X-ray microCT study of pyramids of the sea urchin Lytechinus variegatus

Morphological and Tissue Characterization with 3D Reconstruction of a 350-Year-Old Austrian Ardea purpurea Glacier Mummy

Glaciers are dwindling archives, releasing animal mummies preserved in the ice for centuries due to climate changes. As preservation varies, residual soft tissues may differently expand the biological information content of such mummies. DNA studies have proven the possibility of extracting and analyzing DNA preserved in skeletal residuals and sediments for hundreds or thousands of years. Paleoradiology is the method of choice as a non-destructive tool for analyzing mummies, including micro-computed tomography (micro-CT) and magnetic resonance imaging (MRI). Together with radiocarbon dating, histo-anatomical analyses, and DNA sequencing, these techniques were employed to identify a 350-year-old Austrian Ardea purpurea glacier mummy from the Ötztal Alps. Combining these techniques proved to be a robust methodological concept for collecting inaccessible information regarding the structural organization of the mummy. The variety of methodological approaches resulted in a distinct picture of the morphological patterns of the glacier animal mummy. The BLAST search in GenBank resulted in a 100% and 98.7% match in the cytb gene sequence with two entries of the species Purple heron (Ardea purpurea; Accession number KJ941160.1 and KJ190948.1) and a 98% match with the same species for the 16 s sequence (KJ190948.1), which was confirmed by the anatomic characteristics deduced from micro-CT and MRI.

Constructional design of echinoid endoskeleton: main structural components and their potential for biomimetic applications

The endoskeleton of echinoderms (Deuterostomia: Echinodermata) is of mesodermal origin and consists of cells, organic components, as well as an inorganic mineral matrix. The echinoderm skeleton forms a complex lattice-system, which represents a model structure for naturally inspired engineering in terms of construction, mechanical behaviour and functional design. The sea urchin (Echinodermata: Echinoidea) endoskeleton consists of three main structural components: test, dental apparatus and accessory appendages. Although, all parts of the echinoid skeleton consist of the same basic material, their microstructure displays a great potential in meeting several mechanical needs according to a direct and clear structure-function relationship. This versatility has allowed the echinoid skeleton to adapt to different activities such as structural support, defence, feeding, burrowing and cleaning. Although, constrained by energy and resource efficiency, many of the structures found in the echinoid skeleton are optimized in terms of functional performances. Therefore, these structures can be used as role models for bio-inspired solutions in various industrial sectors such as building constructions, robotics, biomedical and material engineering. The present review provides an overview of previous mechanical and biomimetic research on the echinoid endoskeleton, describing the current state of knowledge and providing a reference for future studies.

Comparison of structure and composition of a fossil Champsosaurus vertebra with modern Crocodylidae vertebrae: A multi-instrumental approach

Information on the adaptation of bone structures during evolution is rare since histological data are limited. Micro- and nano-computed tomography of a fossilized vertebra from Champsosaurus sp., which has an estimated age of 70-73 million years, revealed lower porosity and higher bone density compared to modern Crocodylidae vertebrae. Mid-infrared reflectance and energy dispersive X-ray mapping excluded a petrification process, and demonstrated a typical carbonate apatite distribution, confirming histology in light- and electron microscopy of the preserved vertebra. As a consequence of this evolutionary process, the two vertebrae of modern Crocodylidae show reduced overall stiffness in the finite element analysis simulation compared to the fossilized Champsosaurus sp. vertebra, with predominant stiffness along the longitudinal z-axes.

Growth of second stage mineral in Lytechinus variegatus

Purpose and Aims: Sea urchin teeth consist of calcite and form in two stages with different magnesium contents. The first stage structures of independently formed plates and needle-prisms define the shape of the tooth, and the columns of the second stage mineral cements the first stage structures together and control the fracture behavior of the mature tooth. This study investigates the nucleation and growth of the second stage mineral.

MATERIALS AND METHODS

Scanning electron microscopy (SEM) and synchrotron microComputed Tomography characterized the structures of the second phase material found in developing of Lytechinus variegatus teeth.

RESULTS

Although the column development is a continuous process, defining four phases of column formation captures the changes that occur in teeth of L. variegatus. The earliest phase consists of small 1-2 µm diameter hemispheres, and the second of 5-10 µm diameter, mound-like structures with a nodular surface, develops from the hemispheres. The mounds eventually bridge the syncytium between adjacent plates and form hyperboloid structures (phase three) that appear like mesas when plates separate during the fracture. The mesa diameter increases with time until the column diameter is significantly larger than its height, defining the fourth phase of column development. Energy dispersive x-ray spectroscopy confirms that the columns contain more magnesium than the underlying plates; the ratios of magnesium to calcium are consistent with compositions derived from x-ray diffraction.

