BIO-INSPIRED APPROACHES TO FUNCTIONAL NANOSTRUCTURED MATERIALS

This research proposal focuses on developing methods for the fabrication of new materials with controlled structures and advanced properties. Our approach takes its inspiration from the remarkable materials that are biominerals. Although biominerals, which include structures such as bones, teeth and seashells, are produced under mild reaction conditions, they are characterised by unique morphologies and properties optimised for their function. Many of these properties, such as enhanced resistance to fracture, can be attributed to the fact that biominerals are composite materials - where the hard inorganic mineral is combined with soft organic molecules - and their structures are typically organised over many different length scales. Notably, biominerals comprising single crystals (such as sea urchin spines) are also composite materials, where proteins are embedded within the single crystal host. This is a surprising observation as the process of recrystallisation is traditionally considered as an effective method for purifying crystalline materials. Nature, however, shows us that it is entirely possible to create composite materials in this way.

In the proposed work we will develop methods to incorporate a range of organic and inorganic nanoparticles within single crystal hosts. In doing so, we will create new functional materials by combining functional host crystals with functional guest particles. The project is summarised under three main goals. Firstly, we will determine the fundamental design rules governing the incorporation of particles within single crystals. This will be achieved by investigating how the size, shape and surface functionalisation of the particles affects their incorporation in a range of crystals including calcium carbonate and zinc oxide. This work will require us to synthesise novel polymer particles based on anionic diblock copolymers, and to functionalise the surfaces of inorganic nanoparticles with water-soluble anionic block copolymers. We will also extend the work to study the incorporation of vesicles and worm-like micelles. After establishing the fundamental design rules, we will use these to fabricate novel microencapsulation systems. A key feature of our new host-guest systems is that nanoparticles are completely entrapped within a single crystal, and hence they should be protected from oxidation/reaction, light or thermal degradation, or from leaching. They are therefore ideally suited to microencapsulation applications. A range of materials will be occluded within single crystal CaCO3, including industrially relevant oxidation-sensitive actives such as enzymes and Vitamin E. Finally, we will generate inorganic/inorganic nanocomposites by incorporating inorganic nanoparticles within inorganic single crystals. This provides an unprecedented opportunity to introduce contrasting functionalities (e.g. optical, electrical, and magnetic) - which cannot be achieved with a single component material. The ability to control features such as the size and separation of the occluded nanoparticles, and their interface with the host crystal is expected to lead to unique nancomposites with tunable physical properties.

This integrated approach will provide a general methodology for preparing next-generation nanocomposite crystals that combine functionality with hierarchical structure, and may ultimately provide the intellectual stimulus and scientific impetus to produce vital biomaterials such as artificial bone and tough synthetic dental enamel.

This project centres on a number of topics which are of great significance to UK industry and society. A major theme is crystallisation, which is fundamental to a vast array of technological processes and natural phenomena as diverse and significant as the production of pharmaceuticals, foodstuffs and personal care products, the synthesis of nanomaterials, the formation of biominerals such as bones and teeth, the precipitation of ice in the atmosphere and the prevention of scale. We will focus on the formation of composites, which are hugely important (indeed very many materials in every-day use are composites), and in particular inorganic/ inorganic composites. Here we can expect to generate new properties (eg incorporation of metal nanoparticles within oxide thin films can generate materials with interesting linear and non-linear optical, magnetic, conductivity, catalysis, antimicrobial and electrochromic properties). Finally, our project is also founded on synthetic polymer chemistry, which is again an enormously important area to industry and society.

Armes and Meldrum have worked extensively with many industrial companies. Of particular relevance to this proposal are their recent collaborations with P & G, Unilever and Reckitt-Benckiser, who are each interested in microencapsulation for next-generation laundry formulations. Armes has a current Industrial CASE PhD project with P & G, has just finished a PDRA project with Reckitt-Benckiser and is negotiating a new project with Unilever. Meldrum has previously worked with Unilever (both Vlaardingen and Colworth sites) and P & G. Both Unilever sites funded PhD studentships, as did Nexia Solutions, while technical discussions are on-going with P & G. Armes sold a U. Sheffield patent application to DSM for 125 K euros in 2007, and this technology is now the basis of a successful anti-reflective coatings business. DSM describes its interaction with Armes as an exemplar of its 'open innovation' policy, which aims to acquire external IP of strategic value. Thus Armes is well aware of the value of IP protection. Moreover, he has filed two patent applications arising from his just-ended joint EPSRC research grant with Meldrum to protect the RAFT formulations used to synthesise the new diblock copolymer 'nano-objects' described in the present proposal. This strong IP position has been exploited to leverage £286 K from DSM and Scott Bader for follow-on projects.

Our research will also benefit substantially from our collaboration with Prof. D. W. York, who joins U. Leeds in mid-2012 after 35 years with P & G focused on microencapsulation. Calcite offers unique advantages as an encapsulation matrix: it is cheap, abundant, non-toxic, biocompatible and space filling, so it should allow the long-term retention of small molecule actives such as fragrances. In laundry formulations such as Lenor, the fragrance is the most expensive component, yet around 90 % is lost during the wash cycle. Thus there is substantial room for improved microencapsulation vehicles in such products.

Leeds and Sheffield each have well-established outreach programmes. Leeds hosts the annual "Leeds Festival of Science" where local schools take part in educational workshops related to science and engineering. Meldrum will design a workshop relating to crystal growth, demonstrating the breadth of this topic and its relevance to everyday life. She will also prepare a "Schools Talk" based on this material. Finally, we will organise an international workshop in the final year of this grant focused on bio-inspired approaches to materials synthesis. It will bring researchers from the US, Europe, and Asia together with selected industrialists and feature both tutorial sessions as well as contributed talks and posters. This forum will allow timely dissemination of our results, raise awareness with industry, and give our PDRAs the opportunity to organise an international meeting.