The development of a technology platform for producing novel cosmetic hydrogels containing active agents

Abstract

The cosmetic industry is a market that is constantly increasing in size and scope with the products offered. This thesis focuses on the development of a technology platform to produce novel cosmetic hydrogels that incorporate active ingredients. The hydrogels were produced from poly(N-vinylformamide) (PNVF) and NVF-copolymers through photopolymerization to create cosmetic hydrogel patches. In order to fully investigate these hydrogels the work was separated into two approaches. The first approach was to investigate a series of PNVF hydrogels and various copolymers, including N-hydroxyethyl acrylamide (HEA) and 2-carboxyethyl acrylate (CEA). For a guide in the selection of the most suitable properties for cosmetic hydrogels, a series of commercial cosmetic hydrogel masks were first studied. The PNVF-based materials were evaluated and then compared with the commercial products. The method used to produce all hydrogels in this work was photopolymerization using a UV-LEDs light source, which has a high throughput and short processing time. This is the major advantage of this method with the ability to simply and effective scale the fabrication of the hydrogels from batch to continuous production on an industrial scale. The study evaluated the impact of varying the ratio of ingredients in the formula for producing the hydrogels and the effect this had on the base gel properties such as equilibrium water content (EWC), state of water, wettability, and mechanical properties. These were all observed in the hydrogels to determine the optimal composition for the novel cosmetic hydrogel patches. The applied properties, such as skin adhesion and skin irritation, were also studied, along with self-perception questionnaires to determine the suitability of the cosmetic hydrogel patches. The results for the homopolymer of PNVF gave a hydrogel with an EWC of ~95%. When decreasing NVF content in copolymer hydrogels the water content also decreased. As these gels are designed for incorporation and release of active agents a series of controlled drug release studies were undertaken. Three different dyes were investigated: Orange II Sodium salt, Crystal Violet and Congo Red. The dyes were incorporated to the hydrogels and the amount of each dye released from the hydrogel was measured. Water structure played a key role in the amount of dye released from the hydrogels, with the amount released depending on two parameters: first, the ratio of freezing water (free) and non-freezing water (bound), and second, the hydrophilicity and structure of the dye. This series of hydrogels can therefore control the amount of dye released by controlling the structure and amount of water contained in the hydrogel through the monomer ratio. In terms of in-vivo clinical applications with adhesion ability and skin irritation after application, the results were successful in terms of adhesion, with no slippage of the hydrogels. After a single application of the cosmetic hydrogel patch on the skin, the skin erythema value showed no difference. Additionally, no signs of skin irritation were observed during this study, indicating that the developed hydrogels for novel cosmetic hydrogel patch applications are mild on the skin.

The second approach was to fabricate the pH responsive hydrogels and their potential ability as delivery carriers for cosmetically active ingredients. This was achieved by producing hydrogels that contain poly(vinylamine) (PVAm). We first prepared a poly(N-vinyl formamide)-co-poly(N-hydroxyethyl acrylamide) (poly(NVF-co-HEA)) hydrogel via photopolymerization (UV-LEDs) using N,N-methylenebisacrylamide (MBAAm) as the crosslinker. This hydrogel was then hydrolyzed to convert the vinylformamide groups in the polymer to vinyl amine, the hydrolysis was carried out under acidic conditions, at 80 °C using 0.01 M aqueous HCl. These pH sensitive hydrogels were characterized by EWC, DSC and swelling behavior in both water and ethanol. The hydrogel swelling at different pHs was observed, non-hydrolyzed hydrogels (poly(NVF-co-HEA)) swelling was consistent across the entire pH range but after hydrolysis the hydrogels show different behavior with reduced swelling ratios observed at acidic and basic conditions (pH2 and pH 10 and 12). In our design of a controlled release system, Lactobionic acid was used as a model ingredient. All the results show that the functionalized hydrogel was successfully prepared to form the poly(NVF-co-VAm-co-HEA) hydrogels, which have the potential for use as a pH-responsive carrier for cosmetic ingredients triggered by an external pH change. The results of pH-responsive release provide an understanding of the active delivery properties and help identify the best suitable cosmetic active ingredients. PNVF-based hydrogels were synthesized over a wide range of compositions included different copolymers. This gave a wide range of useful properties for novel cosmetic hydrogel patches.

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