Mussel foot
proteins (Mfps) show strong adhesion to underwater substrates, making mussels tightly cling to reefs to withstand the sea current. Therefore, Mfps-inspired
tissue adhesives have aroused much research interest, but tough underwater
biological tissue adhesion is still a great challenge. Herein, we report a tough and reversible wet tissue-selective adhesive
hydrogel made of
poly(acrylic acid-co-
catechol) and
chitosan (CS). It provides negatively charged -
COO-, positively charged -NH3+,
catechol group and hydrophobic alkyl chain, resemble
amino acids,
catechol and hydrophobic units in Mfps. Due to the covalent/electrostatic attraction/π-π/cationic-π/hydrogen bonding, in addition to the hydrophobic interaction from the long hydrophobic alkyl chain of the
catechol derivative, the
hydrogel has a high cohesion strength and toughness, i.e., tensile
stress, fracture strain and fracture toughness of ∼0.57 MPa, 2510% and 6620 J m-2, respectively. As a
tissue adhesive, its adhesion bonding to the porcine skin surface is so strong that its adhesion strength is almost equal to the tearing strength of the
hydrogel. The 180-degree peeling adhesion energy of the
hydrogel to blood-wetted porcine skin is notably ∼1010 J m-2. It can tightly and seamlessly adhere to the porcine small intestine, and has a bursting pressure of up to 520 mmHg. The
hydrogel can be handily debonded from the porcine skin surface in the presence of aqueous
solution at pH 8.0, and its adhesiveness is reversible for at least 20 cycles. It is supposed that the synergistic interactions of the adhesive
catechol group, displacement of water on the wet skin surface by the positively charged -NH3+ groups of CS and the water-repelling potential of the hydrophobic unit of the
catechol derivative, the protection of the
catechol group from oxidation into a less adhesive
quinone group, and the energy dissipation capacity of the mechanically tough
hydrogel contribute to the strong and repeatable wet
tissue adhesion.