Drug transport mechanisms and release kinetics from molecularly designed poly(acrylic acid-g-ethylene glycol) hydrogels

Controlled drug release devices of pH-sensitive, complexing poly(acrylic acid-g-ethylene glycol) (P(AA-g-EG)) hydrogels were prepared by free radical solution UV polymerization. The effects of hydrogel composition, polymerization conditions and surrounding environment on theophylline release kinetics and drug transport mechanisms were evaluated in these P(AA-g-EG) polymer networks. Release studies indicated a dependence of the theophylline release kinetics and diffusion coefficients on the hydrogel structure, polymerization conditions and pH of the environment. The theophylline transport mechanism was studied by fitting experimental data to five different model equations and calculating the corresponding parameters. The Akaike information criterion was also considered to elucidate the best-fit equation. Results indicated that in most release cases, the drug release mechanism was anomalous (non-Fickian). This indicates that such systems may, under certain conditions, provide release characteristics approaching zero-order release. The pH of the dissolution medium appeared to have a strong effect on the drug transport mechanism. At more basic pH values, Case II transport was observed, indicating a drug release mechanism highly influenced by macromolecular chain relaxation. The results obtained in this research work lead us to the conclusion that P(AA-g-EG) hydrogels can be successfully used as drug delivery systems. Their versatility to be designed with specifically tuned release properties renders these biomaterials promising pharmaceutical carriers for therapeutic agents.