Safe and Transparent Mineral-Based UV Filter for Sunscreens and Cosmetic Products: MicNo®-ZnO

The ozone layer, which is a natural filter protecting our world from harmful ultraviolet (UV) radiation, is progressively thinning. As a result, more harmful solar radiation is reaching the Earth's surface. UVA and UVB radiation reaching the Earth's surface can damage DNA that forms the skin's structure, which can lead to aging and, most importantly, skin cancer. According to World Health Organization (WHO) data, the incidence rate of skin cancer in European Union countries is reported as 13.2 per 100,000 people, making skin cancer one of the 10 most common types of cancer [1]. To address this problem, the most widely accepted solution is the regular and effective use of sunscreens and/or cosmetic products with UV-filtering properties. For this reason, due to adverse environmental conditions today, sunscreen use has become mandatory and the sunscreen market has reached approximately USD 6 billion. Despite their widespread use, current sunscreen products fail to fully meet customers' expectations such as high transparency, effective UV filtration, non-irritating and non-allergenic properties, ease of application, absence of harmful chemicals, and natural (preferably mineral-based filter) formulation content. The most important component in sunscreens and cosmetics with UV-filtering properties is UV filters. However, many UV-filter materials used for UV-filtering purposes have significant drawbacks and limitations in providing complete protection of people from harmful solar radiation. Today, as expectations from sunscreen products have increased, new regulatory measures have begun to take effect. For example, in the past, having a high sun protection factor (SPF) value showing protection against UVB radiation alone was sufficient to call a sunscreen a "good" product, but today broad-spectrum sunscreens have become the standard. Broad spectrum means protection up to radiation with a wavelength of at least 370 nm and a UVA/UVB protection ratio greater than 0.3. To achieve this broad-spectrum protection, both chemical and physical UV filters are used in sunscreen and cosmetic product formulations. Some chemical filters break down in sunlight and/or generate free radicals, which cause skin damage and irritation. Additionally, among chemical UV filters, there is no single filter that can provide broad UV spectrum protection [2,3]. There are two physical (mineral-based) filters approved by the U.S. Food and Drug Administration (FDA) and the European Union (EU) for use in sunscreen and cosmetic products: Zinc Oxide (ZnO) and Titanium Oxide (TiO2). Between these two systems, Zinc Oxide is, according to FDA data, the only sunscreen ingredient UV filter that provides protection against both UVA and UVB. Although ZnO can provide broad-spectrum UV protection, manufacturers have reported certain issues with using ZnO in sunscreen and cosmetic product formulations. When micron-sized ZnO particles are used, they create whiteness on the skin and produce an unpleasant roughness sensation. To eliminate the whiteness effect, nano particles are used. On the other hand, when nano particles are used, uncontrolled agglomeration is observed, which reduces the surface coverage per unit mass of the UV filter, negatively affecting filtering performance. Additionally, the use of nano particles raises concerns about whether nano particles can penetrate the skin [4]. Anti-nano groups have been formed over possible hazards of nano materials, and strict measures have been taken for the safe use of products. EU Regulation 1223/2009 regulates limitations on the use of nano materials in cosmetic products. This regulation also indicates that with technological advancement, the use of cosmetic products containing nano materials will increase and that their use must be carried out in accordance with this regulation. Discussions continue regarding whether nano particles penetrate the skin and cause skin cancer. Beyond this, there are significant concerns about whether these particles harm the environment, as nano particles can reach plant roots and accumulate there, pollute groundwater, and have other such effects. To overcome the problems mentioned above regarding micron and nano-sized ZnO and to use ZnO as an effective UV filter, there is a need to develop new unconventional ZnO-based particle technologies. Our company, Entekno Materials, developed a patented unconventional technology called MicNo® particle technology. MicNo® particles are micron-sized hexagonal plate-shaped powders formed by strongly bonding nano-primary particles to each other with chemical bonds, designed to preserve the positive aspects of micron and nano-sized particles while eliminating their negative aspects. Figure 1 shows an electron microscope image of MicNo®-ZnO particles and their particle size distribution. MicNo® powders exhibit both micron and nano powder characteristics—they behave like safe micron particles on the skin while appearing like transparent nano powder under light. For this reason, these particles are named MicNo® particles, meaning the combination of micron (Micron) and nano dimensions. Figure 2 shows the UV-Vis transmission spectra of commercial nano ZnO UV filter and MicNo®-ZnO particles. MicNo®-ZnO particles exhibit higher filtration in the UV region (lower transmission) compared to commercial nano ZnO, and higher transmission in the visible light region (>400 nm), meaning higher transparency. These results show that the high UV protection and transparency expected from an ideal UV filter are demonstrated by MicNo® particles.

Figure 1. Electron microscope image of MicNo®-ZnO particles and particle size distribution.

