Structure-property relationships of a biological mesocrystal in the adult sea urchin spine

Abstract

Structuring over many length scales is a design strategy widely used in Nature to create materials with unique functional properties. We here present a comprehensive analysis of an adult sea urchin spine, and in revealing a complex, hierarchical structure, show how Nature fabricates a material which diffracts as a single crystal of calcite and yet fractures as a glassy material. Each spine comprises a highly oriented array of Mg-calcite nanocrystals in which amorphous regions and macromolecules are embedded. It is postulated that this mesocrystalline structure forms via the crystallization of a dense array of amorphous calcium carbonate (ACC) precursor particles. A residual surface layer of ACC and/or macromolecules remains around the nanoparticle units which creates the mesocrystal structure and contributes to the conchoidal fracture behavior. Nature’s demonstration of how crystallization of an amorphous precursor phase can create a crystalline material with remarkable properties therefore provides inspiration for a novel approach to the design and synthesis of synthetic composite materials.

Structure and mechanical properties of selected protective systems in marine organisms

“…There is a gradient in porosity, with porosity increasing substantially from~10% on the surface and in the growth rings to~60% in the medullary core. These spines are a model for biologically controlled crystal growth and consist of a mesocrystal [164,165]. Originally Fig.…”

“…thought to be a single crystal [166,167], it has recently been shown that the structure consists of periodic and uniform nanocrystals, 30-50 nm in diameter, with parallel crystallographic alignment (Fig. 22a-b) [68,[163][164][165]. These nanocrystals are held together with layers of amino acids (mainly aspartic and glutamic acid) with a thickness of several hundred nanometers [165][166][167].…”

“…This results in a structure that fractures in a manner similar to glass (Fig. 22c) but presents the diffraction pattern of a single crystal [164].…”

Genetic Algorithm‐Guided Discovery of Additive Combinations That Direct Quantum Dot Assembly

“…[1][2][3] These bioinspired methods are characterized by mild reaction conditions and promise the ability to generate structures comparable to those found in nature. Central to biogenic control over mineralization is the use of soluble organic additives, where these can even guide the assembly of composite materials [4][5][6][7][8][9] with superior mechanical properties. [ 3,4,10 ] Many bioinspired mineralization strategies therefore utilize either naturally extracted biomacromolecules or their synthetic analogues, [ 1,2,5,7,9,10 ] and even small organic species such as amino acids and surfactants can exert considerable control over mineralization, sometimes supporting the formation of complex particle assemblies.…”

“…Central to biogenic control over mineralization is the use of soluble organic additives, where these can even guide the assembly of composite materials [4][5][6][7][8][9] with superior mechanical properties. [ 3,4,10 ] Many bioinspired mineralization strategies therefore utilize either naturally extracted biomacromolecules or their synthetic analogues, [ 1,2,5,7,9,10 ] and even small organic species such as amino acids and surfactants can exert considerable control over mineralization, sometimes supporting the formation of complex particle assemblies. [ 5,6,8,[11][12][13] While attractive, however, this approach is still hampered by the diffi culty in selecting appropriate organic additives-and in particular combinations of additives-to give materials with target structures and properties.…”