Electromagnetic assistance enables 3D printing of silicone-based thin-walled bioinspired soft robots

Material Extrusion (MEX) is emerging as the leading manufacturing method for fabricating complex silicone structures and is demanded in different fields such as soft robotics, space exploration, and biomedicine. At the state-of-the-art level, the fabrication of small-scale silicone structures (low value of layer height parameter) remains challenging owing to the high printing forces involved. In this study, an innovative approach to considerably decrease the printing force while extruding at low layer heights is presented, thereby enabling the fabrication of thin-walled silicone structures. The proposed approach is based on leveraging silicone mixed with Fe3O4 magnetic nanopowder, which is extruded using a custom-made syringe equipped with 325 electrically charged (4.5 Ampere) copper coils. The electromagnetic force (FEM) generated by these coils pushes the magnetic ink from the syringe towards the build plate, thereby reducing the overall printing force (FT). Here, a maximum reduction of 21.08% is achieved when the layer height of 0.1 mm is set. Further, all the forces involved in the proposed electromagnetic-assisted manufacturing approach are numerically modeled and experimentally measured after equipping the 3D printing system with piezoresistive sensors: a model accuracy of 95.63% is obtained at low layer heights and flow rate values. Finally, small-scale self-transforming soft robots and bioinspired monolithic structures obtained by jointly extruding magnetic ink and stiff thermoplastic materials in the same manufacturing cycle are presented, thereby proving the potential of the proposed additive manufacturing approach.