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The inhomogeneity of alginate gel beads prepared by an external diffusion method has been characterised using spatially resolved nuclear magnetic resonance or “magnetic resonance imaging” (MRI) and transmission electron microscopy (TEM). The beads exhibited various degrees of inhomogeneity although reducing the length of exposure to the gelling bath and the presence of non-gelling ions decreased gel inhomogeneity. In order to gain information regarding the gastro-intestinal functionality of these beads for in vivo applications, they were exposed to simulated gastro-intestinal conditions. The increased polymer concentration at the edge of the beads was shown to persist throughout our gastro-intestinal model despite the centre of the bead becoming progressively more porous in nature. The porosity of the alginate gels has been quantified by image analysis of transmission electron micrographs and shown to depend on both location within the bead and gastro-intestinal conditions. We suggest that such changes in porosity of these alginate beads during simulated gastro-intestinal conditions may make these an attractive option for controlled delivery applications in vivo.

Directed crystallization is found in many natural systems, where the inorganic material provides the organism with superior barrier and mechanical properties. Using this principle of controlled nucleation and growth on a biopolymer (pectin) substrate, hollow shells of calcium carbonate were formed in certain reaction conditions that were generally more perfect at lower reactant concentrations. The nucleation mechanism required the presence of calcium-binding acidic groups on the biopolymer. These served to initially gel the biopolymer, thus providing the template upon which crystallization could occur, and then provided the calcium-rich sites at the template surface that promoted crystallization. The propensity of the system to crystallize on the gel particle surface thereby led to the formation of a complete shell of calcium carbonate, in the form of calcite, which in certain conditions was shown to effectively encapsulate small molecular weight hydrophilic species such as sodium chloride. Importantly, h...

We demonstrate that it is of critical importance to prepare Janus particles with a high degree of control over the surface roughness. To elucidate information regarding the behaviour of Janus particles at an interface, we have used a gel-trapping technique coupled with metal evaporation to prepare Janus particles. Since one face is covered in gold, direct observation of the different faces at air–water and water–oil interfaces can be carried out. For particles prepared by this gel-trapping technique, the interface between hemispheres is rough and this leads to the observed orientation being random. We show that for these particles the surface roughness can dominate over the surface chemistry with regards to particle orientation. This has important implications for many of the synthetic routes towards Janus particles suggesting that, for optimum performance, it is necessary to prepare particles where the surface roughness is kept to a minimum.

A series of poly(ethylene oxide)-block-poly(N,N-diethylaminoethyl methacrylate) (PEO−PDEAMA) block copolymers with relatively high polydispersity (1.36 < PDI < 1.96) have been prepared to determine the effect that polydispersity has on the self-assembly of amphiphilic block copolymers in dilute solution. Because monodisperse macroinitiators were used for the ATRP reactions, the polydispersity resides within the hydrophobic block. By adjusting the relative block lengths, spherical micelles, wormlike micelles, vesicles, or a precipitate is formed. Here, we show that relatively high polydispersity in the block copolymer does not preclude efficient self-assembly. We also discuss the effect of increasing the concentration of NaCl in the systems and show that this can result in a shift from one morphology to another. These shifts are reversible in some cases, but for PEO12−PDEAMA39, this method allows access to giant vesicles of between 500 nm and 1 μm in diameter.

Autoantibodies to a normal component of stratified squamous epithelia, the bullous pemphigoid antigen (BPA), are synthesized in patients with the disease bullous pemphigoid. We have used these sera to study the distribution of BPA in vivo and in vitro. At low magnification, indirect immunofluorescent staining for BPA is linear at the basement membrane zone (BMZ) of skin and many other epithelial tissues. At higher magnification however, we observed a punctate staining pattern for BPA which was regular in appearance and suggested localization of BPA to discrete structures at the BMZ. Subsequent immunoelectron microscopy using both peroxidase and colloidal gold labeling techniques with patients' sera or IgG, revealed that BPA is associated with hemidesmosomes--putative adhesion structures at the BMZ, based on their similarity in ultrastructure to desmosomes. More specifically BPA was immunolocalized to the cytoplasmic face of hemidesmosomes and was not observed extracellularly in the basement membrane. In stratifying and nonstratifying cultures of rat keratinocytes, BPA is expressed intracellularly and not in the cell-derived matrix, unlike other known basement membrane components. These cells also synthesize BPA in vitro, and immunoprecipitation from metabolically labeled cultures revealed a 220 kD polypeptide under reducing conditions. From these observations we conclude (1) that BPA is a 220 kD polypeptide component either of or associated with hemidesmosomes, and (2) that it is localized intracellularly both in vivo and in vitro. We suggest that BPA is not normally a lamina lucida component, but that it may form part of a linkage between the cytoskeleton and the basement membrane.

Fibronectin distribution during fetal rat skin development has been studied immunocytochemically at the light and electron microscope level from 16 days of gestation to birth. The dermal-epidermal junction, the dermis, and connective tissue around developing muscle were shown by light microscopy to be heavily stained throughout this period. The development of hair follicles from about 18 days onward was not associated with any consistent change in fibronectin distribution. The heavy staining of the upper dermis was associated with a high density of mesenchymal cells, and immunoelectron microscopy revealed fibronectin on the surface of many of these cells and in association with the surrounding fine collagen fibrils. At the dermal-epidermal junction, both follicular and interfollicular, fibronectin was localized mainly in the plasma membrane and lamina lucida regions of the basement membrane, and there was also staining associated with the underlying fine collagen fibrils. These observations are further evidence for the proposed role of fibronectin as a mediator of the cell- matrix interactions which are of importance for tissue development and maintenance.