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Biomedical subjects

A Ascenzi

Publications and source records attributed to A Ascenzi.

At least 37 records · Page 2Linked to original sources
PubMed1985

A low-angle X-ray diffraction analysis of osteonic inorganic phase using synchrotron radiation.

Using synchrotron radiation the low-angle X-ray diffraction method has been applied to single osteon samples to yield new data on the texture of the inorganic bone fraction. Two sample types--cylindrically shaped osteonic samples and osteonic radial hemisections--were prepared from longitudinal and alternate osteons at both the initial and final stages of calcification. The results indicate that the diffraction pattern is due to the inorganic phase, which reveals the same axial periodicity as native collagen fibrils and fits into the main band. No change is appreciable as osteons pass from the initial to the final stage of calcification. This means that when crystallites covering much more than a collagen axial period are observed under the electron microscope, they do not appreciably affect the calcified banding of collagen fibrils. The osteonic axis corresponds to the main direction of collagen orientation both in longitudinal and alternate osteons. The degree of orientation, however, is lower in alternate osteons than in longitudinal ones, where only few thin, incomplete transversal lamellae are found.

Adult↗
PubMed1985

Mechanical hysteresis loops from single osteons: technical devices and preliminary results.

The purpose of this paper is to describe an original apparatus for recording hysteresis loops from single osteons and a special microgrinding lathe for preparing osteonic samples for testing. The results obtained by testing isolated osteons, and composite bone samples ground to the same size as an osteon sample justify one to draw the following main conclusions: at an equal degree of calcification, longitudinal osteons show larger hysteresis loops under compression and alternate osteons show larger hysteresis loops under tension; there seems to be little chance of acquiring detailed information on the mechanical effects of osteon calcification recording hysteresis loops; collagen orientation in lamellae is the main factor determining the kind of hysteresis loops displayed by a composite bone sample.

Adolescent↗
PubMed1985

Immunological detection of hemoglobin in bones of ancient Roman times and of Iron and Eneolithic Ages.

Using an immunological method (immunoblot), we have established that hemoglobin (or hemoglobin fragments) can be quantitatively determined in old and ancient bones, some of them dating back 4500 years. It is shown that the total recovery decreases with time, but it is still effective in the older specimens. Thus, the immunological assay may prove useful to solve problems relevant to paleontology and paleopathology.

Antibodies, Anti-Idiotypic↗
PubMed1984

Collagen orientation in compact bone: I. A new method for the determination of the proportion of collagen parallel to the plane of compact bone sections.

Previous work has shown that different types of osteons that have different mechanical properties with regard to tension and compression can be identified and studied by polarized light microscopy. This study reports the development of an automated method for the analysis of that proportion of collagen in transverse sections of human femurs that lies parallel with the plane of section. The method is based upon the use of circularly polarized light to detect collagen with a major component lying in the plane of the section, correcting the measurement for bright collagen under these circumstances with a corresponding darkfield measurement to determine the area of bone within each field of the section analyzed. The method has been validated in several different ways. The measured value of bright collagen under circularly polarized light depends upon the section thickness, since a linear relationship was found between section thickness and bright areas for a large number of microscopic fields. Plane parallel sections are therefore recommended for this study. The pattern of distribution of bright areas was the same for different observers and different set detection levels in any one section. The pattern found in adjacent sections from the same region of the shaft was identical.

Adult↗
PubMed1984

Collagen orientation in compact bone: II. Distribution of lamellae in the whole of the human femoral shaft with reference to its mechanical properties.

Starting from a previous personal investigation (Portigliatti Barbos et al., 1983) indicating that the distribution of osteons and interstitial bone in the middle of the femoral shaft is related to their structure, a new procedure has been devised to allow information of the same kind to be gathered from the whole of the femoral diaphysis. Twenty-three exactly plane parallel cross-sections, 100 micron thick, each located 1 cm from the next, were prepared using an annular blade microtome. The distribution of longitudinal lamellae (whose fiber bundles and crystallites have longitudinal course and withstand loading by tension) and transverse lamellae (whose fiber bundles and crystallites have a transverse course and withstand loading by compression) was determined for both osteonic and interstitial bone, using circularly polarized light as the illuminating source and a Quantimet 720 image analyzing computer. The results show that along the femoral shaft the transverse and longitudinal lamellae from osteonic and interstitial bone have a characteristic rotational distribution consistent with the distribution of the bending forces normally operative in bone.

Adult↗
PubMed1983

X-ray diffraction analysis of transversal osteonic lamellae.

When isolated osteon samples are submitted to wide-angle X-ray diffraction, it is not possible to detect any preferential orientation of the hydroxyapatite crystallites of the lamellae with transversally arranged fiber bundles. So a complete and exhaustive X-ray diffraction analysis of an osteon needs adequately prepared osteonic subunits. For the present investigation, 2 types of samples were prepared from longitudinal and alternate osteons: osteonic radial sections and isolated straightened transversal lamellae. An X-ray diffraction microcamera has been used with a rotating anode X-ray generator. In accordance with the data provided by the polarizing microscope, the orientation of crystallites runs parallel to the osteon axis in longitudinally structured osteons, whereas in alternate osteons the orientation changes by about 90 degrees in successive lamellae. Neither crystallites associated with the collagen fibrils that run alongside the osteocyte canaliculi nor those associated with the fibrils that run transversally in longitudinally structured osteons are revealed by X-ray diffraction, because there are so few of them.

