Studying On The Elasticity Of Red Blood Cell In Vitro By Optical Tweezers

The elasticity of red blood cell(RBC)is a critical mechanical index for evaluating the activity of RBC and the blood quality,so study of the inherent mechanism for RBC elasticity transformation is attention-getting all along.This research characterizes the in vitro RBC elasticity change through cell membrane shear modulus measurement and direct stretching respectively,using the acousto-optic deflector(AOD)scanning optical tweezers technology.Biochemical and biophysical mechanisms of in vitro RBC decay are investigated by both experiment and Finite Element Method(FEM)simulation.Firstly,this paper proposes an optimized measurement method of RBC membrane shear modulus incorporating AOD scanning optical tweezers system innovatively.By use of this method,membrane shear moduli of RBCs with different in vitro times were determined.The initial fresh RBCs' membrane shear modulus measured was 10.95 ± 2.67 ?N/m.Then RBCs' membrane shear moduli would increase,which reveals that RBCs elasticity declined by degrees with in vitro time extension.At same time,RBCs' size would decrease to a steady value during the subsequent preservation period.The analysis considered that the S-nitrosylation change of spectrin related to RBC elasticity is the main reason for this decline.As proof,semiquantitative measurements of S-nitrosothiol content in blood using fluorescent spectrometry during in vitro storage show that RBCs elasticity change is positively associated with the S-nitrosylation content of blood.Further analysis shows that the diminished activity of the nitric oxide synthase makes the S-nitrosylation of in vitro blood weaker gradually.Then S-nitrosylation effect of spectrin fades,elasticity of the in vitro RBC becomes worse.Secondly,a double parameters(membrane thickness h and membrane shear modulus H)erythrocyte shell model was built to complete the finite element method(FEM)simulation of the whole process of RBC linear stretching in this paper,from the angle of elastic mechanics theory.Through discussing the structure of RBC and comparing the simulation results with experimental data,it is found that this RBC shell model based on linear elasticity material was enough to analysis the mechanical change states of erythrocytes with the FEM.The evolution law of cell membrane thickness and cell elasticity was obtained.During the in vitro process,RBC membrane thickness is decreasing,contrary to the membrane shear modulus change.The analysis express that the protein of RBC membrane skeleton and lipid bilayer are decomposed partly during storage,which lead to thinner erythrocyte membrane and low bending resistance.Finally,this paper reports an exploratory investigation on the changes regulation of the red blood cells irradiated by laser.It provides valuable reference for laser physical therapy with different wavelength and power.RBCs' elasticity changes were measured by the direct drawing method without handle under 300 mW laser irradiation of 1064 nm wavelength.It found that there were no significant changes in the morphology,size and elasticity of the control group.The RBCs irradiated by laser also didn't change in the first 15 minutes.However the maximum relative elongation of RBC decreased rapidly from 15 to 35 min.The RBCs size tended to be constant after a small decrease from 15 min to 25 min due to the specific adherence force or the balance between RBC spreading and shrink.It is analyzed that the biological heat effect of 1064 nm laser accelerates the decay and death of RBC.These study results provide reasonable explanations for the decay and biological effect of RBCs in vitro,and play a important guidance role for the detection of RBCs quality and the safety of blood transfusion.