A particular sub-branch of 3D printing is extrusion-based printing (EBP) of metallic and ceramic colloidal materials, where highly concentrated suspensions of particles are deposited to construct near-net shaped parts with complex geometries. Large-area magnets, transformers, magnets with complex shapes, constant-flux inductors, and electrochemical devices can be realized through EBP. However, polymer-based composites of Neodymium Iron Boron (NdFeB) family, iron, and NiCuZn ferrite are the only magnetic systems that are formulated as inks for EBP. The presence of high amounts of additives (5-8 wt. % to 69 wt. %) intrinsically lowers the loading of magnetic particles and limits the performance of fabricated objects due to the reduction in the magnetic material filling factor. To harness the full potential of EBP, there is a need for maximum purity inks. We systematically pursued a particle-specific approach to design an additive that can cater the surface charge and its distribution in iron oxide particles (IOPs) to stabilize and control the viscosity of suspensions of IOPs. We synthesized poly(ethylene glycol) (PEG)-grafted copolymers of N-[3(dimethylamino)propyl]methacrylamide (DMAPMA) and acrylic acid (AA) and investigated the effect of i) comonomer ratios, and ii) the density of PEG side chains on the stability of suspensions. The optimized ink contained 81 wt. % of IOPs in the presence of 1.15 wt. % of a single additive (by weight of IOPs) in a fully aqueous medium. To demonstrate the printability of various geometries, we printed three different shapes of magnetic cores (rectangular, thick-walled toroidal, and thin-walled toroidal cores) and a porous lattice structure. We characterized the electrical and magnetic properties of magnetic cores through impedance spectroscopy (IS) and vibrating sample magnetometry (VSM), respectively. To the best of our knowledge, this fully aqueous ink is the first of its kind for EBP in terms of comprising a magnetic material of choice at highest amounts through the minimum use of a single additive.