A self-defensive bilayer hydrogel coating with bacteria triggered switching from cell adhesion to antibacterial adhesion

We report on a self-defensive bilayer hydrogel coating which can switch from a cell adhesion surface to an antibacterial adhesion surface. To covalently attach the coating, an antifouling hydrogel thin film was firstly prepared on a thiol modified substrate as the bottom layer via the thiol–ene click reaction of the ene-functionalized copolymer of poly(sulfobetaine methacrylate-acrylate acid-2-hydroxyethyl methacrylate) (P(SBMA-AA-HEMA)). Thereafter, heparin-mimicking polymer chains were grafted onto the hydrogel film surface as the upper layer via surface initiated atom transfer radical polymerization. The ester group of HEMA was designed as the sensitive part which could be cleaved in a bacterial infectious environment, while the hydroxyl group was designed as the anchoring point of the upper layer. The surface morphology and chemical composition after each modification step were characterized by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The bilayer coating could promote cell adhesion and proliferation, as well as bacterial adhesion. After being immersed into a cholesterol esterase solution (simulative bacterial infectious environment), the upper layer could be detached rapidly, and the exposed bottom layer then showed strong resistance to bacteria. Our approach towards bacteria-responsive “intelligent” coating gives new insights into the antibacterial protection of biomedical devices.