DARU Journal of Pharmaceutical Sciences61-2Swelling characteristics of hydroxyethylmethacrylate/ methacrylic acid pH -sensitive hydrogel as a drug delivery system110M. Falamarzian- J. Varshosaz20151006Hydroxyethyl methacrylate /methacrylic acid (HEMA/MAA) copolymer cross-linked with ethylenglycol dimethacrylate was prepared by a bulk.free radical polymerization method. The results indicate that this polymer is a pH -sensitive hydrogel which is collapsed in the acidic medium but completely swollen in the alkaline and neutral pH . it was determined that a proportion of 40% of MAA, the ionizing monomer of this hydrogel, was the best concentration among the different percentages used which showed a non-Fickian water transport mechanism. Increasing MAA content from 20 to 70% was accompanied with a change in water transport mechanism from Fickian to non-Fickian. However, increasing the percentage of MAA from 40 to 70 didn't improve the swelling capacity of this polymer. Pore size determination by a solute exclusion technique, showed the greatest distribution in the hydrogel with 40% MAA compared to other percentages of this monomer used. About 75% of the pores were less than 16.5 A in diameter in this polymer which is important specially in loading the hydrogel with macromoiecular drugs like proteines.https://daru.tums.ac.ir/index.php/daru/article/view/56https://daru.tums.ac.ir/index.php/daru/article/download/56/56