Chitosan, a nontoxic and biocompatible polysaccharide, has been widely explored for the gastrointestinal delivery of drugs, proteins, peptides and genes for different therapeutic purposes. Because a pH gradient exists in the gastrointestinal tract, chitosan-based formulations in response to specific pH conditions, such as the low pH in the stomach and a high pH in the intestine, have been developed as a general strategy for disease diagnosis and therapy. Tailored pH-responsive drug release in the gastrointestinal tract can be achieved with various chitosan-based formulations such as nanoparticles, microspheres, hydrogels and nanocomposites. This review focuses on the most recent development of chitosan-based pH-sensitive formulations for gastrointestinal delivery, covering various types of chitosan-based formulations, their pH-responsive mechanisms and biomedical applications.
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