Mechanical property quantification of endothelial cells using scanning acoustic microscopy A. Shelke 1 , S. Brand 2 ,T. Kundu 3 , J. Bereiter-Hahn 1 , C. Blase 1 1 Institute for Cell Biology and Neurosciences Kinematic Cell Research Group, Goethe University, Frankfurt am Main, Germany 2 Fraunhofer Institute of Material Mechanics, Department of Microelectronics and Microsystems, Halle/S. Germany 3 Department of Civil and Engineering Mechanics, University of Arizona, Tucson, USA ABSTRACT The mechanical properties of cells reflect dynamic changes of cellular organization which occur during physiologic activities like cell movement, cell volume regulation or cell division. Thus the study of cell mechanical properties can yield important information for understanding these physiologic activities. Endothelial cells form the thin inner lining of blood vessels in the cardiovascular system and are thus exposed to shear stress as well as tensile stress caused by the pulsatile blood flow. Endothelial dysfunction might occur due to reduced resistance to mechanical stress and is an initial step in the development of cardiovascular disease like, e.g., atherosclerosis. Therefore we investigated the mechanical properties of primary human endothelial cells (HUVEC) of different age using scanning acoustic microscopy at 1.2 GHz. The HUVECs are classified as young (t D < 90 h) and old (t D > 90 h) cells depending upon the generation time for the population doubling of the culture (t D ). Longitudinal sound velocity and geometrical properties of cells (thickness) were determined using the material signature curve V(z) method for variable culture condition along spatial coordinates. The plane wave technique with normal incidence is assumed to solve two-dimensional wave equation. The size of the cells is modeled using multilayered (solid-fluid) system. The propagation of transversal wave and surface acoustic wave are neglected in soft matter analysis. The biomechanical properties of HUVEC cells are quantified in an age dependent manner. Key words: Acoustic microscopy, Cell aging, HUVEC, Plane wave theory, Material signature curve 1. INTRODUCTION Cellular components (cytoplasm and organelles) show a viscoelastic material behavior. The mechanical properties of cells have been evaluated using local aspiration of cytoplasm using micropipette [1, 2], magnetometry [3], and scanning force microscopy [4, 5]. However, above techniques is invasive involving imposition of known deformation and measuring the force to derive stress-strain curves of cytoplasm. Scanning acoustic microscopy (SAM) is a noninvasive imaging technique suitable for the study of living cells. SAM is suitable for studying cell mobility and dynamics. The SAM provides fast and reliable measure of morphology and cell movement with spatial resolution of 3 m 2 . The biomechanical properties of cells and tissues have been investigated using shear ultrasonic waves [6] and longitudinal waves [7]. Previous studies on cells have dealt with cell thickness measurement and morphological characterization [8-12]. The speed of sound in the cells has been measured using interference ring [11] and phase contrast imaging [13]. Kundu et. al, 2000 has used plane wave ultrasonic wave theory for evaluating speed of sound, thickness profile and attenuation of the cell using voltage variation with defocusing distance and frequency [14]. In the present paper, Human umbilical vein endothelial cells (HUVEC) were cultured. The HUVEC cells are used as a model to study the changes in the biomechanical property with aging. The aging of cells induces changes in physiological, morphological and biomechanical properties. The classification of age group of cell is matter of definition. In the present study, cells with a doubling time of 24-90 hrs are defined as young cells and greater than 90 hours are defined as old cells. The young and old HUVEC cells were cultured on glass slides and fixed using formaldehyde. SAM microscopy was performed at 1.2 GHz and imaging was performed at variable Health Monitoring of Structural and Biological Systems 2012, edited by Tribikram Kundu, Proc. of SPIE Vol. 8348, 83481T · © 2012 SPIE · CCC code: 0277-786X/12/$18 · doi: 10.1117/12.917512 Proc. of SPIE Vol. 8348 83481T-1 Downloaded From: http://spiedigitallibrary.org/ on 02/08/2014 Terms of Use: http://spiedl.org/terms