Learning lessons from nature to build organic structures

A novel project based at the University of Sheffield is seeking to model how natural structures, such as bones and egg shells, form and grow. The research could lead to a number of important applications in a range of fields such as bio-devices and medicine.

Professor John Harding, of the Department of Engineering Materials at the University of Sheffield, is leading the project to investigate how biomaterials self-assemble and regulate their growth and structure. Bones, teeth and shells are all examples of biominerals for which an organic scaffold controls how and where mineral crystals will grow, thereby determining their final structure. The result is a complex material, which has characteristic structure at many lengthscales, as well as unusual properties. An understanding of these properties is essential in medicine, where biocompatible prosthetics are needed. These materials also offer clues to how new materials and structures can be designed.

Biomaterials self-assemble and, under the right conditions, ordered structures emerge from simple nanoscale components. Professor Harding's project, which involves four UK universities (Sheffield, Warwick, UCL and Cambridge) and several industry partners, is seeking to understand how all this happens. For example, eggshell is made from calcium carbonate, a constituent of rocks such as calcite and limestone. As Professor Harding explains: "If we could understand the mechanisms by which chickens and other organic systems produce unusual crystals, we could use these mechanisms to design new materials with useful properties".

Professor Harding's team performed simulations which involved adding a protein, found in eggshells, to nanoparticles in order to discover how the protein would affect the particles' growth rate and structure. In a similar set of simulations, the team looked at coccoliths, individual plates of calcium carbonate (the main constituent of chalk) used by algae to build a protective casing. All of these studies centred on one central question: 'How do organic molecules succeed in controlling the growth and formation of natural structures?'.

In order to simulate how protein and water molecules marshal nano-sized particles of calcium carbonate to build up the structure of eggshell, the team turned to HECToR, the UK National Supercomputing Service. Many simulations, each involving 100,000 atoms, are needed to work out just how the molecules and particles interact, but few computers worldwide are powerful enough to tackle these questions. HECToR, however, is capable of 63 million million calculations a second. "The computational modelling we undertook using HECToR enabled us to determine how proteins control the structure of calcium carbonate. This is a big step towards understanding how the chicken makes the shell. We couldn't have done a project of this size before HECToR" said Professor Harding.

Professor Harding looked at how crystal growth is affected by water molecules. In a related study, he worked with polysaccharide and peptide molecules to determine which molecules will bind to specific surfaces – essentially pairing up molecules with surfaces they bind best to. In doing so, Professor Harding is aiming to determine how organic molecules control crystal growth, and likewise how crystal surfaces can control the shape of the molecules. This has important implications for the design of biosensors and in particular the use of micro-cantilevers for assessing the composition of solutions and the assaying of biomolecules.

For further information, please contact Ian Kingsbury:

tel: 0114 22 25957

email : i.r.kingsbury@sheffield.ac.uk

Suggested link:

www.shef.ac.uk/materials/staff/jharding.html

Image credits: Top: Photo of Emiliana by Steve Groom, at MicrobeWiki. Middle: Image courtsey of the National Oceanography Centre, Southampton. Bottom: Image of Flamborough Head, at www.manorhouse.clara.net

Notes: This research was funded by the Engineering and Physical Sciences Research Council (EPSRC), one of the UK Government's 7 Research Councils.