Improving U-shaped traps in a microfluidic chip to trap cancer cells to form spheroids using simulation

Microfluidic systems have made substantial progress over the last decade, finding numerous applications in various scientific fields, including biomedical engineering. These systems provide advanced methods for investigating the effects of anticancer drugs in in vitro environments, often referred to as organ-on-a-chip technology. Cancer spheroids, a type of cell aggregation, serve as the simplest 3D cancer model in laboratories, possessing histological and functional characteristics similar to tumor tissue. To form spheroids on a chip, cells must be trapped in suitable structures and allowed to grow and proliferate under appropriate conditions. Consequently, the design of these traps, with regard to their shape, dimensions, and arrangement within the chip, is crucial. An appropriate trap arrangement ensures uniform cell trapping. In this study, we investigated the performance of two types of U-shaped traps -one without apertures and one with 9 $\mu \mathrm{m}$ apertures- for trapping cancer cells with a diameter of $\mathbf{1 0}$ $\mu \mathrm{m}$. Using STAR CCM software, we found that traps without apertures exhibited poor performance due to fluid accumulation within them, which hinders cell entry. In contrast, traps with 9 $\mu \mathrm{m}$ apertures on the sides demonstrated good cell-trapping efficiency, and the experimental results confirmed this observation. Based on existing studies, we examined three arrangements of 8 and 9 traps with apertures within the chip, assessing the performance of each arrangement in terms of the number of trapped cells and the velocity field inside the chip. Finally, we identified the best arrangement among the three, featuring 8 traps, as the most suitable layout for capturing cancer cells. In this arrangement, an average of 27-28 cells are trapped in the trap, and the number of trapped cells is approximately uniform in all traps.