The role of polyelectrolytes in the permeability control of insulin: behaviour of poly(N-acryloyl-glycine) grafted on porous cellulose membrane

The insulin permeation of poly(N-acryloyl-glycine), P1, was studied using a porous cellulose membrane grafted with this polymer. The permeability of insulin through the graft system changed according to the pH: the insulin flowed only at low pH, no release of insulin being observed under alkaline conditions. This means that the P1 polymer acts like a chemical gate for the passage of insulin. The response of the pH change was determined by titrating the grafted polymer with hydrochloric acid or sodium hydroxide solutions. A hysteresis loop was observed, the width of which depended on the constant time interval used in the titration. Interaction between the uncharged polymer and the membrane was revealed by the FT-IR spectra and was responsible for the slowness of the protonation reaction. The enzyme GOD (glucose oxidase) was immobilized on the grafted polymer, and the permeability of insulin through the cellulose membrane system was studied in response to glucose concentration. No release of insulin was observed at higher pH until glucose was added to the solution, after which the response was immediate and the insulin flowed through the pores of the membrane.