Living tissues, such as muscle, autonomously grow and remodel themselves to adapt to their surrounding mechanical environment through metabolic processes. By contrast, typical synthetic materials cannot grow and reconstruct their structures once formed. We propose a strategy for developing “self-growing” polymeric materials that respond to repetitive mechanical stress through an effective mechanochemical transduction. Robust double-network hydrogels provided with a sustained monomer supply undergo self-growth, and the materials are substantially strengthened under repetitive loading through a structural destruction-reconstruction process. This strategy also endows the hydrogels with tailored functions at desired positions by mechanical stamping. This work may pave the way for the development of self-growing gel materials for applications such as soft robots and intelligent devices.

Quantitative characterization of the energy dissipation zone around a crack tip is the focal point in the fracture mechanics of soft materials. In this report, we present a mechanochemical technique for the visualization and quantification of the degree of polymer strand scission in the damage zone of tough double-network hydrogels. This technique uses mechanoradicals generated by covalent bond scission to initiate radical polymerization, which records the internal fracturing around the crack tip during crack opening or propagation. We adopted the mechanoradical polymerization of N-isopropylacrylamide, which forms a thermoresponsive polymer and whose distribution was visualized using an environment-responsive fluorescent probe. Two-and three-dimensional damage distributions were captured using a laser scanning confocal microscope. This technique also allowed for the quantitative estimation of the spatial distribution of stress, strain, and energy dissipation around the crack tip. The advantages and limitations of this technique are also discussed.

The high fracture energy of tough soft materials can be attributed to the large energy dissipation zone around the crack tip. Hence, quantitative characterization of energy dissipation is the key to soft matter fracture mechanics. In this study, we quantified the energy dissipation in the damage zone of a double-network (DN) hydrogel using a mechanochemical technique based on mechanoradical polymerization combined with confocal fluorescence microscopy. We found that, in addition to energy dissipation in a relatively narrow yield region, the dissipation in the wide preyielding region and the intrinsic fracture energy also has a large contribution to the fracture energy. Moreover, the fracture energy of a prestretched sample, in which the dissipative capacity is nearly depleted, suggests that the intrinsic fracture energy is higher than the fracture energy of the second network. These findings modify the previous understanding that the fracture energy of DN gels is dominated by the energy of the yielding zone formation.

Quantitative characterization of the energy dissipative zone around the crack tip is the central issue in fracture mechanics of soft materials. In this research, we present a mechanochemical technique to visualize the bond scission of the first network in the damage zone of tough double-network hydrogels. The mechanoradicals generated by polymer chain scission are employed to initiate polymerization of a thermoresponsive polymer, which is visualized by a fluorophore. This technique records the spatial distribution of internal fracturing from the fractured surface to the bulk, which provides the spatial profiles of stress, strain, and energy dissipation around the crack-tip. The characterized results suggest that, in addition to the dissipation in relatively narrow yielded zone which is mostly focused in the previous works, the dissipation in wide pre-yielding zone and the intrinsic fracture energy have also significant contribution to the fracture energy of a DN gel.

Quantitative characterization of the energy dissipative zone around the crack tip is the central issue in fracture mechanics of soft materials. In this research, we present a mechanochemical technique to visualize the bond scission of the first network in the damage zone of tough double-network hydrogels. The mechanoradicals generated by polymer chain scission are employed to initiate polymerization of a thermoresponsive polymer, which is visualized by a fluorophore. This technique records the spatial distribution of internal fracturing from the fractured surface to the bulk, which provides the spatial profiles of stress, strain, and energy dissipation around the crack-tip. The characterized results suggest that, in addition to the dissipation in relatively narrow yielded zone which is mostly focused in the previous works, the dissipation in wide pre-yielding zone and the intrinsic fracture energy have also significant contribution to the fracture energy of a DN gel.