Dynamic covalent polymer hydrogels and organogels crosslinked through acylhydrazone bonds: synthesis, characterization and applications

Abstract

We review recent literature on the rapidly expanding field of dynamic covalent polymer networks (DCPNs) crosslinked with acylhydrazone bonds, classified according to their structural perfection: randomly crosslinked and model DCPNs. The dynamic covalent acylhydrazone bond is greatly sensitive to environmental conditions, pH in particular, and is characterized by great stability under neutral and mildly alkaline conditions, and instability under acidic conditions. The dynamic nature of this bond endows DCPNs crosslinked with acylhydrazone bonds with self‐healing ability, reversibility and injectability. The last property enables the in vivo site‐specific delivery of drugs, biomolecules or cells that have been loaded into DCPN hydrogels. © 2018 Society of Chemical Industry

Doubly Dynamic Hydrogel Formed by Combining Boronate Ester and Acylhydrazone Bonds

“…The crossover time decrease to 33,680, 15,760, and 8121 s as the solid content increased to 10, 15, and 20 wt%, respectively, indicating that polymer concentration plays a key role in gelation kinetics. The long gelation time is due to the fact that the hydrogel was prepared at pH 8.6, where the formation rate of the acylhydrazone bond is extremely low [17,26]. The critical gelation concentration of arylhydrazone-based hydrogels is above 5 wt%, 3.5 wt%, 3.5 wt%, for PAD1@ADH, PAD2@ADH, and PAD3@ADH, respectively.…”

“…As a representative DCB, acylhydrazone bond, which is formed from acylhydrazine and aldehyde/ketone, have been successfully used to prepare self-healing and stimuli-responsive hydrogels [15][16][17][18][19]. The favorable reaction conditions and high hydrolytic stability of acylhydrazine have proven particularly promising for the application of these hydrogels in the field of biomaterials [20][21][22][23].…”

“…However, the low reaction rate, and the locking of reversible reactions under neutral/weak base conditions severely limit the practical applications of these hydrogels [24,25]. Typically, arylhydrazone-based hydrogels are prepared over long periods depending on the reaction conditions, the self-healing of hydrogels also takes several hours [17,26]. Compared with the acylhydrazone bond, the boronic ester bond is more chemically active and can form with fast reaction kinetics [27][28][29].…”

A seawater‐assisted self‐healing metal–catechol polyurethane with tunable mechanical properties

“…This disadvantage is overcome by using a three‐dimensional microvascular network through which the healing agents can continuously be delivered to cracks and therefore a certain number of healing cycles can be achieved . To develop a material that can theoretically heal endlessly, great effort has recently been made to develop an intrinsic self‐healing polymer, including dynamic covalent bonds such as acylhydrazone bonds, disulfide bonds, the Diels–Alder reaction and alkoxyamine and dynamic non‐covalent bonds such as hydrogen bonds, host–guest interactions, ionic associations and metal–ligand interactions . Generally, self‐healing polymers based on dynamic covalent bonds exhibit better mechanical strength but limited healability, whereas polymers based on dynamic non‐covalent bonds show better healability but poorer mechanical properties.…”

Physical organic studies and dynamic covalent chemistry of picolyl heterocyclic amino aminals

“…[18][19][20][21] Imine is one of the known dynamic covalent systems, which have been widely utilized in several elds, such as many enzymatic processes and development of dynamic materials. [22][23][24][25][26] Although dynamic imine formation processes are known to include several reversible reactions such as hydrolysis, 27 transimination [28][29][30][31][32] and imine metathesis, [33][34][35] limited studies have reported the observation and isolation of the corresponding intermediates such as aminals, hemiaminals and hemiaminal ethers. [36][37][38][39][40][41][42][43][44][45] To develop new functions by understanding the thermodynamic and bonding properties, there is still a great demanding to explore suitable systems which can be successfully detected intermediates.…”