In vitro investigation of potential application of pH-sensitive poly(vinylidene fluoride)–poly(acrylic acid) pore-filled membranes for controlled drug release in ruminant animals

The potential application of the developed membranes on controlled drug release in ruminant animals was explored by studying the membrane performance for a model drug, salicylic acid, in both a pressure-driven system and a diffusion dialysis system. The rejection of salicylic acid (83%) was much higher at pH neutral than that at pH acidic (5%). The permeability at pH neutral (0.84 × 10−7 to 4.35 × 10−7 m/s) was much lower than that at pH acidic (9.82 × 10−7 to 12.0 × 10−7 m/s) mainly due to the Donnan exclusion effect. The permeabilities at both pH acidic and neutral decreased as the mass gain increased due to the influence of the membrane porosity and tortuosity, the partition coefficient, and the drug diffusion coefficient. As the mass gain increased, the ratio of the membrane permeability at pH acidic to that at pH neutral became greater. The result of the drug half time study indicated that the membranes could effectively protect the model drug at pH neutral environment and release at pH acidic environment, as required.