pH-sensitive swelling and release behaviors of anionic hydrogels for intelligent drug delivery system

The pH-sensitive swelling and release behaviors of the anionic P(MAA-co-EGMA) hydrogels were investigated as a biological on-off switch for the design of an intelligent drug delivery system triggered by external pH changes. There was a drastic change of the equilibrium weight swelling ratio of P(MAA-co-EGMA) hydrogels at a pH of around 5, which is the pK(a), of poly (methacrylic acid) (PMAA). At a pH below 5, the hydrogels were in a relatively collapsed state but at a pH higher than 5, the hydrogels swelled to a high degree. When the molecular weight of the pendent poly(ethylene glycol) (PEG) of the P(MAA-co-EGMA) increased, the swelling ratio decreased at a pH higher than 5. The pK(a), values of the P(MAA-co-EGMA) hydrogels moved to a higher pH range as the pendent PEG molecular weight increased. When the feed concentration of the crosslinker of the hydrogel increased the swelling ratio of the P(MAA-co-EGMA) hydrogels decreased at a pH higher than 5. In release experiments using Rhodamine B (Rh-B) as a model solute, the P(MAA-co-EGMA) hydrogels showed a pH-sensitive release behavior. At low pH (pH 4.0) a small amount of Rh-B was released while at high pH (PH 6.0) a relatively large amount of Rh-B was released from the hydrogels. (c) 2007 Wiley Periodicals, Inc.