WATER, SOLUTE AND PROTEIN DIFFUSION IN PHYSIOLOGICALLY RESPONSIVE HYDROGELS OF POLY(METHACRYLIC ACID-G-ETHYLENE GLYCOL)

Grafted poly(methacrylic acid-g-ethylene glycol) [P(MAA-g-EG)] copolym ers were synthesized and their pH sensitivity was investigated. P(MAA- g-EG) membranes showed pH sensitivity due to complex formation and dis sociation. Uncomplexed equilibrium swelling ratios were 40 to 90 times higher than those of the complexed states and varied according to cop olymer composition and poly(ethylene glycol) (PEG) graft length. Mesh sizes in the two states were determined. Swelling under oscillatory pH conditions revealed the dynamic sensitivity of P(MAA-g-EG) membranes as well as the diffusional mechanisms causing network expansion and co llapse. Network collapse (complexation) occurred more rapidly than net work expansion (decomplexation). A Boltzmann superposition model was u sed to analyse this behaviour. Mechanical testing was used to evaluate the strength of P(MAA-g-EG) membranes and to elucidate the mesh size under various conditions. Solute diffusion coefficients were higher in uncomplexed than in complexed P(MAA-S-EG) membranes and decreased as solute size increased. Lower diffusion coefficients were observed with membranes or hydrogels containing longer PEG grafts, since in the unc omplexed state the PEG grafts dangled into the polymer mesh space. Mem brane permeability was responsive to changing pH conditions, and separ ation of solutes was achieved. (C) 1996 Elsevier Science Limited.