Ischemia/reperfusion (I/R) injury was induced in primary porcine cardiomyocytes in a low-shear microfluidic culture chip. The chip was capable of sustaining cardiomyocyte culture and inducing I/R injury by subjecting the cells to periods of hypoxia lasting 3-4 hours followed by normoxia. Mitochondrial membrane potential was assayed using MitoTracker Red to follow mitochondrial depolarization, the earliest stage of apoptosis. Cell adhesion and morphology were also determined simultaneously with fluorescence measurements. Changes in membrane potential were observed earlier than previously reported, with mitochondria becoming depolarized as early as 2 hours into the ischemia period. The cells with depolarized mitochondria were deemed apoptotic. Out of 38-61 cells per time frame, the fraction of apoptotic cells was found to be similar to control samples (3%) at two hours of ischemia, which increased up to 22% at the end of ischemia period as compared to 0% in the control samples. Morphological analysis of cells showed that 4 hours of ischemia followed by reperfusion produced blebbing cells within 2 hours of restoring oxygen to the chip. This approach is a versatile method for cardiomyocyte stress, and in future work additional analytical probes can be incorporated for a multi-analyte assays of cardiomyocyte apoptosis.

A new cell analysis method, differential mobility cytometry (DMC), was developed to monitor cells spatially and temporally or to separate cells based on affinity interactions. DMC combines an oscillation system with open-tubular capillary cell affinity chromatography (OT-CAC), although any separation volume (capillaries, channels, etc.) can be used. This unique separation approach uses oscillating flow and differential imaging to analyze cells as they retard and adhere to an affinity surface. Three main factors of the oscillation system were studied: the pump speed, oscillation frequency, and cell velocity at different oscillation speeds. The optimized oscillation frequency and intensity were determined. Cell-surface interactions were used to estimate the number of bonds formed during cell capture. An average of 200 bonds (standard deviation of 150 bonds) were formed during cell capture. The variability was due to differences in cell-capture times (0.8 +/- 0.6 s). Cells expressing the target protein on the surface oscillated slower and were captured by the corresponding ligand on the capillary surface. Cells were detected by differential imaging of a charge-coupled device camera. DMC measurements were optimized with respect to the camera frame difference. Cells were observed to slow as they reached the surface and could be observed to sway in the oscillating flow as they were tethered to the surface by a capture antibody. With the advantage of high cell-capture efficiency and temporally monitoring cell adhesion by the differential mobility of cells, DMC has proven to be a useful tool in cell analysis for basic biological studies and biomedical research.