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Abstract

Biological tissues in animals generally consist an extracellular matrix often with cells embedded in it. These materials are primarily comprised of different protein building blocks, as well as polysaccharide and mineral components in certain cases. Prominent examples include tendon, skin and bone. In contrast, other organisms fabricate protein-based materials that function extracorporeally – that is, outside the body and without embedded living cells. Typical examples include spider and insect silk or the byssus filaments by which mussels attach to rocks. Regardless of whether these materials function inside or outside the body and whether or not they contain living cells, natural protein-based materials perform essential life functions that are very often highly dependent on their load-bearing mechanical properties. In the current review, we explore the relationship between specific features of these protein building blocks (e.g. their sequence, conformation, cross-linking and hierarchical structure) and the higher-level mechanical function of the materials that they comprise. The extracted structure–property relationships have crucial importance for understanding the biological function of these materials, but also have implications for bio-inspired design of new polymers and composites, as well as relevance for ongoing efforts to bioengineer artificial tissues.