Добірка наукової літератури з теми "Mineralized skeleton"

This paper presents a review of the literature describing calcium regulation mechanisms of chondrichthyans, with particular emphasis being given to implications for the nature of the skeleton. A further review of the literature describing mineralized skeletal tissues explores the many conflicting claims about the presence or absence of bone in chondrichthyans. The fine structure of axial and appendicular mineralized tissues from five genera is then described, and evidence is presented to support or refute the hypotheses of others concerning the presence of bone, turnover in the skeleton, and growth without resorption.

The Precambrian-Cambrian transition saw the burgeoning of diverse skeletal organisms (“small shelly fossils”), represented in the fossil record by spicules, tubes, tests, conchs, shells, and a variety of sclerites and ossicles. Whereas calcareous biomineralization as such may have been facilitated by changes in ocean chemistry at this time, the utilization of biominerals in mineralized skeletons is a different process. The massive appearance of skeletons is most likely an epiphenomenon of the general radiation of body plans and tissues. The “choice” of biominerals (mainly calcium carbonates, calcium phosphates, and silica) may reflect the environmental conditions under which the particular skeleton first evolved.

The assembly of the gnathostome bodyplan constitutes a formative episode in vertebrate evolutionary history, an interval in which the mineralized skeleton and its canonical suite of cell and tissue types originated. Fossil jawless fishes, assigned to the gnathostome stem-lineage, provide an unparalleled insight into the origin and evolution of the skeleton, hindered only by uncertainty over the phylogenetic position and evolutionary significance of key clades. Chief among these are the jawless anaspids, whose skeletal composition, a rich source of phylogenetic information, is poorly characterized. Here we survey the histology of representatives spanning anaspid diversity and infer their generalized skeletal architecture. The anaspid dermal skeleton is composed of odontodes comprising spheritic dentine and enameloid, overlying a basal layer of acellular parallel fibre bone containing an extensive shallow canal network. A recoded and revised phylogenetic analysis using equal and implied weights parsimony resolves anaspids as monophyletic, nested among stem-gnathostomes. Our results suggest the anaspid dermal skeleton is a degenerate derivative of a histologically more complex ancestral vertebrate skeleton, rather than reflecting primitive simplicity. Hypotheses that anaspids are ancestral skeletonizing lampreys, or a derived lineage of jawless vertebrates with paired fins, are rejected.

To characterize the magnitude and location of mineralized bone loss, 40 patients (20 men, 20 women, 29 white, 11 black) with clinically significant renal osteodystrophy who could be unambiguously classified based on histologic criteria as having osteitis fibrosa (OF; 20 cases) or osteomalacia (OM; 20 cases) were studied; they had been on maintenance hemodialysis for 4.6 +/- 3.0 yr. One hundred forty-two healthy women of similar age and ethnic composition served as control subjects. In all subjects, the proportions of mineralized bone, osteoid, and porosity (nonbone soft tissue) were measured separately in cortical and cancellous bone tissue, from intact full-thickness biopsies of the ilium, representative of the axial skeleton. The results were related to the volumes of cortical and cancellous bone tissue separately and to the volume of the entire biopsy core. Approximately three-quarters of the patients had measurements in the appendicular skeleton by single photon absorptiometry of the radius and morphometry of the metacarpal. Disease effects did not differ significantly between ethnic groups. Mineralized cortical bone volume (per unit of core volume) was reduced by approximately 45% in both patient groups. Mineralized cancellous bone volume was significantly increased by 36% in the patients with OF and nonsignificantly reduced by 9% in the patients with OM; however, the reduction in the latter patients was significant in relation to tissue volume. The combined total deficit for both types of iliac bone was approximately 20% in the patients with OF and approximately 40% in the patients with OM. Significant reductions in appendicular cortical bone were demonstrated in both patient groups at both measurement sites. Regardless of the current histologic classification, the major structural abnormality in the skeleton is generalized thinning of cortical bone due to increased net endocortical resorption, the most characteristic effect on bone of hyperparathyroidism. Protection of the skeleton from the adverse consequences of renal failure will require therapeutic intervention in patients with no symptoms of either renal or bone disease.

