(1 of 10) 1605350 materials exhibiting both excellent loadbearing capacity and fracture resistance, as can be observed from both hard tissues [3][4][5][6][7] (e.g., nacre and bone) and soft tissues (e.g., ligament and tendon), [8][9][10] by combining rigid, brittle components (either inorganic or organic) and soft, organic components into composite materials. Most of these natural materials have highly complex hierarchical architectures existing over multiple length scales, which results in composite properties that far exceed what could be expected from a simple combination of the individual components. [3] Many researchers have attempted to mimic the unique natural structures of tough, hard hybrid materials, but only a few studies have achieved remarkable success comparable to that of nature. [11][12][13][14] For example, a bioinspired alumina hybrid material with specific strength and toughness comparable to aluminum alloys was synthesized by combining a hard yet brittle ceramic with relatively soft poly(methyl methacrylate), where nacre-like multiple toughening mechanisms at multiple scales resulted in exceptional fracture resistance. [12] As a vital class of soft materials, tough hydrogels have shown strong potential as structural biomaterials. [15][16][17][18][19][20] These hydrogels alone, however, still possess limited mechanical properties (low modulus) when compared to some load-bearing tissues, e.g., ligaments and tendons. To reproduce the exceptional strength and toughness seen in soft load-bearing tissues, one strategy is to combine an energy-dissipative tough hydrogel with rigid yet flexible fibers to create a composite, similar to fibrous tissues. [21][22][23] In this composite concept, the rigid fiberbased component increases the specific strength while the gel matrix dissipates energy. Based on this concept, some attempts have been made to fabricate fiber reinforced hydrogel composites. [24][25][26][27][28][29] Utilizing this technique, researchers have been able to increase and tune the stiffness and toughness achievable with hydrogel-based systems. However, developing soft composites with synergistically improved mechanical properties, such as those seen in hard bioinspired composites, is still a challenge.Recently, our group has developed a new class of tough hydrogels, polyampholyte (PA) gels (fracture energy, T = 3000 J m −2 ), based on multiple ionic bonds acting as reversible sacrificial bonds in the gel network. [18,30] Interestingly, PA gels also demonstrate unique interfacial bonding to charged surfaces, either positive or negative, due to the self-adjustable Coulombic interaction of the dynamic ionic bonds of the PA. [31] The PA gels are synthesized from radical polymerization of oppositely
Energy-Dissipative Matrices Enable Synergistic Toughening in Fiber Reinforced Soft CompositesYiwan Huang, Daniel R. King, Tao Lin Sun, Takayuki Nonoyama, Takayuki Kurokawa, Tasuku Nakajima, and Jian Ping Gong* Tough hydrogels have shown strong potential as structural biomaterials. These hydrogels a...