Weak ionic hydrogels. Effects of pH, ionic strength, and buffer composition on swelling equilibria, kinetics, and solute release

When the polymer contains ionizable groups, then the rate of polymer swelling and drug release is determined, at least partially, by the ionic environment. The authors report investigations of the swelling and release properties of glassy, hydrophobic gels consisting of poly(methyl methacrylate-co-N,N-dimethylaminoethyl methacrylate) (MMA/DMA). It is shown that swelling rates for such gels are sensitive not only to pH and ionic strength, but also of the precise buffer composition. It is also shown that for certain solutes incorporated into the dry gels, release is determined by the swelling rate. These results have implications regarding the swelling mechanism, and also bear on the potential of these gels as pH-sensitive drug carriers.