Progestin permeation through polymer membranes IV: Mechanism of steroid permeation and functional group contributions to diffusion through hydrogel films

Hydrogel films were prepared from hydroxyethyl methacrylate, both with (Film II) and without (Film I) 5.25 mole % of ethylene glycol dimethacrylate. Permeation, diffusion, and partition coefficients for progesterone, testosterone, nandrolone, norethindrone, 17α‐hydroxyprogesterone, estradiol, and hydrocortisone were determined. A solute permeation model was proposed based on the separation of a domain (B) composed of “bulk‐like” water and a domain (A) composed of polymer, interfacial water, and bound water present in the films. The separate contributions from the “pore” and “solution‐diffusion” mechanisms to the total permeability were calculated from the model. Steroid permeabilities through Films I and II were analyzed in accordance with this model. Permeation of Film II occurred via the solution‐diffusion mechanism. Permeation of Film I occurred predominately by the pore mechanism with a small contribution (∼20%) from the solution‐diffusion mechanism. The latter contribution was dependent on the solubility of the solute within the A domains of the hydrogel film. Functional group contributions to permeation of Film II were ascribed to either steric or hydrogen bonding effects.