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Developing Mechanically Robust Hydrogel Composites

Daniel R. King Hokkaido University, Sapporo, Japan

Developing synthetic materials which possess contradicting properties, such as stiffness, toughness, and flexibility while containing water is a significant challenge. Hydrogel composites incorporating high stiffness fabrics is a strategy to develop such unique materials ; however, the ability to produce these materials has proven difficult, since common hydrogels swell in water and interact poorly with solid components, limiting the transfer of force from the fabric to the hydrogel matrix. We have overcome this problem and successfully produced extraordinarily tough hydrogel composites by strategically selecting a recently developed tough hydrogel that de-swells in water and exhibits adhesive abilities on solid surfaces. These new composites, consisting of polyampholyte hydrogels and glass fiber woven fabrics, are tunable, and can exhibit extremely high effective toughness (250,000 J/m2), high tensile modulus (606 MPa), and low bending modulus (4.7 MPa). Even though these composites are primarily composed of water-containing, biocompatible materials, their mechanical properties are comparable to high toughness Kevlar/polyurethane blends and fiber-reinforced polymers. Importantly, the mechanical properties of these composites greatly outperform the properties of either individual component.
Of crucial importance is the unique ability of the hydrogel to bond tightly with the glass fiber fabric. A toughening mechanism is proposed based on established fabric tearing theory, due to three events : 1) fiber-fiber friction, 2) fiber-hydrogel adhesion, and 3) bulk energy dissipation within the hydrogel. Understanding this energy dissipation mechanism will enable the development of a new generation of mechanically robust composites materials. These results will be important towards developing soft biological prosthetics, and more generally for commercial applications such as tear-resistant gloves and bullet-proof vests.