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 (Fe 3 O 4 , NiMnFe 2 O 4 ) 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 NiMnFe 2 O 4 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. A custom post‐print magnetization method enables the patterning of 16 discrete magnetic poles, unlocking new actuation modes. This platform provides an integrated approach to architecting MAPs with tunable properties, bridging processing, structure, and function.