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Soft interfacial materials: from fundamentals to formulation

Event

Location

The Royal Society, London, 6-9 Carlton House Terrace, London, SW1Y 5AG

Overview

Scientific discussion meeting organised by Professor Michael Cates FRS, Professor John Seddon, Dr Nicholas Brooks, Dr Paul Clegg and Professor Alex Lips

Biological membranes with controlled structure and dynamics can be used as inspiration for functional membrane assemblies for bio-technical applications such as drug delivery, reaction compartmentalisation and protein crystallisation. Courtesy of Dr Nick Brooks, Imperial College London.

The science of soft interfaces (lipid membranes, emulsions, particle‐stabilised droplets etc) is rapidly moving into an era of predictive capability that allows the design and development of advanced materials to be based on secure scientific knowledge. The meeting will not only address fundamental science, focussing on generic design principles for self‐organisation and interfacial structure, but also explore the resulting prospects for 'informed formulation' of new and improved industrial products.

You can download the draft programme (PDF), and biographies of the organisers and speakers are available below, together with speaker abstracts. 

Attending this event

This meeting has already taken place. Recorded audio of the presentations can be found below, and papers from the meeting will be published in a future issue of Philosophical Transactions A.

Enquiries: Contact the events team

Event organisers

Select an organiser for more information

Schedule of talks

12 October

09:00-12:30

Session 1: Functional amphiphiles and lipids

4 talks Show detail Hide detail

Chairs

Professor Dominic Tildesley CBE FRSC, EPFL-CECAM, Switzerland

09:05-09:30 Self assembled structures to increase nutrient efficiency

Dr Laurent Sagalowicz, Nestlé Research Center, Switzerland

Abstract

A major challenge in the development of drug, nutrient or flavour delivery systems is to guarantee bioactive efficacy. The fast degradation and poor bioavailability are limitations, which need to be overtaken through the use of appropriate vehicles. Classical micro-encapsulates obtained by powder technology and encapsulation of the compounds into an amorphous matrix, represent the majority of encapsulation systems. Their ease of handling/dosing and their good stability in dried applications make them ideal for many products. However, these technologies are costly and usually not efficient in products with high water activity and liquids in general.

In the present contribution, we will introduce another type of delivery systems, lipid self-assembled structures, and discuss their advantages and limitations. These delivery systems can be obtained by structuring oil present in products, often resulting in a price advantage. This presentation will focus on their specific features to deliver benefits such as increased yield of Maillard reaction products and controlled release. In particular, systems made with oil and lecithin show good performance in terms of sustained delivery of caffeine. In addition, they have the advantages to be easily processed and can be made from ingredients that are naturally present in many food products.

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09:45-10:15 Predicting non-ionic surfactant phase diagrams

Dr Gordon Bell, Syngenta, UK

Abstract

Agrochemical formulations are often optimised for biological performance. Surfactants are effective adjuvants for pesticide uptake into plants however they display complex phase behaviour and this can be a problem. Where they form hexagonal or cubic phases in water the associated viscosity is usually too high.   

A model which relates surfactant chemical structure to phase behaviour was developed. The model describes the shape of the surfactant and from this the phase structure under different conditions can be predicted. The model requires four parameters in order to estimate the shape of the surfactant. These parameters are simple counts of the number of carbon atoms or ethoxylate groups in the molecule. The model uses the shape, the temperature, and the concentration, to estimate which type of phase is most likely to be present.  

The model can be used to design or screen surfactants such that they are easy to build-in to formulations. A commercially important design is used as an example.

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11:00-11:30 The physics of stratum corneum lipid bilayer membranes

Professor Peter Olmsted, Georgetown University, USA

Abstract

The skin is a remarkable organism. The outer 40-100 microns constitute a protective layer, the stratum corneum, which is a composite material of keratin bodies (10-100 microns) embedded in a matrix of lipid bilayers. These bilayers are very different from the fluid phospholipid bilayers familiar from the plasma membrane that surrounds living cells, or that constitute organelles such as the Golgi apparatus and endoplasmic reticulum. I will discuss the physical properties of these fascinating materials which we have studied using extensive Molecular Dynamics simulations, and indicate how special features such as asymmetric lipids and extensive hydrogen bonding are essential for humidity control, flexibility, and biological function of skin, and help make skin the remarkable self-healing material that it is.

