The Influence of Physical and Physiological Cues on Atomic Force Microscopy-Based Cell Stiffness Assessment

Abstract

Atomic force microscopy can provide researchers not only high-resolution surface topography but also the mechanical properties of samples By using the contact the semi-contact and the non-contact operating model of atomic force microscopy several experiments such as indentation creep friction coefficient phase lag fatigue and so forth can be achieved In indentation experiment the mechanical properties of sample can be calculated by obtaining the relations between load the deflection of cantilever and the movement of cantilever In addition the atomic force microscopy allows sample to be assessed in the pseudo-physiological environment Hence the surface morphology and mechanical properties of cells which attached to the surface in normal culturing conditions can be obtained Amongst all mechanical properties cell elasticity has been abundantly used to represent the structural stiffness of cells in different conditions This study investigated whether physical or physiological cues affect cell elasticity in atomic force microscopy-based assessments The physical cues include the geometry of the atomic force microscopy tips the indenting force and the operating temperature of the atomic force microscopy All of these cues show a significant influence on the cell elasticity assessment Sharp atomic force microscopy tips create a two-fold increase in the value of the effective Young's modulus (Eeff) relative to that of the blunt tips Higher indenting force at the same loading rate generates higher estimated cell elasticity Increasing the operation temperature of the atomic force microscopy leads to decreases in the cell stiffness because the structure of actin filaments becomes disorganized The physiological cues include the presence of fetal bovine serum or extracellular matrix-coated surfaces the culture passage number and the culture density Both fetal bovine serum and the extracellular matrix are critical for cells to maintain the integrity of actin filaments and consequently exhibit higher elasticity Unlike primary cells mouse kidney progenitor cells can be passaged and maintain their morphology and elasticity for a very long period without a senescence phenotype Finally cell elasticity increases with increasing culture density only in Madin-Darby canine kidney (MDCK) epithelial cells In summary for researchers who use atomic force microscopy to assess cell elasticity the results of this study provide basic and significant quantitative results about the effects of physical and physiological cues on the measuring results of atomic force microscopy-based assessment Eventually the results of this study help the atomic force microscopy users to consider the effects of these physical and physiological cues consequently to reduce the possibility of misjudge the mechanical properties of cells

Date of Award	2015 Aug 12
Original language	English
Supervisor	Ming-Long Yeh (Supervisor)