Palaenigma wrangeli (Schmidt) is a finger-sized fossil with a tetraradiate conical skeleton; it occurs as a rare component in fossiliferous Upper Ordovician strata of the eastern Baltic Basin and is known exclusively from north Estonia. The systematic affinities and palaeoecology of P. wrangeli remained questionable. Here, the available specimens of P. wrangeli have been reexamined using scanning electron microscopy and x-ray computed tomography (microCT). Additionally, the elemental composition of the skeletal elements has been checked using energy dispersive X-ray spectroscopy. The resulting 2D-, and 3D-scans reveal that P. wrangeli consists of an alternation of distinct calcium phosphate (apatite) lamellae and originally organic-rich inter-layers. The lamellae form four semicircular marginal pillars, which are connected by irregularly spaced transverse diaphragms. Marginally, the diaphragms and pillar lamellae are not connected to each other and thus do not form a closed periderm structure. A non-mineralized or poorly mineralized external periderm existed originally in P. wrangeli but is only rarely and fragmentary preserved. P. wrangeli often co-occurs with conulariids in fossil-rich limestone with mudstone–wackestone lithologies. Based on the new data, P. wrangeli can be best interpreted as a poorly mineralized conulariinid from an original soft bottom habitat. Here the new conulariinid family Palaenigmaidae fam. nov. is proposed as the monotypic taxon for P. wrangeli.

Elasmobranchii is a clade of chondrichthyans (cartilaginous fishes) that comprises sharks, skates and rays represented today by approximately 1,200 species. Chondrichthyans have a long evolutionary history dating back to the Late Ordovician (ca. 450 million years ago [Mya]) based on isolated dermal denticles (Janvier 1996). Other remains such as articulated skeletons and teeth are known from the Lower Devonian (ca. 410 Mya: Mader 1986; Miller et al. 2003). The fossil record of modern elasmobranchs (Neoselachii) can be traced back to the Early Permian (ca. 290 Mya) and is represented by isolated teeth (Ivanov 2005), with fossils of crown group sharks and rays appearing in Lower Jurassic (ca. 200 Mya) rocks (e.g., Cappetta 2012). Since their appearance in the geological record, elasmobranchs are mainly represented by isolated teeth, whereas articulated skeletons are very rare and restricted to a small number of fossil localities (e.g., Cappetta 2012). The scarcity of skeletal remains in their fossil record is due to their poorly mineralized cartilaginous skeleton that requires special taphonomical conditions to be preserved. Elasmobranch teeth, in contrast, are composed of highly mineralized tissues (hydroxyapatite) that have a strong preservation potential (Shimada 2006). In addition, elasmobranchs replace their teeth continuously over the course of their life span (polyphyodonty) and therefore shed thousands of teeth in their lifetime (Reif et al. 1978; Schnetz et al. 2016) leading to large numbers of potential fossils. These morphologically highly diverse isolated teeth constitute much of the rich fossil record of elasmobranchs, and largely form the basis of our understanding of elasmobranch diversity and evolution through geological time.

Abstract Repairing damage in the craniofacial skeleton is challenging. Craniofacial bones require intramembranous ossification to generate tissue-engineered bone grafts via angiogenesis and osteogenesis. Here, we designed a mineralized collagen delivery system for BMP-2 and vascular endothelial growth factor (VEGF) for implantation into animal models of mandibular defects. BMP-2/VEGF were mixed with mineralized collagen which was implanted into the rabbit mandibular. Animals were divided into (i) controls with no growth factors; (ii) BMP-2 alone; or (iii) BMP-2 and VEGF combined. CT and hisomputed tomography and histological staining were performed to assess bone repair. New bone formation was higher in BMP-2 and BMP-2-VEGF groups in which angiogenesis and osteogenesis were enhanced. This highlights the use of mineralized collagen with BMP-2/VEGF as an effective alternative for bone regeneration.

