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M Raspanti

Publications and source records attributed to M Raspanti.

At least 37 records · Page 2Linked to original sources
PubMed1996

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.

Animals↗
PubMed1995

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.

Animals↗
PubMed1995

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.

Animals↗
PubMed1994

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.

Animals↗
PubMed1994

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.

Amino Acids↗
PubMed1993

Collagen-glutaraldehyde interaction as revealed by the D-banding of negatively stained fibrils and computer-drawn band patterns.

Band patterns exhibited under electron microscope by native collagen fibrils fixed with glutaraldehyde (2.5%-5% GA diluted in 0.1M phosphate buffer, pH 7.4) and negatively stained with phosphotungstic acid (1% PTA diluted in the same buffer) were digitized to form both bandings and microdensitometric traces. Collaterally, computer-drawn band patterns and traces were yielded on the basis of the "quarter stagger" model and primary structure of alpha 1(I) and alpha 2(I) tropocollagen chains and by selecting options related to specific collagen-GA interactions. Comparisons between actual and simulated patterns suggest that lysines and hydroxylysines should react with GA residues in a 1:3 ratio, while GA-reactivity of histidyl and tyrosyl residues seem to be excluded. On the other hand, an improvement of simulations was achieved by also selecting hydroxyprolines (in addition to lysines and hydroxylysines), which seemed to react with GA in a 1:1 ratio. Considering the bifunctionality of GA, it is suggested that during fixation, heteropolymers form, composed of GA-hexamers bonded to couples of lysyl and/or hydroxylysyl residues. The hypothesis is advanced of an additional formation of GA-dimers, each bonded to two hydroxyprolines.

Animals↗
PubMed1992

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.

Basement Membrane↗
PubMed1992

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.

Animals↗
PubMed1991

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.

Achilles Tendon↗
PubMed1991

Negative staining and genesis of D-periodicity in native collagen fibrils.

An investigation was carried out on the mechanism which gives rise to the banding exhibited by collagen fibrils after negative staining. The negative staining (phosphotungstic acid) band patterns of native collagen fibrils (type I), isolated from calf reticular dermis, were compared with computer-drawn band patterns. The stimulations were based on the primary structure of bovine type I collagen, the "quarter stagger" molecular packing and different conformations of telopeptides. The results suggest that in negative staining, the stain exclusion effect depends on both spatial factors and water repelling factors being the "bulkiness" (molecular volume/length ratio) as well as the hydrophobicity of the amino acids of alpha 1 (I) and alpha 2 (I) chains directly involved. No final conclusion could be drawn about the contribution of positive staining to negative staining. Improvements in the simulations were achieved when the telopeptides were shaped according to particular conformational models.

Animals↗
PubMed1991

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.

Animals↗
PubMed1990

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.

Animals↗
PubMed1989

[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.

Composite Resins↗
PubMed1989

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.

Animals↗
PubMed1989

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.

Amino Acid Sequence↗
PubMed1988

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.

Animals↗