Influence of buoyancy-driven flow on mass transfer in a two-stream microfluidic channel: Introduction of cryoprotective agents into cell suspensions

Amiri H, Mas-hafi S, Banerjee B, Vesey G, Miansari M, Ebrahimi Warkiani M. Rapid and Continuous Cryopreservation of Stem Cells with a 3D Micromixer

Cryopreservation is the final step of stem cell production before the cryostorage of the product. Conventional methods of adding cryoprotecting agents (CPA) into the cells can be manual or automated with robotic arms. However, challenging issues with these methods at industrial-scale production are the insufficient mixing of cells and CPA, leading to damage of cells, discontinuous feeding, the batch-to-batch difference in products, and, occasionally, cross-contamination. Therefore, the current study proposes an alternative way to overcome the abovementioned challenges; a highly efficient micromixer for low-cost, continuous, labour-free, and automated mixing of stem cells with CPA solutions. Our results show that our micromixer provides a more homogenous mixing of cells and CPA compared to the manual mixing method, while the cell properties, including surface markers, differentiation potential, proliferation, morphology, and therapeutic potential, are well preserved.

Microfluidics for cryopreservation

Cryopreservation has utility in clinical and scientific research but implementation is highly complex and includes labor-intensive cell-specific protocols for the addition/removal of cryoprotective agents and freeze-thaw cycles. Microfluidic platforms can revolutionize cryopreservation by providing new tools to manipulate and screen cells at micro/nano scales, which are presently difficult or impossible with conventional bulk approaches. This review describes applications of microfluidic tools in cell manipulation, cryoprotective agent exposure, programmed freezing/thawing, vitrification, and in situ assessment in cryopreservation, and discusses achievements and challenges, providing perspectives for future development.

A numerical study on distributions during cryoprotectant loading caused by laminar flow in a microchannel

In this work, we conduct a computational study on the loading of cryoprotective agents into cells in preparation for cryopreservation. The advantages of microfluidics in cryopreserving cells include control of fluid flow parameters for reliable cryoprotectant loading and reproducible streamlined processing of samples. A 0.25 m long, three inlet T-junction microchannel serves as an idealized environment for this process. The flow field and concentration distribution are determined from a computational fluid dynamics study and cells are tracked as inert particles in a Lagrangian frame. These particles are not confined to streamlines but can migrate laterally due to the Segre-Sildeberg effect for particles in a shear flow. During this tracking, the local concentration field surrounding the cell is monitored. This data are used as input into the Kedem-Katchalsky equations to numerically study passive solute transport across the cell membrane. As a result of the laminar flow, each cell has a unique pathline in the flow field resulting in different residence times and a unique external concentration field along its path. However, in most previous studies, the effect of a spatially varying concentration field on the transport across the cell membrane is ignored. The dynamics of this process are investigated for a population of cells released from the inlet. Using dimensional analysis, we find a governing parameter α, which is the ratio of the time scale for membrane transport to the average residence time in the channel. For [Formula: see text], cryoprotectant loading is completed to within 5% of the target concentration for all of the cells. However, for [Formula: see text], we find the population of cells does not achieve complete loading and there is a distribution of intracellular cryoprotective agent concentration amongst the population. Further increasing α beyond a value of 2 leads to negligible cryoprotectant loading. These simulations on populations of cells may lead to improved microfluidic cryopreservation protocols where more consistent cryoprotective agent loading and freezing can be achieved, thus increasing cell survival.