Red blood cells (RBCs) are subjected to recurrent changes in shear stress and oxygen tension during blood circulation. The cyclic shear stress has been identified as an important factor that alone can weaken cell mechanical deformability. The effects of cyclic hypoxia on cellular biomechanics have yet to be fully investigated. As the oxygen affinity of hemoglobin plays a key role in the biological function and mechanical performance of RBCs, the repeated transitions of hemoglobin between its R (high oxygen tension) and T (low oxygen tension) states may impact their mechanical behavior. The present study focuses on developing a novel microfluidic-based assay for characterization of the effects of cyclic hypoxia on cell biomechanics. The capability of this assay is demonstrated by a longitudinal study of individual RBCs in health and sickle cell disease subjected to cyclic hypoxia conditions of various durations and levels of low oxygen tension. The viscoelastic properties of cell membranes are extracted from tensile stretching and relaxation processes of RBCs induced by the electrodeformation technique. Results demonstrate that cyclic hypoxia alone can significantly reduce cell deformability, similar to the fatigue damage accumulated through cyclic mechanical loading. RBCs affected by sickle cell disease are less deformable (significantly higher membrane shear modulus and viscosity) than normal RBCs. The fatigue resistance of sickle RBCs to the cyclic hypoxia challenge is significantly inferior to that of normal RBCs, and this trend is more significant in mature erythrocytes of sickle cells. When the oxygen affinity of sickle hemoglobin is enhanced by anti-sickling drug treatment of 5-hydroxymethyl-2-furfural (5-HMF), sickle RBCs show ameliorated resistance to fatigue damage induced by cyclic hypoxia. These results indicate an important biophysical mechanism underlying RBC senescence in which the cyclic hypoxia challenge alone can lead to mechanical degradation of the RBC membrane. We envision that the application of this assay can be further extended to RBCs in other blood diseases and other cell types.

中文翻译：

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反复缺氧情况下红细胞变形能力受损的单细胞特征体外测定

红细胞 (RBC) 在血液循环过程中会受到剪切应力和氧张力的反复变化。循环剪切应力已被认为是单独削弱细胞机械变形能力的重要因素。周期性缺氧对细胞生物力学的影响尚未得到充分研究。由于血红蛋白的氧亲和力在红细胞的生物功能和机械性能中起着关键作用，血红蛋白在 R（高氧张力）和 T（低氧张力）状态之间的反复转变可能会影响其机械行为。本研究的重点是开发一种新型的基于微流体的测定法，用于表征循环缺氧对细胞生物力学的影响。通过对处于不同持续时间和低氧张力水平的循环缺氧条件下的健康和镰状细胞病个体红细胞的纵向研究证明了该测定的能力。细胞膜的粘弹性特性是从电形成技术引起的红细胞的拉伸和松弛过程中提取的。结果表明，仅循环缺氧就可以显着降低细胞变形能力，类似于循环机械载荷累积的疲劳损伤。受镰状细胞病影响的红细胞比正常红细胞变形更小（膜剪切模量和粘度显着更高）。镰状红细胞对周期性缺氧挑战的抗疲劳能力明显劣于正常红细胞，且这种趋势在镰状细胞的成熟红细胞中更为显着。当通过 5-羟甲基-2-糠醛 (5-HMF) 的抗镰状药物治疗增强镰状血红蛋白的氧亲和力时，镰状红细胞对循环缺氧引起的疲劳损伤的抵抗力得到改善。这些结果表明了红细胞衰老的一个重要的生物物理机制，其中循环缺氧挑战本身就可以导致红细胞膜的机械降解。我们预计该测定的应用可以进一步扩展到其他血液疾病和其他细胞类型中的红细胞。