Thermoresponsive polymers: insights into decisive hydrogel characteristics, mechanisms of gelation, and promising biomedical applications

Thermally induced gelling systems have gained enormous attention over the last decade. They consist of hydrophilic homopolymers or block copolymers in water that present a sol at room temperature and form a gel after administration into the body. This article reviews the main types of thermoresponsive polymers, with special focus on decisive hydrogel characteristics, mechanisms of gelation, and biocompatibility. Promising biomedical applications are described with a focus on injectable formulations, which include solubilization of small hydrophobic drugs, controlled release, delivery of labile biopharmaceutics, such as proteins and genes, cell encapsulation, and tissue regeneration. Furthermore, combinations of thermoresponsive hydrogels and various nanocarriers as promising systems for sustained drug delivery are discussed through selected examples from the literature. Finally, there is a brief overview of current progress in nano-sized systems incorporating thermoresponsive properties.