Programming the microstructure of magnetic nanocomposites in DLP 3D printing

The ability to program the behavior of magneto-reactive polymers requires the fine control of their magnetic microstructure during each step of the printing process. Here, a systematic study of magnetically driven self-assembly of Fe₃O₄ nanoparticles into chain-like structures is presented and used in a 3D printable formulation. The kinetics of chains formation, as well as their rotation, are studied by varying several experimental parameters: i.e. the viscosity of the formulation, the content of nanoparticles, the intensity of the applied magnetic field, and its application time. Experimental results are coupled to numerical simulations based on the dipolar approximation model, and the collected data are used to produce a dataset to precisely program the microstructure during the printing step. Thus, a desired microstructure in a 3D printed piece can be obtained by controlling the orientation and the length of the magnetic chains in each printed layer. This is achieved by modifying a commercial Digital Light Processing (DLP) 3D printer to apply magnetic fields of tunable intensity and direction. Finally, as a proof of concept, a pyramid-like structure was 3D printed, where each layer contains a specific and spatially oriented microstructure.