Manipulating the Barrier Function of a Cell Monolayer Using a High-power Miniature Ultrasonic Transducer

Ultrasound (US) and cavitation agents such as microbubbles (MBs) have been demonstrated to decrease the barrier function of endothelial and epithelial layers. However, in vitro experiments that study this effect are often hindered by the inability to deliver buoyant contrast agents in proximity to cell monolayers in order to adequately control the decrease in barrier function whilst insonating a sufficiently large tissue area. We have addressed this by adapting a cell culture system and fabricating a bespoke high-power miniature unfocused US transducer. The setup was used to control the drop in barrier function and to determine how varying the mechanical index (MI) and the duty cycle affected the barrier function. It was found that buffer solution alone and buffer + MBs did not decrease the transepithelial electrical resistance (TEER) of the cell monolayer. Buffer + US decreased the TEER by ~40%, with 10% TEER recovery 9 min after switching US off. Buffer + MBs + US decreased the TEER by 80%, with little or no recovery following treatment. In the presence of MBs, the barrier function was decreased by a duty cycle = [1% - 50%] and by an MI = [0.25 - 0.5], without any recovery following treatment. Detectable amounts of fluorescent dextran were delivered across the Caco-2 monolayer only by a combination of US + MBs. These results suggest that our adapted setup and custom-built miniature transducer permits control of the decrease in barrier function for further therapeutic investigations.