Pinning-Induced Folding-Unfolding Asymmetry in Adhesive Creases

The compression of soft elastic matter and biological tissue can lead to creasing, an instability where a surface folds sharply into periodic self-contacts. Intriguingly, the unfolding upon releasing strain is usually not perfect: small scars remain that serve as nuclei for creases during repeated compressions. Here we present creasing experiments with sticky polymer surfaces, using confocal microscopy, which resolve contact line region folding occurs. It found tension induces second fold, at edge self-contact, leads singular stress self-similar crease morphologies. However, these profiles exhibit intrinsic folding-unfolding asymmetry caused by pinning, in way resembles wetting liquids on imperfect solids. Contact pinning therefore key element creasing: it inhibits complete gives surfaces memory.