface of the target chromosomes and chromosome sites. Thus, this procedure is useful to clarify the positional relationship between the chromatin filaments and the probe.

Microvascularization of the human digit as studied by corrosion casting

The aim of this study was to describe microcirculation in the human digit, focusing on the vascular patterns of its cutaneous and subcutaneous areas. We injected a functional supranumerary human thumb (Wassel type IV) with a low-viscosity acrylic resin through its digital artery. The tissues around the vessels were then digested in hot alkali and the resulting casts treated for scanning electron microscopy. We concentrated on six different areas: the palmar and dorsal side of the skin, the eponychium, the perionychium, the nail bed and the nail root. On the palmar side, many vascular villi were evident: these capillaries followed the arrangement of the fingerprint lines, whereas on the dorsal side they were scattered irregularly inside the dermal papillae. In the hypodermal layer of the palmar area, vascular supports of sweat glands and many arteriovenous anastomoses were visible, along with glomerular-shaped vessels involved in thermic regulation and tactile function. In the eponychium and perionychium, the vascular villi followed the direction of nail growth. In the face of the eponychium in contact with the nail, a wide-mesh net of capillaries was evident. In the nail bed, the vessels were arranged in many longitudinal trabeculae parallel to the major axis of the digit. In the root of the nail, we found many columnar vessels characterized by multiple angiogenic buttons on their surface.

The 3D structure of the human urinary bladder mucosa: a scanning electron microscopy study

We performed a scanning electron microscopy study on the human urinary bladder tunica mucosa. Specimens from bladder biopsies were treated with OsO4 maceration and 1N NaOH maceration methods prior to SEM observation to disclose the three-dimensional organization of the lamina propria, basal lamina and urothelium. The lamina propria housed a well developed capillary plexus just below the basal lamina; the urothelium presented a typical three-layered organization with basal, intermediate and superficial cells. The intermediate cells appeared essentially similar to basal cells in their external features and stretched from the basal lamina up to the superficial layer. The most superficial cells appeared consistently flattened and interconnected by extensive junctional complexes. They showed a peculiar specialization, their apical plasmalemma being thickened with distinctive, stiff plaques, in contrast with the underlying globular or spindle-shaped cells whose plasmalemma was only covered by short microvillosities.

The microvasculature of the lateral choroid plexus in the rat: a scanning electron microscopy study of vascular corrosion casts

The three-dimensional microvascular structure of many organs can be adequately investigated only using the corrosion casting technique. We applied this method, consisting of an injection of low viscosity acrylic resin through the major vessels and the subsequent digestion of the organic component with strong alkali or acids, to the choroid plexus of the lateral ventricles in the rat, focusing on its structural vascular features. This approach allowed a qualitative morphological description of the choroid plexus of the lateral ventricles, revealing several aspects of their capillary architecture as well as the morphological details underlying its main functional activity, essential to cerebrospinal fluid turnover. Observation of the casts with scanning electron microscopy gave a detailed picture of the choroid plexus of the lateral ventricles of the rat and enabled us to distinguish four different regions, depending on the site that the lateral ventricles occupied: the anterior olfactory region, the main central region, the longer branch and the inferior horn. Each region mostly consisted of spiral capillaries and had specific characteristics. At high magnification, the casts revealed distinctive vascular specializations, such as numerous bulges regularly placed on the capillaries. This morphological investigation underpins a better comprehension of the pathological mechanisms involving the choroid plexus in the lateral ventricles.

Detachment of titanium and fluorohydroxyapatite particles in unloaded endosseous implants

The shape, surface composition and morphology of orthopaedic and endosseous dental titanium implants are key factors to achieve post-surgical and long-term mechanical stability and enhance implant osteointegration. In this study a comparison was made between 12 titanium screws, plasma-spray-coated with titanium powders (TPS), and 12 screws with an additional coating of fluorohydroxyapatite (FHA-Ti). Screws were implanted in the femoral and tibial diaphyses of two mongrel sheep and removed with peri-implant tissues 12 weeks after surgery. The vibrational spectroscopic, ultrastructural and morphological analyses showed good osteointegration for both types of implants in host cortical bone. The portion of the FHA-Ti implants in contact with the medullary canal showed a wider area of newly formed peri-implant bone than that of the TPS implants. Morphological and EDAX analyses demonstrated the presence of small titanium debris in the bone medullary spaces near the TPS surface, presumably due to the friction between the host bone and the implant during insertion. Few traces of titanium were detected around FHA-Ti implants, even if smaller FHA debris were present. The present findings suggest that the FHA coating may act as a barrier against the detachment of titanium debris stored in the medullary spaces near the implant surface.

