Polymerization of glycinamide-conjugated monomer alone in concentrated aqueous solution enables facile formation of a mechanically strong and a highly stable supramolecular polymer (SP) hydrogel because of the cooperatively hydrogen-bonded crosslinking and strengthening effect from dual amide motifs. This SP hydrogel exhibits thermoplastic processability, injectability, and self-reparability because of the dynamic destruction and reconstruction of hydrogen bonds in response to temperature change.

In recent years, cardiac patches have been developed for the treatment of myocardial infarction. However, the fixation approaches onto the tissue through suture or phototriggered reaction inevitably cause new tissue damage. Herein, a paintable hydrogel is constructed based on Fe -triggered simultaneous polymerization of covalently linked pyrrole and dopamine in the hyperbranched chains where the in situ formed conductive polypyrrole also uniquely serves to crosslink network. This conductive and adhesive hydrogel can be conveniently painted as a patch onto the heart surface without adverse liquid leakage. The functional patch whose conductivity is equivalent to that of normal myocardium is strongly bonded to the beating heart within 4 weeks, accordingly efficiently boosting the transmission of electrophysiological signals. Eventually, the reconstruction of cardiac function and revascularization of the infarct myocardium are remarkably improved. The translatable suture-free strategy reported in this work is promising to address the human clinical challenges in cardiac tissue engineering.

The emerging 3D printing technique allows for tailoring hydrogel‐based soft structure tissue scaffolds for individualized therapy of osteochondral defects. However, the weak mechanical strength and uncontrollable swelling intrinsic to conventional hydrogels restrain their use as bioinks. Here, a high‐strength thermoresponsive supramolecular copolymer hydrogel is synthesized by one‐step copolymerization of dual hydrogen bonding monomers, N‐acryloyl glycinamide, and N‐[tris(hydroxymethyl)methyl] acrylamide. The obtained copolymer hydrogels demonstrate excellent mechanical properties—robust tensile strength (up to 0.41 MPa), large stretchability (up to 860%), and high compressive strength (up to 8.4 MPa). The rapid thermoreversible gel ⇔ sol transition behavior makes this copolymer hydrogel suitable for direct 3D printing. Successful preparation of 3D‐printed biohybrid gradient hydrogel scaffolds is demonstrated with controllable 3D architecture, owing to shear thinning property which allows continuous extrusion through a needle and also immediate gelation of fluid upon deposition on the cooled substrate. Furthermore, this biohybrid gradient hydrogel scaffold printed with transforming growth factor beta 1 and β‐tricalciumphosphate on distinct layers facilitates the attachment, spreading, and chondrogenic and osteogenic differentiation of human bone marrow stem cells (hBMSCs) in vitro. The in vivo experiments reveal that the 3D‐printed biohybrid gradient hydrogel scaffolds significantly accelerate simultaneous regeneration of cartilage and subchondral bone in a rat model.

applications such as cell scaffolds, soft tissue substitutes and bioactuators. [ 1,3 ] However, their load-bearing applications are often limited by the poor mechanical performances. [ 4,5 ] Conventional hydrogels do not exhibit high mechanical properties because of uneven crosslinking and weak interaction among the chains. Recently, several high mechanical hydrogels have been developed and investigated as potential soft tissue replacements, [ 6,7 ] but few of them exhibit a combination of high mechanical properties including stiffness, toughness, tensile and compressive strengths, anti-fatigue as well as mechanical recoverability. [ 8,9 ] The well-known slide-ring [ 10 ] and tetra-PEG [ 11 ] hydrogels are designed to have ideally homogeneous networks to eliminate the intrinsic defects to a maximum extent, eventually leading to the enhanced mechanical properties. Other strategies are advanced to increase the functionalities [ 12 ] between two crosslink points to toughen the hydrogels, such as inorganic nanocomposite hydrogels, [13][14][15] macromolecular microsphere composite hydrogels, [ 16 ] graphene [ 17,18 ] or its oxide [ 19 ] composite hydrogels and micro- [ 20 ] or nano-structure [ 21 ] hydrogels. All of these gels have high compressive strength and large elongation, but their tensile strength (ranging from 190 kPa to 600 kPa) and modulus are not satisfi ed enough; furthermore, their high elastic properties show no hysteresis behavior, thus lacking a mechanism for mechanical energy dissipating. As a result, the mechanical properties are observably reduced when the gels contain a defect. [ 9 ] In order to solve these problems, a variety of mechanical energy dissipation mechanisms are implemented into the network to toughen the hydrogels. For instance, the PAMPS/PAAm double network (DN) gels can sacrifi ce the rigid chemical bond of the fi rst network to dissipate energy to achieve MPa magnitude order of tensile and compressive stress but the fatigue resistance is low, and the preparation process is relatively complicated. [22][23][24][25] Suo and his co-workers [ 9 ] reported synthesis of a hydrogel with high stretchability and astonishing fracture energies of 9,000 J/m 2 by forming interpenetrating polymer networks of covalently crosslinked PAAm and ionically crosslinked zipper-like High strength hydrogels were previously constructed based on dipole-dipole and hydrogen bonding reinforcement. In spite of the high tensile and compressive strengths achieved, the fracture energy of the hydrogels strengthened with sole noncovalent bondings was rather low due to the lack in energy dissipating mechanism. In this study, combined dipole-dipole and hydrogen bonding interactions reinforced (DHIR) hydrogels are synthesized by onestep copolymerization of three feature monomers, namely acrylonitrile (AN, dipole monomer), acrylamide (AAm, H-bonding monomer), and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS, anionic monomer) in the presence of PEGDA575, a hydrophilic crosslinker. The electrostatic repulsion from PAM...

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