Abstract
In this review, the authors have discussed scientific advances in thermosensitive hydrogels over the past two decades. The ability of the thermo-sensitive hydrogel to undergo rapid changes with response to temperature makes it an attractive candidate for many biomedical applications such as targeted drug delivery, wound healing, soft contact lenses, sensors, tissue regeneration, gene, and protein delivery. This review aims to deliver a brief overview of gelation properties, merits, and demerits of various natural and synthetic thermo-sensitive polymers that have significant clinical relevance. The report emphasizes the importance of injectable thermosensitive hydrogels, as it can offer improved solubility of hydrophobic drugs and site-specificity, extended-release of drugs and macromolecules, improved safety, and local administration of drugs. The authors has also provided a commentary on the delivery of drugs or macromolecules from thermo-sensitive hydrogels through various approaches. This review highlights the current status of research in thermo-sensitive hydrogels and emphasizes the importance of developing nontoxic thermo-sensitive hydrogels, dual responsive, and multi-responsive hydrogel systems.
Highlights
Hydrogels are water-insoluble, randomly cross-linked threedimensional polymeric systems that have an incredible capability to swell and retain a significant amount of water within their structural framework
Physical cross-linking of hydrogels results from weak interactions such as hydrogen bonds, hydrophilic/hydrophobic interactions, ionic/electrostatic interactions, reversible intermolecular interactions, stereo-complex formation, metal coordination, π-π stacking, and polymerized entanglements
Evidence from various in vitro and in vivo studies showed that existing thermo-sensitive hydrogels exhibits reduced cell viability and reduced capability to deliver the cells to the target tissues
Summary
Hydrogels are water-insoluble, randomly cross-linked threedimensional polymeric systems that have an incredible capability to swell and retain a significant amount of water within their structural framework. Chemical crosslinking results in the formation of stable hydrogel with considerable mechanical strength and are usually created by photo-polymerization; Diels-Alder clicks reaction, Michael type addition, oxime formation, Schiff base formation, and enzyme-induced crosslinks [2, 5]. Placing hydrophilic groups such as amides, sulfonic acids, hydroxyl groups, and carboxylic acids into the structure, hydrogels can absorb large amounts of water and form hydrophilic polymers [6]. Some of the limitations associated with hydrogels are lower mechanical strength, difficulty to handle, and difficult to load with nutrients or drugs. Smart hydrogels are developed [12]
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