Inspired by the dissipative assembly in biological systems, transient hydrogels based on supramolecular interactions have been developed that are under thermodynamic nonequilibrium states. Host-guest interactions possess excellent properties including high selectivity and adjustable association constants, which are beneficial for controlling the properties and behaviors of transient colloidal materials. In this work, a host-fueled transient supramolecular hydrogel system is reported. The hydrogels based on host-guest interactions are formed by addition of a chemical fuel, α-cyclodextrin (α-CD), to the aqueous solutions containing Pluronic F127 and α-amylase. Meanwhile, as the host molecule of α-CD consumes, the hydrogel networks start to collapse. The lifetime of the transient supramolecular hydrogels can be precisely controlled by adjusting the temperature and hydrogel composition, and repeated sol-to-gel-to-sol transitions can be realized by refueling the system with α-CD. This study provides a new approach to regulate the nonequilibrium host-guest inclusion system by fueling it with host molecules.

In nature, biological systems maintain their unique structures and functions by using nonequilibrium processes driven by chemical fuels. Inspired by natural systems, transient hydrogel systems based on chemical reaction networks have been developed that are in thermodynamically nonequilibrium states. The formation of dynamic covalent bonds is an effective tool for designing analogous systems. Herein, we design a transient polymer hydrogel based on fuel-mediated covalent borate ester bonds. The pH-sensitive covalent borate ester bond is formed by the reaction between polyvinyl alcohol (PVA) and boric acid (B(OH) 3 ). Sodium hydroxide (NaOH) and 1,3-propanesulfonate (PrS) are used together as the chemical fuels to temporally control the pH of the system. Meanwhile, the lifetime of the transient hydrogel can be simply controlled by adjusting the composition of the chemical fuel, and the cyclic phase transitions can also be achieved. These programmable transient hydrogels have potential applications in the fields of information transmission and fluid guidance.