In vitro permeation testing (IVPT) or skin permeation testing is a critical tool for evaluating drug delivery into the various skin layers and for understanding the formulation selection for topical or transdermal application. The Center for Dermal Research (CDR) is well equipped with Franz diffusion permeability testing equipment, which includes water-jacketed models as well as heat block models. FDC- 24 heat blocks have the capacity to handle up to 24 Franz diffusion cells which allows the evaluation of six replicates for three different formulations with a control in a single heat block.
We develop and validate suitable HPLC analytical methods for screening drugs as well as personal care and cosmetic actives. Optimized formulations are evaluated for drug/active distribution in different skin layers. The flux of actives across human cadaver skin can be determined by quantifying levels of compounds in the Franz cell receptor medium, collected at various time intervals. We have access to various U.S. accredited tissue banks and companies specializing in donated skin samples and disease-state tissue models. Depending on the project needs, an appropriate model can be selected for testing. We have explored various skin models including freshly-excised human skin (mostly from abdominal surgeries), human cadaver skin, skin from porcine ears (to study anti-acne drugs), tissue engineered skin models (EpidermFT for example), Strat-M (MilliporeEMD) and in-vitro disease-state skin such as the atopic dermatitis model.
Stratum corneum (SC) the uppermost layer of the skin forms a major barrier to permeation of topically applied compounds. It is important to use undamaged skin samples in our permeability experiments where the SC is intact and performing as it would in vivo. Thus, a skin integrity test is always performed as part of any IVPT protocol. At CDR, we use a fairly sophisticated, wireless, portable and easy-touse instrument Vapometer (Delfintec, Finland) to measure transepidermal water loss (TEWL) as an indicator of skin integrity. Vapometer data is stored for every IVPT experiment we perform at the Center.
Release studies of actives through polymeric synthetic membranes such as polysulfone, cellulose acetate/nitrate mixed ester is termed in-vitro release testing (IVRT). This is performed to order to understand and establish the release kinetics of a drug from the formulations such as polymer or lipid based nanoparticles, organogels, complexes and liposomes. IVRT studies can be performed either by mounting cellulose acetate membranes on Franz diffusion cells to closely simulate topical application or by using dialysis tubes or dialysis cassettes with appropriate molecular weight cut-off values. Rates of drug release from particular formulations and fluxes through human cadaver skin are important data required for research and development endeavors and FDA filings.