Chemically Fueled Reinforcement of Polymer Hydrogels

Abstract

Carbodiimide-fueled anhydride bond formation has been used to enhance the mechanical properties of permanently crosslinked polymer networks, giving materials that exhibit transitions from soft gels to covalently reinforced gels, eventually returning to the original soft gels. Temporary changes in mechanical properties result from a transient network of anhydride crosslinks, which eventually dissipate by hydrolysis. Over an order of magnitude increase in the storage modulus is possible through carbodiimide fueling. The time-dependent mechanical properties can be modulated by the concentration of carbodiimide, temperature, and primary chain architecture. Because the materials remain rheological solids, new material functions such as temporally controlled adhesion and rewritable spatial patterns of mechanical properties have been realized.

Bio‐Inspired Far‐From‐Equilibrium Hydrogels: Design Principles and Applications

“…As the fuel undergoes decomposition, the transient building blocks (M 1 ‐F 2 ‐M 2 ) dissociate, and the system returning to its initial state (Figure 2B). [116] …”

“…In addition, EDC is further used to generate temporary cross‐linkers in polymer systems, thus enabling spatiotemporal control of various properties of the polymer networks. In the latest work from Konkolewocz's group, [116] the anhydride bonds formed upon the incorporation of carbodiimide fuel enhanced the mechanical properties of the permanently crosslinked polymer network, causing the material to exhibit a transition from a soft gel to a covalently reinforced gel, with the anhydride bonds ultimately restoring the system to its initial state due to hydrolysis. The permanently cross‐linked network poly(Am‐AA‐MBAm) was built through the polymerization of a carboxylic acid‐containing active monomer acrylic acid (AA), acrylamide (Am) monomer, N,N′ ‐methylenebisacrylamide (MBAm) cross‐linker in the presence of 2((ethylthio)‐carbonylthio)propionic acid (PAETC) chain transfer agents and 2,2′‐azido[2‐(2‐imidazolin‐2‐yl)propane] dihydrochloride (VA‐044) free radical initiator (Figure 6D).…”

Cyclic Macroscopic Assembly and Disassembly Driven by Ionic Strength Fuel: A Waste-Free Approach

“…17−21 Till now, many advances have been made in chemically fueled transient assembling systems with microscopic building blocks (e.g., molecules, colloids) 4,16,22,23 that can construct various transient structures and materials 17,24−27 based on temporally controlled redox reactions, 28,29 pH changes, 30−32 and formation and hydrolysis of metastable esters or anhydrides. 22,27,33,34 By contrast, macroscopic nonequilibrium assembly/disassembly is in its infancy, and one of the few examples was presented in our previous work, where a pH-regulated and temporally controlled system was designed for achieving the precise transient assembly of hybrid hydrogels. 35 Despite these achievements, the accumulation of waste has always been a problem in both microscopic and macroscopic nonequilibrium assembly/disassembly because the response can be damped by waste accumulation 32,36 and the waste may additionally influence the packing of the self-assembled structures.…”

“…Self-assembly processes in nature involve components at all scales and typically exist in the states that are at global or local nonequilibrium and dissipate energy. , In synthetic systems, the biomimetic nonequilibrium assembly/disassembly − with promising applications in drug delivery, , catalysis, , sensing, molecular imaging, , self-healing, − and transient electronics is mainly achieved by time-dependent consumption of chemical fuels. − Till now, many advances have been made in chemically fueled transient assembling systems with microscopic building blocks (e.g., molecules, colloids) ,,, that can construct various transient structures and materials ,− based on temporally controlled redox reactions, , pH changes, − and formation and hydrolysis of metastable esters or anhydrides. ,,, By contrast, macroscopic nonequilibrium assembly/disassembly is in its infancy, and one of the few examples was presented in our previous work, where a pH-regulated and temporally controlled system was designed for achieving the precise transient assembly of hybrid hydrogels . Despite these achievements, the accumulation of waste has always been a problem in both microscopic and macroscopic nonequilibrium assembly/disassembly because the response can be damped by waste accumulation , and the waste may additionally influence the packing of the self-assembled structures. , Therefore, novel strategies and new chemical fuels for efficient waste removal or waste-free regulation represent an important direction in the development of nonequilibrium systems.…”

Transient regulation of gel properties by chemical reaction networks

“…45 In recent years, many excellent works about gels with transiently regulatable properties have been reported. 39,[46][47][48] The rapid development of this field has made the need for upto-date summaries in this area urgent. Hence, we herein summarize the characterization techniques for transiently regulatable gels and the latest advances and challenges in this field in order to highlight the importance of CRNs in modulating gel properties.…”