Programming Hydrogels with Complex Transient Behaviors via Autocatalytic Cascade Reactions

Abstract

It is challenging to design complex synthetic life-like systems that can show both autoevolution and fuel-driven transient behaviors. Here, we report a new class of chemical reaction networks (CRNs) to construct life-like polymer hydrogels. The CRNs are constituted of autocatalytic cascade reactions and fuel-driven reaction networks. The reactions start with only two compounds, that is, thiol of 4-arm-PEG-SH and thiuram disulfides, and undergo thiol oxidation (k 1), disulfide metathesis (k 2), and thionate hydrolysis-coupling reactions (k 3) subsequently, leading to a four-state autonomous transition of sol­(I) → soft gel → sol­(II) → stiff gel. Moreover, thiuram disulfides can be applied as a fuel to drive the repeated occurrence of metathesis and hydrolysis-coupling reactions, generating dissipative stiff gel → sol­(II) → stiff gel cycles. Systematic kinetics studies reveal that the event and lifetime of every transient state could be delicately tailored-up by varying the thiuram disulfide concentration, pH of the system, and thiuram structures. Since the consecutive transient behaviors are precisely predictable, we envision the strategy’s potential in guiding the molecular designs of autonomous and adaptive materials for many fields.

Recent Progress of Fuel‐Driven Temporary Materials

“…Besides the above typical reaction networks, there are some unusual strategies for constructing a fuel‐driven temporary gel. [ 30,33‐35,71‐72 ] In 2015, A. K. Das prepared a temporary hydrogel that could be used for human umbilical cords via a lipase‐catalyzed reaction network. [ 71 ] As shown in Figure 8a, a peptide bolaamphiphile (HO‐WYSuc‐YW−OH) reacted with p ‐hydroxy benzylalcohol in the presence of lipase forming an activated diester building block (BHO‐WYSuc‐YW−OHB).…”

Recent progress of fuel-driven temporary materials

“…Similarly, the "gel-sol-gel" temporary process was also realized by a thiuram disulfides-driven reaction network. As reported by Y. J. Zheng and coworkers [62], the hydrogel was synthesized by crosslinking a 4-armed, star-like, branched PEG terminated with a thiol group. As shown in Figure 8d, the addition of thiuram disulfides (chemical fuel) can break the disulfide linkages via dynamic disulfide exchange.…”

Dynamic supramolecular hydrogels mediated by chemical reactions

“…The group of van Eelkema and van Esch pioneered the development of out-of-equilibrium supramolecular hydrogels using methylation reagents as the fuels. 22,53 After that, various beautiful examples of out-of-equilibrium supramolecular assemblies powered by different chemical fuels, including carbodiimide, [57][58][59][60][61][62] ATP, 55,[63][64][65][66][67][68][69] pH regulators, [70][71][72][73][74][75] enzymatic reactions, 15,66,[76][77][78] carbon dioxide, 79,80 and others, [81][82][83][84] have been carefully developed. The resultant supramolecular hydrogels show high dynamics, tunable lifetime and stiffness, and a regenerative capability.…”