Doubly Dynamic Hydrogel Formed by Combining Boronate Ester and Acylhydrazone Bonds

Abstract

The incorporation of double dynamic bonds into hydrogels provides an effective strategy to engineer their performance on demand. Herein, novel hydrogels were PREPARED by combining two kinetically distinct dynamic covalent bonds, boronate ester and acylhydrazone bonds, and the synergistic properties of the hydrogels were studied comprehensively. The functional diblock copolymers P(N-isopropyl acrylamide-co-N-acryloyl-3-aminophenylboronic acid)-b-(N-isopropyl acrylamide-co-diacetone acrylamide) (PAD) were prepared via reversible addition−fragmentation chain transfer (RAFT) polymerization. The hydrogel was constructed by exploiting dynamic reaction of phenyboronic acid moieties with polyvinyl alcohol (PVA) and ketone moieties with adipic dihydrazide (ADH) without any catalyst. The active boronate ester linkage endows the hydrogel with fast gelation kinetics and self-healing ability, and the stable acylhydrazone linkage can enhance the mechanical property of the hydrogel. The difference in kinetics endows that the contribution of each linkage to mechanical strength of the hydrogel can be accurately estimated. Moreover, the mechanical property of the hydrogel can be readily engineered by changing the composition and solid content, as well as by controlling the formation or dissociation of the dynamic linkages. Thus, we provide a promising strategy to design and prepare multi-responsive hydrogels with tunable properties.

Injectable Acylhydrazone‐Linked RAFT Polymer Hydrogels for Sustained Protein Release and Cell Encapsulation

“…Specifically, hydrogel shear moduli peaked ( G ’ = 4.3 kPa) at a stoichiometric ratio (i.e., Hz/K = 1) and decreased with either component in excess, a result consistent with that reported by Liu et al. [ 24 ] The imbalance between hydrazide and ketone led to partial dissociation of acylhydrazone bonds and decreased the shear moduli of hydrogels. These moduli results agreed well with the hydrogel microstructure as revealed in the SEM micrographs (Figure 2C–F; and Figure S2, Supporting Information), wherein hydrogels with smaller pores exhibited stronger mechanical properties.…”

Recent progress in self-healing polymers and hydrogels based on reversible dynamic B–O bonds: boronic/boronate esters, borax, and benzoxaborole

“…In 2020, Tan et al synthesized a hydrogel that simultaneously employed boronate ester and acylhydrazone bonds. 108 The boronate ester bond was formed rapidly upon gelation, but the acylhydrazone bond was formed slowly. In addition, acylhydrazone contributed to the increased mechanical strength of the hydrogel owing to its relatively less dynamic nature.…”

Current Trends in Biomedical Hydrogels: From Traditional Crosslinking to Plasma-Assisted Synthesis

“…Michael addition involves a reaction between nucleophiles called Michael donors and activated electrophilic olefins/alkynes (Michael acceptors) [95,96]. Lastly, the boronate ester bond is an integral part of the dynamic covalent bond (DCB)based hydrogels where it is formed through the condensation reaction between boronic acid and 1,2-or 1,3-diols [97,98].…”