Hard-soft matter interfaces: from understanding to engineering

The term material is extremely broad, so for simplicity's sake, materials are often described as either hard or soft . While hard materials such as ceramics are strong, they are often brittle. In contrast, soft materials such as polymers are often mechanically weak, but can show valuable elastic properties. Combining these two in one new composite can therefore give rise to remarkable new materials, which benefit from the advantages of both components. This is just one benefit of combining hard and soft materials. In fact, interaction between hard and soft materials occurs in all walks of life. Whether a medical implant is accepted in the body depends on how cells recognise and interact with the hard implant surface. Controlling this requires that we understand molecular-scale processes, which govern how soft biomolecules interact with surfaces - and also processes occurring on much larger length-scales, most importantly how cells interact and recognise a hard surface. In this case, the soft matter must adapt to the hard surface, potentially changing its shape and chemical properties. This is important for many applications - from the toxicology of nanoparticles to strategies for environmental remediation. Perhaps surprisingly, it is not only hard materials which control the soft - the converse also occurs. Biomineralisation - the formation of mineral structures such as bones, teeth and seashells by organisms - shows this beautifully. It is through interaction of growing minerals with soft, organic matter that Nature produces these materials with their remarkable shapes and properties. Biominerals are often very different from synthetic minerals. While a crystal of calcite (calcium carbonate) precipitated in the lab has a regular, geometric form, in the spines of a sea urchin a calcite single crystal is sponge-like, with curved surfaces replacing flat crystal planes. Biominerals are also almost always composites - soft organic molecules are embedded within the crystal. It is this structure which gives biominerals such wonderful mechanical properties - indeed, tooth enamel is one of the hardest materials known. Soft matter not only affects the properties of biominerals, but controls almost every stage of their formation - from the earliest stages of nucleation, through growth, to production of the final biomineral. Insoluble organic molecules define the special environments in which biominerals form and nucleate, while small, soluble organic molecules bind to a crystal during growth, influencing its shape. Clearly, understanding how soft and hard materials interact and control each other is of great importance, and has applications spanning disciplines from medicine to geology, from climate science to nanotechnology. The strategies used by biology to produce biominerals can be applied to the design and fabrication of new materials - where the structure can be controlled at the atomic scale, and the synthesis carried out under mild conditions. If we can design molecules to attach to surfaces strongly, we can use them to inhibit crystal growth. Crystals growing where they should not - in boilers, heating systems and oil wells - remains a major problem in industry and domestic life. Finally, many biomaterials are carbonates. They are a part of the planet's carbon cycle - a major way in which carbon dioxide is removed from the atmosphere for long periods. In the oceans, structures such as coral reefs are under threat due to changes in oceanic conditions; we need to understand the mechanisms of their growth to understand fully why. Removing carbon dioxide from the atmosphere and converting it into carbonates is a possible carbon capture strategy. The research carried out in this grant will use both experiment and theory in a unique way to shed light on the fundamental mechanisms behind this most fascinating and essential capability of the biosphere and to harness this knowledge to develop of novel materials.

The thrust of this project is to develop understanding that will enable new technologies in many environmental and industrial areas of key importance. Progress will be monitored by the Steering Committee (which involves our private sector partners) to produce an optimised transfer of knowledge to partners and user communities. The project has the potential to deliver maximal impact, particularly in the medium to longer term. The chemical interaction of cell macromolecules with solid surfaces is the basic mechanism underlying an enormous range of microbial processes in industry and nature. Natural attenuation and biodegradation of pollutants relies on the bacterial colonisation of surfaces in habitats such as soils, sediments or aquifers. This work relates strongly to Environment Agency programmes in the area of environmental quality and safety (contacts through the Sheffield Cell-Mineral Centre). These areas of environmental remediation also link to the broad area of environmental biotechnology for the treatment of waste and industrial effluent and biofouling of fluid transfer in water and oil pipelines. The interaction of radionuclides with cell and mineral surfaces is of major importance in the environmental behaviour of radionuclides arising from industrial contamination and waste disposal (working with the Nuclear First DTC). Biphosphonates are known to be effective in the treatment of osteoporosis. Our work will enable the design of better inhibitors for bone resorption (project partner: Pfizer Institute). Results on the nanoscale structure of bone will lead to new replacement biocomposites. Work on the control of crystal growth and inhibition (leading to the design of better inhibitor molecules) will provide the means to prevent scaling or deposition in heating plant pipes, in beer production and in the use of consumer products (Proctor and Gamble). New models of nucleation and growth as the aggregation of nanoparticles will inform biomimetic strategies for the manufacture of nanoscale biocomposites. New strategies for recovering the 60% of oil remaining in chalk reservoirs after standard extraction methods rely on understanding the growth and structure of the fossil coccoliths in chalk and their interaction with the oil (Copenhagen and industrial partner Maersk). Carbon capture strategies involving the removal of carbon dioxide as carbonates in the pores of sedimentary rocks require knowledge of the nucleation and growth of carbonates under confinement. Consortium work on nucleation, growth in confinement and crystal growth control will feed into new energy strategies (project partner Molecular Foundry and the Center for Nanoscale Control of Geologic CO2). High level electron microscopy of the hard-soft interfaces characteristic of biomineralising systems will be applied and developed to access these systems down to the atomic level. This will lead to new techniques relevant for the next generation of electron imaging (project partner JEOL). The integrated use of molecular and mesoscale methods will open up new methodological developments in simulation (Accelrys). The project will train at least 10 PhD students (not counting studentships gained by leveraged funding) and about 13 postdocs in a multidisciplinary project with major international collaborations. Joint theoretical/experimental collaboration will be strongly encouraged and specific training will be given as required. This will produce people with an exceptionally broad base of skills, including transferable skills. Students and postdocs will have many opportunities to gain international recognition. They will be encouraged to enter the annual House of Commons SET for Britain to meet UK policymakers and see their work in a public context. The results and implications of the work will be communicated to the general public through school, public discussions (Caf Scientifique) and the media - all routes for advocacy of the physical sciences.