AbstractDragastanella transylvanica n. gen. n. sp. is described. Its calcified skeleton contains numerous voids, partly related to the molds of soft parts of the alga, but also related to lack of calcification. Interpretation of these voids, especially their attribution to original structures (e.g., primary lateral versus reproductive organ), has important implications for the taxonomic position of the alga, even at the family level. Examination of key sections that include the boundary between sterile and fertile parts of the alga excludes the occurrence of external reproductive organs. Unusual, paired pores in the outer part of the mineralized skeleton reflect an asymmetry within the whorl, excluding the presence of secondary laterals. The alga is characterized by a cylindrical to club-shaped thallus bearing only phloiophorous primary laterals arranged in whorls and flaring outwards, forming a cortex. Mineralized lenticular reproductive organs containing cysts set in the equatorial plane (Russoella-type gametophores) occur inside primary laterals (cladosporous arrangement of the reproductive organs). These characters support establishment of the new genus Dragastanella. Dragastanella transylvanica n. gen. n. sp. resembles species previously referred to Zittelina (Zittelina hispanica and Zittelina massei) and Triploporella (Triploporella matesina and Triploporella carpatica). Except for Triploporella carpatica, whose mineralized skeleton does not permit confident attribution to either Triploporella or Dragastanella n. gen., the other species must be ascribed to Dragastanella n. gen. Therefore, the following new combinations are proposed: Dragastanella hispanica n. comb., Dragastanella massei n. comb., and Dragastanella matesina n. comb. Despite widely overlapping biometrical measurements, these species can be differentiated by the size and location of their reproductive organs, the pattern of calcification around the primary laterals, and relationships among structural parameters such as the size of laterals, number of laterals per whorl, and distance between whorls.

An accepted uniting character of modern cartilaginous fishes (sharks, rays, chimaera) is the presence of a mineralized, skeletal crust, tiled by numerous minute plates called tesserae. Tesserae have, however, never been demonstrated in modern chimaera and it is debated whether the skeleton mineralizes at all. We show for the first time that tessellated cartilage was not lost in chimaera, as has been previously postulated, and is in many ways similar to that of sharks and rays. Tesserae in Chimaera monstrosa are less regular in shape and size in comparison to the general scheme of polygonal tesserae in sharks and rays, yet share several features with them. For example, Chimaera tesserae, like those of elasmobranchs, possess both intertesseral joints (unmineralized regions, where fibrous tissue links adjacent tesserae) and recurring patterns of local mineral density variation (e.g. Liesegang lines, hypermineralized ‘spokes’), reflecting periodic accretion of mineral at tesseral edges as tesserae grow. Chimaera monstrosa 's tesserae, however, appear to lack the internal cell networks that characterize tesserae in elasmobranchs, indicating fundamental differences among chondrichthyan groups in how calcification is controlled. By compiling and comparing recent ultrastructure data on tesserae, we also provide a synthesized, up-to-date and comparative glossary on tessellated cartilage, as well as a perspective on the current state of research into the topic, offering benchmark context for future research into modern and extinct vertebrate skeletal tissues.

