LCST/UCST behavior of polysaccharides for hydrogel fabrication

Hydrogel-based scaffolds play a crucial role in widespread biotechnological applications by providing physicochemical stability to loaded cells or therapeutic agents, interacting with organismal microenvironments, and controlling cargo release. Polysaccharides are regarded as attractive candidates among substrate materials because of their high water-retaining capacity, reactive functional groups, ease of gelation, low immunogenicity, biodegradability, and biocompatibility. However, employing polysaccharide-based hydrogel scaffolds for practical use in response to ongoing physiological and pathological changes within the human body, such as insufficient mechanical strength, uncertain degradation, and uncontrollable release patterns, is challenging. Several physically noncovalent or chemically covalent crosslinking strategies have been utilized to modify the physicochemical properties and biofunctionality of polysaccharide-based hydrogels. Among them, thermo-responsive gelation systems have been considered a promising approach for fabricating advanced scaffolds, referred to as 'stimuli-responsive' or 'smart' hydrogels. This is because of the sol-gel transition with a single trigger, requiring no further environmental or chemical intervention, and in situ and reversible gelation under ambient physiological temperature changes in a minimally invasive manner. This review highlights the classification, reaction mechanisms, characteristics, and advanced studies on thermo-responsive polysaccharides exploited in various biomedical fields.