Schemes of circular wound-healing (CWA) and circular invasion assays (CIA). For both methods, a stabilized, rotating, silicone-tipped drill press was used to create uniform, circular wounds in an intact confluent monolayer of cells (black ring) in a standard Petri dish. In contrast to the CWA method (A), the CIA technique (B) incorporates a Matrigel™ overlay (shown in gray), which acts as an extracellular matrix barrier that allows cells to invade more similarly to in vivo physiology. This added component enables detection of various degrees of cell invasion displayed over time, whereas a measurement of cell migration (or motility) is taken in its absence. Quantitation of wound closure is made by comparing the final wound size after a given incubation period (TFinal) to the original wound size at 0 h (T0).