Using Brightfield Microscopy to Assess the Balloon Expansion Performance of a Microfluidic Cell Compression Device

Previously, we used photolithography and soft lithography to make a microfluidic cell compression device with a thin layer of polydimethylsiloxane (PDMS) for use with mechanobiological studies. When the microchannel was pressurized, the thin PDMS layer deformed and inflated like a balloon. Cells embedded within hydrogel scaffolds were placed on the balloons and, when inflated, were compressed between the balloon and a glass plate. The balloon’s inflation height played a key role in the amount of compression cells experienced, and understanding the inflation height of the microfluidic balloons is key to assessing the performance of the cell compression device. The device fabrication was then improved by utilizing 3D printed molds. In this study, a microfluidic cell compression device fabricated with a 3D printed mold, soft lithography, and spin-coating was investigated. Each balloon’s height and diameter were measured using brightfield microscopy. The device’s fabrication method was slightly altered to improve balloon diameter control, and thus, balloon height control. Hydrostatic pressure was used to improve the control and steadiness of the applied pressure. We found that brightfield microscopy-based height measurements were repeatable and were validated using side-view imaging. The obtained height measurements were then compared with previously obtained data and showed qualitative agreement with confocal laser scanning microscopy. Although there was disagreement between the heights measured with brightfield microscopy and confocal laser scanning microscopy, brightfield microscopy imaging was preferred due to its low cost, time efficiency, and accessibility.