Mucus models to evaluate nanomedicines for diffusion

In the fast-growing field of nanomedicine, mucus is often the first barrier encountered by drug products in the body, and can be the only barrier if it is not overcome by the drug delivery system. Thus, there is a need to design new nanomedicines that are able to diffuse easily across mucus to reach their pharmacological targets. In this design process, mucus diffusion studies are mandatory and have an important role in the selection of the best drug candidates. However, there is currently no standard procedure for diffusion studies across mucus. In this Foundation Review, we discuss the differences observed within mucus models and experimental protocols in diffusion studies, with an emphasis on nanomedicine diffusion.