CONCLUSION

Columns grow from both bounding plates. The presence of first phase columns interspersed among third stage mesas indicates very localized control of mineralization.

Mineral in skeletal elements of the terrestrial crustacean Porcellio scaber: SRμCT of function related distribution and changes during the moult cycle

Terrestrial isopods moult first the posterior and then the anterior half of the body, allowing for storage and recycling of CaCO₃. We used synchrotron-radiation microtomography to estimate mineral content within skeletal segments in sequential moulting stages of Porcellio scaber. The results suggest that all examined cuticular segments contribute to storage and recycling, however, to varying extents. The mineral within the hepatopancreas after moult suggests an uptake of mineral from the ingested exuviae. The total maximum loss of mineral was 46% for the anterior and 43% for the posterior cuticle. The time course of resorption of mineral and mineralisation of the new cuticle suggests storage and recycling of mineral in the posterior and anterior cuticle. The mineral in the anterior pereiopods decreases by 25% only. P. scaber has long legs and can run fast; therefore, a less mineralised and thus lightweight cuticle in pereiopods likely serves to lower energy consumption during escape behaviour. Differential demineralisation occurs in the head cuticle, in which the cornea of the complex eyes remains completely mineralised. The partes incisivae of the mandibles are mineralised before the old cuticle is demineralised and shed. Probably, this enables the animal to ingest the old exuviae after each half moult.

Microstructure and micromechanics of the heart urchin test from X-ray tomography

The microstructure of many echinoid species has long fascinated scientists because of its high porosity and outstanding mechanical properties. We have used X-ray microtomography to examine the test of Echinocardium cordatum (heart urchin), a burrowing cousin of the more commonly known sea urchins. Three dimensional imaging demonstrates that the bulk of the test is composed of only two distinct, highly porous, fenestrated regions (stereom), in which the thickness of the struts is constant. Different degrees of porosity are achieved by varying the spacing of the struts. Drawing an analogy to vertebrate trabecular bone, where for example, human bone has a connectivity density of ≈1/mm(3), we measure up to 150,000 strut connections per mm(3). Simulations of mechanical loading using finite element calculations indicate that the test performs at very close to the optimum expected for foams, highlighting the functional link between structure and mechanical properties.

Tailored order: the mesocrystalline nature of sea urchin teeth

We investigated the pattern of crystal co-orientation at different length scales, together with variations in chemical composition and nanomechanical properties in the teeth of the modern sea urchin Paracentrotus lividus with electron backscatter diffraction (EBSD), electron probe microanalysis, energy-dispersive X-ray spectroscopy and nanoindentation testing. Modern sea urchin teeth are Mg-dominated calcite composite materials. They are distinctly harder than inorganically precipitated calcite. Some parts exceed even the hardness of dolomite. The teeth show a structuring of their mechanical properties that can be correlated to variations in major element chemical composition, such that their hardness is positively correlated to their magnesium contents. Mg/Ca ratio in Paracentrotus lividus varies between 10 and 26mol.%. Nanohardness of the tooth scatters between 3.5 and >8GPa compared to values of 3.0±0.2, 7.3±0.1 and 9.2±0.9GPa measured on the (104) planes of inorganic calcite, dolomite and magnesite, respectively. High-resolution EBSD shows that major structural units and subunits of the tooth of Paracentrotus lividus are tilted to each other by ∼3-5° and 1-2°, respectively. This indicates that the tooth is not a single crystal. With EBSD we can show that the tooth of the sea urchin Paracentrotus lividus is a hierarchically assembled biological mesocrystal with a mosaic texture. In comparison to the misorientation spread of 0.5° of calcite grown from solution, misorientation in the tooth varies between 2° and 4°. Thus, the self-sharpening feature of the tooth is enabled by a close interplay of its highly evolved micro- to nanostructure, structural unit size variations with a varying degree of crystal orientation, chemical structuring of the mineral component and a gradation of incorporated organic polymers.

