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The electrokinetic properties of the endotoxins of Escherichia coliand Serratia marcescenshave been examined. Both endotoxins are negatively charged, with the zetapotential being increased by the presence of cations whose relative influence resembles the Schulze-Hardy rule for colloid stability. Fe3+and Th4+ions are capable of reversing the negative charge of the endotoxin particles to positive. These cations were found to have a strong inhibitory effect on the activity of endotoxins in the limulus amoebocyte lysate test but the inhibitory effect did not parallel changes in the zetapotential because the effect occurred at concentrations too low to affect this parameter.

Hydrogel patches based on water swellable polyacrylates have been developed for long-term transdermal drug delivery. Two properties, relevant to the performance of hydrogel patches in-vivo have been investigated in humans over five days. These were: (i) the kinetics of water exchange between the skin and the patches; (ii) the skin compatibility of the patches. It was found that initially there was a gradually increasing uptake of water from the skin by the patches, but after about 20 h the water exchange followed a regular fluctuating pattern, peaking once a day and once a night. The skin compatibility of the patches was satisfactory, in that no redness or pustulation was noticed throughout the five days. This was most likely due to the capability of the patches to exchange water with the skin.

Endotoxins of Escherichia coli, Salmonella abortus equiand Serratia marcescenswere examined using freeze-etch electronmicroscopy and light scattering techniques, with emphasis on their aggregation state. These endotoxins show distinct features of particle size and mass and they may be affected by the presence or absence of Ca2+ions. No important differences were observed in the particle characteristics of the respective endotoxins in various infusion fluids.