Lessons from Nature for the Construction of Ceramic Cellular Materials for Superior Energy Absorption

Abstract

Sea urchins (Echinoidea) are an evolutionary highly successfully and diverse class of animals populating earth's oceans for more than 450 millions of years. [1] Depending on the environmental challenges, sea urchins have adapted in behavior, size, and shape of their test (i.e., shell) resulting in a large variety of spine types. [2] Ranging from disk-like sand dollars living on and underneath the seabed to reef-dwelling spherical melon sea urchins: all sea urchins employ nanocrystalline calcium carbonate as a basic building material [3,4] forming lightweight-constructed shells and spines. The sponge-like calcite network (stereom) of spines, indeed, can reach ultra-high porosity levels of up to 75 vol%. [5] While advanced foams can reach an equally high porosity, [6] most porous ceramic materials derived from conventional processing techniques (e.g., starch-blended casting) are characterized by a maximum characteristic porosity of % 68 vol%.Living in high tidal energy environments, pencil [Heterocentrotus mammillatus (HM)] and lance [Phyllacanthus imperialis (PI)] sea urchins have long ( 150 mm) and thick (Ø % 10-15 mm) blunt spines which are not only used as spacers for predators but also to wedge the animals into pits of the reef. For this habitat, evolution has optimized spines of these sea urchins for combined light-weight and graceful failure fracture behavior. The large pore volume is accessible to sea water and is partially filled with organic material to enable spine growth and repair. Also, it is important to note that the spines are not characterized by a simple, homogenous porosity throughout the entire spine: there are layers and gradients of various pore sizes, geometries, and porosity levels.The entire solid body of sea urchins, i.e., including spines and teeth, is composed out of magnesium calcite (Ca x Mg 1Àx )CO 3 [3,7,8] grown (and regenerated) by a complex process of biomineralization. [4] In particular, sea urchin teeth COMMUNICATION [*] Dr. Sea urchin spines combine extreme lightweight construction with impact resistance and improved mechanical strength although being made of presumably brittle calcium carbonate (calcite). Lance and pencil sea urchins (Phyllacanthus imperialis and Heterocentrotus mammillatus) are of particular interest as they exhibit large and mechanical very stable spines and the constructional concepts of these spines was translated into graded porous alumina ceramics derived from starch-blended slip casting. A high level of porosity (>30 vol%) is identified as the important element for graceful failure in polycrystalline alumina and graded porosity, i.e., layers of higher and lower density, can significantly improve the impact resistance of the material giving raise to what we refer to as cascading graceful failure: a mechanical response of porous materials with curved layers of graded porosity that maintains a high level of compressive strength even after the linear elastic threshold is surpassed and local structural collapse occurs. 1042 wileyonlinelibrary.com ß

3D-printed cellular tips for tuning fork atomic force microscopy in shear mode

“…As a succession to natural instances in motion deceleration, shockwave suppression, and mechanical force reduction 14 , porous structures widely found in biological skeletal systems such as cancellous bones have been extensively investigated in numerous energy-absorbing applications [15][16][17][18] . Emulating these geometrical constructions and coupling with advanced additive manufacturing techniques in microscale, artificial cellular microarchitectures, referred to as controlled microstructural architectured (CMA) material [19][20][21] , can be structurally programmed with a controllable geometry and spatial configuration for advantageous sizedependent metamechanical properties 22,23 , such as low density but strong robustness 24 , high stiffness-to-weight ratio 25 , excellent resilience 26,27 , mechanical tunability 28,29 , and in particular, energy absorption [30][31][32][33] .…”

Echinoid skeleton: an insight on the species-specific pattern of the Paracentrotus lividus plate and its microstructural variability

“…In living organisms, this stereom offers an attachment site for the catch apparatus fibres connecting the spine to the tubercle [33][34][35]. Similarly to the suture galleried stereom, this trabecular system can disseminate directionally applied stress; however, the growth bandings could presumably influence the mechanical response of the tubercle as shown in the spines [36][37][38][39]; hence, further investigations are necessary. Finiteelement analysis reported the direction of higher stiffness at −73.872°.…”

The Plant-Like Structure of Lance Sea Urchin Spines as Biomimetic Concept Generator for Freeze-Casted Structural Graded Ceramics

“…Small quantities of organic macromolecules (<1 wt.%) are within the magnesium calcite domains [ 13 ]. The hierarchical organized lightweight construction of the spine is characterized by remarkable mechanical properties such as high strength [ 14 , 15 ] and beneficial failure behavior dissipating energy in large quantities [ 16 ] despite their cellular, brittle microstructure. The transfer of such desirable properties such as strength, high energy dissipation capacity and lightweight into ceramic-based materials and structures is of particular interest for the area of separation technology/filtration (e.g., particle filtration, liquid filtration), in chemical and thermal process engineering (e.g., catalyst carriers, pore burners), medical technology (e.g., bone substitute) and in lightweight construction under high pressure.…”