Covalently and ionically crosslinked chitosan nanogels for drug delivery

Chitosan nanogels present a very interesting combination of valuable characteristics for drug delivery; those derived from their nanometric size, such as, large surface area, rapid stimuli-response, and easy functionalization; and those emerged especially from their biocompatibility, biodegradability and mucoadhesive nature. Due to this, chitosan nanogels have reached a prominent position as nanocarriers and have originated accelerated research worldwide. Diverse methods to prepare chitosan nanogels have been reported, showing a dependence on final swelling, drug encapsulation capability and release properties with different synthesis variables, in such a way that they can be exploited to be modulated. The present review describes the properties of chitosan nanogels, along with the different methods of crosslinking and confining chitosan in nanosized particles, and the various fields of drug delivery where they have been applied. This work aims to emphasize the connection between the characteristics of chitosan and the synthetic variables with the final properties of chitosan nanogels in order to enhance controlled drug loading and a sustained release.