Dr Shaher Duchi, Chief Scientist, and Dr Danny Goldstein, Head of R&D, Tagra. Expression Cosmétique, Guide of Cosmetic Ingredients, December 2021, pp. 284–288 (published in French and English; English text reproduced here).

What happens if you fuse advanced microencapsulation technology with SPF? The result is an innovative way to protect the skin from the sun's powerful UVA and UVB rays, as new research shows.

In recent years, the use of mineral UV filters titanium dioxide (TiO2) and zinc oxide (ZnO) has increased rapidly (1). Mineral UV filters have become more popular these days mainly thanks to their natural mineral sources, regulatory developments (2) and "reef-safe" claims. The advantages of using mineral UV filters are well-known: they have an excellent safety profile, high SPF efficacy and they offer broad spectrum protection.

Despite these advantages, there are various challenges and disadvantages associated with them, primarily due to the poor aesthetics and sensorial feel, such as white cast and how the skin feels when the product is applied. In addition, the nano debate continues to be discussed, with speculation that the small particles might penetrate through the skin, leading to as-yet-unknown hazards. Generally, developing a mineral sunscreen product is a challenging task and not always straightforward formulation work. Vast knowledge and expertise are required in order to formulate with inorganic sunscreens in an effective and elegant way.

New research has shown that Tagra's mineral SunCaps™, an advanced microencapsulation technology which uses inorganic UV filters, is an innovative solution for both manufacturers and consumers. It provides enhanced transparency on skin, improved skin feel, ease of use and compatibility with other ingredients, all while preserving its UV protection efficacy.

This article explains the preparation of Tagra's patented mineral UV filter microcapsules, named Cellu TitanCap™ and Cellu ZinoCap™, which are made of bio-based and biodegradable polymer. Both the characterization of the microcapsules' physico-chemical properties and their performance are discussed.

Non-Nano Mineral UV Filter

The micron size mineral UV filter microcapsules, Cellu TitanCap™ and Cellu ZinoCap™, were prepared using the solvent extraction method (3, 4). The physical appearance of the microcapsules obtained is a powder form. Particle size and size distribution were determined using the Horiba LA350 laser diffraction particle size distribution analyzer (Horiba Ltd., Japan) as depicted in Figure 1.

Figure 1: Microcapsule size distribution of Cellu TitanCap™ (A) and Cellu ZinoCap™ (B). Both products exhibit a micron size range.

Aesthetics: Transparency and Invisible Mineral Sunscreen

The transparency and white cast appearance of two formulations containing either free or encapsulated mineral UV filters were compared and evaluated. The final % of both TiO2 and ZnO in each formulation was the same (11% of Cellu TitanCap™ and 21% Cellu ZinoCap™, equivalent to 7.7% of free TiO2 and 14.7% of free ZnO). Evaluation was made by visual observation following application upon skin and was confirmed by analytical measurement using an XRite VS450 device (% reflection) following application upon a black plate. The results show that the formulation made with encapsulated mineral UV filters is more transparent and has a significantly less white cast appearance when compared to the formulation made with free UV filters (Figures 2 and 3).

• Figure 2: Visual observation of transparency and white cast appearance following application of formulation with Cellu TitanCap™ and Cellu ZinoCap™ (A) compared to formulation with free TiO2 and ZnO (B).

• Figure 3: XRite analysis for % transparency. An empty plate without formulation (C) served as a reference and was analyzed for transparency after being covered with a formulation containing either Cellu TitanCap™ (A) or free TiO2 (B).

Sensorial Analysis: Superior Skin Feel

The two formulations were assessed by a trained panelist using descriptive sensory analysis. The results are depicted in Figure 4. The formulation containing the mineral SunCaps™ showed an improvement in all following parameters, in comparison with the free UV filters:

• Higher spreadability and tactile smoothness during application.

• A higher complexion evenness after application.

• Higher lightness.

• Much less white cast appearance.

Figure 4: The results of sensory assessment of formulations with mineral SunCaps™ (A) or free inorganic UV filters (B).

Efficacy: In Vitro SPF Test

Cellu TitanCap™ and Cellu ZinoCap™ were incorporated in a W/O formulation. F1 represents the formulation with Cellu TitanCap™; F2 is the formulation containing Cellu ZinoCap™. The detailed composition of those formulations is shown in Table 1. F1 and F2 were made to obtain sunscreens with a theoretical SPF of 27 and 6 respectively. BASF Sunscreen Simulator software was used to evaluate the theoretical performance of the formulations regarding SPF.

Table 1: Detailed composition of each formulation tested for in vitro SPF

Formulations were prepared according to the following method:

1. Phase B ingredients were mixed and stirred at 300 rpm for 15 min at 60°C.

2. Phase A was gradually added to phase B under stirring at 60°C, followed by 5 min at 10,000 rpm with a T18 Ultra Turrax (IKA).

3. Phase C ingredients were mixed and stirred at 300 rpm for 10 min at 60°C following the addition of phase D.

4. At the end, phase CD was added to phase AB and homogenized for 10 min, and then mixing was continued without heating until the formulation reached room temperature.

Both formulations were tested for in vitro SPF using the Solarlight SPF290AS equipment at a wavelength range of 290-400nm using a PMMA plate as a substrate. The measured in vitro SPF for F1 and F2 was 67 and 8.4, respectively. The UV blocking performance was also evaluated visually using a UV chamber, as depicted in Figure 5.

Figure 5: UVA/B blocking performance of formulation containing either free TiO2 and ZnO or its encapsulated form. Both formulations contain the same % of TiO2 and ZnO.

Conclusion

Based on these results, it can be concluded that an efficient mineral sunscreen product with improved aesthetics and skin feel can easily be developed using Tagra's mineral SunCaps™. Providing safe and effective protection with an attractive look and feel is not just nice to have; it's a must have. This study shows SunCaps™ are superior to their free non-encapsulated form, therefore making them favorable for developing efficient sun care products with improved aesthetics and improved skin feel.

References

1. Solish, et al. Dermatologic Surgery: official publication of the American Society for Dermatologic Surgery. 2020; 46(12):1508-1513.

2. Food and Drug Administration proposed rule, Sunscreen drug products for over-the-counter human use, 2019.

3. Jelvehgari M, Montazam SH. Jundishapur Journal of Natural Pharmaceutical Products. 2012; 7:144-152.

4. Freitas S, Merkle HP, Gander B. Journal of Controlled Release. 2005; 102: 313-332.