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From Confinement to Composites: Bio-inspired Crystallisation

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Biominerals exhibit many remarkable features which ensure that they are optimised for their particular function, including complex morphologies, hierarchical organisation and superior mechanical properties. Further, unlike their synthetic counterparts, biominerals are produced under mild reaction conditions. It is envisaged that elucidation of the key strategies employed by organisms to produce biominerals will provide inspiration for the design and fabrication of new materials. This talk will focus on two key features of biominerals – that these structures form within constrained reaction environments rather than in bulk solutions, and that they are typically composite structures where organic macromolecules are embedded within inorganic crystals. Biological systems are based on compartmentalisation, and the formation of biominerals is no exception. We are currently investigating a series of systems including crossed cylinders, track-etch membrane pores and droplet arrays which offer confinement from the nanometer to the micron scale, and experiment demonstrates that confining the reaction volume can significantly affect crystal nucleation and growth processes. The composite structure of crystalline biominerals is also fascinating, especially when it is considered that recrystallisation is a common technique for purifying crystalline materials. Experiments are being carried out to better understand how such composite crystals form, using the entrapment of polymer particles within calcite single crystals as a model system. We demonstrate that very high levels of entrapment can be achieved, generating crystals occluding over 20 vol% of particles, according to the particle surface chemistry and the reaction conditions. High resolution transmission electron microscopy (TEM) is used to visualise how the particles are embedded within the calcite lattice. That such composite crystals show modified properties from pure calcite is also shown through nanoindentation studies.

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