Hydrogels are three-dimensional networked materials that are similar to soft biological tissues and have highly variable mechanical properties, making them increasingly important in a variety of biomedical and industrial applications. Herein we report the preparation of extremely high water content hydrogels (up to 99.7% water by weight) driven by strong host-guest complexation with cucurbit[8]uril (CB[8]). Cellulosic derivatives and commodity polymers such as poly(vinyl alcohol) were modified with strongly binding guests for CB[8] ternary complex formation (K(eq) = 10(12) M(-2)). When these polymers were mixed in the presence of CB[8], whereby the overall solid content was 90% cellulosic, a lightly colored, transparent hydrogel was formed instantaneously. The supramolecular nature of these hydrogels affords them with highly tunable mechanical properties, and the dynamics of the CB[8] ternary complex cross-links allows for rapid self-healing of the materials after damage caused by deformation. Moreover, these hydrogels display responsivity to a multitude of external stimuli, including temperature, chemical potential, and competing guests. These materials are easily processed, and the simplicity of their preparation, their availability from inexpensive renewable resources, and the tunability of their properties are distinguishing features for many important water-based applications.

A major scientific challenge of the past decade pertaining to the field of soft matter has been to craft 'adaptable' materials, inspired by nature, which can dynamically alter their structure and functionality on demand, in response to triggers produced by environmental changes. Amongst these, 'smart' surfactant wormlike micelles, responsive to external stimuli, are a particularly recent area of development, yet highly promising, given the versatility of the materials but simplicity of the design-relying on small amphiphilic molecules and their spontaneous self-assembly. The switching 'on' and 'off' of the micellar assembly structures has been reported using electrical, optical, thermal or pH triggers and is now envisaged for multiple stimuli. The structural changes, in turn, can induce major variations in the macroscopic characteristics, affecting properties such as viscosity and elasticity and sometimes even leading to a spontaneous and effective 'sol-gel' transition. These original smart materials based on wormlike micelles have been successfully used in the oil industry, and offer a significant potential in a wide range of other technological applications, including biomedicine, cleaning processes, drag reduction, template synthesis, to name but a few. This review will report results in this field published over the last few years, describe the potential and practical applications of stimuli-responsive wormlike micelles and point out future challenges.

This Article investigates different types of networks formed from tilapia fish gelatin (10% w/w) in the presence and absence of the enzymatic cross-linker microbial transglutaminase. The influence of the temperature protocol and cross-linker concentration (0-55 U mTGase/g gelatin) was examined in physical, chemical, and hybrid gels, where physical gels arise from the formation of triple helices that act as junction points when the gels are cooled below the gelation point. A combination of rheology and optical rotation was used to study the evolution of the storage modulus (G') over time and the number of triple helices formed for each type of gel. We attempted to separate the final storage modulus of the gels into its chemical and physical contributions to examine the existence or otherwise of synergism between the two types of networks. Our experiments show that the gel characteristics vary widely with the thermal protocol. The final storage modulus in chemical gels increased with enzyme concentration, possibly due to the preferential formation of closed loops at low cross-linker amount. In chemical-physical gels, where the physical network (helices) was formed consecutively to the covalent one, we found that below a critical enzyme concentration the more extensive the chemical network is (as measured by G'), the weaker the final gel is. The storage modulus attributed to the physical network decreased exponentially as a function of G' from the chemical network, but both networks were found to be purely additive. Helices were not thermally stabilized. The simultaneous formation of physical and chemical networks (physical-co-chemical) resulted in G' values higher than the individual networks formed under the same conditions. Two regimes were distinguished: at low enzyme concentration (10-20 U mTGase/g gelatin), the networks were formed in series, but the storage modulus from the chemical network was higher in the presence of helices (compared to pure chemical gels); at higher enzyme concentration (30-40 U mTGase/g gelatin), strong synergistic effects were found as a large part of the covalent network became ineffective upon melting of the helices.

A wormlike micellar system that undergoes a fully reversible, repeatable "sol-gel" transition upon alternative treatment with CO2 and N2 has been developed based on a C18-tailed polyamine surfactant.

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