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Biomedical subjects

A Ascenzi

Publications and source records attributed to A Ascenzi.

At least 19 recordsLinked to original sources
PubMed1998

X-ray diffraction on cyclically loaded osteons.

The results of a study on the fine structural distortion due to the two previously observed types of degradation in cyclically loaded single osteons (i.e., stiffness degradation and pinching effect) are presented. Fully calcified longitudinal and alternate osteons were isolated from 350-microns-thick longitudinal sections of human femoral cortical bone. The samples were prepared from 500-microns-long central cylindrical portions of an osteon, whose two ends were penetrating into rectangular lugs for fixation to an electromechanical device that cyclically loaded the samples. This device was connected to a microwave micrometer and a recorder. The structural distortions induced by cyclic loading were investigated by high- and low-angle X-ray diffraction on conventional and synchrotron radiation sources. Cyclic loading results in a reduction in the degree of orientation of apatite crystallites, especially in longitudinal osteons, in which the most abundant longitudinal lamellae are not protected against buckling by transverse lamellae as they are in alternate osteons. In contrast, the degree of orientation of collagen fibrils does not seem to be affected by cycling loading in the two osteon types, possibly because the disorientation of collagen fibrils is, within limits, a reversible process. Finally, the contrast between the disorientation of inorganic crystallites and the apparently unaltered distribution of collagen fibrils suggests that the degradation of cyclically loaded osteons may be due to a separation of the crystallites from the fibrils.

Adult↗
PubMed1997

Pinching in longitudinal and alternate osteons during cyclic loading.

Pinching is a degrading phenomenon which occurs during cyclic loading of certain materials. A change in the slope of the deflection curve reveals pinching lesions, either flexural cracks or bond degradation, cause pinching. This paper investigates pinching for 20 longitudinal and 18 alternate fully calcified osteonic samples of cylindrical shape and 500 micron length. Each sample was axially loaded beyond the proportional limit using an electromechanical device acting as a transducer of the variations in length of the sample into changes in the resonance frequency of a microwave micrometer. A cubic polynomial served as a mathematical model to investigate the stress-strain diagrams at the first and last cycles through the study of strain limits, stiffness and pinching behaviours, and energy absorption. The hysteretic behaviour of the two types of osteons differs and is far from ideal. The presence of pinching may derive from the existence of longitudinal fibrils, in particular the yielding of the incompletely calcified ones. In longitudinal osteons consisting mainly of longitudinal collagen fibrils, the deformation under compression is not protected by lamellae consisting of transverse fibrils, therefore the lesions inducing pinching are magnified. In contrast, in alternate osteons, where the fibrils having a longitudinal orientation are reduced and protected by lamellae containing transversely oriented fibrils, the lesions-inducing pinching are lessened.

Adult↗
PubMed1994

The torsional properties of single selected osteons.

The aim of the present investigation is to determine the mechanical behavior of single selected osteons loaded by torsion along their axis. Two osteon types were chosen: (a) fully calcified 'longitudinal' osteons, whose fibers (and, consequently, crystallites) have a marked longitudinal spiral course in successive lamellae, (b) fully calcified 'alternate' osteons, whose fibers (and, consequently, crystallites) have a marked longitudinal spiral course in one lamella, and an apparently transverse or circular course in the next. The osteon samples, which were cylindrically shaped, and whose extremities fitted into two rectangular lugs, were prepared on a microturning lathe. The principle of the specially manufactured torsional device was that of a pendulum set oscillating around a very sharp wedge so as to reduce friction to negligible levels. The results indicate that longitudinal osteons are those most resistant to torsional loading. The low resistance to torsional loading of the lamellae whose fibers apparently have an almost transversal course is discussed with reference to recent views on the microstructure of this type of lamella.

Adult↗
PubMed1991

Brief communication. on the problem of immunological detection of antigens in skeletal remains.

A detailed investigation with affinity-chromatography-purified fractions of antihemoglobin serum from rabbit shows that the hemoglobin content of human bones dating back 15 to 3,000 years may be very small. Some of the previous results (Ascenzi et al., 1985) indicating a high hemoglobin titer were +vitiated because of an unexpected cross-reactivity of bone extracts with the hemoglobin-unreactive fraction of the antiserum.

Animals↗
PubMed1991

Macroscopic shape of, and lamellar distribution within, the upper limb shafts, allowing inferences about mechanical properties.

Collagen orientation maps were determined for the long bones of the upper forelimb (humerus, ulna, radius) using previously described techniques. All three bones had characteristic, non-random patterns of collagen fibre orientation. In the humerus, transverse collagen predominated in the medial and posterior cortices proximally and in the anterior and posterior cortices at the mid diaphysis. In the distal radius, the medial and anterior cortices contained mostly transverse collagen. In the proximal ulna, transverse collagen was found in the anterior and anterolateral cortices. These findings may be correlated to the distribution of bending forces that may be operative in these bones.

