Influence of storage and buffer composition on the mechanical behavior of flowing red blood cells

International audience; On-chip study of blood flow has emerged as a powerful tool to assess the contribution of each component of blood to its overall function. Blood has indeed many functions, from gas and nutrient transport to immune response and thermal regulation. Red blood cells play a central role therein, in particular through their specific mechanical properties, that directly influence pressure regulation, oxygen perfusion, or platelet and white cells segregation towards endothelial walls. As the bloom of in-vitro studies has led to the apparition of various storage and sample preparation protocols, we address the question of the robustness of the results involving cell mechanical behavior against this diversity. The effects of three conservation media (EDTA, citrate and glucose-albumin-sodium-phosphate) and storage time on the red blood cell mechanical behavior are assessed under different flow conditions: cell deformability by ektacytometry, shape recovery of cells flowing out of a microfluidic constriction, and cell flipping dynamics under shear flow. The impact of buffer solutions (phosphate-buffered saline and density-matched suspension using iodixanol/Optiprep) are also studied by investigating individual cell flipping dynamics, relative viscosity of cell suspensions and cell structuration under Poiseuille flow. Our results reveal that storing blood samples up to seven days after withdrawal and suspending them in adequate density-matched buffer solutions has in most experiments a moderate effect on the overall mechanical response, with a possible rapid evolution in the first three days after sample collection. SIGNIFICANCE Blood is in intimate contact with all organs in the body, supplying oxygen, nutrients and drugs while removing waste. It carries cells involved in immune response, wound repair and tumor dissemination. Blood is easily collected, revealing the presence of disease through biomarker analysis. It is storable and transfusable. Thus, blood is the subject of many in-vitro studies for research and medical purposes. Guidelines associated to sample preparation or storage conditions have been established, but these may affect its mechanical behavior. In this collaborative study, we provide new guidelines to minimize the impact of specific experimental requirements (e.g. density matching, blood freshness) by focusing on the single or collective motion of red blood cells in a large range of flow conditions.