Le squelette minéralisé est une structure clé des vertébrés. À l'instar de nombreux autres groupes de métazoaires, celui-ci assure des fonctions essentielles (soutien, protection, alimentation et divers rôles physiologiques). Depuis son origine, ce squelette minéralisé s’est diversifié à plusieurs échelles. Aujourd'hui, il comporte une variété d'éléments, constitués de divers tissus, dont la composition et la structure peuvent varier. Pour mieux appréhender la répartition actuelle des propriétés histomorphologiques du squelette minéralisé des vertébrés, nous pouvons nous interroger sur les origines et l'histoire évolutive de cette diversité. L'étude de la distribution des tissus minéralisés chez les vertébrés actuels et passés a permis de mieux comprendre leurs origines phylogénétiques et temporelles. Certains des tissus minéralisés parmi les plus anciennement connus ont été découverts chez les ptéraspidomorphes (stem-gnathostomes ; Ordovicien-Dévonien). Leur squelette dermique minéralisé prenant la forme de deux plaques céphalothoraciques, accompagnées de nombreuses écailles recouvrant le reste de leur corps. Ces structures se composaient de deux couches osseuses, une compacte et une spongieuse, surmontées d'odontodes (dents extra-buccales) faites de dentine, parfois associées à de l'émailloïde (tissu semblable à l'émail). Bien que ces éléments fournissent des indications sur les origines et l'évolution des tissus chez les vertébrés, les mécanismes précis de leur diversification restent assez énigmatiques. L’objectif de cette thèse est ainsi d’explorer, de manière intégrée, les mécanismes développementaux ayant pu favoriser l'émergence des tissus durant l’évolution du squelette minéralisé des vertébrés. Une première partie a été consacrée à la révision des concepts liés aux tissus dentaires, à leur méthode d'identification, ainsi qu'à leur distribution actuelle et passée. Cela a contribué à clarifier la nomenclature et la validité des identifications antérieures des tissus dentaires, tout en proposant un cadre phylogénétique pour discuter de leurs étapes évolutives clés. Une deuxième partie s’est portée sur la construction d’un modèle histogénétique actualiste de la dentine, l’émailloïde et l’émail. Celui-ci a permis d’étudier les mécanismes de transition entre les tissus en explorant in silico l’impact de paramètres développementaux sur la formation de tissus dentaires. Diverses modifications développementales menant à la transition entre émailloïde et émail ont ainsi pu être mis en évidence, suggérant que la mise en place de nouveaux tissus ne nécessite pas nécessairement l’acquisition de nouveaux gènes. Une troisième partie, ajoutant une dimension morphogénétique au précédent modèle histogénétique, s’est intéressée à la formation des structures dentaires composées de dentine, d’émailloïde et d’émail. L’exploration in silico de l’impact de la courbure initiale de l’épithélium et du timing spatio-temporel d’activation des cellules a permis de montrer que la modification de ce type de paramètres intercellulaires influençait la présence et la répartition des tissus au sein d’une structure. Une quatrième partie révisant la paléohistologie d'Astraspis avait pour but de reconstruire l’ontogénie de l'une des premières structures « dentaires ». En plus de renforcer l'identification du tissu recouvrant en tant qu'émailloïde, cela a permis de comparer les mécanismes de développement de ces premières structures avec ceux des actuelles. Une différence majeure étant que les odontodes des stem-gnathostomes semblaient se former suite à une activation synchrone, et non décalée, des cellules mésenchymateuses. Une cinquième partie se penchait sur l’histomorphogenèse des structures en « empreinte digitale » et « nid-d'abeilles » présentes chez Anglaspis. Cela a permis de discuter des mécanismes de structuration, tels que les mécanismes de réaction-diffusion, qui ont pu influencer la formation du squelette des premiers vertébrés
The mineralized skeleton is a key structure in vertebrates. Like many other metazoan groups, it serves essential functions, including support, protection, feeding, and various physiological roles. Since its origin, this mineralized skeleton has diversified at multiple scales. Today, it comprises a variety of elements made up of different tissues, with varying composition and structure. To better understand the current distribution of histomorphological properties in the mineralized skeleton of vertebrates, we can examine the origins and evolutionary history of this diversity.The study of the distribution of mineralized tissues in present and past vertebrates has enhanced our understanding of their phylogenetic and temporal origins. One of the oldest known mineralized tissues have been notably found in pteraspidomorphs (stem-gnathostomes; Ordovician-Devonian). Their mineralized dermal skeleton takes the form of two cephalothoracic plates, accompanied by numerous scales covering the rest of their bodies. These structures generally consisted of two bone layers, a compact one and a spongy one, topped with odontodes (extra-buccal teeth) made of dentine, sometimes associated with enameloid (a tissue similar to enamel). Although these elements provide insights into the origins and evolution of tissues in vertebrates, the precise mechanisms of their diversification remain quite enigmatic. The objective of this thesis is to explore, in an integrated manner, the developmental mechanisms that may have favored the emergence of tissues during the evolution of the mineralized skeleton in vertebrates. The first part was dedicated to the revision of concepts related to dental tissues, their method of identification, as well as their current and past distribution. This contributed to clarifying the nomenclature and validity of previous identifications of dental tissues, while also proposing a phylogenetic framework to discuss their key evolutionary stages. The second part focused on constructing a current histogenetic model of dentin, enameloid, and enamel. This allowed for the study of transition mechanisms between tissues by exploring the in silico impact of developmental parameters on the formation of dental tissues. Various developmental modifications leading to the transition between enameloid and enamel were thus identified, suggesting that the establishment of new tissues does not necessarily require the acquisition of new genes. The third part, adding a morphogenetic dimension to the previous histogenetic model, focused on the formation of dental structures composed of dentin, enameloid, and enamel. The in silico exploration of the impact of the initial curvature of the epithelium and the spatiotemporal activation timing of cells revealed that modifying such intercellular parameters influenced the presence and distribution of tissues within a structure. The fourth part, revising the paleohistology of Astraspis, aimed to reconstruct the ontogeny of one of the earliest 'dental' structures. In addition to strengthening the identification of the covering tissue as enameloid, it allowed for a comparison of the developmental mechanisms of these early structures with those of contemporary ones. A major difference was that the odontodes of stem-gnathostomes appeared to form through synchronous, rather than delayed, activation of mesenchymal cells. The fifth part delved into the histomorphogenesis of the 'fingerprint' and 'honeycomb' structures found in Anglaspis. This facilitated a discussion of structuring mechanisms, such as reaction-diffusion processes, that could have influenced the formation of the skeletons in early vertebrates

