In the absence of surfactants, certain molecules can directly aggregate via hydrophobic interactions to form energydissipating clusters within the hydrophilic network (Figure ). Within this category, two double networks are reported, one made from PAAm and the microphase-separating block copolymer P(BuMA-b-AAc-b-BuMA), the other combining xanthan gum-Ca 2+ and P(AAc-stat-OMA). Beside the previous ones, various single networks have been reported involving PU/P(AAc-stat-SA), P(NIPAAmstat-FOSA), P(AAm-stat-PhA), as well as different AN-based copolymers. Additionally, one formulation consists of a polyether-based PU, a second one simply combines PDMAAm with hydrophobic lignin. With a slightly higher water content than (62% vs. 54%), Feng, Liu, and co-workers used a P(AN-stat-AAm) network, cross-linked with a 3 kDa PEG dimethacrylate (PEGDMA). The authors reported an elastic modulus of E = 16.0 MPa and a fracture toughness of Γ = 16.6 kJ/m 2 . When hydrophobic and metal-ligand interactions were combined through use of a P(AN-stat-AAc) copolymer and Zn 2+ ions, a similar competitive elastic modulus was observed (E = 17.4 MPa). The strong hydrogel (σ b = 21.9 MPa) exhibited a fracture toughness of Γ = 7.1 kJ/m 2 at a water content of 68%. The stiffest hydrogel through hydrophobic interactions was created by copolymerization of AAm, phenyl acrylate (PhA) and varying amounts of MBA. The solvent of the resulting P(PhA-stat-AAm) network was changed from DMSO to water for mechanical testing. With a water content of 60% and a fracture energy of Γ = 7.45 kJ/m 2 , the elastic modulus reached a value of E = 145 MPa. Interestingly, within this category most of the described single networks outperform the two respective double network hydrogels. This demonstrates, how collective hydrophobic interactions can be a potent energy dissipation pathway, generating good fracture energies along with high stiffness values. More generally, the above data also confirms the previously observed trend that decreasing water content correlates with increasing stiffness. Nonetheless, some examples manage to reconcile the two; something that otherwise can be conflicting, as high moduli require the chain length between cross-links to be short. Composites. Tough (nano)composite hydrogels were grouped according to their morphology into hydrogels using (nano)spheres, nanosheets or (nano)fibers (Figure ). SiO 2 nanospheres were employed in several studies, while isolated cases employed Ag, or Fe 3 O 4