In nanoparticles formulations wide variety of polymers can be used according to the nature of drug and usage. (i.e.) Biodegradable polymers for short term therapy (e.g. Chemotherapeutic agents) and non-biodegradable polymers for long term therapy (e.g. Vaccines) [83].
The PNPs are obtained from synthetic polymers, such as poly- Ɛ-caprolactone [84], poly-acrylamide [85] and polyacrylate [86], or natural polymers, e.g., Albumin [87], DNA[88], chitosan [88, 89] and gelatin [90].Based on in vivo behavior, PNPs may be classified as biodegradable, i.e., Poly (L-lactide) (PLA) [91], polyglycolide (PGA) [92], and non biodegradable, e.g. Polyurethane [93].

The drug release along the GIT can be controlled using pH-sensitive materials, in which the drug is released particularly in the small intestine near the absorption site. PH-dependent materials, which are insoluble in the acidic medium of the stomach, but dissolve in the intestinal fluid, are called enteric materials [94, 95].

These materials have been used to avoid the degradation of labile drugs caused by the acidic medium or gastric enzymes, to lessen irritation of the gastric mucosa, and to deliver drugs selectively to the site of absorption [94, 95]. Enteric coating materials are polymers, which have acid groups. In the acidic medium of the stomach the acid groups are nonionized, and the coating material is insoluble. Fast dissolution and drug release take place in the upper intestine as a function of pH change in the environment. The polymer acid groups are ionized at higher pH and the material dissolves [95].

Cellulose acetate phthalate (CAP) was the first synthetic polymer described in 1937, which gained soon high popularity as a gastric resistant polymer.