Session B47: Invited Session: Physical Organizing Principles of Biomineral Formation

Phase transitions and their energetics in calcite biominerals

Biominerals include mollusk shells and the skeletons of algae, sponges, corals, sea urchins and most other animals. The function of biominerals are diverse: mechanical support, attack, defense, grinding, biting, and chewing, gravitational and magnetic field sensing, light focusing, and many others. The exquisite nanostructure of biominerals is directly controlled by the organisms, which have evolved to master the chemico-physical aspects of mineralization. By controlling the inorganic precursor nanoparticle size, packing, and phase transitions, organisms efficiently fill space, produce tough and hard structures, with micro- or macroscopic morphology optimized for their functions. Specifically, this talk will address two key questions: Q: How are the beautiful biomineral morphologies achieved? A: Using amorphous precursor phases, with phase transitions kinetically regulated (retarded) by proteins. Q: How do organisms co-orient their single-crystalline biominerals? A: Controlling the propagation of crystallinity one nanoparticle at a time, not atom-by-atom.   

Bottom-up molecular models of hierarchical mineralized tissues: Structure, mechanics, biology

Biological materials are intriguing examples of advanced materials, which are synthesized, controlled and used for an astonishing variety of purposes—structural support, force generation, mass transport, catalysis, or energy conversion. By incorporating concepts from biology and engineering, computational modeling has led the way in identifying the core principles that link the molecular structure of biomaterials at scales of nanometers to macroscopic scales through hierarchical structures. Here we review case studies of a range of mineralized tissues, focused on bottom-up models and analyses of the structure and mechanics of mineralized tissues. We report an atomistic model of collagen, bone and describe the process of mineralization and the interplay of different hierarchical levels. Combined with experimental studies, such \textit{in silico} models allow us to simulate disease, understand catastrophic failure of tissues, and enable us to translate concepts from the living world into material designs that blur the distinction between the living and non-living systems.   

Bio-Inspired Approaches to Crystals with Composite Structures

Advances in technology demand an ever-increasing degree of control over material structure, properties and function. As the properties of monolithic materials are necessary limited, one route to extending them is to create a composite by combining contrasting materials. The potential of this approach is beautifully illustrated by the formation of biominerals where organic macromolecules are combined with brittle minerals such as calcite to create crystals with considerable fracture toughness. This talk will discuss how bio-inspired approaches can be used to generate single crystals with composite crystals through a simple one-pot method. By precipitating calcite crystals in the presence of ``occlusion species'' ranging from latex particles, to organic and inorganic nanoparticles and finally small molecules we demonstrate that high amounts of foreign species can be incorporated through control over the additive surface chemistry, and that this can lead to an enhancement of the mechanical properties of the calcite. Occlusion of 20 nm anionic diblock copolymer micelles was achieved at levels of over 13 wt{\%}, and the properties of the resuktant composite calcite crystals were measured using a range of techniques including IR spectroscopy, high resolution powder XRD and high resolution TEM. Incorporation of these macromolecules leads to crystals with structures and mechanical properties similar to those of biominerals. With sizes in the range of some intracrystalline proteins, the micelles act as ``pseudo-proteins'', thereby providing an excellent model system for investigation of the mechanism of macromolecule insertion within biominerals. Extension of these studies to the incorporation of small molecules (amino acids) again demonstrated high levels of incorporation without any change in the crystal morphology. Further, occlusion of these small molecules within the calcite lattice again resulted in a significant increase in the hardness of the calcite, a result which appears to derive from an increase in lattice strain on molecular occlusion. Finally, the generality of this strategy is demonstrated by its extension to the incorporation of inorganic particles such as magnetite and gold within calcite, leading to the formation of inorganic-inorganic composites.