Recyclable Synthetic Polymer Nanoparticles for Sustained Target Neutralization

Synthetic polymers have emerged as protein-affinity materials capable of binding and neutralizing biological targets through optimized functional monomer compositions. However, these materials are often implicitly treated as single-use systems, largely because they are assumed to be unavailable for further interaction after cellular internalization. The intracellular fate of such materials, including their potential rerelease and sustained functional activity, remains poorly understood. Here, we demonstrate that synthetic polymer nanoparticles (NPs) can undergo cellular recycling while preserving their functional activity. Using N-isopropylacrylamide (NIPAm)-based polymer NPs as a proof-of-concept system, we investigated their cellular uptake, intracellular trafficking, and extracellular release. We evaluated their functional performance using melittin as a model target. A fraction of internalized NPs was rereleased in a cell-type-dependent manner, with transient colocalization with Rab11 suggesting the possible involvement of recycling-associated pathways. Importantly, the released NPs retained their ability to bind and neutralize melittin, even after prior interaction with the target toxin, and remained functionally competent for subsequent binding events. Moreover, the NPs appeared to maintain their association with melittin during intracellular processing, indicating that their functional integrity is preserved throughout the recycling process. Collectively, these findings demonstrate that synthetic polymer NPs can function as reusable systems with extended functional lifetimes, thereby challenging the conventional single-use paradigm. This study provides a foundation for the design of next-generation nanomaterials with enhanced functional durability in biological environments.