Nanocomposite hydrogels were prepared by temperature-induced self-assembly of agarose and diphenylalanine (FF) mixtures in water. We investigated the mechanical and thermal properties, and the structure of agarose/FF composite systems. The FF assembly was significantly influenced by the existence of agarose molecules, which formed relatively thin FF nanowires (NWs) (microwires form from pure FF solutions) passing through meshes of agarose networks. The storage and compressive moduli of the nanocomposite gels significantly increased by increasing the FF content (up to 2 wt% for a 1 wt% agarose matrix). The nanocomposite gels did not fracture, even at a strain of 95%, but contracted uniformly by expelling most of the water during a compressive deformation. The highly compressed gels re-swelled in water and slowly recovered their original cylindrical monolithic shape. The unusual viscoelastic and compressive behaviors of nanocomposite gels is attributed to the unique nanostructure of interpenetrating networks between rigid NWs and the agarose matrix. Osteoblast-like cells (MG63) cultured on the nanocomposite hydrogels demonstrated that the FF assemblies could improve the cell viability of the agarose gel. (C) 2018 Elsevier Ltd. All rights reserved.