Modern manufacturing has a pressing

Modern manufacturing has a pressing need for lightweight yet strong structural materials in transportation, civil engineering, construction, automotive applications, and aerospace. To meet these needs, scientists and engineers have developed a range of remarkable materials with excellent mechanical properties, such as those based on petroleum products (e.g., carbon fibers,[1–3] carbon nanotubes,[4,5] and graphene[6,7]), ceramics,[8,9] as well as metals and alloys.[10] However, most synthetic strong mate- rials require complex and high-cost manufacturing processes (e.g., carbon fibers), generate adverse environmental impacts (e.g., steels, alloys), or are too heavy for many applications. Furthermore, the two key structural properties—strength and toughness—tend to be mutually exclusive in structural material design, in which strong materials are usually brittle, whereas tough materials are frequently weak.[11,12] To address this chal- lenge, tremendous efforts have been devoted in developingbioinspired structural materials that can offer the combination of both strength and toughness at low density (i.e., light- weight) while also manufactured at high volume and low cost.[13–19]