Cytocompatible Biocatalyzed Surface-Initiated PhotoATRP Mediated by Red Light Irradiation in Open Air

Surface-initiated atom transfer radical polymerization (SI-ATRP) enables the fabrication of functional polymer brushes, yet achieving simultaneous oxygen tolerance and controlling polymer growth and compatibility to biological environments remains challenging. Here, we report a hemoglobin (Hb)-catalyzed, red light-mediated SI-ATRP (SI-bioATRP) that proceeds efficiently in open air. In the presence of methylene blue (MB⁺) as a photosensitizer and trace dimethyl sulfoxide (DMSO) as an oxygen scavenger, red light excitation provides the rapid reduction of Hb-(Fe^III) to Hb-(Fe^II), which acts as activator for ATRP. This cooperative Hb/MB⁺/red light system promotes the controlled growth of chemically different brushes exceeding 300 nm in thickness, while analogous polymerizations in solution proceed in an uncontrolled manner. Mechanistic and calorimetric analyses reveal that the controlled behavior of SI-bioATRP arises from the intrinsic tendency of Hb to physisorb on initiator surfaces and dormant/propagating brush interfaces, ensuring an effective activation-deactivation equilibrium. The resulting process is fully oxygen-tolerant and cytocompatible and operates even in cell-culture media, enabling in situ polymer brush formation under biologically relevant conditions.