Joie N. Marhefka, Steven D. Hudson, and Kalman B. Migler


Changes in rheological properties of blood, caused at least in part by alterations of the mechanical properties of red blood cells (RBCs), can provide valuable information for the diagnosis and understanding of various pathologies including cardiovascular disease, diabetes, sepsis, and mechanical blood trauma caused by blood contacting medical devices. A decrease in the deformability of the RBC, caused by stiffening of its membrane, is an indicator of many of these conditions. Using microfluidic methods for measuring RBC deformability requires a very small sample volume and probes the deformation of a large number of cells while providing data on individual cells. Another benefit of microfluidic methods is their ability to be used to test the cells quickly after their trauma or damage

In order to quantify RBC deformation and characterize the viscoelastic properties of the RBC membranes, microfluidic devices were fabricated containing a constricted region to produce extensional flow. The width of the constricted region was chosen to be large enough that all RBCs, even those with reduced deformability, could pass through the channel, but small enough so that sufficient strain rate occurs at flow velocities compatible with imaging constraints and single cells could be easily identified for analysis. A series of images was recorded for each individual RBC flowing through the constriction and subsequent expansion, and deformation, velocity, and extension rate were calculated as the RBC passed through the constricted region.  Both normal cells and those with reduced deformability to mimic pathological RBCs were characterized. In addition, RBC deformation in extensional flow was compared to deformation in steady shear flow.

This microfluidic technique provides a tool which can be used to characterize the rheological properties of individual RBCs quickly while using small sample volumes necessary when dealing with patient blood. This system can be used to detect alterations in these cell properties and provide a better understanding of changes in blood rheology and blood damage associated with various pathologies.