A Parametric Analysis of Capillary Height in Single-Layer, Small-Scale Microfluidic Artificial Lungs

Microfluidic artificial lungs (mu ALs) are being investigated for their ability to closely mimic the size scale and cellular environment of natural lungs. Researchers have developed mu ALs with small artificial capillary diameters (10-50 mu m; to increase gas exchange efficiency) and with large capillary diameters (similar to 100 mu m; to simplify design and construction). However, no study has directly investigated the impact of capillary height on mu AL properties. Here, we use Murray's law and the Hagen-Poiseuille equation to design single-layer, small-scale mu ALs with capillary heights between 10 and 100 mu m. Each mu AL contained two blood channel types: capillaries for gas exchange; and distribution channels for delivering blood to/from capillaries. Three designs with capillary heights of 30, 60, and 100 mu m were chosen for further modeling, implementation and testing with blood. Flow simulations were used to validate and ensure equal pressures. Designs were fabricated using soft lithography. Gas exchange and pressure drop were tested using whole bovine blood. All three designs exhibited similar pressure drops and gas exchange; however, the mu AL with 60 mu m tall capillaries had a significantly higher wall shear rate (although physiologic), smaller priming volume and smaller total blood contacting surface area than the 30 and 100 mu m designs. Future mu AL designs may need to consider the impact of capillary height when optimizing performance.