Mixing in an enclosed microfluidic chamber through moving boundary motions

Mixing in enclosed culture micro-chambers is an important criterion on achieving the long-term cell growth with more consistent characteristics spatially distributed in the microfluidic environments. Here, we report a microfluidic mixer composed of multiple deformable membranes to drive circulation flows within the culture region in a peristaltic manner. This mechanically driven mixing scheme has the advantages over many others existing mixing schemes by inducing negligible shear stress over cells without side effects to the viability and growth characteristics. The membrane movements can induce moving boundary motions of the liquid volume contained in the culture chamber. The flow characteristics such as the velocity profile and shear stress are investigated by lumped-element modeling and computational simulations. Both experiments and simulations are performed to show the effectiveness of the mixing of both soluble substances and sub-microscale particles, including bacteria. The mixing performance under different operation parameters (e.g., membrane size and membrane switching time) is also investigated for the optimized operation. Further, the dental bacteria Streptococcus mutans are cultured for 2 days to demonstrate that the reported mixing scheme can generate a more even distribution of growth, which may be further applied for a uniform dental biofilm development in vitro for the related biofilm research. Additionally, this micro-mixer is highly compatible with the widely used soft lithography technique, and hence, it can be directly integrated with general microfluidic devices for extended biomedical diagnosis and bio-sample processing applications.