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.

Gelation kinetics of hydrogels is closely linked to many applications such as the development of injectable and printable hydrogels. However, the control of gelation kinetics without compromising the structure and other properties of the hydrogels, remains a challenge. Here, we demonstrate a method to control the gelation kinetics of cucurbit[7]uril-adamantane (CB[7]-AD) cross-linked supramolecular hydrogels by using competing guest molecules. The association between CB[7] and AD moieties on the polymer backbone was impeded by pre-occupying the CB[7] cavity with competing guest molecules. By using various guest molecules and concentrations, the gelation of the hydrogels could be varied from seconds to hours. The strong interaction of CB[7]-AD pair endue the hydrogels good mechanical properties and stability. Moreover, the binding of functionalized guest molecules of CB[7] moieties offers a facile approach for tailoring of the hydrogels’ scaffold. Combined with hydrogel injection and printing technology, this method offers an approach for the development of hydrogels with advanced temporal and spatial complexity.

Novel thermo-responsive supramolecular hydrogels consisting of cucurbit[6]uril(CB[6]) and butan-1-aminium 4-methylbenzenesulfonate (BAMB) were prepared, which were based on hydrophobic interaction, π–π stacking interaction and van der Walls interaction. Furthermore, hydrogels were not only sensitive to the thermal stimulation, but also showed an interesting property of the inducing action of CB[6] threaded in [2]pseudorotaxane. In this paper, the external morphology and sol–gel transition process of hydrogels were observed by polarized microscopy observation (PMO) and digital camera. DSC results show that the gel–sol transition temperature rose with increasing the concentration of either BMAB or CB[6]. The characteristics of the xerogels were determined by ¹H NMR, FT-IR, SEM and TGA. It was found that the CB[6] was threaded in the butyl amine units of BAMB, and the inducing action of CB[6] threaded in [2]pseudorotaxane was essential for the hydrogel formation. Only when the concentrations of both BAMB and CB[6] reached certain values, hydrogels with three-dimensional network structure could be formed. And the viscosity changes for increasing the temperature of the hydrogel systems with different concentration of either CB[6] or BMAB were determined by the rheometer. A possible model was proposed to explain the driving forcing of the gelation.