This workshop is focused on understanding structure-property relations in biocomposites with a hierarchy of microstructure, such as nacre, bone and coral. In particular, we are seeking to unite the extensive and growing body of knowledge on modelling the nucleation of biominerals, such as calcium carbonate and apatites, with coarse-grained approaches to study self-assembly of biopolymers, such as proteins and polysaccharides, and relate this to the latest experimental measurements of microstructure and mechanical properties of biocomposites. We welcome contributions from molecular, mesoscale and continuum modellers with an interest in biological or bioinspired systems, and from experimentalists using cutting-edge techniques to study the morphology or functional properties of such materials.
Confirmed invited speakers include:
- Prof Lia Addadi, Weizmann Institute
- Prof Matthew Collins, University of York
- Prof Lara Estroff, Cornell University
- Prof John Spencer Evans, New York University
- Prof John Harding, University of Sheffield
- Dr Daria Kokh, Heidelberg Institute for Theoretical Studies
- Prof Nora de Leeuw, University College London
- Prof Harry van Lenthe, KU Leuven
- Prof Bernd Markert, University of Stuttgart
- Dr Boaz Pokroy, Technion - Israel Institute of Technology
The microstructure of different biominerals with respect to inorganic and organic components, as well as the organic/inorganic interfaces is now being explored in great detail. State of the art electron microscopy has been successfully applied to nacre (Gries, Kröger et al. 2009). Furthermore, X-ray nanotomography on the coral skeleton allows 3D imaging of structural features, with resolution down to 50 nm, enabling the characterization of the internal structure of biocomposites and possibly the differentiation of the organic and inorganic components. Characterisation of the distribution of organics inside corallites is also being undertaken, along with composition analysis (polysaccharides, chitin). Several key proteins involved in the eggshell structure and formation have now been identified and sequenced (Mann and Siedler 1999). Coupled with structural studies (Chien et al 2009) these identify potential growth pathways for this complex mineral.
Based on all these results, several different biopolymers can and have been identified as good candidates for theoretical modelling of mineral formation in a variety of biomineral systems. Simulations of large biomolecules and their mineral counterparts have now become possible on an atomistic level (Freeman et al 2011, Kubiak and Mulheran 2009) and have been extended to tackle crystallization with the addition of a biomineralizing molecule (Freeman et al 2010) with the long time scale method metadynamics. We propose to bring together modelling work that will investigate the structure and mechanics of biominerals produced with and without inhibitors, their organic matrices and mineral phases in order to identify suitable organic components with phase transition potentials by interdisciplinary techniques (Weiss et al. 2009).
Collagen comprises one third of the human proteome. Type I collagen, which comprises half of the volume of bone, melts in solution at below body temperature. However, following assembly into fibrillar bundles, the melting temperature rises by almost 30 °C. Numerous efforts to further enhance the denaturing temperature by organic tanning have been attempted for thousands of years but, until the advent of metal salts, it was not possible to raise the temperature by more than 15 °C. Chrome tanning can raise the denaturation temperature by more than 50 °C, and it has been speculated (Covington et al. 2008) that the mechanism for this is not cross-linking, but the result of molecular constraints formed within the fibril bundles, locking them together. Bone arguably represents an extreme example of the same process, since the intergrowth of apatite minerals so contained in the composite that the chains cannot melt, but instead decompose at temperatures above 150 °C (Covington et al. 2008).
To clarify the mechanisms of collagen stabilization, there is a clear need to model a very large-scale structure (e.g. a Smith micro-fibril of five triple helices within a single quarter-stagger) in order to understand the physical properties of the material and age related changes which appear to be linked to changes in both the mineral (Fratzl et al. 2004) and collagen (Wang et al. 2002). Some significant advances have already been made, notably the first (low resolution) structure of the microfibrillar structure (Orgel et al. 2006). Despite considerable investigation of the role played by residues in the stability of the triple helix in solution (e.g. Kar et al. 2008), the complete collagen biocomposite has not been modelled. We therefore propose to bring together researchers working on molecular modelling of apatites (e.g. Almora-Barrios et al. 2010) with those undertaking the latest coarse-grained models of collagen (Russo et al. 2010) and generic models of surface-induced phase transitions (Antypov and Elliott, 2008) to examine the stability of the collagen triple helix, and examine the role of compression in collagen stabilization.