An Improved Transwell Design for Microelectrode Ion-Flux Measurements.

The microelectrode ion flux estimation (MIFE) is a powerful, non-invasive electrophysiological method for cellular membrane transport studies. Usually, the MIFE measurements are performed in a tissue culture dish or directly with tissues (roots, parts of the plants, and cell tissues). Here, we present a transwell system that allows for MIFE measurements on a cell monolayer. We introduce a measurement window in the transwell insert membrane, which provides direct access for the cells to the media in the upper and lower compartment of the transwell system and allows direct cell-to-cell contact coculture. Three-dimensional multiphoton lithography (MPL) was used to construct a 3D grid structure for cell support in the measurement window. The optimal polymer grid constant was found for implementation in transwell MIFE measurements. We showed that human umbilical vein endothelial cells (HUVECs) efficiently grow and maintain their physiological response on top of the polymer structures.