Sample Solution

molecularly dispersed in the polymer matrix, and the release of drug close to the absorption site [36, 103, 111].
The dissolution of the particles should not be too fast, however, as this might cause drug precipitation [109] or crystallization [112], but should not be too slow which lead to the rapid elimination of the particles before absorption, either[109].

The advantages of pH-sensitive nanoparticles over other nanoparticles include: (a) the majority of carriers have been used as enteric-coating materials for a long time, and their safety has been approved. (b) The carriers show rapid drug release and then high drug concentration gradient as they undergo quick dissolving at definite pH and definite sites. The phenomenon is beneficial for the drug absorption. (c) They improve drug absorption comparing to the other conventional nanoparticles as they turn from the solid state to the hydrogel state at certain dissolution pH and so, the bioadhesion of the carrier to the mucosa becomes greater at specific fragment. (d) The drug stability can be enhanced more effectively using pH sensitive nanoparticles.
Different materials can be used for preparation of pH-sensitive nanoparticles:
a- pH-sensitive nanoparticles prepared from polyanions:
Such as Eudragits and HPMC phthalate.
b- pH-sensitive nanoparticles prepared from publications:
Chitosan is the main cationic polymer used to prepare pH-sensitive nanoparticles. It is the second most plentiful polymer in nature after cellulose.