pH-Switchable and self-healable hydrogels based on ketone type acylhydrazone dynamic covalent bonds

Abstract

Stimuli-responsive hydrogels using dynamic covalent bonds (DCBs) as cross-links may exhibit simultaneously the stimuli-responsibility of the physical gels and stability of the chemical gels. We prepared well-defined, ketone-based polymers based on commercially available diacetone acrylamide (DAAM) by a reversible addition-fragmentation chain transfer (RAFT) polymerization technique. The polymers could react with hexanedihydrazide yielding hydrogels. The mechanics, flexible properties and gelator concentration of the hydrogels can be tuned by varying the ratio of DAAM. Gelation time and hydrogel stability were gravely affected by the pH of the surrounding medium. The hydrogels possess self-healing ability without any external stimuli and undergo switchable sol-gel transition by the alternation of pH. In addition, the hydrogels showed pH-responsive controlled release behavior for rhodamine B. These kinds of ketone-type acylhydrazone DCB hydrogels, avoiding the aldehyde component, may ameliorate their biocompatibility and find potential applications in biomedicines, tissue engineering, etc.

Doubly Dynamic Hydrogel Formed by Combining Boronate Ester and Acylhydrazone Bonds

“…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].…”

Stimuli-responsive hydrogel consisting of hydrazide-functionalized poly(oligo(ethylene glycol)methacrylate) and dialdehyde cellulose nanocrystals

“…Rheological recovery tests were employed to evaluate the self-healing capability of the hydrogels. 17,19,50 Measurements of the linear viscoelastic regime of the hydrogels revealed the critical strain where the dynamic network of hydrogels was destroyed (Fig. S4, ESI †).…”

“…Acylhydrazone bond exhibits pH-responsive characteristics, 23,50 where the bond forms slowly in neutral condition, and the kinetics of bond formation accelerate in the presence of catalytic amounts of acid. 51 The pH of surrounding medium has a large influence on the thermo-mechanical properties and self-healing behavior of the hydrogels prepared with acylhydrazone bonds.…”

Cross‐linking induced thermoresponsive hydrogel with light emitting and self‐healing property

“…The structure and the composition of the TPE‐P(AM‐ stat ‐DAA) were determined by 1 H NMR, which is shown in Figure a. The peak c derived from DAA segment increased with increasing of DAA feeding ratio and the composition calculated from peak b, c, and d was almost consistent with monomer feeding ratios . At the same time, the peak from 7.8 to 6.8 ppm indicated the TPE unit was imported onto the polymer chain end.…”