Elasto-Inertial Microfluidic Separation of Prolate Ellipsoids and Spheroids in a Coflow of Newtonian and Viscoelastic Fluids.

The ability to separate particles and cells by shape, independent of size, is essential for accurate chemical and biological assays. Here, we present an elasto-inertial microfluidic platform that enables shape-selective separation of isovolumetric prolate ellipsoids and spheroids in a coflow of Newtonian and viscoelastic fluids within a straight rectangular channel. By engineering the balance among inertial, elastic, and rotation-induced lift forces, prolate ellipsoids experience enhanced lateral migration toward the viscoelastic fluid in the microchannel center, while spheroids of identical volume remain confined within the Newtonian fluid on both sides of the microchannel. We systematically investigate the effects of flow rate ratio, channel length, and Reynolds number on particle lateral migration and identify operating conditions that maximize shape selectivity. Under optimized conditions, isovolumetric particles are separated with high purity. We further demonstrate shape-based manipulation of normal oblate and abnormal prolate red blood cells generated under shape deformation, achieving selective enrichment of prolate cells in the viscoelastic stream. This work establishes an innovative elasto-inertial microfluidic strategy for size-independent, shape-selective separation, providing a new sample preparation tool for cell-based analytical assays.