Membrane Properties for Permeability Testing: Skin versus Synthetic Membranes

Strat-M is a new polymeric version of the skin membrane that has been developed by EMD Millipore. CDR researchers compared this new membrane with real human skin and found it is much better than cellulose acetate, another polymeric membrane which was used in the past. The study suggests that Strat-M can be used as a cheap alternative for screening topical formulations and actives for the pharmaceutical, cosmetic, and personal care industries.

In order to eliminate the need for biological membranes in pilot studies, synthetic membranes are often used. In most of the artificial membranes, either the aqueous domain (hydrophilic drug pathway) or the lipid domain (lipophilic pathway) of the skin is mimicked. However, there is a significant need for a synthetic membrane that can mimic both hydrophilic and lipophilic drug pathways, as seen in normal human skin. One of the synthetic membranes that has been used in diffusion studies for the past decade, is cellulose acetate (CA). CA is a simple, porous synthetic membrane for assessing topical formulation performance that acts as a barrier with no rate-limiting property. The limitation of CA as a porous membrane is that it completely does not correlate to human skin barrier properties. In addition, it may interact with some chemicals in a drug formulation which may affect drug permeation, consequently showing an incorrect drug permeability value.

One recently introduced synthetic membrane, that predicts both lipophilic and hydrophilic drug permeation with better correlation to human skin, is the Strat-M membrane. This membrane is a synthetic polymeric membrane for transdermal diffusion testing that is more predictive of diffusion in human skin without lot-to-lot variability or safety and storage limitations. This membrane is composed of multiple layers of polyether sulfone with a very tightly packed surface layer that creates a morphology resembling that observed in human skin.

The team compared the permeation of several compounds using human skin in vitro and two synthetic membranes, CA and Strat-M, in order to examine whether these artificial membranes can be useful for topical drug delivery testing/screening studies. The data obtained from this study suggests that hydrophilic compounds have higher permeation in Strat-M membranes compared with lipophilic ones. High variation in permeability values, a typical property of biological membranes, was not observed with Strat-M. In addition, the permeability of Strat-M was closer to that of human skin than that of cellulose acetate (CA>Strat-M>Human skin). With little or no lot-to-lot variability, Strat-M has the potential to be used for initial screening studies for formulations in place of human skin samples, which can then be used later on in the optimization process. The full research report was published in March 2018 in International Journal of Pharmaceutics.