Design and application of a dissolution-permeation apparatus with scalable surface area and controllable hydrodynamic conditions at the membrane interface

The evaluation of drug release from enabling formulations often requires a coupled measurement of dissolution and permeation processes. While dissolution testing alone is well established in pharmaceutical development, coupled dissolution-permeation studies often face challenges due to limited permeation surface area and poor control over local hydrodynamic conditions that affect the thickness of the unstirred water layer at the membrane interface. This study presents adissolution-permeation device integrating a standard USP II dissolution vessel and a custom-built permeation module with a sandwich structure, offering a permeation area that is scalable by multiplication. The functionality of the apparatus was demonstrated using carboxyfluorescein and caffeine as model solutes permeating across polycarbonate and polyvinylidene fluoride membranes under varying hydrodynamic conditions. The results provide a clear dependence of the apparent permeability on the flow velocity at the membrane interface, indicating a significant influence of the unstirred water layer. Simultaneous dissolution-permeation experiments with tablet prototypes exhibiting immediate and sustained drug release demonstrated the ability of the device to capture dynamic permeation behaviour, revealing an initial non-steady permeation phase that transitions into pseudo steady-state conditions. It has been shown that the permeation flux can be increased by multiplication of the basic permeation module to increase the membrane area to 100 cm². The findings establish the apparatus as a platform suitable for dynamic in vitro dissolution-permeation experiments with a potential to support formulation development and provide data for in-vivo-in-vitro correlations.