Abstract
Film-forming systems are highly relevant to the topical administration of active ingredients (AI) to the body. Enhanced contact with the skin can increase the efficacy of delivery and penetration during prolonged exposure. However, after the evaporation of volatile solvents to form a thin film, the distribution of the ingredient should remain homogenous in order to ensure the effectiveness of the formula. This is especially critical for the use of hydrophobic molecules that have poor solubility in hydrophilic films. In order to address this concern, hydroxyphenethyl esters (PHE) of Punica granatum seed oil were prepared as a nanosuspension stabilised by poloxamers (NanoPHE). NanoPHE was then added to a formulation containing polyvinyl alcohol (PVA) as a film forming agent, Glycerol as a plasticiser and an antimicrobial agent, SepicideTM HB. Despite their reliability, reference methods such as high-performance liquid chromatography are increasingly challenged due to the need for consumables and solvents, which is contrary to current concerns about green industry in the cosmetics field. Moreover, such methods fail to provide spatially resolved chemical information. In order to investigate the distribution of ingredients in the dried film, Confocal Raman imaging (CRI) coupled to Non-negatively Constrained Least Squares (NCLS) analysis was used. The reconstructed heat maps from a range of films containing systematically varying PHE concentrations highlighted the changes in spectral contribution from each of the ingredients. First, using NCLS scores it was demonstrated that the distributions of PVA, Glycerol, SepicideTM HB and PHE were homogenous, with respective relative standard deviations (RSD) of 3.33%, 2.48%, 2.72% and 6.27%. Second, the respective relationships between ingredient concentrations in the films and their Raman responses, and the spectral abundance were established. Finally, a model for absolute quantification for PHE was be constructed using the percentage of spectral abundance. The prepared %w/w concentrations regressed against predicted %w/w concentrations, displaying high correlation (R2 = 0.995), while the Root Mean Squared Error (0.0869% w/w PHE) confirmed the precision of the analysis. The mean percent relative error of 3.75% indicates the accuracy to which the concentration in dried films could be determined, further supporting the suitability of CRI for analysis of composite solid film matrix. Ultimately, it was demonstrated that nanoformulation of hydrophobic PHE provides homogenous distribution in PVA based film-forming systems independent of the concentration of NanoPHE used in the formula.
Highlights
The effectiveness of a topical product depends on the physicochemical properties of the active substances and on the capacity of the formula to maintain close contact with the skin for prolonged exposure, enabling the diffusion of the molecules in or through the skin
Topical film-forming systems are increasingly studied for drug delivery because they adhere to the skin, forming a thin transparent film in situ and providing delivery of the active ingredients (AI) to the body tissue [1,2,3]
The hydrophobic active ingredient Punica granatum seed oil hydroxyphenethyl esters (PHE) has been housed in the polypropylene oxide hydrophobic core, producing NanoPHE structures
Summary
The effectiveness of a topical product depends on the physicochemical properties of the active substances and on the capacity of the formula to maintain close contact with the skin for prolonged exposure, enabling the diffusion of the molecules in or through the skin. Topical film-forming systems are increasingly studied for drug delivery because they adhere to the skin, forming a thin transparent film in situ and providing delivery of the active ingredients (AI) to the body tissue [1,2,3]. Plasticisers can be added to formulations to render them appropriately flexible for use on the skin and to increase drug diffusion [7]. Some chemical enhancers can be added to polymeric film formulations in order to improve the skin penetration of active ingredients [11]
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