AbstractAll components of the musculoskeletal system can be involved by metabolic disorders as a result of endocrine diseases, genetic alterations, and environmental or nutritional aspects, with important worldwide variations in prevalence and severity. Early detection of these disorders is crucial because of the efficacy of preventive measures and availability of treatments. The current chapter will focus on the imaging appearance of metabolic disorders of bone marrow and of the mineralized skeleton. Marrow and bone disorders in athletes, the elderly, and individuals with eating disorders will be reviewed.

AbstractStable isotope analysis has become an essential tool in investigations of ancient migration and paleodietary reconstruction. Because the biogeochemistry of bone collagen and apatite is well known, current methods rely almost exclusively on analyses of bones and teeth; however, dental calculus represents a potentially additional biological source of isotopic data from ancient skeletons. Dental calculus is a mineralized bacterial biofilm that forms on the surfaces of teeth. Sampling dental calculus does not damage the dentition and thus can be used in cases where it is not possible to perform destructive analyses of conventional mineralized tissues. Like bone and dentine, dental calculus contains both inorganic and organic components, allowing measurement of C, N, O, H, and Sr isotopes. Additionally, dental calculus forms as serial, non-remodeling laminar accretions on the tooth surface, opening up the possibility of analyzing discrete time points during the lifetime of an individual. However, as a microbial biofilm and not a human tissue, the biochemistry of dental calculus is complex, containing multiple calcium phosphate mineral phases, organic and inorganic food remains, hundreds of human and bacterial proteins, and diverse biomolecules from thousands of endogenous bacterial taxa. Isotopic investigation of dental calculus is still in its infancy, and many questions remain regarding its formation and processes of diagenesis. This chapter (1) reviews the unique advantages presented by dental calculus as a novel source of biological isotopic data, (2) critically evaluates published isotopic studies of dental calculus, and (3) explores the current challenges of dental calculus stable isotope analysis through a case study of an Ancient Puebloan Basketmaker II population from the American Southwest.

