Rapid and strong adhesion of hydrogel adhesives is required
for
instant wound closure and hemostasis. However, in situ hydrogel formation
and sufficient adhesion at target tissue sites in biological environments
are severely compromised by the presence of blood and body fluids.
In this work, an underwater adhesive hydrogel (named SHCa) is fabricated
with rapid in situ gelation, enhanced mechanical toughness, and robust
underwater adhesion. The SHCa can undergo rapid UV irradiation-induced
gelation under water within 5 s and adhere firmly to underwater surfaces
for 6 months. The synergistic effects of crystalline β-sheet
structures and dynamic energy-dissipating mechanisms enhance the mechanical
toughness and cohesion, supporting the balance between adhesion and
cohesion in wet environments. Importantly, the SHCa can achieve rapid
in situ gelation and robust underwater adhesion at various tissue
surfaces in highly dynamic fluid environments, substantially outperforming
the commercially available tissue adhesives. The lap shear adhesion
strength and wound closure strength of SHCa on blood-covered substrates
are 7.24 and 12.68 times higher than those of cyanoacrylate glue,
respectively. Its fast hemostasis and wound sealing performance are
further demonstrated in in vivo animal models. The proposed hydrogel
with strong underwater adhesion provides an effective tool for fast
wound closure and hemostasis.