Microfluidic Technologies for Deformability-Based Cell Sorting

There are many situations in medicine and biology where it is desirable to distinguish specific cells within a population based on their mechanical deformability, which can potentially serve as a proxy for morphology or pathology. This biophysical characteristic is particularly relevant for cells in the circulatory system because deformability determines the capacity for these cells to transit through the microvasculature. These circulating cells include the abundant hematological cells such as erythrocytes (red blood cells, RBCs) and leukocytes (white blood cells, WBCs), as well as rare cells, such as circulating tumor cells (CTCs). Since deformability is such a fundamental characteristic of blood cells, deviations in normal cell deformability can contribute to a range of pathological conditions and potentially serve as a biomarker to evaluate them during treatment. In this chapter, we first discuss the role of deformability in circulating cells, including erythrocytes, leukocytes, and CTCs. We then briefly introduce our recent efforts in measuring cell deformability, and then compare the deformability of various circulating cells. Subsequently, we review the principles and applications of established strategies for deformability-based cell separation, including hydrodynamic chromatography and microfiltration. Finally, we will describe a recently developed method to sort cells based on deformability using the microfluidic ratchet mechanism, as well as its application in deformability-based separation of CTCs and deformability-based sorting of RBC infected with P. falciparum, the parasite that causes malaria.