Interestingly, the zeta potential (ζ-potential) did not change dramatically between naked (polymer-less) cells and decorated ones, indicating that the slipping plane was not shifted outwards by the polymers (SI Figure ). Furthermore, we tested whether the polymer chains could be extended in a subsequent polymerization: in P11, a first PPEGMA:PPEGMA-N3 (9:1 molar) polymer was produced on the cell surface. The same cells were then subjected to another iteration of a similar copolymerization (P12) (Table , SI Figure ). The monomer conversion was lower than in the first step, the number average molecular weight increased slightly, and Đ increased above 2.