Microfluidic measurement of RBC bending stiffness changes in blood storage

In transfusion medicine, the deformability of stored red blood cells (RBCs) changes during storage in blood banks. Compromised red blood cell (RBC) deformability can lower the transfusion efficiency or intensify transfusion complications such as sepsis. The controversial results in present literature are caused by the differences in the mode of RBC deformation and the metrics for indicating RBC deformability. This paper reports microfluidic mechanical measurement of stored RBCs under the physiological deformation mode (i.e., bending). Instead of using phenomenological metrics of deformation or elongation indices (DI or EI), RBCs' bending stiffness, a flow velocity independent parameter, is for the first time defined and used to evaluate the mechanical degradation of RBCs during storage. Fresh RBCs and RBCs stored up to six weeks in the blood bank were measured, revealing that the bending stiffness of RBCs increases over the storage process. RBCs stored for one week already started to show significantly higher stiffness than fresh RBCs, and stored RBC stiffness degraded faster in the last three weeks than in the first three weeks.