In a typical bioPISA experiment, HPMA (2 mL, filtered on basic alumina) was measured in a 4 mL vial that was closed with a septum. A certain amount of mPEG-BiB and sodium ascorbate was dissolved in a certain volume PBS-Br buffer pH 7.4 spiked with 5 vol% DMSO in a 4 mL vial closed with a septum. A certain amount of myoglobin was suspended in PBS-Br buffer pH 7.4 in a 10 mL Schlenk flask. All the solutions were degassed with Ar for 1 h. The mPEG-BiB/NaAsc solution was added to the Schlenk flask, and the resulting solution was stirred for 15 min. The colour of the reaction mixture changed from brown to red (myoglobin oxidation). Then, purified HPMA was added. The reaction mixture was stirred for 4 h at room temperature before being opened to air to quench the polymerization by atmospheric oxygen. The final suspension was diluted with 15 mL of PBS. The reagent amounts are specified in Table . All encapsulations were performed with HPMA 20 wt% and aimed DP 400.