A variety of methods have been used to introduce chemicals into a stream or to mix two or more streams of different compositions using
microfluidic devices. In the following paper, the introduction of
cryoprotective agents (CPAs) used during cryopreservation of cells in order to protect them from freezing
injuries and increase viability post thaw is described.
Dimethylsulphoxide (
DMSO) is the most commonly used CPA. We aim to optimize the operating conditions of a two-stream
microfluidic device to introduce
a 10% vol/vol
solution of
DMSO into a cell
suspension. Transport behavior of
DMSO between two streams in the device has been experimentally characterized for a spectrum of flow conditions (0.7 < Re < 10), varying initial donor stream concentrations, (1% vol/vol < C o < 15% vol/vol) and different flow rate fractions (0.23 < f q < 0.77). The outlet cell stream concentration is analyzed for two different flow configurations: one with the cell stream flowing on top of the
DMSO-rich donor stream, and the other with the cell stream flowing beneath the heavy
DMSO-laden stream. We establish a transition from a diffusive mode of mass transfer to gravity-influenced convective currents for Atwood numbers (A t ) in the range of (1.7 × 10(-3) < A t < 3.1 × 10(-3)) for the latter configuration. Flow visualization with cells further our understanding of the effect of A t on the nature of mass transport. Cell motion studies performed with Jurkat cells confirm a high cell recovery from the device while underscoring the need to collect both the streams at the outlet of the device and suggesting flow conditions that will help us achieve the target
DMSO outlet concentration for clinical scale flow rates of the cell
suspension.