Hierarchical structures in fibrillar collagens

The collagen family includes several large transcripts, usually exceeding 1000 amino acid residues per single chain. As a group, they make up 1/3 of all the protein of the body and are responsible for modelling the framework of connective tissues; individually, they show both a wide variety and a complex hierarchy of mutual interactions, and form a range of functional aggregates including a variety of fibrils, microfibrils and basal membranes. Of the collagens, the fibril-forming types (i.e. the types I, II III, V and XI) are the most abundant and the most extensively studied. At the primary structure level, the amino acid sequence of all collagens is now known in detail and it shows a distinctive domain organization, its composition being dominated by the amino acid glycine (roughly 1/3 of all residues) and by post-translational hydroxylation of proline and lysine residues. Collagen secondary and tertiary structure, which together give origin to a classic triple helix, were painstakingly determined in the 1950s and 1960s. In contrast with the primary, secondary and tertiary structure, the supramolecular arrangement within collagen fibres seems to be far more elusive, and none of the models so far advanced can be said to be universally accepted. Half a century of research and debate spawned numerous mutually incompatible models, most of them focussing either on a quasi-crystalline supramolecular array or on several forms of microfibrillar aggregates, while radial fibrils, epitaxial fibrils and other structural models have almost been ignored. In many cases, data gained with a single technique from a single tissue were arbitrarily given a general legitimacy, whilst other well-documented morphological evidence went virtually unnoticed by the scientific community.Moreover, in recent years there has been a growing interest in the multiple interactions of collagens with the other macromolecules of the extra-cellular matrix, as their structure and their functional role become known. It is now indisputable that collagen interacts and forms functional entities with several other macromolecules of the extracellual matrix. This paper will succinctly review some current concepts on the structural biology of collagen higher-order structures.

Electromagnetic stimulation on the bone growth using backscattered electron imaging

The events at the hydroxyapatite implant material/tissue interface following electromagnetic stimulation were studied in the rabbit. Two kinds of hydroxyapatite were used: natural (NA) and synthetic (HA) both with a grain size of <50 microm. Bone defects, artificially created in rabbit tibiae, were filled with the material examined. One group of animals was exposed immediately after surgery and every 12h thereafter to 30-min treatments with electromagnetic fields (PEMFs). A second group was used as a control (untreated). Two and 4 weeks after implantation, animals were sacrificed and bone samples processed for LM, TEM and SEM using a backscatter electron detector for the evaluation of bone growth. This study indicates that HA has more osteoconductivity than NA, and shows that PEMF-treatment results in a benefit in accelerating bone formation at early time periods.

Tapping-mode atomic force microscopy in fluid of hydrated extracellular matrix

Fragments of native, hydrated rat tail tendon were imaged by tapping-mode atomic force microscopy while immersed in fluid. The specimens were soft and sensitive to the operating parameters, and with minimal imaging pressure the collagen fibrils appeared covered by irregular blobs or by filamentous material. A slight increase in pressure caused the underlying fibril surface to appear, with an evident D-period, gap- and overlap-zones and three intraperiod ridges. Fibrils often ran parallel and in phase, implying some coupling mechanism. Longitudinal subfibrils, 8-9 nm thick, occasionally appeared. The simultaneous acquisition of the "tapping amplitude" along with the usual "height" channel clearly confirmed the presence of longitudinal subfibrils, indicative of the inner architecture of the fibril.

