Abstract
Supramolecular polysaccharide-based hydrogels have attracted considerable research interest recently due to their high structural functionality, low toxicity, and potential applications in foods, cosmetics, catalysis, drug delivery, tissue engineering and the environment. Modulation of the stability of hydrogels is of paramount importance, especially in the case of stimuli-responsive systems. This review will update the recent progress related to the rational design of supramolecular hydrogels with the objective of understanding the gelation process and improving their physical gelation properties for tailored applications. Emphasis will be given to supramolecular host–guest systems with reference to conventional gels in describing general aspects of gel formation. A brief account of the structural characterization of various supramolecular hydrogels is also provided in order to gain a better understanding of the design of such materials relevant to the nature of the intermolecular interactions, thermodynamic properties of the gelation process, and the critical concentration values of the precursors and the solvent components. This mini-review contributes to greater knowledge of the rational design of supramolecular hydrogels with tailored applications in diverse fields ranging from the environment to biomedicine.
Highlights
Polymer gels are generally defined as 3D networks swollen by a large amount of water [1].In particular, polysaccharide-based hydrogels are important due to their diverse chemical structure and rich functionality [2,3]
Not directly support gel formation, it can be used as a supplementary technique to show evidence of structure of gels giving an insight into their molecular arrangements [7]
It can be concluded that for hydrogels which are composed of an amphiphilic block copolymer and a CD, the driving force for gelation is a combination of inclusion complexation between CD and polyethylene glycol (PEG) blocks, as well as the aggregation of the hydrophobic Ada blocks via favourable interactions illustrated in Scheme 3
Summary
Polymer gels are generally defined as 3D networks swollen by a large amount of water [1]. A number of responsive hydrogel systems based on natural and synthetically modified polysaccharides have been reported. Polysaccharides are abundant and readily available from renewable sources such as plants and algae, and various microbial organisms [26] Such polysaccharides have a large variety of compositional and structural properties, making them facile to produce and versatile for gel formation as compared with synthetic polymers. The formation of supramolecular materials through host–guest interactions is a powerful method to create non-conventional stimuli-responsive hydrogels. This relates to the host–guest interactions present which can be modulated to fine tune the stability and responsiveness of the resulting gel system based on the choice of macromolecular scaffold. Examples of inherent responsive hydrogel systems include the temperature-induced rod-to-coil transition of poly(N-isopropyl acrylamide) (PNIPAM) [32,33,34] and oligo(ethylene glycol)s (OEGs) [35,36], the pH induced-protonation of poly(vinyl pyridine) [37,38], and the photosensitive behaviour of azobenzenes [4,39,40]
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