All collections were considered Limited Impact Research except the collections of L. variegatus from Mangrove Bay which were conducted under collection permits 140409 and 140803 from the Government of Bermuda, Department of Environmental Protection. High stress concentration occurs in the small region of the wedge between the barbs, counterbalanced by lower stress zones extending axially into the body of the wedge. This primarily involved imaging and microCT analysis of spine morphology, but also included preliminary analysis of some aspects of the chemical composition. Preliminary chemical analyses were made on polished sections of spines to search for chemical variation in the materials being investigated (see Materials and Methods). To better understand the complexity of the spines microstructure we created a model of a Sea Urchin spine which incorporates 3D geometry based on microCT imaging (Figure 2), and anisotropic material properties (see Materials and Methods for details). Top arrow points to the root of crack initiation. Appendage length data are means, s.e.m., n = 12 (full length spines), n = 6 (cut spines), n = 1030 (tube feet, TF). Research School of Engineering, Australian National University, Canberra, Australian Capital Territory, Australia. Structure-property relationships of a biological mesocrystal in the The unique physical properties of sea urchin spines are well studied and have been shown to consist of a large single crystal of magnesium-containing calcite [8,9]. C: Fracture surface of a wedge of the spine (scale bar=100 micron). Obtained microCT images: HNL. Each voxel was converted into an 8-node hexahedral element. We present a functional assay to investigate mechanisms of tissue regeneration and biomineralization by measuring the regrowth of amputated tube feet (sensory and motor appendages) and spines in the sea urchin, Lytechinus variegatus. Biological cylindrical structures often fail in elastic buckling due to combined axial compression and bending loads [11]. The 3D microCT image was converted into a finite element mesh by the direct voxel conversion method; a discussion of the method is detailed elsewhere [20]. Top: outer surface of spine. Tissues and cells were fixed in 4% paraformaldehyde in PBS. However, much more careful analytical work is required to definitely establish the patterns and examine whether they apply to all wedges and spines. No stress is seen on the body of barbs and central cylinder. epidermis) it promotes differentiation [21,42]. The unique micromechanical properties of sea urchin spines are likely related to their intricate mesoscopic structure and microscopic architecture (Tsafnat et al., 2012),

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