Environmental responsiveness of biopolymer multilayers

The food manufacturing industry needs to be able to make food structures which deliver health, well-being and enjoyment. Clinical nutritionists are increasingly able to identify food compositions, and molecular species, which are associated with a positive health benefit. In addition, microbiologists are involved in research on how a 'healthy' bacterial population may be maintained in the gut. A challenge is to be able to make food structures which enable the delivery of these potential health benefits. For example, even though certain bitter-tasting plant chemicals might have a proven benefit, we will not eat foods which contain them if the bitter taste is released in the mouth, conversely we will not eat low-fat foods if they do not deliver enjoyable tastes and flavours. To deliver the benefits to our immune system associated with the ingestion of certain bacteria we need to ensure that they can survive passage through the harsh environment of the stomach and small intestine. Pharmaceutical researchers have developed a range of technologies which allow both the site-specific and controlled release of therapeutics to different regions of the human gut. These technologies can provide a more effective therapy, while at the same time reducing side effects. For example, enteric coatings allow delivery to the small intestine and help avoid the inflammation of the stomach which some drugs can produce. Controlled and site-specific delivery requires environmentally responsive structures which can protect and encapsulate an active ingredient in certain environments, yet provide a release of the active component in others. In pharmaceutical formulations these structures are derived from synthetic polymers. Although the pharmaceutical technologies are relevant to the food sector there are important differences in requirements. Firstly, there is the need to protect the active ingredient in a complex food environment rather than that of a pharmaceutical formulation. Secondly, the structures which provide useful encapsulation and release behaviour should be derived from food components. We propose to study the assembly and properties of structures from charged natural polymers which would enable the fabrication of biomaterials for the encapsulation of active ingredients in foods and then ensure their release in the human gut. The approach that we will adopt will involve the sequential deposition of oppositely charged natural polymers to form layered structures. Through the control of molecular size, and the way that charge is distributed along the polymer chain, this will enable the assembly of structures which have substantial variation in the way that charge is distributed within the structure. From our knowledge of the behaviour of charged polymer structures, we propose that through this we can control environmental responsiveness, to produce structures which provide controlled release in the gut. To do this in a rational way we need to understand the relationship between charge distribution and responsiveness. We will probe the assembly and consequent responsiveness of surface layers using a range of techniques including Fourier transform infrared spectroscopy (FTIR), quartz crystal microbalance with dissipation monitoring (QCMD) and surface plasmon resonance (SPR). These techniques allow us to probe different aspects of the structure. SPR gives information on the mass of polymer assembled at the surface; FTIR information on its chemistry, more particularly the state of ionisation of charged residues within the structure; and QCMD information on the extent of hydration of the surface layers. By examining the responsiveness of the structures to changing pH, ionic strength, osmotic pressure and degradative enzymes, we can discover the relationships between responsiveness, structure and charge distribution, and enable the production of useful structures.

We propose that oppositely charged biopolyelectrolytes and biopolyampholytes can be used to fabricate environmentally responsive structures for the encapsulation and then delivery of active ingredients to the gastrointestinal tract of man. We further propose that the control of charge density and charge distribution within the structure will provide the required environmental responsiveness. Rules governing the assembly of mixed biopolyelectrolyte layers on surfaces will be determined using state-of-the-art physico-chemical techniques, including, surface plasmon resonance (SPR), Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR) and a quartz crystal microbalance with dissipation monitoring (QCMD) allowing characterisation of the mass of material deposited, its chemical characteristics and hydration, including the way that the hydration responds to different environmental conditions. Though using oppositely charged biopolyelectrolytes which differ in their molecular size, charge and charge spacing we propose to produce multilayer structures which differ in the way that charge is distributed within the structure and hence have a different responsiveness to changing environmental conditions. We will investigate the stability and responsiveness of the structures to changing environment, including pH, ionic strength and osmotic stress, and for some structures their susceptibility to enzymic degradation. In this way we will determine the underlying physical chemistry which influences the material properties of these structures associated with the encapsulation and release of active ingredients in the types of environment found in the gastrointestinal tract.