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11:45-12:15 Model biomimetic lipid membranes based on quaternary lipid-water systems for protein encapsulation

Professor Calum Drummond, RMIT, Australia

Abstract

Self-assembled lipidic bicontinuous cubic phases are attracting increasing interest as biocompatible carriers of large biomolecules including proteins, peptides, DNA and drugs.  The lipid bilayer structure of these materials is particularly useful for the encapsulation of amphiphilic proteins and peptides as it mimics their native cell membrane environment. The lipidic cubic phase has been observed in nature, including in virally infected cells. As well as potentially retaining the protein in a functionally active form, the lipidic material can be biocompatible, and may protect the protein against degradation. However lipidic cubic phase systems formulated to date have been mainly based on a single lipid, or ternary systems comprising two lipids and water. Such materials are not representative of the native cell membrane which can contain up to one hundred different lipids. Herein we investigate the phase behaviour of more complex lipidic cubic phases comprised of three different lipids in excess water. High-throughput techniques have been exploited to screen the large compositional space associated with these systems. Lipidic cubic phases based around a more biomimetic bilayer is of potential use in a wide range of applications including pharmaceutical (drug delivery, gene therapy and medical imaging), materials science (biosensors), biology (long-term storage of fragile proteins, crystallisation) and chemistry/physics (fundamental protein – lipid interactions).

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12:30-13:30 Lunch

13:30-16:15

Session 2: Membranes and delivery

3 talks Show detail Hide detail

Chairs

Professor Alice Gast, Imperial College London, UK

13:30-14:00 Cationic membrane-nucleic acid complexes used in gene delivery and gene silencing

Professor Cyrus Safinya, University of California, Santa Barbara, USA

Abstract

Cationic liposomes (CLs) are studied worldwide as carriers of DNA and short interfering RNA for gene delivery and gene silencing, and related clinical trials are ongoing. Optimisation of transfection efficiency and silencing efficiency requires elucidation of the interactions of CL–nucleic acid nanoparticles (NPs) with cell membranes including events leading to release of active nucleic acids within the cytoplasm. As an introduction, synchrotron x-ray scattering data will be described, which reveals the distinct liquid crystalline phases of CL–nucleic acid complexes including the lamellar, inverse hexagonal, hexagonal, and gyroid cubic phases. This talk will describe experiments with surface-functionalised PEGylated CL–DNA nanoparticles (NPs) [R. N. Majzoub et al. Biomaterials 2014, 35, 4996-5005], including fluorescence microscopy co-localisation with members of the Rab GTPases, which has revealed CL–DNA pathways and interactions with cells [R. N. Majzoub et al. Biochim. Biophys. Acta – Biomembranes 2015, 1848, 1308-1318]. The functionalisation, achieved through custom synthesis, is intended to address and overcome cell targeting and endosomal escape barriers to nucleic acid delivery faced by NPs designed for in vivo applications. This work was done in collaboration with Ramsey N. Majzoub and Kai K. Ewert. Funded by the US National Institutes of Health.

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14:15-14:45 Some physics mechanisms behind membrane shaping

Professor Patricia Bassereau, Institut Curie, France

Abstract

Membrane proteins and lipids are internalised, externalised or transported within cells, not by bulk diffusion of single molecules, but embedded in the membrane of small vesicles or thin tubules. The formation of these "transport carriers" follows sequential events: membrane bending, fission from the donor compartment, transport and eventually fusion with the acceptor membrane. Similar sequences are involved during the internalisation of drug or gene carriers inside cells. These membrane-shaping events are generally mediated by different proteins binding to the membrane. The mechanisms behind these biological processes of membrane transformation are actively studied both in the cell biology and the biophysics contexts. Different physical methods have been developed in the past years to quantify and model the action of these proteins, in particular soft membrane nanotube with controlled curvature pulled from giant vesicles (GUVs). I will show in one example how simple soft matter principles can account for membrane deformation by proteins, and how it is possible to measure the intrinsic curvature of these proteins using membrane nanotubes combined with optical tweezers and confocal microscopy. Eventually, I will also present our current understanding of membrane scission, a necessary step for the detachment of the carrier from the parent membrane and its further trafficking inside the cell.

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15:30-16:00 Delivery and controlled release from nanoparticles for drug delivery and imaging

Professor Robert K Prud'homme, Princeton University, USA

Abstract

Nanoparticles are becoming increasingly important in drug delivery and multimodal delivery and imaging. In some cases nanoparticles afford rapid release of very hydrophobic therapeutics, which is required for effective treatment. In other cases controlled/sustained release is required to maintain drug concentrations in vivo for appropriate times. And still in other cases it is desirable to retain the drug in the nanoparticle and to have some form of triggered release; for example, when targeting a cancer tumour. We will present an overview of nanoparticle formulations to achieve these goals. The process we have developed based on block-copolymer-directed, kinetically-controlled self-assembly, called Flash NanoPrecipitation (FNP), enables the production of 50-400 nm nanoparticles. Successful nanoparticle production involves controlling micromixing to effect supersaturations as high as 10,000 in 1.5 ms, and then controlling nucleation and growth rates to match block copolymer assembly rates. The rapid assembly enables the encapsulation of multiple drugs and imaging agents into the same nanoparticle, and the production of multivalent targeted nanoparticles. The flexibility of the assembly process enables the preparation of imaging nanoparticles based on fluorescence, PET, x-ray, and MRI. 

Finally, the drug release from nanoparticles poses some special problems. Most release data of hydrophobic drugs from nanoparticles erroneously report release rates that are dominated by mass transfer artefacts. Techniques to accurately assess release rates will be presented.