Sea urchins have teeth? A review of their microstructure, biomineralization, development and mechanical properties

Sea urchins possess a set of five teeth which are self-sharpening and which continuously replace material lost through abrasion. The continuous replacement dictates that each tooth consists of the range of developmental states from discrete plates in the plumula, the least mineralized and least mature portion, to plates and needle-prisms separated by cellular syncytia at the beginning of the tooth shaft to a highly dense structure at the incisal end. The microstructures and their development are reviewed prior to a discussion of current understanding of the biomineralization processes operating during tooth formation. For example, the mature portions of each tooth consist of single crystal calcite but the early stages of mineral formation (e.g. solid amorphous calcium carbonate, ions in solution) continue to be investigated. The second stage mineral that cements the disparate plates and prisms together has a much higher Mg content than the first stage prisms and needles and allows the tooth to be self-sharpening. Mechanically, the urchin tooth's calcite performs better than inorganic calcite, and aspects of tooth functionality that are reviewed include the materials properties themselves and the role of the orientations of the plates and prisms relative to the axes of the applied loads. Although the properties and microarchitecture of sea urchin teeth or other mineralized tissues are often described as optimized, this view is inaccurate because these superb solutions to the problem of constructing functional structures are intermediaries not endpoints of evolution.

Micro-computed X-ray tomography: a new non-destructive method of assessing sectional, fly-through and 3D imaging of a soft-bodied marine worm

The detailed examination of the internal and functional anatomy of soft-bodied marine worms has, until now, only been possible using the time consuming and destructive techniques of dissection, histology and electron microscopy. This is the first description of soft body morphology in polychaetes (Nephtys hombergii) derived by means of a bench-top X-ray micro-CT scanner. The data are augmented, for comparison, by dissections, microscopy and scanning electron microscopy of the same species to show how this non-destructive technique can rapidly and reliably produce high-quality morphological data. It can also be applied to rare or unique invertebrate soft tissue material from museum collections and also to large-scale invertebrate comparative anatomical studies possibly leading to greater evolutionary and taxonomic understanding. High-definition images were obtained without the use of special tissue enhancing stains or radio-opaque fluids and it is believed that this is the first time the technique has been successfully applied to this group of invertebrates. Extrapolation of the sectional imaging of regions of the gut and the production of three-dimensional rotating and 'fly-through' imaging can assist in assessment of aspects of functional anatomy.

Skeletal deformations in medaka (Oryzias latipes) visualized by synchrotron radiation micro-computer tomography (SRmicroCT)

Synchrotron radiation micro-computer tomography (SRmicroCT) offers the possibility to investigate biomineralized structures in high detail. Two animals of adult medaka fish (Oryzias latipes) were analyzed by SRmicroCT with a resolution of 6.55 microm: the wild-type animal was normally developed whereas the second animal showed an idiopathic deformation of the cranial and axial skeleton. These deformations could be followed on the macro- and on the microscale (i.e., on the level of the individual ribs and fin bones). Our study clearly demonstrates that SRmicroCT is an excellent technique to study alterations in the skeletal structure of fish in detail.

Pushing the limit: masticatory stress and adaptive plasticity in mammalian craniomandibular joints

Excessive, repetitive and altered loading have been implicated in the initiation of a series of soft- and hard-tissue responses or ;functional adaptations' of masticatory and locomotor elements. Such adaptive plasticity in tissue types appears designed to maintain a sufficient safety factor, and thus the integrity of given element or system, for a predominant loading environment(s). Employing a mammalian species for which considerable in vivo data on masticatory behaviors are available, genetically similar domestic white rabbits were raised on diets of different mechanical properties so as to develop an experimental model of joint function in a normal range of physiological loads. These integrative experiments are used to unravel the dynamic inter-relationships among mechanical loading, tissue adaptive plasticity, norms of reaction and performance in two cranial joint systems: the mandibular symphysis and temporomandibular joint (TMJ). Here, we argue that a critical component of current and future research on adaptive plasticity in the skull, and especially cranial joints, should employ a multifaceted characterization of a functional system, one that incorporates data on myriad tissues so as to evaluate the role of altered load versus differential tissue response on the anatomical, cellular and molecular processes that contribute to the strength of such composite structures. Our study also suggests that the short-term duration of earlier analyses of cranial joint tissues may offer a limited notion of the complex process of developmental plasticity, especially as it relates to the effects of long-term variation in mechanical loads, when a joint is increasingly characterized by adaptive and degradative changes in tissue structure and composition. Indeed, it is likely that a component of the adaptive increases in rabbit TMJ and symphyseal proportions and biomineralization represent a compensatory mechanism to cartilage degradation that serves to maintain the overall functional integrity of each joint system. Therefore, while variation in cranial joint anatomy and performance among sister taxa is, in part, an epiphenomenon of interspecific differences in diet-induced masticatory stresses characterizing the individual ontogenies of the members of a species, this behavioral signal may be increasingly mitigated in over-loaded and perhaps older organisms by the interplay between adaptive and degradative tissue responses.

