Poster Y19 - Inertial Microfluidics for Size-Based Sorting and Detection of Circulating Tumor Cells

Introduction: Inertial microfluidics is characterized by being able to direct particles and cells in fluid streams at the microscale . This technology uses the inertial and viscous forces produced by fluid flow through tiny channels for specific sorting of cells as a label-free method (Zhu et al., 2021). It has great potential for improving how we detect and study circulating tumor cells (CTCs), which play a key role in detecting and monitoring cancer progression. Even though traditional methods like fluorescence-activated and magnetic-activated cell sorting have moved forward in the past few years, there is still a need to deal with problems related to throughput, cost, scalability, and maintaining cellular integrity (Wiener et al.; Bowles et al.). We have previously performed computational modeling to identify potential experimental conditions for inertial separation in our system (Giolando, 2021). Our current study demonstrates the experimental capabilities of using high-throughput inertial microfluidics for sorting and detecting large particles for breast cancer CTCs separation.

Materials and

Methods: The setup for our experiment is a microfluidic device made from polydimethylsiloxane (PDMS), having a straight channel with a length of 50 microns and a depth of 125 microns with side cavities of different geometries, including square, rectangle, V shape, and semi-circle, which utilize inertial focusing to trap cells. Initial COMSOL modeling demonstrated that particle separation potential is highly influenced by the side cavity geometry and flow rate. For example, numerical simulations predicted size-selective trapping for both 300x300 µm and 400x400 µm wells, indicating that the geometry significantly impacts separation efficiency and capture rates (Giolando, 2021). We carried out the experiments with 5 μm (representing red blood cells, RBCs) and 20 µm (representing CTCs) polymethacrylate beads to evaluate how biological cells would behave when exposed to flow. These beads were added to the microfluidic system using a syringe pump at various flow rates (1-3 ml/minute), in order to assess sorting efficiency according to size and flow rate.

Results, Conclusions, and Discussions: The 5 and 20 μm sized beads are sorted based on their sizes, with larger beads moving towards the side cavities and becoming predictably trapped, whereas the smaller beads follow the natural flow and exit the system. Based on the COMSOL model simulated with the assistance of Dr. Hui Ma, the side cavity geometry plays a significant role in cell separation (Figure 1). Trapping occurs most effectively in all geometries except for the semi-circle (Figures 2-5). The system maintained high throughput, processing 1-3 mL of bead suspension per minute.

This proof of concept, using polymethacrylate beads, has shown that our microfluidic design is capable of sorting particles by size and separating 20 μm from 5 μm diameter particles. This concept could be applied to isolating CTCs from blood samples. The results provide a basic understanding, but more experiments with RBCs and CTCs will be needed to determine if this device works well in a clinical environment. The successful use of high flow rates at 1-3 mL/min is amenable to larger blood volume sampling. Future work is aimed at making the system ready for handling biological cells, with special attention paid to maintaining cell viability while performing sorting operations.

Acknowledgements (Optional): Dr. Tamara Kinzer-Ursem's NSF Career Fund #1752366

References:

Bowles, K. R., W., J. T. C., Qian, L., Jadow, B. M., & Goate, A. M. "Reduced variability of neural progenitor cells and improved purity of neuronal cultures using magnetic activated cell sorting."

Giolando, P. A. (2021). Mathematical and Computational Modeling in Biomedical Engineering. Purdue University Graduate School. Thesis. https://doi.org/10.25394/PGS.15079443.v1

Wiener, D. M., Huynh, E., Jeyakumar, I., Bax, S., Sama, S., Cabrera, J. P., Todorova, V., Vangipuram, M., Vaid, S., Otsuka, F., Sakai, Y., Leonetti, M. D., & Gómez-Sjöberg, R. "An open-source FACS automation system for high-throughput cell biology."

Zhu, Z., Wu, D., Li, S., Han, Y., Xiang, N., Wang, C., & Ni, Z. (2021). A polymer-film inertial microfluidic sorter fabricated by jigsaw puzzle method for precise size-based cell separation. Analytica Chimica Acta, 1143, 1–9. https://doi.org/10.1016/j.aca.2021.02.026