Different fibrillar architectures coexisting in Haversian bone

Samples of compact bone were deproteinated by heat treatment and analysed by SEM. This technique removes very effectively cells and vascular structures and brings into full view the mineralization front along the wall of the Havers canal. The present study was confined to samples of equine bone that are known to be subjected to different functional requirements. Bone subjected to high tensile stress exhibited collagen fibrils substantially aligned with the stress direction, and the vast majority of its osteons appeared made of almost parallel fibrils crossing at very narrow angles. On the contrary, bone subjected to prevalent compressive forces showed either an orthogonal alternation of collagen lamellae, or a multidirectional arrangement corresponding to the twisted plywood described by other authors. Our observations substantiate the classical concept of the osteon structure as well as the twisted plywood; they indicate that several osteon architectures coexist in the same specimen, and that the different structures have a different preferential distribution in different parts of the same bone; and suggest that the relative distribution of the osteon ultrastructure across the bone matrix is modulated by mechanical factors.

Different patterns of collagen-proteoglycan interaction: a scanning electron microscopy and atomic force microscopy study

The extracellular matrix of unfixed, unstained rat corneal stroma, visualized with high-resolution scanning electron microscopy and atomic force microscopy after minimal preliminary treatment, appears composed of straight, parallel, uniform collagen fibrils regularly spaced by a three-dimensional, irregular network of thin, delicate proteoglycan filaments. Rat tail tendon, observed under identical conditions, appears instead made of heterogeneous, closely packed fibrils interwoven with orthogonal proteoglycan filaments. Pre-treatment with cupromeronic blue just thickens the filaments without affecting their spatial layout. Digestion with chondroitinase ABC rids the tendon matrix of all its interconnecting filaments while the corneal stroma architecture remains virtually unaffected, its fibrils always being separated by an evident interfibrillar spacing which is never observed in tendon. Our observations indicate that matrix proteoglycans are responsible for both the highly regular interfibrillar spacing which is distinctive of corneal stroma, and the strong interfibrillar binding observed in tendon. These opposite interaction patterns appear to be distinctive of different proteoglycan species. The molecular details of proteoglycan interactions are still incompletely understood and are the subject of ongoing research.

Collagen structure and functional implications

The bio-mechanical requirements to which the connective tissue is subjected suggest that a causal correlation exist between the substructure and the collagen fibril function. We discuss the relationship between the inner structure of collagen fibrils, their diameter, their spatial layout and the functional requirements they have to withstand, and suggest that collagen fibrils may belong to two different forms indicated as "T-type" and "C-type". The first class, consisting of large, heterogeneous fibrils, parallely tightly packed, subjected to tensile stress along their axis is found in highly tensile structures such as tendons, ligaments and bone. The other class, consisting of small, homogeneous fibrils, helically arranged, resisting multidirectional stresses, is mostly present within highly compliant tissues such as blood vessel walls, skin and nerve sheaths. What causes these architectures to appear is discussed in detail in this review.

Contemporaneous anatomic collections and scientific papers from the 19th century school of anatomy of Bologna: preliminary report

Recently, a strict relationship was demonstrated between scientific pathology reports of the 19th century and a large number of specimens from the museum of pathology 'Cesare Taruffi' of Bologna. Such an experience suggested verifying whether a similar relationship exists between the 19th-century collections of the museum of anatomy and the contemporaneous anatomic scientific literature. The purpose of this preliminary report is to illustrate the first documented samples recovered in Bologna in order to promote such an inventory of old anatomic and pathologic specimens in other museums.

A histological and electron-microscopic study of the architecture and ultrastructure of human periodontal tissues

The structure of periodontal tissues is still far less understood than their clinical relevance would demand. Here the periodontal ligament and radicular cementum in healthy human teeth were studied by light microscopy, transmission and scanning electron microscopy. These observations showed that the extracellular matrix of periodontal ligament is composed of a loose plexus of wavy collagen fibrils immersed in a highly hydrated interfibrillar matrix. Only close to their cemental insertion do these fibrils gather in thick, parallel fascicles (Sharpey's fibres). As these cross the mineralization front, they become infiltrated by the mineral phase and continue directly with the cementum matrix. Sharpey's fibres, "extrinsic" and "intrinsic" fibres all appear to be the same fibres, which bend and branch repeatedly during their course within the thickness of the cementum. Because of its physical continuity with the cementum, a limited portion of the periodontal ligament approximately corresponding to the length of Sharpey's fibres remains unaffected by enzymatic digestion of the interfibrillar matrix while the rest of the ligament is completely dissolved. The findings here indicate that the periodontal ligament and dental cementum join by a continuity rather than a contiguity of structures; that the collagen-mineral relation in cementum has distinctive features in comparison to other hard tissues; that extrinsic and intrinsic fibres of cementum and the adjoining portion of periodontal ligament form a structural, mechanical and metabolic unit distinct from the central, more metabolically active portion of the periodontal ligament.

