Picking out circulating tumor cells (CTCs) from whole blood, known as liquid biopsy, should soon be a regular way to screen for cancer and to monitor patients that have undergone treatment. There is also evidence that there are so-called cancer stem cells (CSCs) that are particularly aggressive and that are able to morph into any kind of cell found in the tumor that they arise from. The race is on to build devices that can pluck these cells from blood, which will provide pathology labs ready-to-use CTCs and CSCs for detailed analysis. A clinical trial is now underway at the University of Michigan that uses a new microfluidic chip to extract breast cancer CTCs.
The investigators created a labyrinth-like device that takes cue from previously developed microfluidic chips that rely on a spiral path to separate cells by size. In those, larger cells end up moving farther down the spiral than smaller cells that stay closer to the walls that keep them back. In the new chip, the cells take a much more complicated route. Sunitha Nagrath, associate professor of chemical engineering at U of M and the lead developer of the chip, explains: “Bigger cells, like most cancer cells, focus pretty fast due to the curvature. But the smaller the cell is, the longer it takes to get focused,” Nagrath said. “The corners produce a mixing action that makes the smaller white blood cells come close to the equilibrium position much faster.”
Because the complicated shape results in a longer path than a simple spiral, the separation between the cells is allowed to be greater, improving precision. Since the chips process their samples in minutes, at 2.5 mL/min, the team was able to string two of them in series. One chip cleaned up the initial sample, which was still impure, while the next chip perfected the results. The final solution had approximately 600 white blood cells per milliliter and the rest circulating tumor cells, which in this business is a rather impressive achievement.
Study in journal Cell Systems: High-Throughput Microfluidic Labyrinth for the Label-free Isolation of Circulating Tumor Cells…