Biocompatible, 3D Printable Magnetic Soft Actuators – Ink Formulation, Rheological Characterization and Hydrogel Actuator Prototypes

Abstract

3D printable inks for the preparation of magnetic hydrogel actuators are difficult to formulate because magnetic nanoparticles tend to aggregate without stabilization through other ink components. At the same time, such inks need to be shear-thinning and recover their high viscosity state sufficiently fast to be suitable for the printing process. Here, the use of chitosan as dispersing agent for Fe2O3 nanoparticles is reported. Combined with Pluronic F127 as a rheology modifier and acrylamide as the base monomer, thermoresponsive and shear-thinning magnetic inks containing well-dispersed particles are obtained. The ink viscosity is tuned over two orders of magnitude by varying the chitosan and Pluronics F127 content. 3D-printed shapes with good shape fidelity are obtained at a print bed temperature of 50 °C, where aggregation of the Pluoronics F127 micelles occurs. This leads to a fast recovery of the high viscosity state of the material, so that the printed shape can then be locked in by UV cross-linking. This treatment yielded magneto-responsive prototypes which are promising for soft robotics applications. Thanks to the simplicity of the ink formulation, it is easily transferable also to nonspecialist laboratories, and the concept is potentially applicable also to other types of nanoparticles.