In the realm of cosmetic science, understanding how products interact with the skin is crucial for developing formulations that not only perform well but also provide a pleasant user experience. One of the key techniques employed to study these interactions is contact angle measurement. This method provides insights into the wettability and adhesion properties of cosmetic ingredients and formulations, which are essential for predicting their behavior on the skin. This blog post delves into how contact angle measurements are utilized in cosmetic product development, drawing on findings from two studies.
Contact angle measurement is a technique used to determine the wettability of a surface by a liquid. It involves placing a droplet of liquid on a solid surface and measuring the angle formed between the liquid's surface and the solid. This angle, known as the contact angle, indicates the degree of wetting:
• A small contact angle (<90°) suggests high wettability, meaning the liquid spreads easily across the surface.
• A large contact angle (≥90°) indicates low wettability, where the liquid forms a compact droplet and does not spread much.
Formulation Optimization:
By understanding the wettability of different ingredients, formulators can optimize the composition of cosmetic products to enhance their performance. For example, selecting surfactants and emollients that exhibit favorable contact angles can improve the spreadability and absorption of creams and lotions.
Capra et. al. explored how contact angle measurements can predict the behavior of various cosmetic ingredients on the skin. By evaluating different classes of cosmetic ingredients and formulations on substrates like glass, Teflon, and human skin, researchers found that the contact angle can provide valuable information about the ingredient's affinity for the skin.
For instance, non-ionic surfactants like Ethylexylhydroxystearate showed lower contact angles on glass compared to Polysorbate 20, indicating better wettability and potential for smoother application on the skin. This kind of data helps formulators choose the right ingredients to achieve desired product characteristics such as spreadability and absorption.
Contact angle measurements also play a role in assessing the stability and performance of cosmetic formulations. The same study demonstrated that finished products like emulsions and oils exhibit different contact angles based on their composition and the surfactants used. For example, oil-in-water (O/W) emulsions stabilized with Decyl Glucoside showed lower contact angles on glass, suggesting better wettability and potentially better skin feel.
One of the critical aspects of cosmetic product development is ensuring that in vitro (laboratory) results correlate well with in vivo (real-life) performance. Capra et. al. found that glass substrates could serve as a reliable replacement for human skin in preliminary testing, as the critical surface tension values of glass and skin were similar (31.1 dyne/cm for glass and 27 dyne/cm for skin). This finding allows for more efficient and cost-effective testing during the early stages of product development.
Targeted Product Design:
Contact angle measurements can guide the development of products for specific skin types. For instance, formulations for oily skin can be designed to interact optimally with the higher lipid content, ensuring better application and efficacy.
Mavon et. al. highlighted the influence of skin lipids on wettability. It was observed that areas with higher sebum content, like the forehead, exhibited lower contact angles for polar liquids, indicating higher wettability. This information is crucial for developing products tailored to different skin types and conditions.
Quality Control:
Regular contact angle measurements can be part of quality control processes to ensure consistency in product performance. Any deviations in contact angle values can indicate potential issues with ingredient quality or formulation stability.
Contact angle measurements are a powerful tool in the arsenal of cosmetic scientists. They provide critical insights into the wettability and adhesion properties of ingredients and formulations, guiding the development of products that meet consumer expectations for performance and feel. By leveraging this technique, cosmetic companies can create innovative products that not only look good but also feel great on the skin.
Susanna is an Application Scientist at Biolin Scientific. In her PhD thesis, she developed fabrication methods for a new type of inorganic-organic polymers. Microfabricated polymer chips were utilized as tool for biomolecule separation in analytical chemistry.