Peri-implant medullary cisternae at the interface of bone-smooth surface titanium endosseous implant

A histological and ultrastructural study was carried out on the spongy bone response to smooth titanium oral implant surfaces. The samples obtained both from monkeys and from patients at various times from the implant insertion revealed that the bone-implant integration developed through different morphological aspects. The implant surface appeared in contact with medullary lacunae, as well as with osteoid tissue or directly with bone matrix. The complementary ultrastructural techniques employed have shown that the medullary lacunae appeared as wide and flattened cisternae delimited by a continuous single layer of flattened cells forming a thin lamina adhering to the implant and an endosteal lamina facing the bone surface. For their position and flattened shape we named them peri-implant medullary cisternae. The presence of blood vessels, reticular cells and myeloid cells in their lumen suggested that these peri-implant medullary cisternae were functional sites of new bone formation.

Intertwined Sharpey fibers in human acellular cementum

We had carried out a detailed morphological study on the human acellular extrinsic fiber cementum (AEFC) in order to support the exclusively extrinsic origin of matrix collagen bundles. Mesial and distal cervical third of fresh premolars from young individuals were examined. Semi-thin and thin section clearly show the Sharpey fibres entering in the cementum at right-angle to the root surface and coursing throughout the cementum to the cemento-dentinal junction. On their way to the dentin the Sharpey fibres divide into smaller bundles which, coursing obliquely or tangentially, intersect with others deriving from neighbouring Sharpey fibres. Both de-proteinated and decalcified samples observed at SEM present Sharpey fibres along the fractured surfaces entering and running trough the cementum perpendicularly to the root surface. Fibril bundles are seen branching out from the main body of a single Sharpey fibre and coursing obliquely or perpendicularly to the original fibre. These morphological evidences obtained both at TEM and SEM further confirm that in AEFC fibril bundles running parallel or obliquely to the root surface are branches of Sharpey fibres and not intrinsic cementum fibres.

How to defuse compliance time bombs. Part 2: Six hypothetical allegations. Panel discussion

In the second and final part of this series, a panel of legal experts discusses more hypothetical allegations against a fictional laboratory, including billing for additional indices, using expired reagents, and falsifying the results of employee competency tests. Learn how to handle these dilemmas before they explode into full-blown legal violations.

Structural and functional macrophages alterations by ceramics of different composition

Biomaterials may initiate several and complex biological reactions in host tissues, and the cell-biomaterial interactions can determine the release of mediators including monocytes and lymphocytes chemotactic factors. The present work was aimed to investigate in vitro the macrophage biological reactions of a natural apatite obtained by heat treatment at 400 degrees C of bovine bone, compared to other ceramics usually used for dental and orthopedic applications, using synthetic apatite and three types of alumina as controls. Particles chemotactic activity and powders oxidative burst evidenced no monocyte macrophages sensitivity reaction for natural and synthetic hydroxyapatite powders at great granulometry (> 50 microm); data were confirmed by ultrastructural observations; electron microscopy analysis showed macrophages with the features of healthy cells in the presence of both natural and synthetic apatites while macrophages grown in the presence of alumina seemed to be negatively affected. In conclusion, among all ceramics tested, natural apatite displayed a good compatibility with living cells, being better tolerated than synthetic hydroxyapatite which in turn is better tolerated than alumina.

Direct visualization of collagen-bound proteoglycans by tapping-mode atomic force microscopy

Most studies on the interaction of collagen with proteoglycans, two universal components of connective tissues, use technical approaches which substantially modify the shape and size of the proteoglycans themselves. In the present study unfixed, untreated collagen fibrils from rat tail tendon were dehydrated and observed by tapping-mode atomic force microscopy. The surface of collagen fibrils immediately reveals a periodic alternation of gap and overlap zones. A thin, transverse ridge decorates the gap zone, while other filamentous structures run on the fibril surface, either parallel or perpendicular to the fibril axis. These surface structures are much enhanced by Cupromeronic Blue preincubation, while pretreatment with chondroitinase ABC removes them completely, leaving barely detectable transverse ridges. The ridge and filaments are likely to represent, respectively, the core protein and the glycosaminoglycan side chains of proteoglycans, displayed with a far better resolution than with conventional histochemical or immunohistochemical techniques. Our data suggest that proteoglycan molecules are capable of different, multiple interactions with the collagen fibril surface as well as with each other.

