4D Printing of Multimaterial Flexible Magneto-Active Polymers

Magneto-active polymers (MAPs) are a promising class of stimuli-responsive materials for soft robotics and adaptive magnetic systems. However, existing additive manufacturing (AM) strategies offer limited control over both magnetic and mechanical properties, often relying on a single filler type with little attention to particle distribution and magnetic programming. This work presents a digital light processing (DLP)-based 3D printing process for fabricating MAPs with programmable magnetic and mechanical properties at ∼100 µm resolution. A wide range of magnetic properties is achieved, spanning from superparamagnetic (Fe₃O₄, NiMnFe₂O₄) to ferromagnetic (NdFeB, AlNiCo) composites, with intrinsic coercivity (H_ci) ranging from 0.2 to 511 kAm⁻¹ and maximum energy products (BH_max) up to 2100 Jm⁻³. Mechanical stiffness (0.1–2.4 MPa) is tuned through filler-matrix interactions. We demonstrate the use of laboratory-synthesized NiMnFe₂O₄ with narrow size distribution and stable suspension, alongside commercial particles exhibiting varied size and agglomeration. Nano-CT imaging was first implemented (in MAPs) to assess volume fraction (0.16–2.5%) and nanoparticle distribution. Functionality is showcased via vibrational, multimaterial membranes under magnetic actuation.