Comfortable skin sunscreens based on waterborne cross-linkable polydimethylsiloxane coatings

Commercial sunscreens suffer from low effectiveness, safety concerns, and feeling uncomfortable on the skin. In this work, by introducing UV filters, i.e., either Fe3+ doped Mg/Al layered double hydroxides (Mg/Al + Fe LDHs), an organic UV absorber, or both of them together, into waterborne cross-linkable polydimethylsiloxane (PDMS) coatings that consisted of vinyl-PDMS emulsion, hydrogen-PDMS emulsion, and Karstedt catalyst capsules, three types of skin sunscreens were facilely fabricated. The new sunscreens can be topically applied to the skin surface and form thick elastic films. The effect of the UV filter content on the UV-vis spectrum, UV-shielding performance, mechanical properties, water vapor transmittance, and adhesion strength of the films was thoroughly investigated. The cross-linked UV-shielding films had a non-greasy surface, moderate adhesion strength to skin, high transparency, a mechanical performance similar to human skin, and high water vapor transmission. All these features made the sunscreens comfortable to use. More importantly, even the sunscreens with a concentration of UV filters as low as 2.08 wt% organic UV absorber and 0.69 wt% Mg/Al + Fe LDHs exhibited the same UV protection performance as those commercial sunscreens with high sun protection factors. Such low UV filter concentrations are beneficial for alleviating safety issues. It is convincing that the cross-linkable PDMS-based sunscreens could be used as next-generation biomimetic sunscreens.