Precise surface patterning of silk fibroin films by breath figures

Silk produced by the silkworm Bombyx mori has gained a second youth as a sustainable material for high-technology applications. Here, we report a simple and cost-effective fabrication technique which allows the preparation of free-standing micropatterned pure protein films under ambient processing conditions. In this view, we take advantage of the auto organization of polymers in microporous films-the so-called breath figure formation-to create a specific morphology, which is then transferred to silk. The method includes, after the construction of a microcavity array, two to four soft-lithographic steps, depending on the desired surface patterning. Arrays of concave or convex microlenses, as well as packed micrometric bumps ordered in a hexagonal fashion, are possible obtainable architectures. Despite the straightforwardness of the procedures proposed, our method is able to produce, with high precision, transparent and stable silk fibroin films shaped with an ordered superficial pattern, which are attractive for the development of new biocompatible photonic devices.