Plasticity of mandibular biomineralization in myostatin-deficient mice

Compared with the normal or wild-type condition, knockout mice lacking myostatin (Mstn), a negative regulator of skeletal muscle growth, develop significant increases in relative masticatory muscle mass as well as the ability to generate higher maximal muscle forces. Wild-type and myostatin-deficient mice were compared to assess the postweaning influence of elevated masticatory loads because of increased jaw-adductor muscle and bite forces on the biomineralization of mandibular cortical bone and dental tissues. Microcomputed tomography (microCT) was used to quantify bone density at a series of equidistant external and internal sites in coronal sections for two symphysis and two corpus locations. Discriminant function analyses and nonparametric ANOVAs were used to characterize variation in biomineralization within and between loading cohorts. Multivariate analyses indicated that 95% of the myostatin-deficient mice and 95% of the normal mice could be distinguished based on biomineralization values at both symphysis and corpus sections. At the corpus, ANOVAs suggest that between-group differences are due to the tendency for cortical bone mineralization to be higher in myostatin-deficient mice, coupled with higher levels of dental biomineralization in normal mice. At the symphysis, ANOVAs indicate that between-group differences are related to significantly elevated bone-density levels along the articular surface and external cortical bone in the knockout mice. Both patterns, especially those for the symphysis, appear because of the postweaning effects of increased masticatory stresses in the knockout mice versus normal mice. The greater number of symphyseal differences suggest that bone along this jaw joint may be characterized by elevated plasticity. Significant differences in bone-density levels between normal and myostatin-deficient mice, coupled with the multivariate differences in patterns of plasticity between the corpus and symphysis, underscore the need for a comprehensive analysis of the plasticity of masticatory tissues vis-à-vis altered mechanical loads.

Biomineralization and adaptive plasticity of the temporomandibular joint in myostatin knockout mice

Mice lacking myostatin (GDF-8), a negative regulator of skeletal muscle growth, show a significant increase in muscle mass versus normal mice. We compared wild-type and myostatin deficient mice to assess the postnatal effect of elevated masticatory loads due to increased jaw-adductor muscle activity and greater bite forces on mandibular condyle morphology. Microcomputed tomography (microCT) was used to provide details of internal condylar morphology and quantify bone density in three condylar regions. Biomineralization levels, as well as external mandibular dimensions, were used to characterize within-slice, within-joint, within-group and between-group variation. Dimensions of the mandible and mandibular condyle were similar between the myostatin knockout and normal mice. Knockout mice exhibited significantly more biomineralization on the outer surface of the condylar subchondral bone and along the condylar neck, most notably on the buccal side of the condylar neck. The buccal side of the inner aspect of the condyle was significantly less biomineralized in knockout mice, both for the pooled data and for the posterior and anterior condylar slices. Whilst normal mice had symmetric subchondral bone surfaces, those of knockout mice were asymmetric, with a lower, less convex surface on the buccal side versus the lingual side. This appears related to the ontogenetic effects of increased masticatory stress in the mandibles of knockout mice as compared to normal mice. Significant differences in biomineralization between normal and myostatin knockout mice, coupled with the lack of significant differences in certain external dimensions, underscores a need for information on the external and internal morphology of mineralized tissues vis-à-vis altered or excessive mechanical loads.

Application of synchrotron-radiation-based computer microtomography (SRμCT) to selected biominerals: embryonic snails, statoliths of medusae, and human teeth

Synchrotron-radiation-based computer microtomography (SRmicroCT) was applied to three biomineralised objects First, embryonic snails of the freshwater snail Biomphalaria glabrata, second, rhopalia (complex sense organs) of the medusa Aurelia aurita, and third, human teeth. The high absorption contrast between the soft tissue and mineralised tissues, i.e. the shell in the first case (consisting of calcium carbonate) and the statoliths in the second case (consisting of calcium sulphate hemihydrate), makes this method ideal for the study of biomineralised tissues. The objects can be non-destructively studied on a micrometre scale, and quantitative parameters like the thickness of a forming a snail shell or statolith crystal sizes can be obtained on a length scale of 1-2 mum. Using SRmicroCT, the dentin-enamel border can be clearly identified in X-ray dense teeth.

