A Sol-Gel Transition and Self-Healing Hydrogel Triggered via Photodimerization of Coumarin

Reversible chemical covalency provides a path to materials that can degrade and recombine with appropriate stimuli and which can be used for tissue regeneration and repair. However, designing and preparing efficient and quickly self-healing materials has always been a challenge. The preparation strategies of photoresponsive gels attract a lot of attention due to their precise spatial and temporal control and their predetermined response to light stimulation. In this work, the linear copolymer PAC was synthesized via precipitation polymerization of acrylic acid and 7-(2-acrylate-ethoxylated)-4-methylcoumarin. The coumarin groups on the copolymer PAC side chains provide a reversible chemical cross-linking via photostimulation, which achieves reversible regulation of the gel network structure. The concentration of 18 wt% PAC solution produces gelation under irradiation with 365 nm. In contrast, PAC gel is restored to soluble copolymers under irradiation with 254 nm. Meanwhile, the mechanical and self-healing properties of the gel were also explored. It is demonstrated that the cracks of the gel can be repaired simply, quickly, and efficiently. Furthermore, the PAC copolymer shows an excellent adhesion property based on the reversible sol-gel transition. Thus, the PAC gel has considerable potential for applications in engineering and biomedical materials.

Stimuli-responsive destructible polymeric hydrogels based on irreversible covalent bond dissociation

Covalently crosslinked stimuli-destructible hydrogels with the ability of irreversible bond dissociation have attracted great attentions due to their biodegradability, stability against hydrolysis, and controlled solubility upon insertion of desired triggers.

Self-Healing Hydrogels with both LCST and UCST through Cross-Linking Induced Thermo-Response

Self-healing hydrogels have drawngreat attention in the past decade since the self-healing property is one of the characteristics of living creatures. In this study, poly(acrylamide-stat-diacetone acrylamide) P(AM-stat-DAA) with a pendant ketone group was synthesized from easy accessible monomers, and thermo-responsive self-healing hydrogels were prepared through a series of diacylhydrazide compounds cross-linking without any additional stimulus. Although the copolymers do not show thermo-response, the hydrogels became thermo-responsive andboth the lower critical solution temperature (LCST) and upper critical solution temperature (UCST) varied with the composition of the copolymer and structure of cross-linkers. With a dynamic covalent bond connection, the hydrogel showed gel-sol-gel transition triggered by acidity, redox, and ketone to acylhydrazide group ratios. This is another interesting cross-linking induced thermo-responsive (CIT) hydrogel with different properties compared to PNIPAM-based thermo-responsive hydrogels. The self-healing hydrogel with CIT properties could have great potential for application in areas related to bioscience, life simulation, and temperature switching.

Determination of ADH in textiles using the HPLC-MS/MS method and the study of its adsorption behaviour towards formaldehyde

In the textile industry, formaldehyde-based resins are used as finishers to make the fabrics crease-resistant, which are the main source of formaldehyde in textiles. In our practical study, there are cases that prove that textile products containing adipic dihydrazide (ADH) will continuously adsorb formaldehyde from the surrounding environment during storage. In this study, a high performance liquid chromatography-tandem mass spectrometry method was established for the precise determination of ADH in textiles. The method was optimized in terms of instrument conditions, extraction temperature, extraction time, and extraction mode. Under optimum test conditions, ADH was determined precisely with the linearity range of 0.05–2 mg L⁻¹ and correlation coefficient (R²) of 0.9993. Recovery rate and repeatability were tested; the data showed that the recovery rate of ADH in textiles was in the range of 85–100%, and the RSD (relative standard deviation) was less than 10%. The ADH-positive textile samples were placed in designed environments for some time to adsorb formaldehyde. The adsorbed amounts of formaldehyde in the textile samples first increase and then decrease with time. The maximum amount of formaldehyde a sample can adsorb increases with an increase in its ADH content and will stop increasing once its ADH content exceeds 1700 mg kg⁻¹. The placement environment has a little effect on the maximum adsorption capacity of the samples towards formaldehyde, but can significantly affect the adsorption rate and equilibrium adsorption capacity.

Study on the adsorption behaviour of textiles containing ADH towards formaldehyde under different placement environments.