Wrinkles form, when a system consisting of a hard, thin layer in strong adhesive contact with a soft, thick elastomer is subjected to in-plane compression, like skin that wrinkles or mountain ranges that fold. The arising buckling instability can be unordered, or – by applying a defined stress-field – a highly periodic surface corrugation with well-defined wavelength. It comprises however side features as cracks and line defects, which form in most wrinkling process and are not predictable yet.
We demonstrate a crack-free method where line defects are arranged by modifying the substrate: A stiffness gradient between two covalently linked PDMS phases changes the wrinkle periodicity of both. This results in several hierarchical line defect patterns along the borderline. Simulations of pattern formation theories were accomplished in MatLab and helped us to understand and quantify the experimental data.  We also utilized the formation of wrinkles vice versa in order to obtain the mechanical properties of a thin film. For this wrinkles were formed on a 0.7 nm thin 2D-polyimine sheet, and eventually the resulting corrugations could be analyzed utilizing the so-called SIEBIMM-method (Strain-induced elastic buckling instability for mechanical measurements). 
Such wrinkles can be applied to biologically functional surfaces, like cell- and virus-reppeling material for medicine, anti-fouling surfaces in large area for diverse bio-industrial applications or friction-minimizing interfaces.
 B. A. Glatz, M. Tebbe, B. Kaoui, R. Aichele, C. Kuttner, A. E. Schedl, H.-W. Schmidt, W. Zimmermann and A. Fery: Hierarchical line-defect patterns in wrinkled surfaces, 2015, Soft Matter, 11, 3332 - 3339
 H. Sahabudeen, H. Qi, B. A. Glatz, D. Tranca, R. Dong, Y. Hou, T. Zhang, C. Kuttner, T. Lehnert, G. Seifert, U. Kaiser, A. Fery, Z. Zheng and X. Feng: Wafer-sized multifunctional polyimine-based two-dimensional conjugated polymers with high mechanical stiffness, 2016; Nature Communications, 7 - 13461