Printing ferromagnetic domains in soft materials : mechanism, modeling, and applications

Abstract

Soft materials capable of transforming between three-dimensional (3D) shapes have applications in areas as diverse as flexible electronics, soft robotics, and biomedicine. This thesis introduces a method of printing ferromagnetic domains in soft materials that yield fast transformation between complex 3D shapes via magnetic actuation. This approach is based on direct ink writing of an elastomer composite containing hard ferromagnetic microparticles. By applying a magnetic field to the dispensing nozzle while printing, we make the particles reoriented along the applied field direction to impart patterned magnetic polarity to printed filaments. This method allows us to design ferromagnetic domains in 3D-printed soft materials encoded with complex programmed shapes. A mathematical model based on a continuum mechanics framework is developed to predict such complex transformation of printed structures under the applied magnetic fields. For this computational model, a constitutive law is developed to describe the behavior of soft materials incorporating hard ferromagnetic microparticles under applied magnetic fields. The capability to quantitatively predict the shape changes enables designing a set of previously inaccessible modes of transformation such as remotely controlled 3D auxetic behaviors in an extremely fast and fully reversible manner via magnetic actuation. The actuation speed and power density of the printed soft materials with programmed ferromagnetic domains are orders of magnitude greater than existing 3D-printed active materials. Diverse functions derived from the fast and complex shape changes such as reconfigurable soft electronics, interaction with quickly moving objects, rolling-based locomotion and delivery of drug pills, and a horizontal leap of a 3D auxetic structure.