A biochemomechanical oscillator has been developed in which a clamped, pH-sensitive hydrogel membrane containing N-isopropylacrylamide (NIPAAm) and methacrylic acid (MAA) separates a chamber containing glucose oxidase from a pH controlled external medium containing a constant concentration of glucose. This system undergoes oscillations in intrachamber pH and concomitant on/off switching of glucose permeation through the membrane due to a nonlinear feedback instability between the enzyme-mediated reaction, which converts glucose to hydrogen ion, and the swelling/glucose-permeability characteristic of the membrane. Oscillation period increases with time due to buildup in the chamber of a buffering product, gluconate ion, and eventually oscillations cease. During operation there is a fluctuating pH gradient between the chamber and the external medium. We have gathered experimental evidence that a sustained pH gradient leads to stress induced pattern formations in the hydrogel due to phase separation, which we believe may be responsible for cessation of oscillations. We have also shown pattern development in clamped thermally sensitive hydrogel membranes based on NIPAAm without MAA), with a temperature gradient applied across the membrane. A mathematical description of the observed phenomena is desirable.