Mucus is a highly hydrated viscoelastic gel present on various moist surfaces in our body including the eyes, nasal cavity, mouth, gastrointestinal, respiratory and reproductive tracts. It serves as a very efficient barrier that prevents harmful particles, viruses and bacteria from entering the human body.
One of the most promising strategies to improve the bioavailability of active pharma- ceutical ingredients is based on the association of the drug with colloidal carriers, for example, polymeric nanoparticles, which are stable in biological environment, protec- tive for encapsulated substances and able to modulate physicochemical characteristics, drug release and biological behaviour.