On the Routines of Wild-Type Silk Fibroin Processing Toward Silk-Inspired Materials: A Review Vadim Volkov, Ana V. Ferreira, Artur Cavaco-Paulo* For years, silk fibroin of a domestic silkworm, Bombyx mori, has been recognized as a valuable material and extensively used. In the last decades, new application fields are emerging for this versatile material. Those final, specific applications of silk dictate the way it has been processed in industry and research. This review focuses on the description of various approaches for silk downstream processing in a laboratory scale, that fall within several categories. The detailed description of workflow possibilities from the naturally found material to a finally formulated product is presented. Considerable atten- tion is given to (bio-) chemical approaches of silk fibroin transformation, particularly, to its enzyme- driven modifications. The focus of the current literature survey is exclusively on the methods applied in research and not industry. 1. Silk Fibroin, a Protein, and a Biopolymer Throughout the years of research a vast amount of information concerning silk diversification is available. Hence, the scope of the current review encompasses only wild type fibrous protein, and not its genetically engineered (chimeric) deviations ( [1] and references within). Hybrid materials, for instance, fibroin-based coatings on various metal [2] and polymeric [3] supports or micro-fabricated meta-material silk-metal composites [4,5] will not be dis- cussed. Silk fibroin (SF) is a natural protein polymer, produced by some of Lepidoptera species, such as silkworms and butterflies. [6] Depending on its source and biological function, the silk composition, structure, and properties may differ significantly. [7] One of the most characterized silks come from the silkworm B. mori due to its history of domestication, [8] uses in textile industry and medicine. [7] Owing to biocompatible and mechanical properties of SF, its use has been increasing dramatically in biotechnology and biomedical areas. [6] Attempts are being made to control the silk fibroin-based technology from scratch and to promote its up-scaling from the laboratory to industrial scale, by developing methods and protocols suitable for biotechnology and sustainable manufacturing. [9] Wild-type silkworm SF, consists of two different proteinaceous parts: the structural fibrous protein and sericin, a glue-like protein that covers the fibroin molecules into larger fiber tread. [8] ‘‘Wild-type’’ protein in the particular context is meant to be a naturally found (or secreted), as opposed to the recombinant one. [10] Different aspects of SF structure, composition, and MW have been extensively discussed elsewhere. [11–17] A number of SF structures have been reported (Figure 1 and see ref. [18] ): the water-soluble state (Silk I), the crystalline silk (Silk II), and an air/water interface orientation (Silk III). [12] Silk I is ordinarily observed in the silkworm glands, [19] it contains random-coil and amorphous regions. [20] Silk I is unstable to mechanical or Prof. A. Cavaco-Paulo, V. Volkov, A. V. Ferreira Centro de Engenharia Biol ogica (CEB), Universidade do Minho, Campus de Gualtar 4710-057, Braga, Portugal E-mail: artur@deb.uminho.pt Fax: þ351 253 604 429 Review ß 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mame.201500179 1199 Macromol. Mater. Eng. 2015, 12, 1199–1216 wileyonlinelibrary.com