Molecular weight, tertiary structure, water binding and colon behaviour of ispaghula husk fibre.

Molecular variables, using aqueous and alkaline extracts, of the polysaccharide from ispaghula husk (IH) were examined using gel-permeation chromatography linked to multi-angle laser light scattering. Progressive extraction can yield a component with a molecular weight (MW)value up to about 7 x 106 Da, and gels, which accompany the extraction, have MW ranging from 10-20 x 106 Da. To mimic the polysaccharide degradation, particularly in the colon, the solid IH was degraded progressively using ionising radiation. A chain break occurs every 7.5 kGy in NaOH and every 15 kGy in water. The solid-state matrix is opened by the radiation to yield increased visco-elasticity of the aqueous extracts at critical radiation doses, before further degradation occurs after about 12 kGy. Differential scanning calorimetry is used to study the mechanism of interaction of water with IH. The first water to be taken up is non-freezing water and represents about twelve water molecules/disaccharide unit of the polysaccharide. As the water content is increased, the water becomes bound to the polysaccharide and freezes and melts at a temperature different from free water. This water is thermodynamically distinguishable from free water. It forms amorphous ice on cooling which crystallises exothermically and subsequently melts endothermically. Saturation occurs at a water content of 2-3 g water/g polymer, showing that about 60% of the water in the system is 'bound'. The most surprising conclusion is that despite the fact that the IH swells in water to form a solid and stiff gel, the greater part of that water in the gel is still free and behaves like liquid water.

Adsorbed pluronics on the skin of human volunteers: effects on bacterial adhesion.

An amphiphilic copolymer, Pluronic F127, has been deposited, by adsorption, to the skin of human volunteers and the ability of the coated skin to resist bacterial colonisation has been evaluated. In parallel, the ability of the same copolymer to act as a bacterial release agent has been evaluated. In both cases, F127 proved to be of little added value in formulations designed to suppress the bacterial colonisation of human skin.

Adsorbed poly(ethyleneoxide)-poly(propyleneoxide) copolymers on synthetic surfaces: spectroscopy and microscopy of polymer structures and effects on adhesion of skin-borne bacteria.

Poly(ethyleneoxide)-copoly(propyleneoxide) (PEO-PPO) polymer coatings were evaluated for their resistance to the attachment of the marker organism Serratia marcescens and the skin-borne bacteria Staphylococcus epidermidis. The copolymers were adsorbed onto poly(styrene) films-chosen as simplified physicochemical models of skin surfaces-and their surface characteristics probed by contact angle goniometry, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). These functional surfaces were then presented to microbial cultures, bacterial attachment was assessed by fluorescence microscopy and AFM, and the structures of the polymer films examined again spectroscopically. Surface characterization data suggest that the adsorbed copolymer was partially retained at the surface and resisted bacterial attachment for 24 h. Quantitative evaluation of cell attachment was carried out by scintillation counting of (14)C-labeled microorganisms in conjunction with plate counts. The results show that a densely packed layer of PEO-PPO copolymer can reduce attachment of skin commensals by an order of magnitude, even when the coating is applied by a simple adsorptive process. The work supports the hypothesis that adhesion of microorganisms to biological substrates can be reduced if a pretreatment with an appropriate copolymer can be effected in vivo.