Fire-shaped cylindrical glass micronozzles to measure cell deformability

Most blood cells exhibit a natural deformation capability. Specifically, red blood cells (RBCs) are characterized by their great ability to deform and squeeze through microcapillary vessels, even with strict restrictions, recovering their shape after crossing them. That capability can be affected by various blood diseases (malaria, diabetes, etc), turning the cells into more rigid, and, as a result, it can generate blood flow disorders in the microcirculatory system. In this work, we propose a new micro-device to study the cell deformability consisting of a simple borosilicate micronozzle whose production is straightforward, fast, and uses low-cost equipment, when compared with other similar microfluidic devices found in the literature. We checked that the optical distortion coming from the glass is negligible when the micronozzle was submerged in a bath of glycerol, being able to perform blood flow visualizations through the micronozzle by using a high-speed video microscopy system. The shape of the converging area of our micronozzles produced an extensional flow. This type of flow is proper to conduct cell deformability assessments. After the characterization of our micro-device, we applied it to obtain the deformation index (DI) of both healthy and chemically treated human RBCs for several sections of our micronozzles. As expected, the experimental results show that the DI of healthy RBCs is much higher than the corresponding for more rigid (chemically treated) ones. These measurements show that the borosilicate nozzles allow to detect changes in the cellular mechanical properties similar to those produced by blood diseases, and suggest that, this microfluidic device could be easily transformed into a clinical tool for detection of blood diseases.