Age-related changes in human anterior cruciate ligament (ACL) collagen fibrils

The correlation between anterior cruciate ligament (ACL) collagen fibril diameter and aging were studied in subjects aged 15 to 87 years. The samples processed for light and electron microscopy showed statistically significant differences in collagen fibril diameter among young (< 20 years), adult (20-60) and elderly subjects (> 60 years). In the young, the ACL was made up of collagen fibrils which were highly variable in size (range 20-180 nm); the diameter distribution curve was very asymmetrical (mean asymmetry +0.895). In adults and elderly subjects, the maximum diameter had decreased remarkably (120 and 110 nm, respectively) and the diameter distribution curve had become less asymmetrical (mean asymmetry +0.527 and +0.297 respectively). Fibril concentration increased considerably from young (68 fib/mu 2) and elderly subjects (140 fib/mu 2). This reduction in diameter and the relative change in collagen fibril concentration may be related to changes in elastic stiffness. The increase in small collagen fibrils and the marked rise in their concentration may make the ligament more pliable. These findings are similar to those we obtained in Achilles tendon. They demonstrate that both ACL and Achilles tendon, a tissue which responds to unidirectional mechanical forces more than ACL does, show a reduction in diameter value during ageing. These data further suggest that collagen fibril diameter is related to the aging process.

Collagen fibril surface: TMAFM, FEG-SEM and freeze-etching observations

Native, unfixed collagen fibrils from rat tail tendon were dehydrated following different procedures and observed under a FEG-SEM and an AFM operated in Tapping Mode (TMAFM). Freeze-etched, untreated fibrils from the same tissue were also observed for comparison. The most notable features of the fibril surface, i.e., the gap/overlap alternation and three prominent intraperiod ridges, were simultaneously visible only in freeze-etched specimens, while under the SEM and the TMAFM their appearance was dependent on both the dehydration procedure and the visualization technique. The different susceptibility of the collagen fibril surface structures to various treatments clearly implies the existence of domains of different composition. Moreover, identical specimens were imaged differently by SEM and TMAFM, highlighting instrument-specific advantages and limitations. The onset of dehydration-dependent, procedure-specific artifacts should be considered in high-resolution studies of connective tissues. As for any biological specimen, the final aspect of collagen fibrils is determined no less by the preliminary treatments than by the visualization approach.

Structure and ultrastructure of the bone/ligament junction

The tibial insertion of the patellar ligament of rat was investigated at light microscopy, scanning electron microscopy and transmission electron microscopy. Until the point of insertion, the patellar ligament showed the typical structure of a tendon. In proximity to the insertion, the ligament increased in diameter and was gradually infiltrated by a different, cartilage-like matrix. Its tenocytes became progressively rounded and displayed some characteristics of chondrocytes. Tendon fibres crossed this fibrocartilage and arrived well beyond the mineralization front. Finally, they appeared to interweave with the tibial diaphysis bone. These fibres were always distinct from the interposed extracellular matrix and exhibited a different pattern of mineralization from the matrix. Our observations indicate that fibrocartilage does not supersede tendon but merely infiltrates it. Thus, the tendon does not splay during articular movement and the tensile stress is redistributed across the insertion area by increasing the mechanical coupling among adjacent fibres. At the same time, this mechanism provides a structural, uninterrupted connection from tendon to bone which is consistent with the biomechanical requirements it has to withstand.

Collagen fibril patterns in compact bone: preliminary ultrastructural observations

A comparative study of the Haversian architecture was carried out on compact bone derived from the anterior and posterior edges of the diaphysis of horse radius, regions which have different mechanical requirements in vivo. Samples were heat-deproteinated prior to SEM analysis, a treatment which effectively removes cells and vascular structures as well as exposing large areas of the mineralization front along the walls of the haversian canals. Bone subject to tensile stress revealed a prevalent alignment of its collagen fibrils in the stress direction, and the vast majority of its osteons were composed of fibrils running almost parallel and crossing at very acute angles. Bone subject to compressive forces showed either an orthogonal alternation of collagen lamellae or a multidirectional arrangement corresponding to the twisted plywood pattern described by other authors. Our observations substantiate both the classical model of the osteon and the twisted plywood concept, and suggest that osteon ultrastructure is modulated according to biomechanical requirements.

