Chemotaxis of Immune Cells in Microfluidic Flow-Free Concentration Gradient Generator

Gradients of soluble molecules regulate many biophysical processes by guiding complex biological events such as tissue regeneration, embryogenesis, angiogenesis, cancer invasion and formation of metastases or immune responses. One common aspect of these biological responses is the chemotactic motility of the cells. Generation of physiologically-relevant concentration gradients is particularly important to understand how chemokines affect cell migration in physiology and many pathologic conditions, including inflammatory diseases and cancer progression. Developing chemotaxis assays that examine cell response to precisely tailored complex microenvironments that can better mimic physiological conditions are crucial to study and characterize directed cell motion. Here, we describe a novel microfluidic device, which is able to generate complex chemokine patterns in flow-free gradient chambers. The device has multiple gradient chambers in which combinatorial gradients of different chemokines can be generated simultaneously while being imaged with high-magnification objectives for direct tracking of chemotactic cells. We simulated and experimentally validated the generation of various concentration gradients and presented design parameters for proper gradient generation. Using this microfluidic device, we studied Jurkat cell chemotaxis in different CXCL12 gradients and fibronectin surface concentrations. Jurkat cell motility ratio and average migration speed have been found to increase with increasing fibronectin surface concentration in the absence of CXCL12 gradients while remaining constant in different CXCL12 gradients. On the other hand, increasing fibronectin concentration is shown to reduce the Chemotactic Index of Jurkat cells in CXCL12 gradients. Lastly, increasing mean CXCL12 concentration with the same gradient steepness have been observed to cause saturation of Jurkat cells and lead to random motion. In summary, we describe an enhanced microfluidic system for cell migration studies and provide novel data on the migratory response of Jurkat cells to CXCL12, relevant to diverse areas, ranging from organogenesis to cancer research.