Magnetic Nanostructures Inside Cells: A Versatile Platform for Cellular Sensing, Manipulation, and Fabrication

Magnetic manipulation of living cells traditionally relies on forces exerted by beads attached to the cell surface, where magnetic gradients are used to manoeuvre cell suspensions. Here, we demonstrate a strategy where cells with internalized magnetic nanostructures can be maneuvered as micro-agents under weak, spatially homogeneous rotating fields (< 8 mT). Using helical magnetic nanostructures, active microrheological measurements reporting local cytoplasmic mechanics are enabled, combined with programmable transport of the cells rolling on a surface. By tuning the magnetic drive while modulating cell-substrate adhesion, we resolve three distinct dynamical regimes: (1) nanomotor-only propulsion in fully adhered cells; (2) intermittent tumbling in semi-adhered cells where cytoskeletal remodelling creates pockets of reduced viscoelastic resistance; and (3) synchronous nanomotor-cell rolling that manoeuvres non-adherent cells from within. Quantitative torque balance reveals how intracellular thrust overcomes substrate friction, closing a key gap in our understanding of force transmission from the nanoscale to the cellular scale. These actuated cell-bots further act as tugboats, hydrodynamically steering neighbouring passive cells without physical contact, enabling label-free cell sorting and patterning, further supported by hydrodynamic simulations. Extending the concept, we demonstrate iron-calcium silicate core-shell nanomotors that guide pre-osteoblastic cells into predefined architectures while supporting mineralized matrix deposition, highlighting the platform's utility in regenerative medicine. Taken together, we describe a promising platform that integrates cellular interrogation, manipulation, and biofabrication within a single experimental system.