Abstract Skeletons are structural elements that provide support, muscle anchoring points, and protection. Skeletons can be external or internal. External skeletons are composed of plates and offer physical protection. Internal skeletons are often composed of bones. For a rigid mineralized skeleton to allow movement, there have to be joints between individual elements. The type of movement and locomotion an animal can carry out depends on what type of skeleton it has, if any. The main muscles used for locomotion tend to be body wall muscles, which can be longitudinal or circular. Coordinated activity of body wall muscles can lead to peristaltic or sinusoidal types of locomotion. Animals with appendages display other types of locomotion, such as walking or swimming. All muscle activity must be done against some sort of support structure. Animals without rigid mineralized skeletons often have a hydrostatic skeleton or coelom, which serves as the semirigid anchoring point for locomotory muscles.

The Echinodermata are certainly one of the most unusual and interesting phyla from the biomineralization point of view. They all live in the marine environment. The five major taxonomic classes (Asteroidea or sea stars, Ophiuroidea or brittle stars, Echinoidea or sea urchins, Crinoidea or sea lilies, and Holothuroidea or sea cucumbers) have quite different anatomical shapes and are characterized by fivefold symmetry. Each group forms mineralized hard parts. In the Echinoidea the skeletal elements are fused together to form a rigid test, whereas in the Asteroidea, Ophiuroidea and Crinoidea the skeletal elements or ossicles are articulated with one another. In the Holothuroidea the skeleton is usually reduced to microscopic ossicles or spicules, and, in some cases, mineralized granules as well. The hard parts of echinoderms vary enormously in shape and function and include not only the diverse skeletal elements, but also spines and teeth. Remarkably, with very few exceptions, the mineralized hard parts are formed from the same mineral, magnesium-bearing calcite [usually 5–15% as magnesium carbonate (Chave 1952, 1954; Raup 1966)], which has some unique and interesting properties. The ultrastructure of many of the macroscopic skeletal hard parts has a characteristic spongy or fenestrate structure (called the stereom) and is riddled with labyrinthine cavities (collectively called the stereom space). In echinoid spines the stereom spaces are secondarily filled in to form areas of solid mineral. The surfaces of the mineral phase are very smooth, even when examined a high magnification in the SEM (Towe 1967; Millonig 1970). Furthermore, the broken surfaces show no characteristic ultrastructural motif, which is observed in almost all other mineralized tissues in which the individual crystals are enveloped by layers of organic material. The fracture surfaces of echinoderm calcite actually have a conchoidal cleavage (Towe 1967), which is characteristic of glassy or amorphous materials. It is, therefore, most surprising that when individual skeletal plates, spines, spicules, ossicles, and even whole teeth are examined in polarized light or by X-ray diffraction, they behave as if they are single crystals! (Towe 1967; Donnay and Pawon 1969).

The human body has been a focus of attention for thousands of years. The ancients wished to mummify it to assure transposition to the life hereafter. Today we expend a lot of effort and money to forestall the effects of aging of such a complicated machine. The mineralized portion of the body, the skeleton, is the most permanent portion of the body and records the basic size and shape of the individual. Underscoring the wish for properly functioning bones and teeth, we today have a medical ‘spare parts’ industry that provides substitute knees, hips, or an entire denture. The need to accomplish these implants/transplants successfully has aligned physicians and dentists with cell and molecular biologists, materials scientists, bioengineers, and mineralogists. All wish to create faithful replicas of the mineralized parts, but any substitutes must be in harmony with the internal dynamic biochemical environment, and be part of a viable functioning skeleton. The general health of every human is a response to the local, regional, and global environment. The interaction noted in the scientific literature almost 50 years ago (Warren 1954) continues (Hopps and Cannon 1972, Ross and Skinner 1994). There is burgeoning interest as many scientists, with ever increasing abilities to detect and measure extremely small amounts of certain elemental species or potentially hazardous substances, focus on the relationships of the environment and health. The roles of the skeletal mineral substance as a participant and faithful recorder in this crossover are outlined here. “Bone” can refer to any one of the more than 200 individual organs with distinctive shapes that make up every human skeleton or to the tissue that is present in each of these organs. The tissues of bone, and teeth, are composites of organic matrix, mineral matter, and specialized cells (Skinner 1987, Albright and Skinner 1987). The cells not only form but also maintain, reconstruct, and repair the bone tissues as required. Cells known as osteoblasts produce a protein and polysaccharide matrix in and on which mineral is deposited. The cells become embedded in this extracellular mineralized matrix but continue to assist and sustain the viability of their products.

