Tannin microcapsules for synergy-enhanced sunscreen formulations

Salicylate and benzoate sunscreen agents have been encapsulated by the green, fast and robust ultrasound technique in tannin microcapsules (TMCs). The generated TMCs, obtained without use of cross linking agents, were fully characterised, including encapsulation efficiencies with respect to the encapsulated actives. Release kinetics of TMCs have been studied mimicking skin conditions. Body cream base samples containing specific concentrations of microcapsules filled with sunscreen actives were prepared and showed synergistic effects in terms of UV-protection abilities generated by the interplay between sunscreen actives and natural tannin polyphenols. The synergistic effect exerted by the tannin and the controlled active release allows to reduce the amount of synthetic sunscreens needed, and does thus contribute to the development of more sustainable and environmentally benign UV-protection systems. 1. Introduction Elevated exposure to ultraviolet radiations causes skin problems as burns and dermatitis and poses risks over time as the development of skin cancer becomes more probable due to irreversible damages (Ichi- hashi et al., 2003; Pfeifer, 2020; Soehnge et al., 1997). The UV spectrum includes UV-A radiations between 290 and 320 nm, the most responsible for immediate tanning, ageing and suppression of immunologic func- tion, and UV-B radiations between 320 and 400 nm, which are respon- sible of sunburns and considered the leading risk factor for melanoma skin cancer. Application of topical sunscreens containing various countermeasures to UV irradiation is essential to provide protection against skin damages. Several sunscreen products are present on the market, grouped in physical and chemical sunscreens according to their modes of actions and corresponding formulation. While physical sun- screens rely on reflection properties of inorganic molecules (Pal et al., 2020; Masui et al., 2006; Lapidot et al., 2003; More, 2007; Kollias, 1999; Jim ́enez Reinosa et al., 2016), the chemical sunscreens are active regarding the absorption of specific wavelengths of UV radiation for protecting the cells of the epidermis (Burnett and Wang, 2011; Dongli- kar et al., 2016; Gasparro et al., 1998; Patel et al., 1992). Among the most frequently used chemical sunscreens are: cinnamates, para-- aminobenzoate (PABA) derivatives, salicylates, benzophenones, camphor derivatives, dibenzoyl methanes, and anthranilates. Cinna- mates, PABA derivatives, salicylates and camphor derivatives are all mainly UV-B absorbers, while benzophenone derivatives, dibenzoyl methanes and anthranilates are mainly UV-A absorbers (Gasparro et al., 1998). Commercial sunscreens are, however, unable to give a complete sunscreen protection and have a limited duration of action. Moreover, the synthetic chemicals contained in these products can cause unex- pected side effects on skin, especially upon long-term application (Burnett and Wang, 2011; Gasparro et al., 1998; Kim and Choi, 2014; Petersen and Wulf, 2014; Scheuer and Warshaw, 2006; Suh et al., 2020), as well as environmental pollution caused by mass production and increased use (Kim and Choi, 2014; Narla and Lim, 2020; S ́anchez-Quiles et al., 2020; Schneider and Lim, 2019).