Novel Developed Systems and Techniques Based on Double-Network Principle

Abstract

The double-network hydrogels (DN gels), developed by our group in 2003, have attracted increasing attention due to their excellent mechanical performance and unique fracture mechanism. The anomalously large fracture energy of DN gels up to 2200 J m ¹2 originates from the specific combination of two networks with contrasting properties. The first brittle network serves as sacrificial bonds, which breaks into small clusters to efficiently disperse the stress around the crack tip into the surrounding damage zone, while the second ductile polymer chains act as hidden length, which extends extensively to sustain large deformation. The DN gels also exhibit good biocompatibility and low friction resistance. Owing to these superior properties, DN gels possess promising prospective in industrial and medicine fields, especially for load-bearing artificial soft tissues such as artificial cartilage. However, there are several critical problems limiting the practical applications of DN gels, such as how to produce tough artificial tissue with complex shapes or bond a gel to a solid substrate. To address these specific issues, we have developed new systems and techniques based on the DN principle. These achievements, including synthesis of ultrathin DN gels, bonding of one gel to another gel or solid substrate, free-shaping of DN gels, enhancing typical single network gels by creating a DN structure, will be briefly introduced in this account paper. We believe that these new techniques will substantially promote the practical applications of DN hydrogels and extent the DN principle to other systems.

Inorganic/Organic Double‐Network Gels Containing Ionic Liquids

“…[14,18] Consequently, the DN ion gels demonstrated high mechanical strength. [14,18] Consequently, the DN ion gels demonstrated high mechanical strength.…”

“…[1] Ion gels have recently attracted considerable interest for their application in electrochemical devices, actuators, and gas-separation membranes. Development of tough ion gels with a large amount of ILs is a critical challenge for overcoming the limitations in practical applications.In the past decade, great progresses have been achieved on developing highstrength and tough hydrogels based on different strategies, [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] which in principle could be adopted to toughen "ion gels." Development of tough ion gels with a large amount of ILs is a critical challenge for overcoming the limitations in practical applications.…”

“…In the past decade, great progresses have been achieved on developing highstrength and tough hydrogels based on different strategies, [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] which in principle could be adopted to toughen "ion gels." [19,21,[23][24][25] Among several tough hydrogels, the double-network (DN) hydrogels, consisting of brittle first network and ductile second network, show extraordinary high strength and toughness comparable to biological cartilages and industry rubbers.…”

“…[19,21,[23][24][25] Among several tough hydrogels, the double-network (DN) hydrogels, consisting of brittle first network and ductile second network, show extraordinary high strength and toughness comparable to biological cartilages and industry rubbers. [10,14] Extensive studies on the mechanism of DN hydrogels have shown that the enhanced toughness of DN gels is due to the internal fracture of the brittle first network, which effectively dissipates energy and increases the resistance against the crack propagation. [26][27][28] The ductile second network gives rise to the rupture of the first network over a large zone through their mutual entanglement.…”

Hydrogels with a macroscopic-scale liquid crystal structure by self-assembly of a semi-rigid polyion complex

“…However, we can greatly improve the strengths of the gels by using the double-network principle, that is, by introducing a second condensed, flexible network into the primary anisotropic gel. 46,[67][68][69] The hydrogels obtained in this manner possess both self-organized structures and mechanical strength; they should find extensive applications in load-bearing artificial tissues and soft actuators.…”