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16:15-18:30 Poster Session

13 October

09:00-12:30

Session 3: Particles and proteins at interfaces

4 talks Show detail Hide detail

Chairs

Professor Bernard Binks, University of Hull, UK

09:00-09:30 Inclusions in soft matter: opportunities for directed assembly

Professor Kathleen Stebe, University of Pennsylvania, USA

Abstract

Colloidal particles can be manipulated using external fields to steer them into well-defined structures at given locations. We are developing alternative strategies based on fields that arise when a colloid is placed within soft matter to form an inclusion that generates a potential field. For example, a particle on a fluid interface can distort that interface to satisfy its wetting boundary conditions. The distortion has an associated energy field given by the product of its interfacial area and the surface tension. Fields generated by neighboring particles interact to drive assembly; preferred orientations for anisotropic objects emerge. 

The particle’s capillary energy depends on the local interface curvature. By molding the interface, we can define fields that drive microparticles along pre-determined paths to well defined locations. This example captures the emergent nature of the interactions, and their potential importance in schemes to make reconfigurable materials, since interfaces and their associated capillary energy landscapes can be readily reconfigured.  

There are important analogies in other soft matter systems. Particles in liquid crystals distort the director field and form defect structures that elicit an elastic energy response that can be used to define particle paths and sites for assembly. Particles adhered to lipid bilayer vesicles are another system in which such fields can be generated and exploited. These example systems have important analogies and pronounced differences which we seek to understand and exploit.

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09:45-10:15 Arrested coalescence in microstructured emulsions

Professor Patrick Spicer, UNSW, Australia

Abstract

Arrested droplet coalescence has been shown to produce stable anisotropic shapes and to be a key mechanism for microstructure development in foods, petroleum, and pharmaceutical formulations. This work builds on a recent study of the dynamic arrest of binary droplet coalescence by internal elastic structures and examines the formation of multi-droplet connections in a microstructured oil-in-water emulsion. Arrested droplet connections are shown to be a strong function of interfacial and rheological variables and their history. New individual mechanisms of arrested droplet connectivity are demonstrated and used to construct a multi-droplet model of emulsion microstructure for applications in advanced formulated products.

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11:00-11:30 Soft electrostatic repulsion in particle monolayers at liquid interfaces: surface pressure and effect of aggregation

Professor Peter Kralchevsky, Sofia University, Bulgaria

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11:45-12:15 Proteins as switchable Janus ellipsoids

Professor Cait McPhee, Professor of Biological Physics, University of Edinburgh, Royal Society Dorothy Hodgkin Fellow 1999-2001

Abstract

Janus particles are micro- or nano-scale particles whose surfaces have two or more distinct physical properties. Such asymmetry results in interesting self-assembly properties, but homogeneous Janus particles can be difficult to synthesise. The protein BslA (Bacterial Surface Layer A) is a small (~4 nm) protein produced by the bacterium Bacillus subtilis that has a hydrophilic ‘body’ to which is appended a surface-exposed hydrophobic ‘cap’. These properties allow the ellipsoidal protein to partition to oil- and air-water interfaces where it self-assembles to form a robust, elastic, and highly hydrophobic film. We have investigated the behaviour of BslA using a combination of biophysical experiments and multiscale simulations. I will describe how BslA provides an intriguing example of a colloidal particle with switchable, environmentally-responsive physical features that have potential applications in nanoscale self-assembly.

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12:30-12:30 Lunch

13:30-17:00

Session 4: Unconventional emulsions and multiphase gels

4 talks Show detail Hide detail

Chairs

Dr Jeffrey Fowler, Syngenta, USA

13:30-14:00 Self-assembly of small peptide amphiphiles, the structures formed and their applications

Dr William Frith, Unilever, UK

Abstract

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.

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14:15-14:45 Cellulose nano-crystals, rod-like particles for highly stable emulsions

Dr Isabelle Capron, INRA, Nantes, France

Abstract

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.

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15:30-16:00 Particles and capsules produced using cross-flow membrane emulsification

Professor Simon Biggs FREng, The University of Queensland, Australia

Abstract

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 [1]. 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 [2]. 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.

[1] Q. Yuan, R. Hou, N. Aryanti, R. A. Williams, S. Biggs, S. Lawson, H. Silgram, M. Sarkar, R. Birch, Desalination, 224 (2008) 215.
[2] Q. Yuan, O. J. Cayre, M. Manga, R. A. Williams and S. Biggs, Soft Matter, 6, (2010) 1580.

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16:15-17:00 Summary of discussions and closing remarks

Professor Alex Lips, University of Edinburgh, UK
Professor Wilson Poon, University of Edinburgh, UK

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Soft interfacial materials: from fundamentals to formulation

12-13 October 2015

The Royal Society, London 6-9 Carlton House Terrace London SW1Y 5AG UK
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