Improvement of microanatomical research by combining corrosion casts with MicroCT and 3D reconstruction, exemplified in the circulatory organs of the woodlouse

A SkyScan-1072 high-resolution desktop microtomograph was used to visualize the 3D morphology of the circulatory system of Porcellio scaber (Crustacea, Malacostraca, Isopoda) at the micrometer level. Prior to MicroCT investigation, the circulatory system was injected with a fast-hardening resin, permitting a better contrast of the vascular structures that are normally hollow after fixation. Stacks of tomographic images were used to reconstruct the circulatory system three-dimensionally. The spatial resolution achieved by the microtomograph is about 3.5 microm. The technique provides detailed tomographic images of the inner organs and makes precise 3D reconstructions of the circulatory system in arthropods possible. The results were compared with conventional histological data. MicroCT permits a high number of specimens to be screened in a short time, which is essential for the improvement of modern morphological research in a cladistic framework. Histological techniques, however, are still essential for gathering information at the cellular level.

Use of X-ray computed microtomography for non-invasive determination of wood anatomical characteristics

Quantitative analysis of wood anatomical characteristics is usually performed using classical microtomy yielding optical micrographs of stained thin sections. It is time-consuming to obtain high quality cross-sections from microtomy, and sections can be damaged. This approach, therefore, is often impractical for those who need quick acquisition of quantitative data on vessel characteristics in wood. This paper reports results of a novel approach using X-ray computed microtomography (microCT) for non-invasive determination of wood anatomy. As a case study, stem wood samples of a 2-year-old beech (Fagus sylvatica L.) and a 3-year-old oak (Quercus robur L.) tree were investigated with this technique, beech being a diffuse-porous and oak a ring-porous tree species. MicroCT allowed non-invasive mapping of 2-D transverse cross-sections of both wood samples with micrometer resolution. Self-developed software 'microCTanalysis' was used for image processing of the 2-D cross-sections in order to automatically determine the inner vessel diameters, the transverse cross-sectional surface area of the vessels, the vessel density and the porosity with computer assistance. Performance of this new software was compared with manual analysis of the same micrographs. The automatically obtained results showed no significant statistical differences compared to the manual measurements. Visual inspection of the microCT slices revealed very good correspondence with the optical micrographs. Statistical analysis confirmed this observation in a more quantitative way, and it was, therefore, argued that anatomical analysis of optical micrographs can be readily substituted by automated use of microCT, and this without loss of accuracy. Furthermore, as an additional application of microCT, the 3-D renderings of the internal microstructure of the xylem vessels for both the beech and the oak sample could be reconstructed, clearly showing the complex nature of vessel networks. It can be concluded that the use of microCT in wood science offers an interesting potential for all those who need quantitative data of wood anatomical characteristics in either the 2-D or the 3-D space.

MicroCT quantification of in vitro bone resorption of neonatal murine calvaria exposed to IL-1 or PTH

This study investigated how effectively a laboratory microCT (X-ray micro-computed tomography) system can quantify bone resorption in an in vitro calvarial model and how well this measure correlates with a conventional assay for calcium release (fluorometric titration). In vitro bone resorption in neonatal murine calvaria was quantified for 0.3 or 1.0 nM interleukin-1 (IL-1) or for 1.0 or 10.0 nM parathyroid hormone (PTH) treatment. Compared to control calvaria, a significantly greater fraction F of the calvarial "shell" (computed from the volumetric microCT data) was resorbed in treated calvaria of 5- to 7-day-old pups from the same litter. Excellent correlation (R2 = 0.8234) was observed between F and calcium release, and, unlike the calcium assay, the 3-D maps revealed where bone was resorbed. Mineral was preferentially lost near the sutures, and areas away from the suture were left relatively intact. MicroCT of calvaria before and after 96 h culture demonstrated that this X-irradiation neither increased control resorption nor prevented responses in the treated calvaria. Observations on calvaria from intact mice aged 1, 3, 5, 8, and 11 days showed uniformly distributed mineral (not a pronounced patchwork of "high" and "low" mineral regions) and increasing levels of mineral with age; this suggested that the spatial patterns of resorption were not related to inhomogeneities in the starting mineral distribution.