4D Printing of Magneto‐Active Soft Elastomers via Efficient Active Mixing Direct Ink Writing

ABSTRACT 4D printing relies on the 3D printing of materials that respond to various stimuli after printing. Among these, magneto‐active elastomers readily react to magnetic fields, particularly at high magnetic particle loadings. For soft silicones with high particle contents, direct ink writing (DIW) is the most appropriate printing technique. However, a major challenge remains, especially for very‐short‐pot‐life silicones: crosslinking starts once the base is mixed with the curing agent. Hence, a helical mixer with large blades operating at low speed within a large chamber is introduced for the first time in active mixing DIW to specifically address high‐particle‐content, short‐pot‐life silicones. This method offers a steady and efficient mixing of the two silicone components, both loaded with magnetic particles and a rheology modifier, just before extrusion, leading to consistent filament extrusion with even particle distribution in addition to extended printing times without further additives or elaborate control systems. A framework is presented for selecting print parameters, where only the extruder speed needs to be adjusted when switching between inks having different particle contents. The impact of printing strategy on mechanical properties is assessed, and magneto‐active structures that can find applications in tunable actuators, soft robotics, deployable structures, and surface morphing are demonstrated.