How to flatten and microbuckle a rough surface with polymer films: biomechanical mechanisms underlying skin...

Human skin degrades with age, developing undesirable wrinkles and folds that many individuals prefer to conceal. In response, a market of anti-wrinkle formulations has emerged that claims to restore skin's youthful appearance. However, the biomechanical mechanisms behind this wrinkle reduction remain poorly understood due to the complex mechanics of multi-layer, furrowed structures. Using a combination of digital microscopy and thin-film mechanics techniques, we show that polymers contained in anti-wrinkle formulations form contracting films on the skin surface. This contraction leads to the appearance of fewer wrinkles in two synergistic ways. First, the amplitude of large wrinkles is reduced as the skin surface tries to match the polymer's reduction in length. Second, the skin-now in compression-microbuckles. These microbuckles diffusely reflect light, helping mask larger wrinkles. Using a simplified theoretical model, we explore how the mechanical properties of the skin and polymer alter both processes. By carefully selecting the chemical composition, novel anti-wrinkle formulations can control the amount of wrinkle reduction, while ensuring that the product remains comfortable throughout use.