Time-Invariant Tensile Necking of Blood on an Electrowetting Digital Microfluidic Platform

Recent developments in electrowetting-on-dielectric (EWOD) technology have expanded the possibilities for testing methods and investigation of blood. This work evaluated the development of necking geometry of whole blood and red blood cell (RBC) suspensions on a digital microfluidic (DMF) platform. This was achieved by applying tension to liquid droplet specimens on an EWOD-based device using applied electrowetting forces, thereby inducing necking. The deformation of 5 μL fluid specimens was recorded using neck radius and minimum neck width as two characteristic geometric parameters. Tensile tests were performed on phosphate-buffered saline (PBS), whole blood diluted in PBS, and RBCs suspended in PBS at hematocrit values of 10%. Although rheological measurements suggested higher stiffness of RBC suspensions when treated with neuraminidase, necking profiles were indistinguishable from those of untreated RBC suspensions. When tested at two different dilutions, whole blood diluted 1:20 and 1:10 in PBS exhibited distinct necking profiles. The necking development was observed to be time-invariant and insensitive to the large variability otherwise observed among distinct DMF chips and distinct locations on the chips