Modes of force stimulation in MNTs. (a–c) Pulling force modes. (a) Gradient magnetic field generated by a single magnet (i) and the corresponding force magnitude exerted by magnetic nanoparticles (MNPs) as a function of the magnet-to-particle distance and the number of MNPs (ii). (b) The pulling force exerted by a single MNP allows for the translocation of membrane receptors. (c) The displacement (top) and migration (bottom) of cells can induced with clusters of MNPs. (d–f) Dipolar attraction and rotation modes. (c) Uniform magnetic field generated between two magnets. (e, f) Dipolar attraction between magnetic nanoparticles induces the receptor clustering (e) and the rotation of particles for torque generation (f). n, number of nanoparticles; m⃗, magnetic moment; B, magnetic field strength; ∇B, magnetic field gradient, r, distance between nanoparticles θ, angle between the direction of external magnetic field and the centerline of two magnetic nanoparticles; τ, torque.