Chemically Fueled Autonomous Sol→Gel→Sol→Gel→Sol Transitions.

Complex non-equilibrium phase behaviors are a hallmark of natural self-assembling systems. Here we show how intricate phase transitions can be achieved through a chemically fueled reaction cycle to yield autonomous sol→gel→sol→gel→sol transitions. A relay of chemical transformations based on thiazinane metathesis leads to two consecutive transient gelations in a closed system. Within seconds of fuel addition to deactivated thiazinane monomers, an imine-based hydrogel forms that consists of fibrillar microspheres. This gel quickly loses its mechanical strength and forms a solution, from which a second aldehyde-based gel nucleates and remains stable for over one day. Overall, our reaction cycle gives rise to two consecutive re-entrant phase transitions without any experimental intervention.

Redox-Mediated, Transient Supramolecular Charge-Transfer Gel and Ink.

Unprecedented spatiotemporal control exhibited by natural systems has aroused interest in the construction of its synthetic mimics. Cytoskeleton proteins utilize fuel-driven dissipative self-assembly to temporally regulate cell shape and motility. Until now, synthetic efforts have majorly contributed to fundamental strategies; however, temporally programmed functions are rarely explored. Herein, we work toward alleviating this scenario by using a charge-transfer (CT) based supramolecular polymer that undergoes structural changes under the effect of a redox fuel. The structural changes in supramolecular assembly amplify into observable macroscopic and material property changes. As a result, we achieve transient chemochromism,  a self-erasing ink and self-regenerating hydrogel, whose temporal profile can be regulated by varying the concentrations of the chemical cues (fuel and enzyme). The redox-mediated transient functions in the CT based supramolecular polymer pave way to create next-generation active, adaptive, and autonomous smart materials.

Chiral Metamolecules with Active Plasmonic Transition.

Energy-dissipating self-assembly is at the basis of many important cellular processes, such as cell organization, proliferation, and morphogenesis. Beyond equilibrium self-assembled molecular systems and materials, it is increasingly recognized that the control of assembly kinetics provides great opportunity for the next generation of molecular materials with intelligent behavior including programmed spatiotemporal organization. Here we show the transient self-assembly of active chiral plasmonic metamolecules (CPMs), which is controlled by the proton flux generated from a positive-feedback chemical reaction network. The fuel-conversion kinetics allows for temporal control and adaptive tuning of multiple structures of plasmonic metamolecules (PMs). This approach enables autonomous tuning of chiroptical properties of metamolecules with dynamic behavior. Moreover, we show that 11 types of spatial configurations of PMs are assembled, and 9 types of temporal configurations of CPMs are differentiated.

Antagonistic Enzymes in a Biocatalytic pH Feedback System Program Autonomous DNA Hydrogel Life Cycles.

Enzymes regulate complex functions and active behavior in natural systems and have shown increasing prospect for developing self-regulating soft matter systems. Striving for advanced autonomous hydrogel materials with fully programmable, self-regulated life cycles, we combine two enzymes with an antagonistic pH-modulating effect in a feedback-controlled biocatalytic reaction network (BRN) and couple it to pH-responsive DNA hydrogels to realize hydrogel systems with distinct preprogrammable lag times and lifetimes in closed systems. The BRN enables precise and orthogonal internal temporal control of the "ON" and "OFF" switching times of the temporary gel state by modulation of programmable, nonlinear pH changes. The time scales are tunable by variation of the enzyme concentrations and additional buffer substances. The resulting material system operates in full autonomy after injection of the chemical fuels driving the BRN. The concept may open new applications inherent to DNA hydrogels, for instance, autonomous shape memory behavior for soft robotics. We further foresee general applicability to achieve autonomous life cycles in other pH switchable systems.