Hydrogels had been mechanically weak materials, which extremely limited their applications. Prof. Gong and her team discovered that a double network (DN) structure consisting of a hard and brittle network and a soft and stretchable network gives the gel strength and toughness comparable to that of industrial rubber, which overturned the common sense that gel is weak. Since 2011, she has developed the research on double network gels, and made remarkable achievements by establishing more general toughness principle of the soft materials and creating various high toughness soft materials. Below are her major achievements.

1. Proof of universality of sacrificial bond principle by creating various high toughness soft materials
Prof. Gong proposed that the chemical bonds in the brittle network of a double-network gel can be considered as "sacrificial bonds" to avoid entire fracture of gel. Furthermore, she proposed that this sacrificial bond principle is universal, and that not only covalent bonds but also non-covalent bonds and other fragile supramolecular structures can toughen gels as like sacrificial bonds. To prove this, in addition to chemically cross-linked polymer networks such as double network gels, she introduced non-covalent bonds such as ionic bonds, hydrophobic bonds, and hydrogen bonds into polymer gels as sacrificial bonds and successfully created various high-toughness gels. When chemical bonds are used, the bonds are irreversible, so once the structure is broken, it cannot be self-repaired, whereas the non-covalent bonds are reversible, and the broken structure has the characteristic of being able to self-repair. She clarified that gels using non-covalent bonds for sacrificial bonds have not only high strength and high toughness but also self-repairing properties and impact absorption due to high internal viscosity. In addition, using amphiphilic molecules that self-assemble to bilayers, she succeeded in developing anisotropic photonic structures in gels. The hydrophobic bonds in the bilayers function as sacrificial bonds to toughen the gels. These gels also show unique functions including anisotropies in swelling, molecular diffusion, and mechanical properties. These gels also show beautiful structural color changes in response to force and environment changes. These functions cannot be found in conventional amorphous-structured gels. These studies showed that various non-covalent bonds function as sacrificial bonds and greatly increase the toughness of gels, proving that "high toughness by sacrificial bonds" is a universal principle.

2. Extension of the sacrificial bond principle
To extend the sacrificial bond principle, Prof. Gong has further developed polymer gels with mesoscale bicontinuous phase separation structures consisting of hard phase and soft phase, bone-like composites from hard bioceramics and soft polymer gels, and macroscopic double network gels with a low melting point metal as the hard skeleton. She clarified that the toughness of these materials is greatly increased when the hard components are brittle and break first at deformation. These studies extended the principle of sacrificial bonds from nanoscale molecular structures to mesoscale and macroscale structures, and from organic materials to inorganic and metallic materials. She further extended the sacrificial bond principle to soft / hard composites. By combining high toughness gels and elastomers as the soft matrix phase and glass fibers and carbon fibers as the hard skeleton, she succeeded in creating super tough "fiber reinforced soft material" that surpasses existing high toughness materials such as metals and fiber reinforced plastics.

3. Establishment of quantitative design indicators for fiber reinforced soft materials
By extensive study on the fracture mechanism of various soft materials developed, Prof. Gong came into the clear picture that developing high toughness materials is the design of the structure that maximizes the sacrificial bond zone size and density at the crack tip. This is because the fracture energy that characterizes toughness can be expressed by the product of energy dissipation zone and density. For the fiber reinforced soft materials, she experimentally elucidated that the size of the dissipation zone is proportional to the root of the elastic modulus ratio of the hard component and the soft component, and that the energy dissipation density is the volume average of each component. In addition, she clarified that in the fiber-reinforced soft material, the ultra-toughness that surpasses that of existing high-toughness materials is owing to the strong interfacial bonding and the extremely large force transmission length. Through these studies, she clarified that the development of super-toughness in soft / hard composites requires three essential conditions: strong interfacial bond, high modulus ratio of hard skeleton to soft matrix, and high toughness of matrix. These results provide a quantitative design index for material creation.

The principle of "high toughness by sacrificial bonds" established by Prof. Gong has already been widely applied worldwide and has led to the creation of many tough and self-healing gels and elastomers. These also results in development of tough hydrogels with biocompatibility and have greatly increased the options for hydrogels as medical and sanitary materials. The principle is also applied to the industry, leading to the development of high toughness rubber materials, and contributing to environmental protection and energy saving through weight reduction and long life of tires.

In summary, Prof. Gong has conducted pioneering research on high toughness soft materials and has played a leading role in recent breakthroughs in this field. Therefore, her achievements are truly remarkable and recognized as worthy of the Chemical Society of Japan Award.