Size-dependent redistribution of surface-associated polymer nanocapsules at T-cell-macrophage biointerfaces

The use of immune cells as non-phagocytic carrier platforms for surface-bound nanomaterials is increasingly explored for cell-mediated delivery and biohybrid systems. However, how colloidal properties of surface-associated nanocargo control its redistribution during dynamic cell-cell interactions remains largely unknown. Here, we report that the size of polymer nanocapsules (PNCs) critically governs their contact-mediated redistribution from T cells acting as carrier cells to macrophages (MΦ-cells) as a stringent phagocytic acceptor model. Monodisperse polymer nanocapsules with defined diameters were assembled via a layer-by-layer approach and associated with T-cell surfaces. Fluorescence microscopy and flow cytometry reveal that nanocapsule redistribution is independent of serum proteins but strongly depends on direct cell-cell contact and macrophage activation state. Small PNCs are stably retained on T-cells, whereas larger PNCs detach more readily but are inefficiently captured by MΦ-cells. A quantitative model is introduced to decouple nanocapsule detachment from donor cell surfaces and capture efficiency during cell-cell contact, identifying two distinct regimes of intercellular exchange and a size window of maximal redistribution efficiency. These findings frame intercellular nanocargo exchange as a colloid-biointerface phenomenon governed by curvature-dependent membrane contact area and interfacial adhesion balance at dynamic cell membranes. This work demonstrates how classical colloid and interface concepts can be applied to surface-based cell-mediated systems and provides physicochemical design principles for contact-dependent nanocargo transfer.