Modulation of drug permeation through interpolymer complexed hydrogels for drug delivery applications

Grafted poly(methacrylic acid-g-ethylene glycol) (P(MAA-g-EG)) copolymers exhibit pH-sensitive, reversible complexation. Equilibrium swelling ratios and mesh sizes of uncomplexed gels were much higher than those of the complexed states and varied according to copolymer composition and PEG graft length. Swelling under oscillatory pH conditions revealed the dynamic sensitivity of P(MAA-g-EG) gels and showed that network collapse (complexation) occurred more rapidly than network expansion (decomplexation). The rates of diffusion of specific ions caused the responses. Solute diffusivity was higher in uncomplexed than in complexed P(MAA-g-EG) membranes and decreased as solute size increased. Lower diffusivities resulted in membranes containing longer PEG grafts since in the uncomplexed state the PEG grafts dangled into the polymer mesh space.