Permeability testing is used to profile the permeation behavior of pharmaceutical compounds. The many factors affecting permeability such as pH or hydrophilicity can make it difficult to perform an in-vitro assay for determining a permeability coefficient. A new generation of permeability testing equipment is able to simulate in-vitro drug permeability behavior without the expense or approval time of actual in-vitro studies. A PAMPA (parallel artificial membrane permeability assay) test can simulate permeability across different membranes by creating a specific lipid charge. In-vitro permeability models can simplify studies and reduce research costs for examining blood-brain barrier or intestinal drug permeation.