1. A react-on-demand (RoD) method of fabricating a three-dimensional electrically conductive hybrid metal-polymer structure on a substrate, the method comprising:(i) coating the substrate with an ink-absorption coating to form an ink absorption layer on the substrate, followed by
(ii) coating the substrate with polyvinyl alcohol (PVA) solution to form a PVA layer having PVA polymers on the ink absorption layer, followed by
(iii) functionalizing the PVA layer with a first solvent containing a reducing agent and evaporating the first solvent to induce formation of crystals of the reducing agent located in between polymer chains of the PVA polymers as well as on the surface of the PVA layer, followed by
(iv) printing or writing a second solvent containing water and a metal salt onto the PVA layer wherein the second solvent dissolves the reducing agent and at the same time the reducing agent reduces the metal salt to produce metal particles to form a three-dimensional electrically conductive hybrid metal-polymer structure in which the metal particles are located on the surface of the PVA layer as well as in between the polymer chains in an interior of the PVA layer.