Fatigue damage to pig erythrocytes during repeated swelling and shrinkage

On-Chip Label-Free Sorting of Living and Dead Cells

With the emergence of various cutting-edge micromachining technologies, lab on a chip is growing rapidly, but it is always a challenge to realize the on-chip separation of living cells from cell samples without affecting cell activity and function. Herein, we report a novel on-chip label-free method for sorting living and dead cells by integrating the hypertonic stimulus and tilted-angle standing surface acoustic wave (T-SSAW) technologies. On a self-designed microfluidic chip, the hypertonic stimulus is used to distinguish cells by producing volume differences between living and dead cells, while T-SSAW is used to separate living and dead cells according to the cell volume difference. Under the optimized operation conditions, for the sample containing 50% of living human umbilical vein endothelial cells (HUVECs) and 50% of dead HUVECs treated with paraformaldehyde, the purity of living cells after the first separation can reach approximately 80%, while after the second separation, it can be as high as 93%; furthermore, the purity of living cells after separation increases with the initial proportion of living cells. In addition, the chip we designed is safe for cells and can robustly handle cell samples with different cell types or different causes of cell death. This work provides a new design of a microfluidic chip for label-free sorting of living and dead cells, greatly promoting the multi-functionality of lab on a chip.

Rapid and continuous on-chip loading of trehalose into erythrocytes

Freeze-drying is a promising approach for the long-term storage of erythrocytes at room temperature. Studies have shown that trehalose loaded into erythrocytes plays an important role in protecting erythrocytes against freeze-drying damage. Due to the impermeability of the erythrocyte membrane to trehalose, many methods have been developed to load trehalose into erythrocytes. However, these methods usually require multistep manual manipulation and long processing time; the adopted protocols are also diverse and not standardized. Thus, we develop an osmotically-based trehalose-loading microdevice (TLM) to rapidly, continuously, and automatically produce erythrocytes with loaded trehalose. In the TLM, trehalose is loaded through the erythrocyte membrane pores induced by hypotonic shock; then, the trehalose-loaded erythrocytes are rinsed to remove hemoglobin molecules and cell fragments, and the extracellular solution is restored to the isotonic state by integrating a rinsing-recovering design. First, the mixing function and the rinsing-recovering function were confirmed using a fluorescent solution. Then, the performance of the TLM was evaluated under various operating conditions with respect to the loading efficiency of trehalose, the hemolysis rate of erythrocytes (ϕ), the recovery rate of hemoglobin in erythrocytes (φ), and the separation efficiency of the TLM. Finally, the preliminary study of the freeze-drying of erythrocytes with loaded trehalose was accomplished using the TLM. The results showed that under the designated operating conditions, the loading efficiency for human erythrocytes reached ~21 mM in ~2 min with a ϕ value of ~17% and a φ value of ~74%. This study provides insights into the design of the on-chip loading of trehalose into erythrocytes and promotes the automation of life science studies on biochips.

Toxicity Minimized Cryoprotectant Addition and Removal Procedures for Adherent Endothelial Cells

Ice-free cryopreservation, known as vitrification, is an appealing approach for banking of adherent cells and tissues because it prevents dissociation and morphological damage that may result from ice crystal formation. However, current vitrification methods are often limited by the cytotoxicity of the concentrated cryoprotective agent (CPA) solutions that are required to suppress ice formation. Recently, we described a mathematical strategy for identifying minimally toxic CPA equilibration procedures based on the minimization of a toxicity cost function. Here we provide direct experimental support for the feasibility of these methods when applied to adherent endothelial cells. We first developed a concentration- and temperature-dependent toxicity cost function by exposing the cells to a range of glycerol concentrations at 21°C and 37°C, and fitting the resulting viability data to a first order cell death model. This cost function was then numerically minimized in our state constrained optimization routine to determine addition and removal procedures for 17 molal (mol/kg water) glycerol solutions. Using these predicted optimal procedures, we obtained 81% recovery after exposure to vitrification solutions, as well as successful vitrification with the relatively slow cooling and warming rates of 50°C/min and 130°C/min. In comparison, conventional multistep CPA equilibration procedures resulted in much lower cell yields of about 10%. Our results demonstrate the potential for rational design of minimally toxic vitrification procedures and pave the way for extension of our optimization approach to other adherent cell types as well as more complex systems such as tissues and organs.