Sea urchin spines protect the animal's body from predators and from the effect of high energy environments. The spines of urchins from different orders, families and genera have very different sizes, morphologies and microarchitectures, and the different designs of sea urchin spines reveal much about the design space available for functional biogenic calcite-based structures. The 3D microarchitecture of primary spines of a number of sea urchins was studied with synchrotron microCT and reconstructed with 5 μm or smaller voxels (volume elements), and similarities and differences were determined in order to better understand the design space. Hollow spines from different genera of the family Diadematidae, order Diadematoida, are one type of solution, but significant differences were observed within this phylogenic subset. Spines from members of order Echinoidea, family Toxopneustidae, employ a very different strategy, one that emphasizes interconnected trabeculae to a greater degree than do the diadematids. Numerical data for some 3D structural characteristics are presented, data that would be impractical to obtain by methods other than microCT.
Study of the composition and 3D chemical distribution of the particles that come from space are of great interest since
they can provide information about the early stages and evolution of the solar system. The size of these samples varies
with the smallest ones in the micron and even sub-micron range. X-ray fluorescence microCT (computed tomography)
with focused X-ray beam can be successfully used to study these kinds of samples. This is especially important when
sectioning is not feasible, or it is undesirable either due to the risk of contamination, as is the case with comet particles
recently collected by the NASA Stardust mission, or the requirement for further analysis by different characterization
techniques. X-ray fluorescence microCT measurements on several space samples were performed at the beamline 6-2
using the existing microprobe setup. Two mirror optical system is used for beam focusing with an additional set of KB
mirrors located in the hutch near the sample to focus the beam further down to 2x4 microns. Incident X-ray energy is
selected with a monochromator in the range of 5 to 20 keV. Fluorescence data was collected with Si(Li) fluorescence
detector and PIN diode was used to collect attenuation data that provides additional information for fluorescence
tomography reconstruction. The results of the measurements of two micrometeorites with sizes of approximately 100
microns, are presented.
Plate-like samples are particularly challenging to reconstruct with computed tomography (CT) while preserving sensitivity to very small features within the sample. Specifically, quantifying fatigue crack openings of ≤ 2.5 μm in compact tension samples with maximum cross-sections of 25 mm is impractical with conventional microCT. If one is constrained to use plate-like samples, then an alternative approach to conventional microCT is needed. Imaging with X-ray phase contrast offers increased sensitivity compared to X-ray absorption-based techniques. Synchrotron X-ray phase contrast microradiographs (propagation method) coupled with multiple-angle stereometry are used to map the 3D position of fatigue crack surfaces within aluminum samples. The method is briefly outlined, and crack positions obtained with phase stereometry are found to agree with those determined from absorption microCT. Preliminary calculations of phase contrast derived from a sample fractured in fatigue are compared with phase micrographs of the same sample: at present agreement is only approximate.
Newts are the most developed vertebrates which retain the ability as adults to regenerate missing limbs; they are, therefore, of great interest in terms understanding how such regeneration could be triggered in mammals. In this study, synchrotron microCT was used to study bone microstructure in control forelimbs and in forelimbs regenerated for periods from 37 to 85 days. The bone microstructure in newts has been largely neglected, and interesting patterns within the original bone and in the regenerating arm and hand are described. Periosteal bone formation in the regenerating arm and finger bones, delayed ossification of carpal (but not metacarpal) bones and the complex microstructure of the original carpal bones are areas where microCT reveals detail of particular interest.
Sea urchins employ as wide a range of composite reinforcement strategies as are seen in engineering composites. Besides tailoring reinforcement morphology and alignment to the functional demands of position, solid solution strengthening (high Mg calcite), inclusion toughening (macromolecules), functional gradients in mineral reinforcement morphology, composition and dimensions and mineral interface tailoring are other tactics important to achieving high toughness and high strength in sea urchin teeth. Teeth from different echinoid families illustrate combinations of reinforcement parameters and toughening mechanisms providing good functionality, a virtual probe of the available design space. This paper focuses on a multi-mode x-ray investigation of sea urchin teeth studied on scales approaching 1 µm in millimeter-sized samples, in particular mapping 3-D microarchitecture with synchrotron and laboratory microCT and mapping Ca1-xMgxCO3 crystal composition x and microstrain and crystallite size via microbeam diffraction.