Biomineralization refers to the processes by which organisms form minerals. It is, therefore, by definition a true multidisciplinary field that spans both the inorganic and the organic world. Although the vast majority of organisms do not form mineralized deposits, the phenomenon is still extremely widespread. All five kingdoms contain members that mineralize and these are distributed among no less that 55 phyla. These organisms are capable of forming some 60 different minerals and it is patently clear that the true diversity of the field is still far from having been ascertained. Some biogenic minerals are formed on such a huge scale in the biosphere that they have a major impact on ocean chemistry and are important components of marine sediments and ultimately of many sedimentary rocks as well. One of the functions of biogenic minerals is to provide mechanical strength to skeletal hard parts and teeth. The resultant materials often have remarkable mechanical properties and are of interest in their own right. When organisms evolved the ability to form mineralized hard parts, they provided themselves with a major adaptational advantage and their durable skeletons constituted the basis for a more complete record of life on earth in the form of their fossilized skeletal remains. The vertebrate skeleton, in particular, fulfills a variety of functions and this brings with it a multitude of health-related problems that plague our own species, such as dental caries, bone fractures, mineral loss from bone, and kidney stones. Biomineralization, therefore, is an unusual field in that it lies at the center of many other disciplines. Figure 1.1 is an imaginary wheel showing on its rim some of the disciplines that overlap the field of biomineralization. There are many scientists in each of these disciplines who have more than a passing interest in biomineralization and one objective of this book is to provide them with easier access to the field. The center of the wheel contains a partial list of some of the fields within biology and chemistry that have a major contribution to make toward a more complete understanding of the processes involved in biomineralization.

Abstract Morphogenesis is regulated by a complex interaction of factors that are intrinsic and extrinsic to the cells composing the organism (e.g. genetic programming, cytokine gradients, and applied mechanical/electrical forces). Mechanical stimulation has been shown to affect bone growth, but the interaction of mechanical forces with biological factors during the development of a cartilage anlage into adult form is not clear. During skeletal development, chondrocytes produce cartilage through differential cell growth, cell volume changes, and extracellular matrix secretion. Cartilage cells at the growth front undergo significant hypertrophy and later their surrounding matrix becomes mineralized. In turn, the mineral is resorbed by osteoclasts and new bone tissue is deposited by osteoblasts. During later stages of prenatal development, contraction of developing muscles applies significant loads to the skeleton which in turn affects the bone growth. This research attempts to elucidate how these processes are controlled by biologic factors in the absence of mechanical factors using a finite element (FE) model of the proximal tibia from a paralyzed chick embryo.

