Taiwan News , Taiwan News
2013-09-16 01:45 PM
The morphology and deformability of human red blood cells (RBCs) are critical for their physiological functions of oxygen transport and other tasks. Each RBC circulates through the entire body for almost 50,000 cycles, passing through capillaries with diameters as small as 3 microns during their 120-day lifespan. RBCs are able to withstand the shear stress during circulation owing to their unique elastic and viscous properties, jointly known as viscoelasticity. The viscoelasticity of not only the RBCs but also many other biological cells play a crucial role in their physiological and pathological functions such as cell division, proliferation, differentiation, migration, invasion, gene expression, and cancer cells metastasis.
Several methods have been developed to apply an external force to a biological cell to measure the dynamic deformation of the cell to probe its mechanical response. In parallel to these so called active methods, a simple passive method is to embed one or more micron-size particles in the test sample of interest as well as to track and analyze the Brownian motion of the particles from which the viscoelasticity of the sample can be deduced.
From a much broader perspective, the measurement of viscoelasticity as a function of frequency (technically known as rheology) is a convenient way to quantify the mechanical properties of a material (or a system) in response to external stimuli. Rheology at a spatial scale on the order of a micron to a few microns is known as microrheology. In addition, the applications of microrheology to measure the viscoelastic properties of biological samples, including living biological cells, is known as bio-microhreology.
In collaboration with Prof. Shu Chien and his colleagues at UCSD, a research group led by Prof. Arthur Chiou at the Institute of Biophotonics and the Biophotonics and Molecular Imaging Research Center (BMIRC) in National Yang-Ming University – which is a partner university of the University System of Taiwan – has been focusing on both active and passive microrheology to measure the viscoelasticity of a wide range of biological samples, including red blood cells and synovial fluid, to find possible correlation with their physiological functions and related pathological pathways. One of the active microrehological methods adapted by the group is to use a laser tweezers system (i.e., a highly focusing laser spot which can be scanned with high-precision and high-speed) to either trap and stretch individual human red blood cells (http://www.youtube.com/watch?v=yfJowMyYpWI&feature=youtu.be) or to trap and oscillate a micron-size particle either inside a cell or attach to a cell membrane to measure the viscoelasticity of the cell.
In a recent paper published in the Journal of Biophotonics (J. Biophotonics 1–9 (2013) / DOI 10.1002), the YMU-UCSD team reported an exciting finding that when a human RBC, in its intact biconcave morphology, was stretched by an optical stretching force approximated by a step function (generated via a specific method of optical tweezers, known as “jumping optical tweezers”, pioneered by the group), the fractional deformation as a function of time followed a simple exponential function which can be fitted to a theoretical model (known as the Kelvin solid model) to deduce its elasticity and viscosity.
Prof. Arthur Chiou commented that these experimental measurements in conjunction with theoretical results would enable us to characterize the mechanical properties of individual human red blood cells in terms of their elasticity (or Young’s modulus) and viscosity under different physical and chemical environments, as well as to study possible correlation of the mechanical properties of RBCs with RBCs-related diseases – in their long journey through the human bodies.
deformability [n.] 可變形性
proliferation [n.] 增殖
Brownian [n.] 布朗運動
viscoelasticity [n.] 黏彈性
rheology [n.] 流變學