Low-temperature heat-deproteinated compact bone to heal large bone defects

The potential of low-temperature (400 degrees C), heat-treated bone matrix in osteorepair has been evaluated in vivo by implantation into defects artificially created in rodent tibia. Histological and ultrastructural analysis of the bone--implant interface has been carried out on samples obtained at 1 to 6 weeks from operation. The obtained data showed that calcined bone is well tolerated and does not cause acute or chronic inflammatory reactions. Osteoid tissue, tightly adhered to the implant, appears within 2 weeks of the operation, while after 6 weeks newly formed bone surrounds and infiltrates the implant. Of greater note, the detection of good adhesion between bone and implant ultrastructurally is demonstrated by the absence of fibrillar connective tissue at the interface. For these reasons, our preliminary observations suggest that low-temperature calcined bone (biological apatite or heat-deproteinated bone) may have a rightful place among the osteointegrators.

Ultrastructure of heat-deproteinated compact bone

Heat-deproteinated bone (calcined bone) is a natural candidate for an osteoreproductive biomaterial. Ultrastructural investigation has pointed out an important aspect of the preparation technique. Treatment of bone at temperatures exceeding 500 degrees C causes complete disruption of the tissue architecture and the reorganization of the mineral phase into tightly packed, dense crystals. At 500 degrees C or less the structure and distribution of the mineral phase remain unaffected, so that cross-banded 'shadows' of collagen fibrils are still readily observable, although collagen is no longer present in the samples. By its excellent structural preservation and natural porosity, low-temperature calcined bone seems to be a promising alternative for osteoreproduction.

Correlations between amino acid hydrophobicity scales and stain exclusion capacity of type 1 collagen fibrils

The relationship between the negative staining band pattern of type 1 native collagen fibrils and the amino acid distribution along the fibril axis was studied by comparing averaged microdensitograms with theoretical traces calculated on the basis of different amino acid parameters. As well as the spatial parameter "bulkiness" (volume/length, ratio), various literature-reported scales of "hydrophobicity" were tested. Two "hydrophobicity" sets allowed a better fit with the actual patterns than "bulkiness" values. However, a general improvement in simulations was achieved by associating most "hydrophobicity" sets with the "bulkiness" set. These results suggest that amino acid "hydrophobicity" plays a key role in the appearance of negative staining patterns but a composite mechanism would seem to occur: the accessibility of available intermolecular interstices may be conditioned by molecular hindrance, corresponding to amino acid "bulkiness" as well as by water-repulsion effect, which correlates with amino acid "hydrophobicity." Moreover, a detailed comparison of actual and simulated patterns suggests that a modulation exists in the effectiveness of these two factors along each D-period according to the different molecular packing and concentration of hydrophobic amino acid clusters within overlap regions and gap regions, respectively.

Ultrastructure of the extracellular matrix of bovine dura mater, optic nerve sheath and sclera

The sclera, the outermost sheath of the optic nerve and the dura mater have been investigated histologically and ultrastructurally. Although these tissues appear very similar under the light microscope, being dense connective tissues mainly composed of collagen bundles and a limited amount of cells and elastic fibres, they exhibit subtle differences on electron microscopy. In the dura and sclera collagen appears in the form of large, nonuniform fibrils, similar to those commonly found in tendons, while in the optic nerve sheath the fibrils appear smaller and uniform, similar to those commonly observed in reticular tissues, vessel walls and skin. Freeze-fracture also reveals these fibrils to have different subfibrillar architectures, straight or helical, which correspond to 2 distinct forms of collagen fibril previously described (Raspanti et al. 1989). The other extracellular matrix components also vary with the particular collagen fibril structure. Despite their common embryological derivation, the dura mater, optic nerve sheath and sclera exhibit diversification of their extracellular matrix consistent with the mechanical loads to which these tissues are subjected. Our observations indicate that the outermost sheath of the optic nerve resembles the epineurium of peripheral nerves rather than the dura to which it is commonly likened.

