A different technique was adopted by Femmer et al. to enhance oxygen uptake in the blood channels. They used passive micromixers and chaotic advection principles to mix the fluid as it travels through a channel and increase oxygen mass transfer in the blood phase. Staggered herringbone micromixer structures with 50 µm depth and 125 µm width were patterned on channels in groups of six. Although this design demonstrated the reduction of oxygen diffusion resistance in blood, the advection phenomena may produce zones of high shear stress as well as stagnation zones along the microchannel which can lead to clot formation.