A pH-Sensitive Hydrogel with Hydrophobic Association for Controlled Release of Poorly Water-Soluble Drugs

A novel pH-sensitive hydrogel has been developed by UV induced radical polymerization of acrylic acid (AA) and amphiphilic macromonomer polyethylene glycol monolaurylether monoacrylate (PEGLA) with crosslinker ethylene glycol dimethacrylate for controlled release of acyclovir, a poor water-soluble model drug. The swelling behavior was investigated in the buffer of different pH at I = 0.1 M, as well as in the ethanol/water mixture. The hydrophobic association formed by the hydrocarbon chains in PEGLA was found to dominate the swelling properties of the hydrogels with subordinate pH sensitivity due to the ionization of the AA segments. Therefore, the drug loading of acyclovir has been improved and the release rate of acyclovir was slowed down with increasing the PEGLA content in the hydrogels. By fitting the release data with Weibull equation, the acyclovir release kinetics was changed from the Fickian diffusion to an anomalous diffusion when the PEGLA content in the hydrogels was beyond 20 mol%.