Hemoglobin-Based Nanoreactors for Intracellular Radical Polymerizations

Abstract

Intracellular radical polymerizations offer a bioorthogonal route to synthesize synthetic polymers within living cells, offering new avenues for cell engineering and the fermentative production of macromolecules. However, efficient delivery of polymerization components and the need for exogenous catalysts remain challenges. Here, we report the development of a hemoglobin-based nanoreactor that self-assembles from amphiphilic hemoglobin-polycaprolactone conjugates (Hb-PCL) into hollow vesicles capable of initiating radical polymerizations inside living cells. When loaded with monomers and initiators, these nanoreactors can be internalized by cells. Upon cellular uptake, the heme groups of the hemoglobin within the nanoreactor catalyze the polymerization without genetic modification of the host or addition of external catalysts. In solution-phase reactions, the nanoreactors achieved 91% monomer conversion for N-isopropylacrylamide (NIPAm) after 36 h. Upon cellular uptake by Raw264.7 macrophages, the Hb–PCL vesicles catalyzed intracellular polymerization of NIPAm, as confirmed by gel permeation chromatography, and supported copolymerization with fluorescein O-methacrylate to produce fluorescent P(NIPAm-co-FOM), enabling direct visualization by confocal microscopy and flow cytometry. This work introduces a new class of protein–polymer hybrid nanoreactors for intracellular chemistry, expanding the toolkit for synthetic biology and cellular engineering.