The C1s and K2p peaks, partially overlapping in the 280-298 eV scans, are fully consistent with the expected chemistry of PSPMA brushes and S2p peaks at 168 and 169.5 eV are confirming the presence of sulfonate residues at high densities in this coating (Figures and) . These results are also in excellent agreement with the spectra obtained from PSPMA brushes generated via conventional ATRP (Supplementary Figure ), confirming the achievement of brushes with comparable chemical structures via both polymerisation techniques. However, ATRP-generated brushes also displayed Cu and N components (e.g. Cu 2p and N 1s peaks) that are proposed to result from residual catalysts and associated ligands (bipyridine; Supplementary Figure ). Upon incubation in buffer (PBS) these components are displaced, irrespective of the brush thicknesses studied, indicating that simple exchange with electrolytes is sufficient to remove traces of catalysts present and recover a pristine PSPMA brush chemistry, although replacing potassium salts with sodium counterions. Interestingly, sparse brushes did not feature residual catalysts, perhaps suggesting that the high density of PSPMA brushes at full density of ATRP initiators constitute an environment stabilising molecular catalytic species.