Smart self-assembled microgel films as encapsulating carriers for UV-absorbing molecules

This article reports the ability of oligo(ethylene glycol)-based stimuli-responsive microgels to spontaneously form self-assembled microgel films under different conditions such as the presence or absence of water soluble polymers (WSP, formed during the microgel synthesis) and the type and/or amount of salt in the microgel dispersion. The unusually high encapsulation of four different cosmetically active molecules has been achieved via hydrophobic interactions and hydrogen-bonding interactions between the –OH groups of active molecules and ether functions of self-assembled microgel films. The loaded-films present absorption higher than 50% of the UVA–UVB wavelengths and can be used for skin protection against sun. The nature of the interactions was determined by NOESY-NMR spectroscopy in the gel state. Moreover, confocal microscopy was used to show that the water solubility of the active molecule plays a crucial role in obtaining a more homogeneous distribution in films after loading.