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Bio-based nanoparticles for broadband UV protection with photo-stabilized UV-filters Douglas Richard Hayden, Arnout Imhof, and Krassimir P. Velikov ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b12933 • Publication Date (Web): 22 Nov 2016 Downloaded from http://pubs.acs.org on November 23, 2016
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Bio-based nanoparticles for broadband UV protection with photo-stabilized UV-filters Douglas R. Haydena*, Arnout Imhof a*, Krassimir P. Velikovb a
Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University,
Princetonplein 1, 3584 CC, Utrecht, the Netherlands b
Dr. Krassimir P. Velikov, Unilever R&D Vlaardingen, Olivier van Noortlaan 120, 3133 AT
Vlaardingen, the Netherlands
ABSTRACT: Sunscreens rely on multiple compounds to provide effective and safe protection against UV radiation. UV-filters in sunscreens, in particular, provide broadband UV protection but are heavily linked to adverse health effects due to the generation of carcinogenic skindamaging reactive oxygen species (ROS) upon solar irradiation. Herein, we demonstrate significant reduction in the ROS concentration by encapsulating an antioxidant photo-stabilizer with multiple UV-filters into bio-based ethyl cellulose nanoparticles. The developed nanoparticles display complete broadband UV protection and can form transparent and flexible films. This system therefore shows significant potential towards effective and safe nanoparticlebased UV protective coatings.
KEYWORDS: Sunscreens, UV-filters, antioxidants, reactive oxygen species, ethyl cellulose
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An essential issue within consumer products is protection against ultraviolet (UV) radiation. UV protection within food and packaging materials is required for retarding chemical degradation, whereas UV protection within personal care products (i.e. sunscreens) is imperative for the preservation of human health as excessive exposure to UV-radiation accounts for the vast majority of skin cancers.1–3 The main requirements and challenges in the preparation of UVprotective coatings are: i) to provide broad protection over the entire UVA/UVB spectrum, and ii) to maintain photo-stability after extended periods of irradiation.4–6 Currently, broad UVspectrum protection is realized via the use of multiple organic UV-filters (e.g. avobenzone, octinoxate, oxybenzone, padimate-O, octocrylene) together in sunscreen formulations where the UV-filters are solubilized via emulsions. There is, however, considerable concern regarding the production of carcinogenic reactive oxygen species (ROS) by organic UV-filters due to photodegradation when exposed to sunlight.7,8 To address the issue, antioxidants (i.e. α-tocopherol) are added to sunscreen formulations in order to scavenge generated ROS, thus providing photostabilization.9–11 Minimising skin contact with UV-filters is also desirable due to concern over adverse effects caused by systemic absorption of UV-filters penetrating the skin.12,13 This has led to interest involving encapsulation into nanoparticles to reduce their (photo)-toxicity.14–17 Encapsulation into nanoparticles provides further advantages such as: the amount of UV-filter added to a formulation is no longer limited by its solubility in the solvent/vehicle,18 photodegradation can be stymied,15 and the need for unnecessary chemicals (i.e. surfactants, organic solvents) is reduced. So far, encapsulation has been most popular using materials such as: solidlipid nanoparticles (SLNs),19 poly(d,l-lactide) particles,12,15 and silica.14,16,20,21 Notably, SLNs have shown to be suitable carriers for encapsulating UV-filter ‘couples’ - two UV-filters into the same carrier - in order to provide broader UV-spectrum protection.22 Nanoparticle-based UV-
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protective coatings still, however, need to meet the requirements currently faced by sunscreens. Therefore, there is a need to develop nanoparticles which can effectively encapsulate multiple UV-filters and antioxidants all together, regardless of their initial physical states (liquid/solid), in order to provide broadband UV-spectrum protection and vital photo-stabilization concerning protection against ROS. Furthermore, the developed nanoparticles should be bio-based for maximum cosmetic appeal and also suitable for multiple solvent systems. Nanoparticles which can be dispersed in multiple solvent systems offer versatility for usage within many different sunscreen formulation types (e.g. oil, emulsion). SLNs for instance, although bio-based, are not suitable for oil-based formulations as they will simply dissolve. Herein, we therefore demonstrate the encapsulation of multiple UV-filters together with an antioxidant into bio-based and environmentally benign nanoparticles designed from ethyl cellulose (EC). EC is a material with potential for use within many solvent systems. We show that broadband UV-spectrum protection can be achieved and that the concentration of ROS within the ethyl cellulose nanoparticles (ECNPs) is reduced upon the encapsulation of an antioxidant. Furthermore, considering the application of UV-protective coatings we show the ability to form uniform, transparent, flexible, UV protective coatings from the ECNPs. ECNPs, with a desirable size for cosmetic applications (
