The supramolecular polymer hydrogels feature self-healability, adjustable mechanical strength, and thermoplasticity, which are derived from the formation of supramolecular physical interactions in the hydrogel networks, such as H-bonding interactions, [6] host-guest interactions, [7] metal-ligand coordination interactions, [8] hydrophobic interactions, [9] multiple combined interactions. [10] Among them, H-bonds are generally weak noncovalent bonds, ubiquitous in biomolecules, but their synergistic interactions can reach a strength of the covalent bond; thus it is commonly utilized in designing supramolecular tough hydrogels. [11] Our previous study suggested that supramolecular polymer hydrogels based on single amide H-bonding interaction were unstable in water, [12] because the competitive solvation of H-bond donor and acceptor in polar solvents weakens its strengthening effect. [13] Inspired by the hydrogen-bonded clusters in the secondary structure of proteins, we constructed a supramolecular poly(N-acryloyl glycinamide) (PNAGA) hydrogel whose dual amide motifs in the side chain contributed to high strengths and outstanding antiswelling ability due to strong shielding of the hydrogen-bonded microdomains from water molecule attack. [12] By utilizing Type II photoinitiated self-condensing vinyl polymerization of N-acryloyl glycinamide (NAGA), the resultant hyperbranched PNAGA hydrogels demonstrated superior mechanical performances to those of linear PNAGA counterparts owing to the higher cross-linking density of H-bonds. [14] In addition, the H-bonding interactions of dual amide motifs could also be modulated by copolymerizing other monomers, [15][16][17][18] thus achieving the versatile hydrogels with mechanical properties spanning from high strength to soft injectability, which show promising applications as 3D printed osteochondral regeneration scaffold, [16] artificial vitreous body, [17] and postoperative antiadhesion barrier. [18] Our recent study revealed that only introducing one methyl group to the double bond of NAGA could lead to a considerable decrease in mechanical strengths and an increase in room temperature autonomous self-healability of the poly(N-methacryloyl glycinamide) hydrogels (MNAGA), which was resulted from the perturbation of one methyl substitution to H-bonds. [19] The intermolecular H-bonding density heavily influences the gelation and rheological behavior of hydrogen-bonded supramolecular polymer hydrogels, thus offering a delicate pathway to tailor their physicochemical properties for meeting a specific biomedical application. Herein, one methylene spacer between two amides in the side chain of N-acryloyl glycinamide (NAGA) is introduced to generate a variant monomer, N-acryloyl alaninamide (NAAA). Polymerization of NAAA in aqueous solution affords an unprecedented ultrasoft and highly swollen supramolecular polymer hydrogel due to weakened H-bonds caused by an extra methylene spacer, which is verified by variabletemperature Fourier transform infrared (FTIR) spectroscopy and s...