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Background Post-menopausal osteoporosis is a common health problem worldwide, most commonly caused by estrogen deficiency. Most of the information regarding the skeletal effects of this disease relates to trabecular bone, while cortical bone is less studied. The purpose of this study was to evaluate the influence of estrogen deficiency on the structure and mechanical properties of cortical bone. Methods Eight ovariectomized (OVH) and eight intact (control) Sprague Dawley rats were used.Structural features of femoral cortical bone were studied by light microscopy, scanning electron microscopy and synchrotron-based microcomputer-tomography and their mechanical properties determined by nano-indentation. Results Cortical bone of both study groups contains two distinct regions: organized circumferential lamellae and disordered bone with highly mineralized cartilaginous islands. Lacunar volume was lower in the OVH group both in the lamellar and disorganized regions (182 ± 75 µm3 vs 232 ± 106 µm3, P 3 vs. 247 ± 106 µm3, P 3 lacunae/mm3 vs. 47 ± 9×103 lacunae/mm3 in the lamellar region, P = 0.003 and 63 ± 18×103lacunae/mm3 vs. 75 ± 13×103 lacunae/mm3 in the disorganized region, P P Discussion Changes to cortical bone associated with estrogen deficiency in rats require high-resolution methods for detection. Caution is required in the application of these results to humans due to major structural differences between human and rat bone.

Manot Cave contains important human fossils and archaeological assemblages related to the origin and dispersal of anatomically modern humans and the Upper Paleolithic period. This record is divided between an elevated in situ occupation area and a connecting talus. We, thus, investigated the interplay between the accumulation of the sediments and their associated artifacts in the occupation areas and the translocation of part of these sediments and artifacts down the talus. We examined the lithostratigraphy of two excavation locations in the occupation area (areas E and I), and two in the talus (areas C and D). We also assessed the diagenetic processes that have affected all these areas. A linear array of stalagmites and stalactites separates the occupation area from the talus, demarcating a major topographic barrier between the two. We infer that during human occupation, sediment accumulation of soil, wood ash, and bone was rapid and that some sediments with their associated artifacts overflowed the barrier and translocated down the talus. During periods of nonoccupation, the ash in the occupation area partially dissolved owing to the release of acid from the degrading bat and bird guano, and the layer thicknesses decreased. The south side of the talus (area C) has a normally stratified archaeological record, with the older archaeological materials underlying the younger materials. This suggests that the barrier between the occupation area and area C was relatively shallow and allowed a fairly continuous sediment accumulation in the talus. In the central part of the talus (area D), the stratigraphy is complex and shows mixing, presumably owing to the steep underlying bedrock topography and the mixing that occurs when sediments move down a steep slope. Finally, the distribution of secondary phosphates is consistent with the location of a main cave entrance to the south of the Paleolithic occupation area.

A small-angle x-ray scattering study of dispersed crystals from rat bone and mineralized turkey tendon shows that the particles in both preparations have the same scattering behavior. The data are very similar to those reported by Fratzl et al. for intact turkey tendon and are consistent with the crystals being plate shaped. These observations have important implications for understanding both the structure and mineralization processes of these tissues.

The Upper Palaeolithic of the Levant (45 000–22 000 BP) represents the full establishment of modern human behavior in this region following the existence of both modern humans and Neanderthals during the Middle Palaeolithic. The Levantine Upper Palaeolithic shares some similarities to its European counterpart but otherwise is quite different.

Bone and tooth mineral generally undergo diagenetic changes. These changes in the carbonate hydroxyapatite structure and composition can affect the signals embedded in the mineral phase, such as migration behavior, age of the specimen and the reconstruction of past environments. Mineral preservation state can be assessed using infrared spectroscopy which provides information on crystal disorder at the atomic level and mineral composition. Here we present a new approach to evaluate carbonate hydroxyapatite atomic disorder using infrared spectroscopy and the standard KBr sample mounting method. We show that by repeated grinding of the sample and then plotting the infrared splitting factor against the width of the major phosphate absorption peak after each grinding, grinding curves with well defined trend lines can be obtained. The offsets between curves reflect differences in atomic disorder. We show that grinding curve offsets can be used to evaluate the state of preservation of bone, dentine and enamel mineral. Les os et les dents subissent généralement des changements diagénétiques. Ces changements de la structure et de la composition de l’hydroxyapatite carbonatée peuvent affecter les signaux inclus dans la phase minérale, tels que les comportements de migration, l’âge des spécimens ou la reconstitution des environnements passés. L’état de préservation de la phase minérale peut être déterminé par la spectrométrie infrarouge qui fournit des informations sur le désordre structural et sur la composition du minéral. Dans cette étude, nous présentons une nouvelle approche permettant d’évaluer le désordre cristallin en utilisant la spectrométrie infrarouge. Nous montrons ici qu’un broyage répété de l’échantillon et la représentation graphique des valeurs de splitting factor et de la largeur à mi-hauteur de la principale bande d’absorption des phosphates après chaque broyage, peut permettre de définir des courbes de broyage avec des tendances bien définies. Un décalage entre ces courbes reflète des différences de désorganisation à l’échelle atomique.

The plate-shaped crystals of rat bone are arranged in parallel layers that form coherent structures up to the level of individual lamellae. The crystal layers of the thin lamellae are parallel to the lamellar boundary, whereas those of the thicker lamellae are oblique to the boundary. The basic structure of rat bone can be described as ‘rotated plywood’; a structure hitherto unrecognized in either biologic or synthetic materials.

