The fixation of hydrogels to biological tissues is a major challenge conditioning the development of implants and surgical techniques. Here, coatings of procoagulant nanoparticles are devised which use the presence of blood to create adhesion between hydrogels and soft internal organs. Those nanostructured coatings are simply adsorbed at the hydrogel surfaces and can rapidly activate the formation of an interfacial blood clot acting as an adhesive joint. This concept is demonstrated on pig liver capsules with model poly­(ethylene-glycol) membranes that are intrinsically poorly adhesive. In the absence of blood, ex vivo peeling tests show that coatings with aggregates of bare silica nanoparticles induce a 2- to 4-fold increase in adhesion energy as compared to the uncoated membrane (3 ± 2 J m–2). This effect is found to scale with the specific surface area of the coating. The highest adhesion energies produced by these nanoparticle-coated membranes (10 ± 5 J m–2) approach the value obtained with cyanoacrylate glue (33 ± 11 J m–2) for which tearing of the tissue is observed. Ex vivo pull-off tests show an adhesion strength of coated membranes around 5 ± 1 kPa, which is significantly reduced when operating in vivo (1.0 ± 0.5 kPa). Nevertheless, when blood is introduced at the interface, the in vivo adhesion strength can be improved remarkably with silica coatings, reaching 4 ± 2 kPa after 40 min contact. In addition, these silica-coated membranes can seal and stop the bleeding produced by liver biopsies very rapidly (<30 s). Such a combination of coagulation and particle bridging opens promising routes for better biointegrated hydrogel implants and improved surgical adhesives, hemostats, and sealants.

The adsorption of polymers at the surface of mesoporous silica nanoparticles (MSNs) has been shown to provide a versatile way to create adhesion between hydrogels or biological tissues. Nevertheless, above a critical number of deposited nanoparticles, thick multilayers accumulate at the interface and the adhesion strength decreases as cracks easily propagate between weakly cohesive polymer-free nanoparticles. In order to suppress this limitation, we prepared spherical aggregates by spray drying during which MSNs are strongly adhered to by thermal annealing. The coatings produced with these microscopic supraballs (SB-MSNs) exhibit the same high specific surface area as MSN layers but with a much stronger cohesion between nanoparticles. Lap-shear tests with polydimethylacrylamide hydrogels clearly showed that the adhesion energy with supraballs can be significantly enhanced compared with nanoparticles (∼200% at 0.4 wt %). Peeling tests showed that the maximum adhesion energy reached with SB-MSNs (8 ± 0.5 J/m2) is significantly higher than the one achieved with nonaggregated nonporous (3 ± 0.1 J/m2) or mesoporous (6 ± 0.4 J/m2) SNs. It can be even further increased (10 ± 0.4 J/m2) by using macroporous supraballs. Moreover, confocal observations reveal that the largest adhesion enhancement obtained at high deposition concentrations is related to the formation of corrugated interfaces stabilized by supraballs. Finally, SB-MSNs degrade in biological media at the same rate as the elementary mesoporous nanoparticles, therefore offering an interesting combination of adhesion and bioresorbability for use as bioadhesives.

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Poly(acrylic acid) (PAAc) hydrogels possess good bioadhesive properties and allow 15 enhanced penetration of drugs. In addition, it is possible to localize the absorption site of the