ABSTRACT
Environmentally sensitive hydrogels are a novel formulation that has developed rapidly in recent years. It could form semi-solid with good adhesion in the topical sites based on different physiological environments. Its long local retention time is conducive for sustained drug release, and the preparation process is relatively simple and easy to realize industrialization. This review summarized the categories, commonly used polymer, and different administration routes based on the recently published literatures. According to different response factors, it can be divided into temperature, pH, ion, light, and multiple sensitive hydrogels, among which temperature-sensitive hydrogels are the most common. The most commonly used polymers include chitosan, poly N-isopropyl acrylamide, and poloxamer. There are different administration routes for environmentally sensitive hydrogels, such as transdermal, ophthalmic, nasal, oral, vaginal, rectal, injection, etc. Environmentally sensitive hydrogels have broad prospects in clinical application.