138]. Hypromellose phthalate is insoluble in gastric fluid, but will swell and dissolve speedily in the upper intestine. These polymers can be used as coating agents because they do not necessitate the addition of plasticizer or other film formers to fabricate coatings for oral formulations [128].
Hydroxypropyl methylcellulose phthalate (HPMCP), available in the market since 1971, it is a monophthalic acid ester of hypromellose, containing methoxy (-OCH3), 2-hydroxypropoxy (- OCH 2CHOHCH3) and phthaloyl (o-carboxybenzoyl C8H5O3) groups so, HPMCP is a cellulose in which some of the hydroxyl groups are replaced with methyl ethers, 2-hydroxy propyl ethers, or phthalyl esters.
Numerous different types of hypromellose phthalate are commercially presented with molecular weights in the range 20 000–200 000. Typical average values are 80000–130000 [133]. These types are (HP50, HP55 and HP55S) where HP55 grade is usually used for enteric coating, HP55S grade, because of its higher degree of polymerization compared with HP-55, it have greater solution viscosity, greater mechanical strength of the film and HP-50 dissolves at a lower pH value and is therefore appropriate for preparations which are designed to disintegrate in the upper part of the small intestine.
Trade name Eudragit S100 HPMCP HP-55
Chemical name Poly (methacrylic acid, methyl methacrylate) 1 : 2 [128]
Cellulose, 2-hydroxypropyl methyl ether, phthalic acid ester [133]
CAS number (25086-15-1 ) [128]
( 9050-31-1 ) [133]
pH solubility ≥ 7 [128, 129]
≥ 5.5 [139]
The most common three methods used to prepare the nanoparticles are: (1) dispersion of preformed polymers; (2) direct polymerization of monomers using classical polymerization reactions; and (3) ionic gelation or coacervation of hydrophilic polymers. However, other methods like supercritical fluid technology [140] and particle replication in non-wetting templates (PRINT) [141] can be also used to prepare nanoparticles.
Polymeric nanoparticles (PNPs) can be prepared from preformed polymers through several methods such as solvent evaporation, salting-out, dialysis and supercritical fluid technology which involving the rapid expansion of a supercritical solution or rapid expansion of a supercritical solution into a liquid solvent. In contrast, PNPs can be directly synthesized through the polymerization of monomers using a variety of polymerization techniques like mini-emulsion, micro-emulsion, surfactant-free emulsion and interfacial polymerization.
The choice of preparation method is made on the basis of a number of factors such as the type of polymeric systems, the area of application, size requirement, and the drug to be loaded. Since, method of preparation mainly affect the properties of produced nanoparticles, it is highly advantageous to have preparation techniques at hand to get PNPs with the required properties for a particular application.
The term nanoprecipitation refers to a quite simple processing method for the fabrication of polymeric nanoparticles. The level of interest in nanoprecipitation waned for some decades, and
