This critical review focuses on the applications of microcapillary films (MCFs) in bioanalytical techniques.

Microcapillary films (MCFs) are plastic films with an array of microcapillaries, which have been widely applied in microfluidics and bioanalytical techniques. However, the precise control of microcapillary size is still a problem hindering the industrial applications of MCFs because the high size uniformity of microcapillaries ensures the production of homogeneous droplets and the robust performance of immunoassays. Here, a novel approach is provided to precisely adjust the size of microcapillaries by liquid‐assisted extrusion and to investigate the combined effects of extrusion, drawing and liquid injection on the microcapillary size. Compared with gas‐assisted extrusion, the size uniformity is improved by at least 5% for 89% experiments and 10% for 42% experiments. Therefore, this method facilitates MCFs’ applications in droplet microfluidics and biotechnologies.