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