Measuring the penetration of a skin sensitizer and its delivery vehicles simultaneously with confocal Raman spectroscopy.

Among the factors determining the propensity of a chemical to induce skin allergy are the penetration into skin and the kinetics of ingress. Confocal Raman spectroscopy can provide such information as it enables direct, spatially resolved measurement of the skin and of any chemical uptake. Several chemicals can be monitored at once, and the method is non-destructive (light in, light out) so that the skin can be kept intact for repeated and continuous measurement. Raman spectroscopy was used to follow the penetration of 2.5 weight percent trans-cinnamaldehyde and its delivery vehicle into skin in vitro, up to 24 h after topical application. A custom-made Bronaugh-type diffusion cell that was suitable for the Raman experiment was used. Four different vehicles were tested: absolute ethanol, 50% aqueous ethanol, propylene glycol and acetone:olive oil (4:1); these gave different time scales for cinnamaldehyde penetration. The acetone:olive oil vehicle phase-separated on the skin surface and the cinnamaldehyde penetrated at different rates in the different phases, which may be of significance since this is the preferred solvent for the local lymph node assay (an in vivo animal test used to generate hazard information on skin sensitization). In conclusion, the Raman method gives valuable detailed information on chemical ingress, clearly differentiates between different delivery rates and allows solvent monitoring alongside the chemical of interest.

GARField magnetic resonance profiling of the ingress of model skin-care product ingredients into human skin in vitro.

A preliminary study of the ingress of mineral oil, decanol, and glycerine into samples of human abdominal skin tissue in vitro made using magnetic resonance profiling with a GARField magnet is reported. Two layers, each circa 50 microm thick and attributed to stratum corneum and viable epidermis, are spatially resolved. Clear differences are observed in the magnetic resonance response of these layers arising from the application of the model skin-care product ingredients. In the case of decanol and glycerine, it is suggested that the profiles show evidence for the effects of moisturization, as distinct from hydration. In the case of glycerine, the effective ingress diffusion coefficient is calculated to be 1.3 +/- 0.5 x 10(-9) cm2s(-1).

Magnetic resonance profiling studies of the drying of film-forming aqueous dispersions and glue layers.

We report magnetic resonance profiling experiments to monitor (i) the drying of alkyd emulsion layers, (ii) the cure of wood glue layers and (iii) water transport through glue lines. The alkyd drying is a two stage process. We report new results which support previous evidence that the alkyd drops do not coalesce until the water fraction is below circa 0.02. The profiles recorded from glue layers suggest that MR is a sensitive probe of the curing process and barrier properties of the glue. The measurements were made using GARField (stray field, STRAFI like) magnetic resonance profiling and an improved GARField magnet design characterized by two values of the gradient-to-field strength ratio at two locations offering the same field strength is also reported.

Vertical water distribution during the drying of polymer films cast from aqueous emulsions.

We present a systematic study of the vertical uniformity of water distribution during the drying of waterborne colloidal films, testing the predictions of a Peclet number Pe defined for this system. Pe indicates the relative contributions of water evaporation and Brownian diffusion in determining the concentration profile in the vertical direction ( i.e. normal to the substrate). When Pe < 1, the water concentration in films cast from an alkyd emulsion is found via magnetic-resonance profiling to be uniform with depth, which is consistent with expectations. When Pe > 1, a gradient in the water concentration develops, with less water near the interface with air. The water profiles reveal that the alkyd particles do not coalesce immediately upon contact in close-packing. At later times, a concentrated surface layer develops, but particles are not coalesced in this layer to form a continuous "skin", but rather the structure is likely to be that of a biliquid foam.