Particular structure of the anterior third of the human true vocal cord

The histological aspects of the true vocal cord mucosa change in the anterior third compared with the posterior two thirds. The anterior third is characterized by an epithelium where the ridges, marked in the posterior two thirds, are very slight or even absent. The underlying basement membrane, which is thin in the posterior two thirds, here appears particularly thick. At the ultrastructural level in this area, beneath a normally thickened basal lamina, a thick layer of finely granulated electron-dense material, interspersed with thin and randomly scattered collagen fibrils and proteoglycan filaments, is detectable. Beneath this thickened basement membrane, a layer of small undulated collagen fibril bundles with very numerous interspersed oxytalan fibres is found. The collagen fibrils, small in diameter (30-40 nm), seem to continue with the collagen fibrils of the basement membrane. In this layer numerous blood vessels with a very thick, delaminated basement membrane are also observed. The underlying area is characterized by the vocal cord ligament, composed by large compact collagen fibril bundles with interspersed elastic fibres. The particular features of the thick basement membrane, the thick-walled and delaminated vessels and the modular distribution of the elastic system together may well form the basic structure enabling the functional integration of the vocal ligament into the overlying mucosa and the underlying vocal muscle.

Ultrastructure of the bovine nuchal ligament

Nuchal ligament is composed almost exclusively of elastic fibres and collagen fibrils, interwoven very closely and lying parallel to the main ligament axis. Elastic fibres are very large, straight and roughly cylindrical; the collagenous matrix consists of septa of diminishing size forming a 3-dimensional matrix that envelops fibre bundles as well as individual elastic fibres. In all areas examined, collagen fibrils are of very uniform size and, on replicas, they reveal a spiral subfibrillar arrangement with an inclination angle of 17 degrees. Collagen fibrils appear to adhere to the elastic fibres very closely, conforming to their irregular shape. Sometimes they impinge directly upon the elastic fibres, while in other cases a space is visible between collagen fibrils and elastic fibres that contains a rich fabric of intermediate filaments. The collagen-elastin complex of the ligamentum nuchae may be considered a fibre-reinforced composite material comprising tough fibres immersed in an amorphous elastic matrix. Its mechanical behaviour is the result of the combined properties of its components and their interactions.

Connective tissues in the optic nerve and in peripheral nerves: ultrastructural observations

The connective tissues of the bovine optic nerve and left recurrent nerve have been investigated at the ultrastructure level by TEM and freeze-fracture. The outermost of three concentric sheaths enveloping the nerve appear very similar; the intermediate sheaths appear different enough to suggest different functionalities, while the innermost sheaths are completely dissimilar. The ultrastructural aspects of the extracellular matrix suggest that all the connective tissues may mainly play a passive role as a packing material for the nerve fibers, while none of the sheaths seems apt to withstand mechanical stresses.

Human Achilles tendon: morphological and morphometric variations as a function of age

Aging of human Achilles tendon results in changes in both cellular and fibrous components. Cells flatten and become less numerous. Their thin and long cytoplasmatic projections tend to shorten and diminish in number. Tendon fibers lose their typical undulating appearance and become quite straight. Collagen fibril diameter, small and uniform in the neonatal period, becomes large and extremely variable from adolescence onwards. Age related morphometric changes include a decrease in the average, maximum diameter and density of collagen fibrils and an increase of fibril concentration. In our opinion these morphological and morphometric variations are strictly related to functional requirements.

Subfibrillar architecture and functional properties of collagen: a comparative study in rat tendons

Collagen fibrils from different rat tendons have been investigated by freeze-fracture and transmission electron microscopy. In all cases, marked differences in both fibril morphology and subfibrillar organisation have been consistently found between the tendon core (composed of large and heterogeneous fibrils comprising tightly-packed, straight, parallel molecules) and sheath (showing small, uniform collagen fibrils with a helical arrangement of the molecules). The bio-mechanical requirements to which these tissues are subjected suggest, as do previous observations on other tissues, that a causal correlation exists between substructure and collagen fibril function.