The mechanical properties of cancellous bone are determined from a combination of bone quantity (volume), the material properties of the mineralized tissue, and microarchitecture. Bone remodeling is the primary process through which bone mass and structure are altered in the adult skeleton. Bone remodeling involves the coordinated activity of osteoclast and osteoblast cells, which resorb and then form bone at an isolated location on the cancellous bone surface. Because bone resorption precedes formation, each bone remodeling event in cancellous bone is associated with a temporary void on the bone surface known as a remodeling cavity. It has been proposed that remodeling cavities can act as stress risers, modifying stress distributions in cancellous bone and potentially impairing bone strength, stiffness and other mechanical properties. While high resolution finite element modeling supports the idea that remodeling cavities have the potential to modify mechanical properties at the micro-scale (in individual trabeculae) [1] and at the apparent level (entire cancellous bone specimens)[2, 3], the experiments required to confirm these findings are limited because a repeatable method of quantifying the number and size (length width and depth) of remodeling cavities in entire cancellous bone specimens has not yet been demonstrated.

Summary To address the challenges associated with the complex preparation process of polymer particles for conformance control and the difficulties in combining injection and conformance control performance, a study was conducted on a thermoplastic elastic particle conformance control agent using polyvinyl alcohol (PVA) as the particle skeleton. The millimeter-scale elastic particles can be prepared in-situ by incorporating a hydrophobic modifier (HM) and a cross-linking agent glutaraldehyde into the aqueous phase. By adjusting the content of HM and stirring speed, the particle size can be regulated. The texture profile analysis indicated that the self-granulated thermoplastic elastic particles exhibit excellent elasticity and high resilience. Furthermore, they can undergo thermoplasticization in highly mineralized water (21×104 mg/L, Ca2+ + Mg2+ = 1.2×104 mg/L) and crude oil at 130 °C, while maintaining exceptional mechanical properties. Physical model experiments demonstrated that the particle system exhibits good migration ability and plugging performance. The particles’ breakthrough pressure significantly increased after high-temperature treatment, reaching 1860 kPa, highlighting the practical potential of these particles for oil reservoir applications. With a simple dropwise stirring "one-pot" synthesis method, the thermoplastic elastic particles offer advantages including straightforward synthesis, environmental friendliness, excellent mechanical performance, thermal stability and salt resistance. These thermoplastic elastic particles show great potential for future industrial production and have promising prospects as a fracture conformance control agent.

Skeletal repair and regeneration involve a dynamic interplay of biological processes that result in spatially and temporally varying patterns of tissue formation and remodeling. For example, during bone fracture healing the cartilaginous callus that is formed initially in the fracture site is subsequently mineralized and remodeled to restore the original form and function to the injured bone. During much of this healing process, the fracture callus is comprised of a heterogeneous mixture of cartilage, fibrocartilage, multipotent mesenchymal tissue, and bone. Adding to this complexity, mechanical stimuli are known to influence the rate and type of tissues formed during skeletal healing [1]. Given the growing body of evidence that controlled mechanical stimulation may be used to enhance healing, it is of substantial interest to elucidate relationships between the distributions of local stresses and strains that develop within the healing region and the distribution of tissue types that form. While histomorphometry is a well established approach for characterizing the latter, it has historically been limited to analyses of a small number of two-dimensional sections of tissue. Such 2D sampling may be inadequate for quantitative characterization of the irregular geometry and heterogeneous composition of healing tissues. In this study, we report on a 3D histomorphometric method and apply this method to an in vivo model of skeletal repair [2] in which a bending stimulus delivered to a healing bone defect results in the formation of predominantly cartilage tissue, rather than bone.

The hierarchical organization of bone entails the tissue level at the nanoscale up to the organ level at the macroscale. In this hierarchical perspective, skeletal fragility is the outcome of a failure cascade that initiates at the molecular level, and propagates to higher levels [1]. This failure cascade is well investigated at the microscale and the macroscale [2] whereas the deformation and fracture mechanisms at the nanoscale are largely unknown. Therefore, our understanding of how mineralized tissues fail is incomplete and requires further investigations so as to formulate the ultrastructural basis of increased fracture susceptibility during disease and aging. In this regard, the first aim of the present study was to experimentally investigate the behavior of bone mineral under mechanical strain. The second aim of this study was to determine whether irreversible changes occur in the mineral crystals following fracture.