Self-assembly of small peptide amphiphiles, the structures formed and their applications
Dr William Frith, Unilever, UK
The self assembly of small peptides and other small molecules containing amino acid or peptide residues is receiving considerable attention in the literature because of their potential usefulness in a variety of fields. Potential applications include: substrates for tissue regeneration, controlled release media, and organic electronics to name a few. They are also of interest as novel structurants and surfactants that could replace existing molecules in home and personal care products, or add specific functionality to them. Indeed, possibly the only commercial product currently available is an amino acid based surfactant.
The current apparent lack of application of these materials is in stark contrast to the great promise that they offer and has many causes, including material cost, consumer acceptability and regulatory issues. But one issue that is possibly not appreciated is that the very broad range of opportunities offered by small peptide self-assembly is in itself a barrier, in that if one can synthesise a peptide to form a particular structure or function, it is likely that many such molecules exist and that there is no clear means of exploring the structural space thus presented, or of optimising the structure for the material function.
In this talk I will give a brief overview of the field and its applications, and discuss the efforts we have been pursuing to improve our understanding of the relationship between structure and function in this class of materials.
Cellulose nano-crystals, rod-like particles for highly stable emulsions
Dr Isabelle Capron, INRA, Nantes, France
It is now well established that surfactant-free emulsions can be stabilised by solid particles to form the so-called Pickering emulsions for which colloidal particles may be irreversibly anchored at the oil-water interface. They typically require an interfacial solid material that exhibits affinity for the two phases of the emulsion.
Rod-like cellulose nanocrystals (CNC) were shown to stabilise highly stable oil-in-water emulsions bending along the interface, and preventing coalescence by steric effect. These CNC provide naturally a large range of particles from 200nm to several microns in length and around 10nm in width leading to variable aspect ratios and presenting a high level of organisation. They form stiff anisotropic versatile platforms with amphiphilic contrasted surfaces that develop hydrogen bonds, electrostatic and van der Waals interactions. Variation of their organisation at the drop interface has been investigated with variation of their surface chemistry. The properties of CNCs make them a good renewable and biocompatible candidate for petroleum derivative alternatives.
This presentation aims to illustrate the potential of polysaccharidic nanoparticles at the oil-water interface to be used as building blocks for functional materials as surfactant-free Pickering emulsions, high internal phase emulsions that occur as a gel structure, or foams.
Particles and capsules produced using cross-flow membrane emulsification
Professor Simon Biggs FREng, The University of Queensland, Australia
A key consideration for many applications that require functional particulates or microcapsules is the accurate control of size and size distribution. Cross-flow membrane emulsification (XME) is an excellent candidate for the production of very tightly size-controlled emulsions, at least in the micron to millimetre droplet size range . Using a latex polymerisation as an example, we show how XME can be used to scale-up a laboratory preparation to multiple litres of product whilst retaining tight control on the final latex. In situ characterisation of the emulsions and resultant latex dispersions using an acoustic backscatter (ABS) system were used to gain insight into the process; the characterisation approach is novel and will be discussed here.
Further developing the opportunities for the use of XME, we can also show that particle stabilised emulsions can be used as templates for a range of microcapsules . The use of particulates as stabilisers is more complex than classical surfactants as a result of the widely different adsorption kinetics onto the growing liquid-liquid interface. Conditions necessary for the accurate control of emulsion stability and the efficient uptake of particulates have been examined. Examples of the types of capsules that can be prepared in this way will be discussed.
 Q. Yuan, R. Hou, N. Aryanti, R. A. Williams, S. Biggs, S. Lawson, H. Silgram, M. Sarkar, R. Birch, Desalination, 224 (2008) 215.
 Q. Yuan, O. J. Cayre, M. Manga, R. A. Williams and S. Biggs, Soft Matter, 6, (2010) 1580.
Summary of discussions and closing remarks
Professor Alex Lips, University of Edinburgh, UK
Professor Wilson Poon, University of Edinburgh, UK