Fast inverted oil-in-water emulsions: stability, colloidal structure and application as a vehicle for photoprotective substances

Uvod Emulzije, ulje u vodi (u/v) i voda u ulju (v/u), su veoma zastupljene u kozmetičkim i farmaceutskim proizvodima. Oba tipa emulzija imaju specifične karakteristike koje definišu njihovu upotrebu. U cilju dobijanja emulzija koje imaju najbolje karakteristike emulzija tipa u/v i v/u, razvijene su SWOP (engl. SWitch-Oil-Phase) emulzije. Ove emulzije su metastabilne emulzije tipa u/v koje podležu brzoj inverziji faza, u emulzije tipa v/u prilikom primene mehaničke energije tokom razmazivanja na koži. SWOP emulzije nastaju kombinacijom odgovarajućih emulgatora tipa v/u, anjonskih surfaktanata i polimernih stabilizatora, ali njihovo formiranje kao i sposobnost inverzije faza tokom primene na koži nisu dovoljno objašnjeni u poznatim radovima o ovim emulzijama. One formiraju lipofilni film na koži mnogo brže od emulzija tipa u/v i zbog toga su pogodne kao vehikulumi/nosači u proizvodima za zaštitu od ultravioletnog (UV) zračenja i za bolju raspoloživost aktivnih supstanci. Primena proizvoda sa antioksidansima na koži predstavlja veoma dobar način za podršku endogenog zaštitnog sistema kože i može biti dobra strategija za smanjenje oksidativnog oštećenja u koži do kojih dovodi UV zračenje. Flavonoidi, prečišćeni ili prisutni u biljnim ekstraktima, su grupa biljnih polifenolnih jedinjenja, koji se dugo koriste u kozmetičkim proizvodima zbog svojih mnogobrojnih, korisnih karakteristika. Flavonoid dihidrokvercetin (DHK) je snažan antioksidans koji deluje slično α-tokoferolu i pokazuje apsorpcionu aktivnost u širokom spektru UV zračenja, pa se može koristiti za smanjenje oštećenja u koži do kojih dovodi UV zračenje. Ove karakteristike DHK ga čine supstancom interesantnom za buduća ispitivanja, posebno u kombinaciji sa klasičnim UV filterima inkorporiranim u SWOP emulziju kao nosač. Cilj Cilj istraživanja ove doktorske disertacije je bio da se izvrši sveobuhvatna fizičkohemijska karakterizacija nove grupe emulzionih sistema tipa u/v, baziranih na SWOP tehnologiji, za koje je karakteristično da tokom primene na koži podležu inverziji faza i prelaze u emulzije tipa v/u. Planirano je da se ispita stabilizacioni potencijal emulgatorskog sistema baziranog na prirodnom nejonskom emulgatoru tipa gliceril estara masnih kiselina (INCI: Polyglyceryl-2 Dipolyhydroxystearate) i blagom anjonskom surfaktantu iz nove generacije alkilpoliglukozida (APG) (INCI: Sodium Lauryl Glucose Carboxylate, Lauryl Glucoside), kao i da se sagleda koloidna struktura ovog emulzionog sistema u cilju boljeg razumevanja koncepta brze inverzije faza SWOP emulzija u kontaktu sa površinom kože (uticaj sastava, znoja, temperature kože)...Introduction Emulsions (oil-in-water (o/w) and water-in-oil (w/o)) are widely used in cosmetic and pharmaceutical formulations and both types of emulsions have specific characteristics that determine their application. To obtain emulsions that would have the best characteristic of both w/o and o/w emulsions, recently so-called SWOP (SWitch-Oil- Phase) emulsions have been introduced as an alternative. SWOP emulsions are metastable o/w emulsions that invert into w/o emulsions on application of mechanical energy while rubbing it onto the skin. These emulsions are formed by a combination of appropriate w/o emulsifiers, anionic surfactants and polymeric stabilizers but their formation and its ability to invert into a w/o emulsion during application on the skin is not sufficiently explained in known works related to SWOP emulsions. They form a lipophilic layer on the skin much faster than o/w emulsions and due to their properties, are especially suitable as a carrier in sun-protection products and for better availability of the active ingredients. Topical administration of antioxidants provides an efficient way to enrich the endogenous cutaneous protection system and thus may be a successful strategy for diminishing ultraviolet radiation-mediated oxidative damage in the skin. Flavonoids, a group of plant polyphenolic compounds, are extensively used in cosmetics because of their many possible beneficial properties. The flavonoid dihydroquercetin (INCI: Dihydroquercetin - DHQ) acts as a powerful antioxidant similarly to α-tocopherol and shows absorption activity over a wide range of ultraviolet (UV) spectrum, it may be used for diminishing skin damage caused by UV radiation. These properties of DHQ indicate that this substance could be interesting for further investigation, especially in combination with other UV filters incorporated into SWOP emulsion as a carrier. Aim The aim of this work was to perform a comprehensive physicochemical characterization of new class o/w emulsions based on SWOP technology, that invert into w/o emulsions during application on the skin. This mean to investigate the stabilization potential of the emulsion system that is based on a natural non-ionic emulsifier from the group of polyglycerol esters (INCI: Polyglyceryl-2 Dipolyhydroxystearate) and mild anionic surfactant from the group of new generation of alkyl polyglucosydes (APG) (INCI: Sodium Lauryl Glucose Carboxylate, Lauryl Glucoside), and to examine the colloidal structure of the emulsion system with the aim to better understand the concept of fast phase inversion of SWOP emulsions in contact with the skin surface..