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Scientific reports 9(1), 3435 (2019). doi:10.1038/s41598-019-39934-4, Biomaterials often display outstanding combinations of mechanical properties thanks to theirhierarchical structuring, which occurs through a dynamically and biologically controlled growth andself-assembly of their main constituents, typically mineral and protein. However, it is still challenging toobtain this ordered multiscale structural organization in synthetic 3D-nanocomposite materials. Herein,we report a new bottom-up approach for the synthesis of macroscale hierarchical nanocompositematerials in a single step. By controlling the content of organic phase during the self-assembly ofmonodisperse organically-modified nanoparticles (iron oxide with oleyl phosphate), either purelysupercrystalline or hierarchically structured supercrystalline nanocomposite materials are obtained.Beyond a critical concentration of organic phase, a hierarchical material is consistently formed. In sucha hierarchical material, individual organically-modified ceramic nanoparticles (Level 0) self-assembleinto supercrystals in face-centered cubic superlattices (Level 1), which in turn form granules of up tohundreds of micrometers (Level 2). These micrometric granules are the constituents of the final mmsizedmaterial. This approach demonstrates that the local concentration of organic phase and nanobuildingblocks during self-assembly controls the final material’s microstructure, and thus enables thefine-tuning of inorganic-organic nanocomposites’ mechanical behavior, paving the way towards thedesign of novel high-performance structural materials., Published by Springer Nature, London