The effect of surface micropatterns on the flow in a lab-on-a-chip with nanowires

Abstract

Nanowire-anchored microfluidic devices have opened new opportunities for in situ extractions of microRNAs (miRNAs) from extracellular vesicles (EVs) in body fluids. The diagnosis precision of the devices largely depends on the EV extraction efficiency. In this article, we demonstrated a maskless photolithography process with direct covalent bonding for fabricating microfluidic devices embedded with zinc oxide (ZnO) nanowires as a lab-on-a-chip for extracting urinary EVs. The chips were designed with two distinct surface micropatterns: herringbone arrow and cylindrical micropillars. We investigated the effect of surface pattern, groove height-to-width ratio and nanowire orientation on the microflow. The computational fluid dynamics (CFD) simulations suggested that the herringbone pattern is more effective in reducing the flow velocity thus prolonging the mixing time. Furthermore, a critical inter-pattern groove width-to-height ratio was shown to induce circulating currents in the concave regions of the micropatterns. This design shows potential in increasing the fluid residency time within the device, thus increasing the probability of trapping EVs in circulating flows. In addition, the randomly oriented nanowires resulted in a significant amount of near-wall vorticity. Overall, the combination of a surface micropattern and the randomness of nanowire orientation suggests enhanced particulate mixing in the wall-adjacent zones and the potential to improve the EV extraction efficiency.