Formulation, characterisation and topical application of oil powders from whey protein stabilised emulsions

Abstract

The available literature indicates that to date, few research has been performed on oil powders for topical delivery. The aim of this project was to investigate the release characteristics of oil powder formulations, as well as their dermal and transdermal delivery properties. Whey protein-stabilised emulsions were used to develop oil powders. Whey protein was used alone, or in combination with chitosan or carrageenan. Nine oil powders, with salicylic acid as the active ingredient, were formulated by using the layer-by-layer method. Three different pH values (pH 4, 5 and 6) were used to prepare the formulations, because of the different charges that polymeric emulsifiers may have. The characteristics of the prepared oil powders were determined, including their droplet sizes, particle size distributions, loss on drying, encapsulation efficiencies, oil leakage and water dispersibility. Release studies (membrane diffusion studies) were conducted by utilising cellulose acetate membranes (0.2 μm pore size) and Franz-type diffusion cells over a period of eight hours. The release of the active ingredient was determined for all nine powders, their respective template emulsions, as well as their respective oil powders redispersed in water. The release of salicylic acid from the respective redispersed oil powders was then further compared to its release from the template emulsions and from the oil powders. The effect of pH and different polymer types used in preparing the oil powders, their respective redispersed oil powders and the template emulsions were determined with regards to the release of the active ingredient from all these preparations. The effect of pH and different polymers used was furthermore determined on the oil powders and their respective redispersed oil powders, with regards to their dermal and transdermal deliveries. Transdermal delivery and skin uptake were investigated on specifically selected powders only, based on the outcomes of the oil powder characterisation and release data. The qualifying formulations were chitosan pH 4, 5 and 6, whey and carrageenan pH 6 oil powders, together with their respective redispersed oil powders in water. Human abdominal skin was dermatomed (thickness 400 μm) for use in the diffusion studies. Franz-type diffusion cells were used over a period of 24 hours. The results of the membrane release studies indicated that the oil powders had achieved a significantly higher release than their respective redispersed oil powders. The release of salicylic acid from the redispersed oil powders and from their respective emulsions was similar. The transdermal delivery test outcomes showed that the effect of pH could have been influenced by the degree of ionisation, resulting in a decrease in permeation with increasing ionisation of salicylic acid, in accordance with the pH partition hypothesis. Furthermore, biopolymers, such as chitosan had demonstrated a penetration enhancing effect, which had led to the enhanced dermal and transdermal delivery of salicylic acid. A correlation was also found between the powder particle size and transdermal delivery.