Fig. 1: Schematic illustration of the adhesion and fault-tolerant mechanism of Electro-Ox hydrogel tape.
a Adhesion mechanism of Electro-Ox hydrogel tape. The hydrogel is mainly crosslinked by covalent bonds between BSA and electro-oxidized alginate-dopa or PAA formed via EDC-NHS. The conjugation between amine groups from BSA and dopaquinone generated during electro-oxidation further strengthens the hydrogel tapes. The unfolding of BSA and rupture of hydrogen bonds between dopa/dopaquinone can dissipate considerable energy and endow the hydrogel tape with high toughness. The adhesion between the hydrogel tape and tissue surface is time dependent. First, mainly non-covalent interactions (ionic interactions, cation–π interactions, and hydrogen bonds) are formed in seconds. As the reaction between amines from the tissue surface and dopaquinone in the hydrogel proceeds, the surface bonding is gradually enhanced in hours. b Comparison of the time-dependent adhesion strength of common hydrogel tapes using either physical bonding or chemical bonding for surface adhesion and the fault tolerant hydrogel tapes using a time-dependent formation of covalent bonding for surface adhesion. The overall adhesion strength (Wadhesion, solid line) depends on the lower one between the break strength of the hydrogel (Whydrogel, dash line) and the surface bonding energy (Wsurface, dash line). Physical surface bonding allows to detach the hydrogels freely but cannot ensure strong adhesion. In contrast, chemical surface bonding ensures strong adhesion but is not detachable. Due to the slow formation of chemical bonds with surface, the fault-tolerant hydrogel tapes can provide strong adhesion as instant chemical bonding hydrogel tapes yet have a time window for reversible detachment, thus combine the merits of both physical and chemical bonding-based hydrogel tapes.
