Spatially selective reagent delivery into cancer cells using a two-layer microfluidic culture system

In this work, we demonstrate a two-layer microfluidic system capable of spatially selective delivery of drugs and other reagents under low shear stress. Loading occurs by hydrodynamically focusing a reagent stream over a particular region of the cell culture. The system consisted of a cell culture chamber and fluid flow channel, which were located in different layers to reduce shear stress on cells. Cells in the center of the culture chamber were exposed to parallel streams of laminar flow, which allowed fast changes to be made to the cellular environment. The shear force was reduced to 2.7 dyn cm⁻² in the two-layer device (vs. 6.0 dyn cm⁻² in a one-layer device). Cells in the side of the culture chamber were exposed to the side streams of buffer; the shear force was further reduced to a greater extent since the sides of the culture chamber were separated from the main fluid path. The channel shape and flow rate of the multiple streams were optimized for spatially controlled reagent delivery. The boundaries between streams were well controlled at a flow rate of 0.1 mL h⁻¹, which was optimized for all streams. We demonstrated multi-reagent delivery to different regions of the same culture well, as well as selective treatment of cancer cells with a built in control group in the same well. In the case of apoptosis induction using staurosporine, 10% of cells remained viable after 24 h of exposure. Cells in the same chamber, but not exposed to staurosporine, had a viability of 90%. This chip allows dynamic observation of cellular behavior immediately after drug delivery, as well as long-term drug treatment with the benefit of large cell numbers, device simplicity, and low shear stress.