Adult↗
PubMed1990

The bending properties of single osteons.

The bending properties of two fully calcified osteon types (longitudinal and alternate) have been investigated in 62 cylindrical samples by applying the technique of three-point bending loading. The bending of each sample was recorded using a microwave micrometer based on the cavity and pulse technique. It has been shown that alternate osteons are better able to withstand bending stress than longitudinal ones. This result offers a definitive explanation for the high concentration of transverse lamellae in pathologically bowed bone shaft.

Biomechanical Phenomena↗
PubMed1989

Orientation of collagen in human tibial and fibular shaft and possible correlation with mechanical properties.

The pattern of collagen orientation in two human tibiae and fibulae was studied. Serial 100 microns plane parallel cross-sections at 1 cm intervals at the same level in tibia and fibula were cut using an annular blade saw. Distribution of transversely oriented collagen was mapped using circularly polarized light and an image analyzing computer. In both the tibia and fibula the pattern of collagen orientation is characteristic, which may be related to the distribution of the bending forces normally operative in these bones.

Biomechanical Phenomena↗
PubMed1988

The micromechanics versus the macromechanics of cortical bone--a comprehensive presentation.

Secondary cortical bone is a complicated patchwork of structures which can be viewed as a hierarchy of four different orders. As far as the biomechanical properties of cortical bone are concerned, the lamellae is the most important of the four. The relative distribution of longitudinal lamellae (whose fiber bundles and crystallites have a longitudinal course and withstand loading by tension) with respect to transverse lamellae (whose fiber bundles and crystallites have a transverse course and withstand loading by compression) governs the mechanical properties of bone at macroscopic level both in normal and pathological conditions.

Biomechanical Phenomena↗
PubMed1987

Micro-biomechanics vs macro-biomechanics in cortical bone. A micromechanical investigation of femurs deformed by bending.

Previous studies have shown that longitudinal and transverse lamellae in compact bone signal the presence of tensile and compressive forces, respectively. On this basis an investigation has been carried out to ascertain the distribution of lamellae in femoral shafts that have been deformed by bending. To do this, a series of undecalcified plane-parallel sections 100 microns thick were prepared, and the proportion of transversely oriented collagen and crystallites in the lamellae was measured, using circularly polarized light as an illuminating source and a Quantimet 720 image-analyzing computer. It has been concluded that the distribution of the two types of lamellae is in accordance with the need to compensate for the deformity produced by the bending of the bones, and that an obvious relationship exists between the macroscopic features of the femurs and their modified microscopic structures.

Biomechanical Phenomena↗
PubMed1987

Distribution of lamellae in human femoral shafts deformed by bending with inferences on mechanical properties.

On the basis of previous investigations indicating that the distribution of osteonic and interstitial lamellae in a normal femur depends on its mechanical properties, a procedure has been devised to provide information on the distribution of lamellae in human femora diaphyses deformed by bending. To achieve this, exactly plane parallel cross sections, 100 micron thick, were prepared from the portion of maximum bending, using an annular blade microtome. An index of the distribution of longitudinal lamellae (whose fiber bundles and crystallites have a 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 using circularly polarized light as illuminating source and a Quantimet 720 image analyzing computer. The results show that, even in a pathologically deformed bone, both the microscopic structure of sections at the level of osteonic and interstitial lamellae, and their macroscopic shape may be governed by the distribution of the forces active in bone.

Biomechanical Phenomena↗
PubMed1987

On the structural symmetry of human femurs.

The distribution of transverse and longitudinal lamellae from osteons and interstitial bone of the two femurs from a woman aged between 25 and 30 was investigated. Exactly plane parallel cross-sections (100 micron) were prepared from the upper, middle and lower thirds of the two bones. The distributions of transverse and longitudinal lamellae was determined for both osteonic and interstitial bone, using circularly polarised light. The results show that (a) as in the male femur, the transverse and longitudinal lamellae in these female femurs have a characteristic rotational distribution along the shaft consistent with the distribution of the bending strains normally operative in bone; and (b) the rotational distribution of the two types of lamellae is slightly asymmetrical in the two female bones, probably because of imperfectly symmetrical use of the lower limbs.

Adult↗
PubMed1986

Orientation of collagen fibers at the boundary between two successive osteonic lamellae and its mechanical interpretation.

By applying an original technique, an investigation has been carried out to determine the orientation of collagen fibrils at the boundary between two successive lamellae in alternate osteons. Evidence is reported that the predominant fiber direction does not change abruptly from one lamella to the next; there is an intermediate system of criss-crossed fibers whose main orientation makes an angle of nearly 45 degrees with the direction of the fibers in the two adjacent lamellae. Taking a composite orthogonally reinforced laminate as a model, a mechanical interpretation of this intermediate system of collagen fibers is given.

Adult↗
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↗