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Theme C: Composites

The central challenge to simulating biocomposite structures is the extreme range of time and length scales required to adequately characterize such materials. For example, in the case of bone, the packing of apatite crystals in and around macromolecular collagen bundles involves millions of atoms, whereas the most common treatment for osteoporosis is based on the use of small molecules of order tens of atoms in size. This theme will address the challenge of simulating hard-soft interfaces in biocomposites materials using a combination of: (i) a robust generic methods for obtaining organic-inorganic force field terms, (ii) coarse-grained polymer models for rapid relaxation and exploration of chain conformations, and (iii) reverse-mapping techniques for fitting atomistic structures to coarse-grained models. These will be integrated with a package of experimental work to characterize stability of collagen fibrils in different environment, and effects of organic additives on apatite and calcium carbonate nanocrystallite morphology in bone and coral.

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Achievements so far, June 2013

  • Coarse-grained models of short, collagen-mimetic oligopetides that can preserve the pyrrolidine pseudorotation, which has been implicated in collagen assembly and dynamics.
  • Mapping of hydroxylation and deamidation patterns from experimental sequence data onto the 3D structure from rat tail collagen of Orgel et al.
  • A REMD methodology that can produce melted collagen molecules at higher temperatures while allowing efficient exchanges of these structures to lower temperature replicas.
  • NST ensemble simulations consisting of a short collagen triple helix surrounded by these solvent models has revealed differences in the stress/strain properties.
  • Microstructural arrangements in corallites imaged using electron microscopy
  • Amino acid compositions of organic phase in corallites determined