Silk-Its Mysteries, How It Is Made, and How It Is Used.

This article reviews fundamental and applied aspects of silk-one of Nature's most intriguing materials in terms of its strength, toughness, and biological role-in its various forms, from protein molecules to webs and cocoons, in the context of mechanical and biological properties. A central question that will be explored is how the bridging of scales and the emergence of hierarchical structures are critical elements in achieving novel material properties, and how this knowledge can be explored in the design of synthetic materials. We review how the function of a material system at the macroscale can be derived from the interplay of fundamental molecular building blocks. Moreover, guidelines and approaches to current experimental and computational designs in the field of synthetic silklike materials are provided to assist the materials science community in engineering customized finetuned biomaterials for biomedical applications.