Red blood cell (RBC) deformability is greatly affected by the osmolality, and maximum deformability, which is determined as maximal elongation index (EI max ), is usually observed in isotonic conditions at high shear stresses (>20 Pa). Therefore, we examined osmotic RBC deformability over a range of shear stresses (0.5-20 Pa). We found that the RBC deformability at low shear stresses (1-3 Pa) was maximum in hypotonic conditions (225-250 mOsm/kg H 2 O), which is slightly lower than the normal range of osmolality in plasma (290-310 mOsm/kg H 2 O). The phenomenon that O max (the osmolality at EI max ) is dependent on applied shear stress could play an important role in microcirculation in which osmolality varies widely.

Single-walled carbon nanotubes (SWNTs) have been increasingly used in a variety of biomedical applications, such as in vivo delivery of drugs and tumor imaging. Potential exposure of SWNTs to human red blood cells (RBCs) may cause serious toxicity including alteration of mechanical properties of cells. The present study investigated the cellular response to exposure of SWNTs with measuring rheological characteristics of RBCs, including hemolysis, deformability, aggregation, and morphological changes. RBCs were exposed to two different dispersion-state samples (i.e. individual SWNTs and bundled SWNTs) in chitosan hydroxyphenyl acetamide (CHPA) solutions. The concentrations of SWNTs were carefully chosen to avoid any hemorheological alterations due to hemolysis. Rheological characteristics were measured using microfluidic-laser diffractometry and aggregometry. Our results show that the bundled SWNTs had higher hemolytic activity than did the individual SWNTs. RBC aggregation apparently decreased as the concentration of SWNTs or incubation time increased. Additionally, bundled SWNTs caused significant alterations in the shape and fusion of RBCs. In conclusion, bundled SWNTs were found to be more toxic than individual SWNTs. These results provide important insights into the interactions between RBCs and SWNTs and will facilitate assessment of the risk of nanomaterial toxicity of blood.