Controlled release of ionic drug through the positively charged temperature-responsive membranes

This work is focused on the investigation of the permeability of the ionic drug through the charged BPPO-g-NIPAAm membrane (CGM) in different release mediums. The CGM has temperature-responsive poly(N-isopropylacrylamide) [poly(NIPAAm)] chains and -N+(CH2CH3)3 ionic groups by means of grafting and then amination to the BPPO membrane (the base membrane). By controlling the amination time, the charged base membranes (CUMs) and CGMs with different ion exchange capacities (IEC) and water contents (WR) are obtained. Results show that the longer the amination time, the higher the IEC and WR values. However, the CUM gains the higher IEC and WR compared with the CGM even within the same amination time, which is possibly due to the decreased opportunity of replacement reaction as well as the blocking of the poly(NIPAAm) chains on the surface of the membrane. The sodium salicylate (SSA) was used as model drug due to its ionization in deionized water. Permeability coefficient of the drug is measured using side-by-side diffusion cells at various temperatures including 25, 37 and 43 °C. It is shown that the permeability coefficient of the drug markedly increases after the grafted membrane is aminated. When NaCl solution is used as the receptor medium, the increased quantity of drug release through the CGM is much more than that through the uncharged grafted membrane in the same change of temperature. Similar results can be also found in the deionized water. Consequently, it can be concluded that the sensitivity of the grafted membrane to temperature can be promoted by amination.