Fig. 2: Swelling behavior of PSIS particles and structure characterizations of PSIS adhesives.

a Schematic illustration of the osmotic pressure measurement of the particles of pressure-sensitive in-situ (PSIS) underwater adhesive. b Osmotic pressure \(\varPi\) versus time t for different volumes ratio \({\varphi }_{{{{\rm{v}}}}}\) of PSIS adhesive particles. \({\varphi }_{{{{\rm{v}}}}}\) is the volume ratio between the PSIS particles and the container. c The swelling ratio in diameter \(a/{a}_{0}\) of individual PSIS particle versus time. \(a\) represents the average diameter of swelling particles and \({a}_{0}\) is the initial average diameter of particles. Values represent the mean ± s.d. (N = 7). d Schematic illustration of the bulk PSIS adhesive contacts with the substrate. The blue area represents the adhesive region, while the white area represents voids. e The upper images show the bulk PSIS adhesive in contact with glass slides, and the lower images show the processed results, where the black region represents the adhesive area, and the white region represents the void area. The scale bar is 1 mm. f The surface adhesive ratio \({\varphi }_{{{{\rm{s}}}}}\) increases with the applied mechanical pressure \(P\).Values represent the mean ± s.d. (N = 3). g Schematic illustration of the porous PSIS adhesive. The blue area represents the material, while the white area represents voids. h 3D images of the PSIS adhesive material and the corresponding histograms showing the relationship between intensity frequency \({f}_{{{{\rm{in}}}}}\) and intensity \({I}\). The scale bar is 400 μm. i The porosity of the PSIS adhesive decreases with applied mechanical pressure \(P\). Values represent the mean ± s.d. (N = 3).