Dynamic Hydrogels with an Environmental Adaptive Self-Healing Ability and Dual Responsive Sol–Gel Transitions

Abstract

Dynamic polymer hydrogels with an environmental adaptive self-healing ability and dual responsive sol–gel transitions were prepared by combining acylhydrazone and disulfide bonds together in the same system. The hydrogel can automatically repair damage to it under both acidic (pH 3 and 6) and basic (pH 9) conditions through acylhydrazone exchange or disulfide exchange reactions. However, the hydrogel is not self-healable at pH 7 because both bonds are kinetically locked, whereas the hydrogel gains self-healing ability by accelerating acylhydrazone exchange with the help of catalytic aniline. All of the self-healing processes are demonstrated to be effective without an external stimulus at room temperature in air. The hydrogel also displays unique reversible sol–gel transitions in response to both pH (HCl/triethylamine) and redox (DTT/H2O2) triggers.

Catalysis of Supramolecular Hydrogelation

“…This reaction proceeds very slowly in the pH 7-10 window, but is significantly accelerated using either Brønsted-Lowry acid catalysis (pH 3-6), or nucleophilic aniline catalysis 37,38 , suggesting that we can use multiple types of catalysis to control the formation of these gelators. Moreover, in certain pH windows or catalyst concentration, they are considered dynamic covalent bonds 39,40 and the rate of exchange can be controlled using a catalyst. Mainly for solubility reasons, we initially fitted the cyclohexane core with three hydrazide groups ( Figure 2).…”

Self-healing of Poly(2-hydroxyethyl methacrylate) Hydrogel through Molecular Diffusion

“…In the first and second healing cycle, the healing percentages are 92 and 91%, respectively. These percentages of healing indicate that the strength of this poly(HEMA) hydrogel is considerable (Deng et al 2012).…”

“…2008;Billiet et al 2013). Of them, self-healing hydrogel has attracted much attention due to their great potential in biomedical applications (Deng et al 2012;Phadke et al 2012).…”

“…Assuming bond cleavage does not occur during damage, chain or intermolecular diffusion is one of the driving forces for self-repairing of polymeric materials and the source of loose chain ends is chain slippage. It is noticed that many self-healing hydrogels are stimuli-healable hydrogels because their repairing process requires the input of a stimulus to be activated (Deng et al 2012;Phadke et al 2012;Tang et al 2007).…”

Self-healing Hydrogels Based on Dynamic Chemistry and Their Biomedical Applications

“…Deng 等 Figure 4 Environmental adaptive self-healing properties of a dynamic hydrogel [28] 2.5 亚胺键 [30,31] , 因此存在大量的分子间和分子内的相互交 换而使得整个水凝胶具有动态网络结构 [32] , 可以在不 借助外力条件下实现快速愈合. 在水凝胶被打孔后, 界 面提供的微小能量即使水凝胶产生流动相, 一段时间后 孔洞消失, 界面变得模糊, 材料完成自愈合(图 5).…”