Biological tissues, such as cartilage, tendon, ligament, skin, and plant cell wall, simultaneously achieve high water content and high load-bearing capacity. The high water content enables the transport of nutrients and wastes, and the high load-bearing capacity provides structural support for the organisms. These functions are achieved through nanostructures. This biological fact has inspired synthetic mimics, but simultaneously achieving both functions has been challenging. The main difficulty is to construct nanostructures of high load-bearing capacity, characterized by multiple properties, including elastic modulus, strength, toughness, and fatigue threshold. Here we develop a process that self-assembles a nanocomposite using a hydrogel-forming polymer and a glass-forming polymer. The process separates the polymers into a hydrogel phase and a glass phase. The two phases arrest at the nanoscale and are bicontinuous. Submerged in water, the nanocomposite maintains the structure and resists further swelling. We demonstrate the process using commercial polymers, achieving high water content, as well as load-bearing capacity comparable to that of polyethylene. During the process, a rubbery stage exists, enabling us to fabricate objects of complex shapes and fine features. We conduct further experiments to discuss likely molecular origins of arrested phase separation, swell resistance, and ductility. Potential applications of the nanocomposites include artificial tissues, high-pressure filters, low-friction coatings, and solid electrolytes.
Keywords: hydrogel; nanocomposite; phase separation; polymer glass; self-assemble.