PRECISE DESIGN SURFACE OF SILK FIBROIN FILM BY BREATH FIGURES

In the recent years, many studies were focused on the modification of the silk fibroin because has a great potential in bio- and nano-technology. Silk fibroin -natural protein fibre from Bombyx mori worm- provides excellent mechanical and optical properties, biocompatibility, biodegradability and implant ability.1 Here we present a simple and cost effective fabrication technique which allows the preparation of free standing micropatterned pure protein films under ambient processing conditions.2 Preparation of silk film with a patterned morphology by combining replica molding and ion etching or by using a rigid master are described in the literature.3,4 We show the preparation of micropatterned silk films through replica molding of templates prepared by breath figure (BF) imprinting procedure. This promising technique is based on the evaporative cooling of a polymer solution in a wet environment, allowing water droplets to produce ordered arrays of pores on the film surface.5 It is interesting to note that honeycomb structured films have been obtained with several macromolecules having different structural complexities such as polystyrene and poly(methyl methacrylate). Our research was focused on the preparation of free standing patterned silk films (B) starting from several honeycomb structures having different morphological features. As a general fabrication procedure, aqueous silk fibroin solution was cast on top of a honeycomb film (A) and allowed to dry. The resulting silk films, depending on the template employed, displays either semi-spherical bumps (C) or ordered microcavities on its surface. Through BF, we are able to prepare different patterned fibroin films in which the fabrication of lithographic masters is not necessary. The micropatterned silk fibroin films prepared with this technique have potential application in the development of biocompatible, low cost sensors, cell culture substrates and photonic devices.