Sea urchin skeletal elements are composed of single crystals of calcite. Unlike their synthetic counterparts, these crystals do not have well-developed cleavage and are consequently much more resistant to fracture. This phenomenon is due in part to the presence of acidic glycoproteins occluded within the crystals. By means of x-ray diffraction with synchrotron radiation, it is shown that the presence of the protein in synthetic calcite only slightly decreases the coherence length but significantly increases the angular spread of perfect domains of the crystals. In biogenic calcite, the coherence length is 1/3 to 1/4 as much as that in synthetic calcite and the angular spread is 20 to 50 times as wide. It is proposed that the presence of macromolecules concentrated at mosaic boundaries that are oblique to deavage planes is responsible for the change in fracture properties. These results may be important in the material sciences, because of the unusual nature of this material, namely, a composite based on the controlled intercalation of macromolecules inside single-crystal lattices.

Sea urchin larvae form an endoskeleton composed of a pair of spicules. For more than a century it has been stated that each spicule comprises a single crystal of the CaCO3 mineral, calcite. We show that an additional mineral phase, amorphous calcium carbonate, is present in the sea urchin larval spicule, and that this inherently unstable mineral transforms into calcite with time. This observation significantly changes our concepts of mineral formation in this well-studied organism.

Textures of calcite crystals from a variety of mineralized tissues belonging to organisms from four phyla were examined with high-resolution synchrotron x-ray radiation. Significant differences in coherence length and angular spread were observed between taxonomic groups. Crystals from polycrystalline skeletal ensembles were more perfect than those that function as single-crystal elements. Different anisotropic effects on crystal texture were observed for sea urchin and mollusk calcite crystals, whereas none was found for the foraminifer, Patellina, and the control calcite crystals. These results show that the manipulation of crystal texture in different organisms is under biological control and that crystal textures in some tissues are adapted to function. A better understanding of this apparently widespread biological phenomenon may provide new insights for improving synthetic crystal-containing materials.

The organization of apatite crystals and collagen fibrils in mineralized turkey tendon has been studied by electron microscopy and electron diffraction. To minimize artifactual distortions the tissue was examined, for the first time, as isolated fibrils in an aqueous environment of vitreous ice, as well as in conventionally prepared sections. The electron micrographs show that the plate-shaped apatite crystals are arranged in parallel arrays across the collagen fibrils. This provides direct evidence for highly asymmetric assembly in collagen fibrils, and, indeed, the fibrils were observed to be elongated rather than round in cross-section. There is, furthermore, a pronounced tendency for the layers of crystals to be coherently aligned in adjacent fibrils. These observations may also be important for understanding the mechanical behavior of bone at the molecular level, as such extended, aligned aggregates of flat crystals could develop into natural fracture planes in mature bone.

The parchments of the Dead Sea Scrolls were prepared from the skins of animals, mainly sheep and goats1,2. They were copied and hidden between the beginning of the first century BC and AD 703. Since then and until their discovery in the late 1940s by local Bedouins, they were located in caves close to the northwestern shore of the Dead Sea4. Having been handled by various intermediaries for periods of up to 8 yr, most of the intact scrolls are housed in the Israel Museum, Jerusalem. We have examined small pieces (≲25 mm2) from these scrolls, together with random fragments without any writing, to study some of the chemical changes which have occurred in the past 2,000 yr or so. Using X-ray diffraction and racemization analyses, we found that a major degradative change is due to the unfolding of the collagen molecules to form gelatin and that the degradation generally occurred many centuries ago.

The organic matrix is thought to play an important role in controlling crystal growth during the formation of skeletal hard parts. The structural organization of the matrix macromolecular constituents can provide a key to understanding the nature of the control processes. Although the data are limited, both vertebrate and invertebrate organic matrices appear to be organized according to the same “basic motif,” namely a core of relatively hydrophobic structural macromolecules (usually proteins) and surface layers of acidic proteins and polysaccharides. Analyses of the latter from different invertebrate phyla using reversed phase high performance liquid chromatography, reveal that the same two classes of macromolecules are present in each of the three cases studied, emphasizing the fundamental importance of these components in crystal growth. Substantial information, at the molecular level, on the conformations and orientations of matrix constituents in relation to the mineral crystal lattice, is available only for mollusk shells, and to some extent on vertebrate tooth enamel. In these cases the major matrix constituents are aligned with one or more mineral crystallographic axes. These observations suggest that the matrix performs active, specific roles in crystal growth. Although it is still premature to assess the importance of various basic crystal growth mechanisms, the data available do not preclude the possibility that epitaxial crystal growth is an important factor

A technique is presented for estimating finite‐amplitude effects for standing acoustic waves. The method consists of equating the nonlinear energy loss from the fundamental mode of oscillation to the work done on this mode by its higher harmonics. The higher harmonics are determined by the assumption that the wave‐form is a sawtooth. Results are obtained for the limiting amplitude of oscillation, which are in qualitative agreement with previous results where these are available. The problems considered are (1) propagation of simple waves; (2) sound produced by a piston in a closed tube; (3) sound resulting from acoustic instability in a closed tube; (4) sound produced by a piston in a closed tube with the even harmonics strongly damped; and (5) sound resulting from acoustic instability in a closed tube with the even harmonics strongly damped.

Transmission electron micrographs of individual mineralized collagen fibrils show that hydroxyapatite crystals are located mainly within the fibrils at the level of the gap regions. The plate-shaped crystals are observed to be more or less uniformly stacked across the fibril diameter. We therefore suggest that the crystals are primarily located in ‘grooves’ created by contiguous adjacent gaps. The proposal is consistent with the observed crystal distribution in the fibril and with their average widths, which are almost 10-times greater than an individual gap diameter.

A significant proportion of the soluble protein of the organic matrix of mollusk shells is composed of a repeating sequence of aspartic acid separated by either glycine or serine. This regularly spaced, negatively charged aspartic acid may function as a template upon which mineralization occurs.