title: Microstructure and micromechanics of the heart urchin test from X-ray tomography.
abstract: 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.
authors.affiliation: Nano-Science Center, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark.
authors.forename: D
authors.initials: D
authors.lastname: Müter
authors.affiliation: Nano-Science Center, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark.
authors.forename: H O
authors.initials: HO
authors.lastname: Sørensen
authors.affiliation: Department of Physics, Technical University of Denmark, Kongens Lyngby, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Oddershede
authors.affiliation: Nano-Science Center, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark.
authors.forename: K N
authors.initials: KN
authors.lastname: Dalby
authors.affiliation: Nano-Science Center, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark.
authors.forename: S L S
authors.initials: SLS
authors.lastname: Stipp
mesh_terms: D060105:Animal Shells / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000502:physiology*; D000818:Animals; D019245:Compressive Strength / Q000502:physiology; D003198:Computer Simulation; D055119:Elastic Modulus / Q000502:physiology; D008954:Models, Biological; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D012617:Sea Urchins / Q000033:anatomy & histology* / Q000502:physiology*; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016474:Weight-Bearing / Q000502:physiology
keywords: Biomineralisation; Echinoids; Finite element modelling; X-ray microtomography