Fig. 1.

Schematic diagram of hydration shell formed by PEG and zwitterions separately. (A) PEG interact with H₂O molecules via hydrogen bonding, while zwitterions attract H₂O molecules through the powerful ion–dipole interaction, so that to form stronger hydration layers to prevent bio-adherent. (B) Incorporation of salt disrupts the previous electrostatic attraction of the charge pairs of intra-monomer, intra-chain and inter-chain, making the conformation of zwitterionic brushes from shrinking to stretching relatively.