examines the propensity of chemicals, drugs or medication, or any blood-contacting medical device or material to lyse red blood cells (erythrocytes). The lysis is easily detected due to the release of hemoglobin. MTT MTT assay is used often in determining cell viability and has been validated for use by international organisations. MTT assay involves two steps of introducing the assay to the chemicals and then a solubilisation step. MTS The colorimetric MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2Htetrazolium) in vitro assay is an updated version of the validated MTT method, MTS assay has the advantage of being soluble. Hence, no solubilisation step is required. ATP ATP assay has the main advantage of providing results quickly (within 15 minutes) and only requires fewer sample cells. The assay performs lysis on the cells and the following chemical reaction between the assay and ATP content of cells produces luminescence. The amount of luminescence is then measured by a photometer and can be translated into number cells alive since ATP assay assumes alive cells still have ATP inside them, and Luminescence level recorded is proportional to the ATP content in the sample cells. Neutral Red Another cell viability endpoint can be Neutral Red (NR) uptake. Neutral Red, a weak cationic dye penetrates cellular membranes by non-diffusion and accumulates intercellularly in lysosomes. Viable cells take up the NR dye, damaged or dead cells do not. Enzyme-linked immunosorbent assay (ELISA) ELISA kits can be used to examine up and down regulation of proinflammatory mediators such as cytokines (IL-1, TNF alpha, PGE2).... Measurement of these types of cellular responses can be windows into the interaction of the test article on the test models (monolayer cell cultures, 3D tissue models, tissue explants). Types of in vitro studies Broadly speaking, there are two different types of in vitro studies depending on the type system developed to perform the experiment. The two types of systems generally used are : a) Static well plate system and b) the multi-compartmental perfused systems. Static well plate system The static well plate or layer systems are the most traditional and simplest form of assays widely used for in vitro study. These assays are quite beneficial as they are quite simple and provide a very accessible testing environment for monitoring chemicals in the culture medium as well as in the cell. However the disadvantage of using these simple static well plate assays is that, they cannot represent the cellular interactions