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Thursday 12 Nov 2015[NEST seminar] Bio-Inspired Approaches to Bespoke Crystals: From Colour to Mechanical Properties

Professor Fiona Meldrum - School of Chemistry, Faculty of Mathematics and Physical Sciences, University of Leeds

HAR/170 (3D Visualisation Suite) 13:30-14:30

Crystals are typically pictured as solids with regular, geometric morphologies and planar faces, where the overall symmetry is determined by the underlying atomic-scale packing. Turning to biology, however, we are met by biominerals such as seashells, teeth and bones, whose hierarchical organization, composite structures and complex morphologies challenge many of these ideas. Biominerals therefore provide a unique inspiration for the design and synthesis of new materials.

This talk explores how a range of bio-inspired approaches can be used to control the properties of synthestic crystals. Looking first at the composite structures of biominerals, even single crystal biominerals contain proteins embedded within the crystal lattice. This is a surprising observation as the process of recrystallisation is traditionally considered as an effective method for purifying crystalline materials. Here, we adapt this biogenic strategy to create a novel one-pot method for creating nanocomposites. Using particles rather than proteins as simple crystal growth additives, we show that it is possible to achieve high levels of particle occlusion by tuning the particle surface chemistry and the crystal growth conditions. Measurement of the mechanical properties demonstrates that occlusion of block copolymer micelles generates "artificial biominerals" with hardnesses comparable to those of biogenic calcite.

We then extend this strategy to investigate the occlusion of amino acids within calcite and show that we can systematically tune the amounts occluded over a large concentration range. Determination of the hardnesses of these series of samples then enables us to determine the mechanism of hardening in these samples.
We then explore the use of mixtures of organic additives to control crystallisation. As this potentially opens up a vast reaction space, we have employed combinatorial approaches, guided by genetic algorithms, to rapidly identify combinations of additives that give crystals with target properties. This approach is inspired by the diversification strategies observed in natural evolution, and uses selection, recombination and mutation strategies to rapidly identify and optimise the reaction conditions. We show that such combinatorial methods can be used in conjunction with high-throughput screening to rapidly identify combinations of small organic molecules capable of directing the formation of photoluminescent quantum dot minerals in aqueous solution and at room temperature.

Finally, we employ microfluidic devices to study crystallisation processes. With features such as flow, confinement, and spatial organisation, these devices provide excellent mimics of biomineralizing systems, and - thanks to their optical transparency - we can watch individual crystals grow. We use these to examine the mechanisms of calcite growth and show that small molecules additives do not affect the morphologies until the crystal are almost micron-sized. We also carry out crystallisation within a microfluidic "crystal hotel" and demonstrate that we can use it to combine biogenic strategies including constrained physical environments, soluble additives, tailored reaction conditions and surface functionalities to generate single crystals with pre-defined macroscopic shapes, patterned microstructures and crystallographic orientations.

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