This paper addresses the modification of poly(dimethylsiloxane), i.e. PDMS, using plasma surface treatment and a novel application of the membrane created. A set of model compounds were analysed to determine their permeation through PDMS, both with and without plasma treatment. It was found that plasma treatment reduced permeation for the majority of compounds but had little effect on some compounds, such as caffeine, with results indicating that polarity plays an important role in permeation, as is seen in human skin. Most importantly, a direct correlation was observed between plasma-modified permeation data and literature data through calculation of membrane permeability (Kp) values suggesting plasma-modified silicone membrane (PMSM) could be considered as a suitable in vivo replacement to predict clinical skin permeation.

This paper addresses the modification of poly(dimethylsiloxane), i.e. PDMS, using plasma surface treatment and a novel application of the membrane created. A set of model compounds were analysed to determine their permeation through PDMS, both with and without plasma treatment. It was found that plasma treatment reduced permeation for the majority of compounds but had little effect on some compounds, such as caffeine, with results indicating that polarity plays an important role in permeation, as is seen in human skin. Most importantly, a direct correlation was observed between plasma-modified permeation data and literature data through calculation of membrane permeability (Kp) values suggesting plasma-modified silicone membrane (PMSM) could be considered as a suitable in vivo replacement to predict clinical skin permeation.

An understanding of the thermodynamics of the complexation process utilized in sustaining drug release in clay matrices is of great importance. Several characterisation techniques as well as isothermal calo-rimetry were utilized in investigating the adsorption process of a model cationic drug (diltiazem hy-drochloride, DIL) onto a pharmaceutical clay system (magnesium aluminium silicate, MAS). X-ray powder diffraction (XRPD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and optical microscopy confirmed the successful formation of the DIL-MAS complexes. Drug quantification from the complexes demonstrated variable behaviour in the differing media used with DIL degrading to desacetyl diltiazem hydrochloride (DC-DIL) in the 2 M HCl media. Here also, the authors report for the first time two binding processes that occurred for DIL and MAS. A competitor binding model was thus proposed and the thermodynamics obtained suggested their binding processes to be enthalpy driven and entropically unfavourable. This information is of great importance for a formulator as care and consideration should be given with appropriate media selection as well as the nature of binding in complexes.