  "MicNo®-ZnO particles were tested by independent laboratories as the main ingredient of sunscreen formulations and showed that, in addition to broad spectrum and high SPF value, the formulation would also impart high transparency, smooth application feel, and high coverage per unit mass, making it a very important UV filter for sunscreens and cosmetic products. As mentioned above, when ZnO particle size is reduced to nano size, the whiteness effect seen in sunscreens disappears, but in this case safety concerns emerge [4]. To demonstrate the advantages of MicNo®-ZnO particles as cytotoxic, genotoxic, and phototoxic compared to commercially available nano ZnO particles, in-vitro tests were conducted on human skin keratinocyte cells. Comprehensive and detailed test results showed that MicNo®-ZnO particles exhibited much lower cytotoxic, genotoxic, and photogenotoxic (under UVA) properties compared to ZnO nanoparticles [5]. These results mean that the biocompatibility of MicNo®-ZnO particles is much higher compared to ZnO nanoparticles. Additionally, when MicNo® is compared to micron and nano ZnO as a UV filter, it provides transparency and higher coverage per unit mass without creating safety risks for humans and the environment. MicNo's original plate shape provides much better skin coverage compared to nanoparticles (Figure 3). This indicates that MicNo® can be used in smaller quantities compared to alternatives for the same level of sun protection, thereby providing cost advantages.

Figure 2. UV-Vis spectra of commercial nano ZnO and MicNo®-ZnO particles

Figure 3. (a) Schematic representation of uncontrolled agglomeration of nano particles and (b) controlled assembly of nanoparticles forming MicNo® particles.

  Another aspect regarding nanoparticles is the potential negative effects of these particles on the environment. To evaluate this issue, the toxicity behavior of MicNo® and commercial nano ZnO particles was tested and compared using green bean samples. As a result of this test, it was found that while nano ZnO particles were transported by water and accumulated significantly in plant roots, MicNo® particles did not exhibit this behavior. These results demonstrate that MicNo® technology has the potential to eliminate environmental concerns raised by the use of nano materials. Table 1 shows a comparison of micron, nano, and MicNo®-ZnO particles as UV filters. In all categories, MicNo®-ZnO particles demonstrate higher performance compared to both micron and nano ZnO. As mentioned above, the market for sunscreens and UV-filtered cosmetic products is growing rapidly because these products have transitioned from the "nice to have" product category to the "need to have" category, and market expectations are becoming more competitive and demanding. New products that can meet these market expectations will gain market superiority. Cosmetic products using MicNo®-powder technology will have greater growth potential through the advantages provided by this technology. MicNo® technology can be synergistically extended to other mineral-based materials and can be designed to address future expectations from sunscreen raw materials such as air pollution protection, strong visible (blue) light protection, and development of preservative-free formulations [6], which could further increase its effectiveness.

In Summary, MicNo®-ZnO Offers Sunscreen and Cosmetic Product Manufacturers;

• Natural, mineral-based broad-spectrum sun protection performance, • The advantage of using up to 40% less material while achieving the same UV protection, • The opportunity to access superior nano properties while eliminating health/safety and environmental concerns associated with nanoparticles, • Transparent and smooth products without residue and whiteness effect, • Cost advantage through zero or minimal dispersant agent use in formulations, • The opportunity to develop different/superior products and differentiate from other manufacturers.

Table 1. Comparison of micron, nano, and MicNo®-ZnO particles.

Prof. Dr. Ender Suvacı Research and Development Manager Entekno Industrial Technological and Nano Materials Inc. M.Sc. Gürol Ö. Demirel Research and Development Engineer Entekno Industrial Technological and Nano Materials Inc.       M.Sc. Oktay Uysal Managing Partner Entekno Industrial Technological and Nano Materials Inc.      

References 1. WHO Skin Cancers-UV Radiation (http://www.who.int/uv/faq/skincancer/en/index1.html) 2. Skin Cancer Foundation-Challenges in Making an Effective Sunscreen (https:// www.skincancer.org/publications/the- melanoma-letter/summer-2012-vol-30- no-2/effective-sunscreen) 3. Ingredients in Sunscreen: Physical vs. Chemical Sunscreen (https://www.tatcha. com/tatcha-institute/ingredients-in-sunscreen- chemical-vs-physical-sunscreen/) 4. Burnett, E.M., Wang, S.Q., 2011. Current sunscreen controversies: A critical review. Photodermatol. Photoimmunol. Photomed. 27 (58-67) 5. Genc, H., Barutca, B., Koparal, A.T., Özöğüt, U., Şahin, Y., Suvacı, E., 2018. Biocompatibility of designed MicNo-ZnO particles: Cytotoxicity, genotoxicity and phototoxicity in human skin keratinocyte cells. Toxicology in Vitro. 47 (238-248). 6. Demirel, R., Suvacı, E., Şahin, İ., Dağ, S., Kılıç, V., 2018. Antimicrobial activity of designed undoped and doped MicNo-ZnO particles. Nanomedicine: Nanotechnology, biology and medicine. (in review).