In contrast to man-made materials, nature assembles materials with remarkable mechanical properties. Exoskeletons are compelling examples: despite being comprised by mineralized materials, they exhibit high levels of strength and toughness. Stiff, hard and tough hierarchical microstructures, which contain a small volume fraction of interfacial biopolymers, are responsible for creating multifunctional composite materials that protect animals. The high strength and toughness of exoskeletons contrasts man-made engineering materials that typically sacrifice strength to achieve greater toughness. First, I will present biologically occurring hierarchical features and mechanisms observed from in situ microscopy experiments which endow remarkable mechanical properties. The acquired understanding is applied towards the design of artificial bio-inspired nanocomposites that are strong and tough. Graphene oxide-polymer nanocomposites illustrate the validation of models used to design materials of interest to multiple communities. A strategy combining multiscale experiments and simulations, to select optimal constituents and geometric parameters, will be presented.