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Atomic force microscopy probing in the measurement of cell mechanics.

Kirmizis D, Logothetidis S - Int J Nanomedicine (2010)

Bottom Line: Atomic force microscope (AFM) has been used incrementally over the last decade in cell biology.Beyond its usefulness in high resolution imaging, AFM also has unique capabilities for probing the viscoelastic properties of living cells in culture and, even more, mapping the spatial distribution of cell mechanical properties, providing thus an indirect indicator of the structure and function of the underlying cytoskeleton and cell organelles.AFM measurements have boosted our understanding of cell mechanics in normal and diseased states and provide future potential in the study of disease pathophysiology and in the establishment of novel diagnostic and treatment options.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Laboratory for Thin Films-Nanosystems and Nanometrology, Aristotle University, Thessaloniki, Greece. dkirmizi@physics.auth.gr

ABSTRACT
Atomic force microscope (AFM) has been used incrementally over the last decade in cell biology. Beyond its usefulness in high resolution imaging, AFM also has unique capabilities for probing the viscoelastic properties of living cells in culture and, even more, mapping the spatial distribution of cell mechanical properties, providing thus an indirect indicator of the structure and function of the underlying cytoskeleton and cell organelles. AFM measurements have boosted our understanding of cell mechanics in normal and diseased states and provide future potential in the study of disease pathophysiology and in the establishment of novel diagnostic and treatment options.

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Related in: MedlinePlus

A nonlinear stress–strain relation (solid line) characterizes most biological soft tissues, with a viscoelastic hysteresis between loading and unloading segments of the curve, as opposed to the linear stress–strain curve of an idealized elastic material which is characterized by the Young’s modulus obtained from the slope of the line.
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f2-ijn-5-137: A nonlinear stress–strain relation (solid line) characterizes most biological soft tissues, with a viscoelastic hysteresis between loading and unloading segments of the curve, as opposed to the linear stress–strain curve of an idealized elastic material which is characterized by the Young’s modulus obtained from the slope of the line.

Mentions: Knowledge of the relation of cell deformation (ie, strain) to internal forces and externally applied loads (ie, stress) acting on the cell is a sine qua non for the study of cell mechanics. As long as stiffness, defined as the slope of the force (F) -deformation (ΔL) curve, depends on geometric characteristics, which vary at each sample and testing device used, it is far better to study the related normalized quantities stress (σ = F/A) and strain ɛ = (ΔL/Lo), which are independent of size or geometry and rather reflect the underlying properties of the cell. The standard constitutive relation for solid materials is Hooke’s law, which states that stress is proportional to strain (σ = Eɛ), where E is the constant of proportionality called the Young’s modulus. Materials that follow Hooke’s law (eg, rubber, steel, bone) are called linear elastic. On the other hand, Newtonian fluids (eg, water, blood plasma) follow another similar constitutive relation for fluid materials which states that stress is proportional to the rate of strain (σ = μdɛ/dt), where the constant of proportionality, μ, is called the viscosity. However, being viscoelastic materials and characterized by heterogeneity, anisotropy, a nonlinear stress–strain relationship and hysteresis between the loading and unloading portions of the stress–strain curve, most soft biological tissues as well as individual cells are more complex than these simple idealized materials (Figure 2).28 Within cells the aqueous gel nature of the cytoplasm,29,30 heterogeneously distributed actin filaments, intermediate filaments, and microtubules,31 cell adhesiveness,32 or the presence of nucleus and other organelles33,34 are important factors that affect the mechanical properties of the cells. It is clear, therefore, that the mechanical behavior of such tissues and cells is not defined adequately by Young’s modulus. Constitutive equations that combine elastic and viscous properties are required to mathematically model their stress–strain behavior. Consequently, reported measurements of the Young’s modulus of cells must be interpreted with caution.


Atomic force microscopy probing in the measurement of cell mechanics.

Kirmizis D, Logothetidis S - Int J Nanomedicine (2010)

A nonlinear stress–strain relation (solid line) characterizes most biological soft tissues, with a viscoelastic hysteresis between loading and unloading segments of the curve, as opposed to the linear stress–strain curve of an idealized elastic material which is characterized by the Young’s modulus obtained from the slope of the line.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2865008&req=5

f2-ijn-5-137: A nonlinear stress–strain relation (solid line) characterizes most biological soft tissues, with a viscoelastic hysteresis between loading and unloading segments of the curve, as opposed to the linear stress–strain curve of an idealized elastic material which is characterized by the Young’s modulus obtained from the slope of the line.
Mentions: Knowledge of the relation of cell deformation (ie, strain) to internal forces and externally applied loads (ie, stress) acting on the cell is a sine qua non for the study of cell mechanics. As long as stiffness, defined as the slope of the force (F) -deformation (ΔL) curve, depends on geometric characteristics, which vary at each sample and testing device used, it is far better to study the related normalized quantities stress (σ = F/A) and strain ɛ = (ΔL/Lo), which are independent of size or geometry and rather reflect the underlying properties of the cell. The standard constitutive relation for solid materials is Hooke’s law, which states that stress is proportional to strain (σ = Eɛ), where E is the constant of proportionality called the Young’s modulus. Materials that follow Hooke’s law (eg, rubber, steel, bone) are called linear elastic. On the other hand, Newtonian fluids (eg, water, blood plasma) follow another similar constitutive relation for fluid materials which states that stress is proportional to the rate of strain (σ = μdɛ/dt), where the constant of proportionality, μ, is called the viscosity. However, being viscoelastic materials and characterized by heterogeneity, anisotropy, a nonlinear stress–strain relationship and hysteresis between the loading and unloading portions of the stress–strain curve, most soft biological tissues as well as individual cells are more complex than these simple idealized materials (Figure 2).28 Within cells the aqueous gel nature of the cytoplasm,29,30 heterogeneously distributed actin filaments, intermediate filaments, and microtubules,31 cell adhesiveness,32 or the presence of nucleus and other organelles33,34 are important factors that affect the mechanical properties of the cells. It is clear, therefore, that the mechanical behavior of such tissues and cells is not defined adequately by Young’s modulus. Constitutive equations that combine elastic and viscous properties are required to mathematically model their stress–strain behavior. Consequently, reported measurements of the Young’s modulus of cells must be interpreted with caution.

Bottom Line: Atomic force microscope (AFM) has been used incrementally over the last decade in cell biology.Beyond its usefulness in high resolution imaging, AFM also has unique capabilities for probing the viscoelastic properties of living cells in culture and, even more, mapping the spatial distribution of cell mechanical properties, providing thus an indirect indicator of the structure and function of the underlying cytoskeleton and cell organelles.AFM measurements have boosted our understanding of cell mechanics in normal and diseased states and provide future potential in the study of disease pathophysiology and in the establishment of novel diagnostic and treatment options.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Laboratory for Thin Films-Nanosystems and Nanometrology, Aristotle University, Thessaloniki, Greece. dkirmizi@physics.auth.gr

ABSTRACT
Atomic force microscope (AFM) has been used incrementally over the last decade in cell biology. Beyond its usefulness in high resolution imaging, AFM also has unique capabilities for probing the viscoelastic properties of living cells in culture and, even more, mapping the spatial distribution of cell mechanical properties, providing thus an indirect indicator of the structure and function of the underlying cytoskeleton and cell organelles. AFM measurements have boosted our understanding of cell mechanics in normal and diseased states and provide future potential in the study of disease pathophysiology and in the establishment of novel diagnostic and treatment options.

Show MeSH
Related in: MedlinePlus