Crystallization↗
PubMed1983

Distribution of osteonic and interstitial components in the human femoral shaft with reference to structure, calcification and mechanical properties.

This paper analyzes the distribution of osteons and interstitial bone in the femoral compacta according to their structure, degree of calcification and mechanical properties. Three cross sections, 100 microns thick, each located 1 cm from the next, were prepared by grinding from the middle third of a human femoral shaft. Starting from the premise that, in lamellar bone, lamellae whose fiber bundles and crystallites have a longitudinal course withstand loading by tension, whereas those whose fiber bundles and crystallites have a transversal course withstand loading by compression, each osteon and fragment of interstitial bone has been given a number recording the percentage of its surface consisting of lamellae with transversally oriented fiber bundles and crystallites (bright under the polarizing microscope). The degree of calcification of the same structures was determined micro-radiographically. The distribution of both osteons and interstitial bone was assessed using a tungsten grid for reference. The total surface of each bone microstructure, and the percentage of that surface consisting of bright lamellae, were all calculated using a Zeiss Video-plan. Our results confirm the view that the distribution of both osteons and interstitial bone is mainly related to their structure--and hence to their mechanical properties. In addition, bone remodeling seems to be most active in areas capable of supporting tensile stress.

Biomechanical Phenomena↗
PubMed1982

The tensile properties of single osteonic lamellae: technical problems and preliminary results.

An investigation on the tensile properties of osteonic lamellae whose fiber bundles have an almost transversal spiral course has been carried out, using samples obtained from alternately structured osteons by applying a procedure described in detail by Ascenzi et al. (1973). A very sensitive microwave extensometer based on cavity and pulse technique was employed in order to record the tensile curve from each lamellar sample. The inhomogeneity in thickness within, and between, single lamellae has ruled out any form of comparison between the curves recorded for ultimate tensile strength and modulus of elasticity. This result is in agreement with the morphological finding that there is usually a wide, continuous range of variation in thickness even along the length of single osteonic lamellae.

Bone and Bones↗
PubMed1980

On radiation-induced extraskeletal osteosarcoma: report of a case.

A case of extraskeletal osteogenic sarcoma arising in the soft tissues of the lower portion of the anterior abdominal wall (subumbelical region) is reported. The tumor developed in an area that had received telecobaltherapy 2 years 8 months previously (total skin dose of 9,000 rads delivered in 45 exposures over two separate periods of 106 and 141 days), after surgical treatment for a Stage I carcinoma of the uterine cervix. The clinical description and histopathology of this unusual neoplasm are presented, and the literature is reviewed.

Abdominal Neoplasms↗
PubMed1978

X-ray diffraction and electron microscope study of osteons during calcification.

To obtain information on the changes in the inorganic bone fraction during calcification, low- and wide-angle X-ray diffraction techniques and electron microscopy have been applied to single osteon samples. The samples were cylindrically shaped and their axes corresponded to the axes of the Haversian canals. The selection was made according to the degree of calcification and the orientation of collagen bundles and inorganic particles. Osteons at both the initial and final stages of calcification were chosen. Arrangements of fiber bundles and inorganic particles in successive lamellae characteristic of three types of osteon were selected, that is, longitudinally structured osteons, transversely structured osteons, and alternately structured osteons. The results indicate that in osteonic lamellar bone there are two types of inorganic particles: (1) granules arranged in linear or needle-shapred entities with maximum width 40-45 A, which are regularly distributed at the level of the main band of the collagen fibrils where their maximum length reaches the length of the main band itself; that is , about 400 A; and (2) very long crystallites, with a diameter of 40-45 A, which grow with their crystallographic c-axis parallel to the collagen fibrils and cover much more than a major collagen period.

Adolescent↗
PubMed1977

Initial studies on the crystallinity of the mineral fraction and ash content of isolated human and bovine osteons differing in their degree of calcification.

Several groups containing 10--15 isolated osteons differing in their degree of maturity were analysed. Samples were isolated from undecalcified human and bovine bone sections. The crystallinity coefficient, defined as the ratio of the number of radiation-induced paramagnetic defects in the crystalline lattice of hydroxyapatite to the total ash content, was calculated. The results were compared with measurements performed on fragments of total cortical bone, primary periosteal bone, and inner circumferential lamellar bone. The results show a higher crystallinity of fully calcified osteons as compared with that found at the initial stage of calcification. No differences in the ash content were observed between human osteons, from different stages of calcification evaluated morphologically and by X-ray absorption. These differences were evident when bovine osteons differing in their stage of calcification were compared. Human fully calcified osteons contain 60% ash and their crystallinity coefficient is 52.1. Human osteons at the initial stage of calcification contain 57% ash and their crystallinity coefficient is 40.6. The same parameters for fully calcified bovine osteons and for bovine osteons at the initial stage of calcification are 59% ash, 62.6 crystallinity coefficient and 46% ash, 43.0 crystallinity coefficient, respectively.

Adult↗