Proteins are the key building blocks of all biological matter. While engineers predominantly use concrete, metals, ceramics and synthetic polymers as structural materials for their high strength and durability, Nature exploits complex mechanical and chemical features of proteins for building strong, elastic and robust materials and structures. For example, spider silk, amyloid (sturdy protein fibrils found in many diseases) and muscle fibers are made entirely of proteins and blend extensibility with high strength to achive extreme toughness. These super-fibers represent an alternative scheme of material design to biomineralization, which allows for incorporation of minerals in protein scaffolds to build very stiff and tough materials such as nacre, mollusk shells and bone. Many scientists have been intrigued by Nature's unknown recipe for creating soft yet durable and strong materials. These materials are different from their synthetic equivalents because they employ hydrogen bonds that are much weaker than covalent or metallic bonds, and exhibit entropic elasticity at the nano-scale.