Programming Hydrogels with Complex Transient Behaviors via Autocatalytic Cascade Reactions

Novel Acid-Driven Bioinspired Self-Resettable Bilayer Hydrogel Actuator Mimicking Natural Muscles

Soft robots have great potential applications in manufacturing, disaster rescue, medical treatment, etc. Artificial muscle is one of the most important components of a soft robot. In previous years, hydrogel actuators that can be controllably deformed by the stimuli of external signals have been developed as good candidates for muscle-like materials. In this article, we successfully prepared a chemical fuel-driven self-resettable bilayer hydrogel actuator mimicking natural muscles with the aid of a new negative feedback reaction network. The actuator can temporarily deform upon the addition of H+ (chemical fuel). Subsequently, H+ accelerated the reaction between BrO3- and Fe(CN)64-, which consume H+. It resulted in the spontaneous recovery of the pH as well as the shape of the actuator. Such an actuator exhibits a great similarity with natural muscles in actuation mechanisms and automaticity in the manipulation compared to the widely reported stimuli-responsive hydrogel actuators. This illustrates that fuel-driven self-resettable hydrogel is a promising dynamic material for mimicking the functions of living creatures.

Dynamic supramolecular hydrogels mediated by chemical reactions

Supramolecular self-assembly in a biological system is usually dominated by sophisticated metabolic processes (chemical reactions) such as catalysis of enzymes and consumption of high energy chemicals, leading to groups of biomolecules with unique dynamics and functions in an aqueous environment. In recent years, increasing efforts have been made to couple chemical reactions to molecular self-assembly, with the aim of creating supramolecular materials with lifelike properties and functions. In this feature article, after summarising the work of chemical reaction mediated supramolecular hydrogels, we first focus on a typical example where dynamic self-assembly of molecular hydrogels is activated by in situ formation of a hydrazone bond in water. We discuss how the formation of the hydrazone-based supramolecular hydrogels can be controlled in time and space. After that, we describe transient assembly of supramolecular hydrogels powered by out-of-equilibrium chemical reaction networks regulated by chemical fuels, which show unique properties such as finite lifetime, dynamic structures, and regenerative capabilities. Finally, we provide a perspective on the future investigations that need to be done urgently, which range from fundamental research to real-life applications of dynamic supramolecular hydrogels.

Self-Stacking Autocatalytic Molecular Circuit with Minimal Catalytic DNA Assembly

Isothermal autocatalytic DNA circuits have been proven to be versatile and powerful biocomputing platforms by virtue of their self-sustainable and self-accelerating reaction profiles, yet they are currently constrained by their complicated designs, severe signal leakages, and unclear reaction mechanisms. Herein, we developed a simpler-yet-efficient autocatalytic assembly circuit (AAC) for highly robust bioimaging in live cells and mice. The scalable and sustainable AAC system was composed of a mere catalytic DNA assembly reaction with minimal strand complexity and, upon specific stimulation, could reproduce numerous new triggers to expedite the whole reaction. Through in-depth theoretical simulations and systematic experimental demonstrations, the catalytic efficiency of these reproduced triggers was found to play a vital role in the autocatalytic profile and thus could be facilely improved to achieve more efficient and characteristic autocatalytic signal amplification. Due to its exponentially high signal amplification and minimal reaction components, our self-stacking AAC facilitated the efficient detection of trace biomolecules with low signal leakage, thus providing great clinical diagnosis and therapeutic assessment potential.