4D Printing of Multifunctional Devices Induced by Synergistic Role of Magnetite and Silver Nanoparticles in Polymeric Nanocomposites

Emerging as a revolutionary strategy to fabricate dynamic three dimesional (3D) structures, 4D printing (4DP) mainly refers to printed materials capable of changing form over time when exposed to a predetermined stimulus. Nevertheless, the 4D concept can be extended beyond shape-morphing, by including also changes in the properties and/or functionalities of printed materials over time. To this end, this work explores the 4DP of multifunctional nanocomposites that can adapt to different application scenarios exploiting the stimuli-activable properties of two functional nanofillers embedded into the polymeric matrix. In particular, a photocurable system loaded with both Fe₃O₄ nanoparticles (NPs) and AgNO₃, as precursors for the in situ photo-induced generation of Ag NPs, is used for the digital light processing of magnetic nanocomposites with integrated electrical and antibacterial functions. The composition of formulations is designed to both optimize their printability and maximize the magneto-responsiveness and the electrical conductivity and/or antibacterial activity of the printed objects, given by Fe₃O₄ and Ag NPs, respectively. Finally, it is shown that the functional responses of the nanocomposites can be activated individually or in combination, which may be of particular interest for the fabrication of smart multifunctional devices with potential applications ranging from soft electronics to biomedicine.