Evaluation of mixing efficiency in a microfluidic cartridge using a finite element method

摘要

In-vitro diagnostics has shifted from using laboratories to analyze samples, to Point-of-Care devices. These devices offer rapid, near-to-patient analysis, either at the patient’s home or the doctor’s office. Most Point-of-Care devices use microfluidic principles, since they use small volumes of fluids, handled by microscale channels. When comparing the Point-of-Care devices to conventional testing methods, they benefit from a much smaller reagent consumption, but suffer when it comes to sensitivity and detection limit. The objective of this research was to study how the mixing performance of a microfluidic immunoassay cartridge can be enhanced. For this purpose, several micromixer geometries, from literature, were studied using a finite element method approach, which was used to characterize and optimize the system. The mixing efficiency of these micromixer was evaluated by measuring the relative concentration variance of the structures at the outlet against the one inlet, a measure which has also been used in other studies. After the most effective structure was identified, the impact of various parameters, such as pressure, channel length, element width and height, were studied using the same methods. For selecting a micromixer design, along with the mixing efficiency, other parameters were taken into account. These parameters were the probability of air droplet formation, which heavily affects the immunoassay performance, and the manufacturing complexity, which directly impacts the cost of the cartridge.The results of the simulations showed that a slanted rip micromixer, with an element height of 0.25 mm, element width 1 mm, a channel length of 40 mm, was best suited for this application. The experimental validation, conducted on injection molded polystyrene cartridges, confirmed the mixing behavior predicted in the simulations. Additionally, it revealed that air droplets were rarely formed when blood plasma was flowed through the cartridge. The approach used in this work is often used when studying micromixer geometries. However, there currently are no studies which investigate the parameter configuration of the slanted rips micromixer and their influence on the mixing efficiency. Moreover, most of the chaotic advection micromixers from literature study the micromixer as a standalone component, rather than in an assembly. In this work, factors influencing the performance of other cartridge components are taken into account.