transwell

Transwell refers to a permeable cell culture insert used to create two separate fluid compartments within a single well of a microplate. Each insert consists of a porous membrane supported by a plastic ring that seals against the well, forming an apical (top) and basolateral (bottom) chamber. The membrane allows diffusion of soluble factors and, depending on pore size, may permit cell migration while keeping cells in their respective compartments.

Membranes are typically made of polycarbonate or polyester and come in various pore sizes to suit different applications. Inserts are available for common plate formats, including 24-well and 6-well plates. The pore size and membrane material influence permeability and barrier properties, making the choice important for experimental design.

Transwell systems are widely used to model epithelial and endothelial barriers in vitro. They enable measurement of barrier integrity through transepithelial electrical resistance (TEER) and permeability assays using tracers or dyes. They also support co-culture arrangements, such as combining epithelial cells with underlying fibroblasts or endothelial/astrocyte layers to simulate tissue interfaces and study cell–cell signaling.

In addition to barrier studies, Transwell inserts are employed in migration and invasion assays. Cells placed in the upper chamber may migrate through the membrane toward chemoattractants in the lower chamber, allowing assessment of motility and invasive behavior.

Transwell is a brand-name term that has become widely used to describe these permeable supports, though similar products are manufactured by multiple vendors. The concept remains a foundational tool in pharmacology, toxicology, and cell biology for studying transport, barrier function, and cell migration.