Different architectures of the collagen fibril: morphological aspects and functional implications

Several tissues known to contain collagen fibrils with a 'helical' arrangement were studied by t.e.m. and freeze-fracture. In all the tissues examined, the diameter of the collagen fibrils appeared to be tissue-specific and fairly constant within the same tissue. No statistical differences, on the contrary, were detectable in the coiling angle which appeared similar in all the tissues and independent of both diameter and age of the fibril. Rat tail tendon was also examined under the same technical conditions and showed collagen fibrils of large and very heterogeneous diameter and with a consistent 'straight' arrangement. These data seem to suggest that the 'helical' and 'straight' arrangements may actually identify different types of collagen fibrils. The authors discuss the possible functional significance of these arrangements and present two hypotheses on the three-dimensional structure of the 'helical' fibril.

[Class V cavities for composites. New preparation principles]

The aim of this study is to establish with the help of a computer a new type of Class V cavity that would ensure minimal marginal gap of restoration work using restorative resins. Comparison of computer graphics has shown that the ideal Class V cavity for restorative resins is cone-like with the apex or smaller base pointing towards the pulp and the walls slightly convex towards the free surface of the cavity. To prepare this sort of cavity new specular-type burrs are required.

Collagen fibril surface structures: freeze-etching data and computer modelling

In order to investigate the correlation between primary structure and surface profile of collagen, freeze-fractured and deep-etched (dehydrated) collagen fibrils have been compared with a fibril model built directly from the amino acid sequence. The model appeared to be almost identical to the freeze-etched collagen fibril with respect to the most relevant features, such as the gap-overlap ratio and the location of the two main intraperiod ridges (X3 and X2). However, it did not show the minor ridges observed in the gap zone (X1 and Y1), thus suggesting that these structures, although consistently present in collagen fibrils, may in fact be due to post-translational modifications or to non-collagenic material adhering to the fibril.

Ultrastructural aspects of freeze-fractured and etched elastin

The ultrastructural organization of fresh and purified elastin from beef ligamentum nuchae was studied by means of the freeze-etching technique. Both fresh and purified elastin showed a regular three-dimensional network of filaments which seemed to be composed of a sequence of globular subunities. There were also areas, along the regular network, in which ridges of various lengths, packed with perpendicular side filaments, were visible. In replicas of deep-etched and rotary-shadowed specimens, a thicker and more defined three-dimensional network was observable. A great variability in appearance among the globular subunits of the filaments was noticed which was at least partially due to the etching treatment. By means of computerized simulation of replicas of various hypothetically collapsed globular structures, we obtained patterns which were superimposable on those obtained in the replicas of the specimens analyzed. It is thus assumed that each globular subunit of the filament, being subjected to collapsing, has a less dense central core.

[Distribution of proteoglycans in the sclera]

The Authors have studied, with histochemical methods, the manner of proteoglycans distribution in superficial and deep layers of the sclera, which are characterized by structural differences regarding collagen. The pictures, on one hand, are in agreement with biochemical data which indicate the presence of dermatan-sulfate, chondroitin-sulfate and hyaluronic acid, on the other hand, show a marked glycosaminoglycans distribution in the deep layers and a lessening of their distribution relative to the superficiality of the layers. Furthermore alcianophilic particles are visualized at the electron microscope. In the superficial layers such particles are in direct relation, often periodically, with the collagen fibrils, while in the deep layers particles without this direct relationship are also observable. The Authors point out a topographic coincidence between variations regarding the proteoglycans distribution and variations regarding collagen. Moreover, the obtained pictures suggest the existence of a particular proteoglycans-collagen interaction corresponding to the deep layers where fibrillogenesis occurs.

[Ultrastructure of collagen fibers in the sclera]

The Authors have studied the microfibrillar packing of the scleral collagen fibrils on thin sections of samples treated with a dissociant agent and on replicas of freeze-fractured fibrils. The only difference in observing the fibrils between the external and internal layers is relative to the diameter, evidencing in general, lower dimensions in the latter. The microfibrillar packing is characterized by a lightly spiralized or wavy running of filamentous subunits and the same is evident in fibrils of different diameter. The ultrastructural pictures are similar to those obtained in the other tissues, such as tendons, fibrous cartilages, fibrous capsules of parenchymatous organs and ligaments, in which the collagen is predominantly type I, like in the sclera.