HETEROGENEOUS POLYELECTROLYTE GELS AS STIMULI-RESPONSIVE MEMBRANES

Stimuli-responsive membranes may act as ''on-off switches'' or ''perme ability valves'', producing patterns of pulsatile release, where the p eriod and rate of mass transfer can be controlled by external or envir onmental triggers (e.g. pH, temperature, electric field), In this work , composite-heterogeneous polyelectrolyte gel (composite-HPG) membrane s consisting of polymethacrylic acid (PMAA) gel particles dispersed wi thin a poiydimethylsiloxane (PDMS) network were developed and evaluate d as pH-responsive membranes. The mechanism of permeability control fo r caffeine and vitamin B-12 through composite-MPG membranes was determ ined to be a synergistic function of membrane hydration and the percol ating volume fraction of PMAA gel. Larger changes in permeation as a f unction of pH were achieved when both hydration and percolation effect s occurred together than when either of these effects occurred on thei r own. Vitamin B-12 permeation was observed when the hydrated gel volu me fraction was above approximately 0.38, but not below. Furthermore, the percolating fraction of composite-MPG membranes containing 28% (dr y basis) PMAA gel particles was manipulated via pH to fall above (pH 7 ) or below (pH 3) this transition in permeability, resulting in membra nes that delivered solutes of high molecular weight (vitamin B12) With large on/off delivery ratios (160). (C) 1998 Elsevier Science B.V. Al l rights reserved.