Poly(methyl methacrylate) membranes with controlled porosity for advanced multi-step drug elution

Most of the systems developed for controlled drug delivery applications depend on membrane technology and their preparation parameters. For some applications, a dense membrane structure used in controlled-release systems can excessively prolong drug release due to the low permeability of the coating to the drug or to the low solubility of the drug in water. In these cases, to increase the drug delivery rate, asymmetric membranes can be prepared by a phase-inversion technique, allowing a different drug delivery approach with respect to dense membranes. In this study, porous poly(methyl methacrylate) membranes with different vacuum degrees were prepared through the phase-inversion process. Ternary homogeneous solutions, obtained by mixing polymer, tetrahydrofuran (THF) and water in the desired amounts, were precipitated by the evaporation of a solvent (THF) and a non-solvent (water) at a controlled temperature and ventilation. Membrane morphology, investigated by scanning electron microscopy, showed it to have a diffuse porosity with a regular arrangement and geometry of pores on the top surface. The porosity degree of the membranes, mainly relying on the starting polymer concentration, was also investigated by the use of the software Image-Pro Plus, indicating the presence of a relationship between porosity and permeability characteristics. Membranes, containing folic acid as a model drug, were tested for their transport characteristics and drug delivery both in diffusive and in convective- diffusive conditions. Transport and release parameters, as well as permeability and effective diffusivity, were found to be dependent on the porosity and vacuum degree, which could be controlled by varying the preparation conditions. Furthermore, these membranes showed high hydraulic permeability and rapid drug release, suggesting their use for applications where an intensive therapy in the first few days is required, followed by a constant and slow release for a longer time (two-step drug delivery).