The double network concept has been revolutionary in its ability to turn soft, brittle hydrogels into tough, robust materials. Double network hydrogels consist of two interpenetrating networks, where each network has a specific mechanical response: the “first network” acts as a sacrificial network, consisting of a rigid, extended network with relatively low loading percentage, and the “second network” is a globally percolated, stretchable network. When a double network hydrogel is stretched, covalent bonds of the first network break, dissipating energy. These materials possess enhanced properties, but in many cases, lack the mechanical properties to act as structural materials. Here, we attempt to utilize “double network theory” at the macroscale, by creating rigid scaffolds and embedding them in a stretchy and tough matrix, mimicking the first and second networks, respectively.<br/><br/>Creating hydrogel composites is difficult because of the swelling mismatch between the rigid materials and the hydrogel matrix. To overcome this problem, we utilize a low melting-point alloy (LMA) as the rigid scaffolding material inside of the hydrogel matrix. After the hydrogel reaches equilibrium, the LMA frame is melted, and the swelling mismatch between the frame and the gel is released. Beyond relieving swelling stress, these composites exhibit unique and remarkable mechanical properties. When stretched, they undergo multiple fracture processes, which results in a dramatic increase in the work of extension compared to the neat hydrogels. When stretched up to 250%, they can be cycled with 100% healing of the sacrificial network. Furthermore, these composites can exhibit shape memory, conductivity, and can act as a base for electro-chemical reactions. We believe this new technique will help create new hydrogel-based materials with properties that are unachievable with neat hydrogel materials.

Creating tough and healable macroscale “double network” hydrogels

255th National Meeting (2018)

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