Abstract
We have developed a novel experimental set-up that simultaneously, (i) applies static and dynamic deformations to adherent cells in culture, (ii) allows the visualization of cells under fluorescence microscopy, and (iii) allows atomic force microscopy nanoindentation measurements of the mechanical properties of the cells. The cell stretcher device relies on a dielectric elastomer film that can be electro-actuated and acts as the cell culture substrate. The shape and position of the electrodes actuating the film can be controlled by design in order to obtain specific deformations across the cell culture chamber. By using optical markers we characterized the strain fields under different electrode configurations and applied potentials. The combined setup, which includes the cell stretcher device, an atomic force microscope, and an inverted optical microscope, can assess in situ and with sub-micron spatial resolution single cell topography and elasticity, as well as ion fluxes, during the application of static deformations. Proof of performance on fibroblasts shows a reproducible increase in the average cell elastic modulus as a response to applied uniaxial stretch of just 4%. Additionally, high resolution topography and elasticity maps on a single fibroblast can be acquired while the cell is deformed, providing evidence of long-term instrumental stability. This study provides a proof-of-concept of a novel platform that allows in situ and real time investigation of single cell mechano-transduction phenomena with sub-cellular spatial resolution.
Highlights
Mechanical stretch induces a wide range of cellular responses, including cytoskeletal remodeling, synthesis of extracellular matrix proteins, and altered expression of genes [1].Cell reorientation is the most visible effect of stretching [2], and it is accompanied by a pronounced reorganization of the actin cytoskeleton [3], which can produce changes in cellular stiffness
Stretching experiments have greatly contributed to the basic understanding of mechanotransduction and mechanobiology, but most of them rely on devices that produce over-simplified uniaxial or equi-biaxial strain fields that may not reproduce complex in-vivo strain fields, which are often dynamic and, more importantly, multi-axial
We denominate the area covered by the electrode as the active zone, and the circular area in the center of the disk that is not covered by the electrodes, the passive zone
Summary
Mechanical stretch induces a wide range of cellular responses, including cytoskeletal remodeling, synthesis of extracellular matrix proteins, and altered expression of genes [1].Cell reorientation is the most visible effect of stretching [2], and it is accompanied by a pronounced reorganization of the actin cytoskeleton [3], which can produce changes in cellular stiffness. The deformation-dependent increase in stiffness has been interpreted as an evidence of the nonlinear elastic response of actin cytoskeletal networks. There are commercial devices, such as the Flexcell® Tension System (Flexcell International Corp., Burlington, NC, USA), that use vacuum pressure to stretch a circular silicone membrane over a fixed loading post, and others that utilize dual motors to biaxially stretch square or rectangular wells. All these devices require substrates that allow for a homogeneous and well-defined strain distribution across the cell culture area, as well as for the application of deformation cycles [7]. Most devices suffer from stray deformations, which result in an additional and unwanted strain component, perpendicular to the stretching direction in uniaxial stretching experiments
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