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Cell mechanics: principles, practices, and prospects.

Moeendarbary E, Harris AR - Wiley Interdiscip Rev Syst Biol Med (2014 Sep-Oct)

Bottom Line: Genetic mutations and pathogens that disrupt the cytoskeletal architecture can result in changes to cell mechanical properties such as elasticity, adhesiveness, and viscosity.Interdisciplinary research combining modern molecular biology with advanced cell mechanical characterization techniques now paves the way for furthering our fundamental understanding of cell mechanics and its role in development, physiology, and disease.We describe a generalized outline for measuring cell mechanical properties including loading protocols, tools, and data interpretation.We summarize recent advances in the field and explain how cell biomechanics research can be adopted by physicists, engineers, biologists, and clinicians alike.

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Four cell mechanical measurement techniques. (a) AFM: A laser beam is reflected off the back of the cantilever and collected by photodiodes. Interactions between the tip and the sample change the bending of the cantilever and consequently the reflection path of the laser beam which is precisely measured by the photodiodes. The bending of the cantilever is converted to force using its spring constant. A piezo-electric ceramic in a feedback loop is used to move the cantilever up and down to adjust bending of the cantilever and the applied force. (a-I) A confocal microscopy image shows the HeLa cell profile as the cell (green) is indented by a spherical bead (blue) attached to AFM cantilever. (a-II) A typical AFM force-indentation curve on cell. This curve can be fitted with an indentation model to estimate the cell elasticity. (Reprinted with permission from Ref 8. Copyright 2013 Nature Publishing Group.) (b) Optical tweezers: A small particle is stably trapped by a highly focused laser beam. The position of the optically trapped particle can be controlled by the movement of trap and small forces can be estimated from the changes in the displacement of the particle from the center of trap. (b-I, II) A tether extraction experiment involves pulling of an optically trapped bead attached to a cell membrane away from the cell. (b-II) The force-distance curve of tether extraction experiments on microglial cell. (Reprinted with permission from Ref 76. Copyright 2013 Public Library of Science.) (c) PTM: The micron or submicron beads disperse within the cytoplasm following injection into live cells. Using a high magnification objective the random spontaneous motions of the beads are captured with high spatial and temporal resolution. (c-I) 100 nm fluorescent beads injected into the cytoplasm of 3T3 fibroblasts. (c-II, III) The recorded time-dependent trajectories (c-II) of the beads are used to calculate their mean squared displacements (c-III) by which the nature of intracellular diffusion and microscopic viscoelastic properties of cellular environment can be studied. (Reprinted with permission from Ref 77. Copyright 2009 Public Library of Science.) (d) TFM: The cell is cultured onto (or within) a bead-embedded polymeric gel. Cellular contractions deform the gel and for a known gel elastic modulus the cellular traction forces can be calculated from the bead displacements. (d-I, II) Deformation vectors and traction stress field of fibroblast cultured on polyacrylamide gel were calculated by monitoring the displacement of fluorescent beads embedded in the gel. (Reprinted with permission from Ref 60. Copyright 2001 Cell Press.)
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fig04: Four cell mechanical measurement techniques. (a) AFM: A laser beam is reflected off the back of the cantilever and collected by photodiodes. Interactions between the tip and the sample change the bending of the cantilever and consequently the reflection path of the laser beam which is precisely measured by the photodiodes. The bending of the cantilever is converted to force using its spring constant. A piezo-electric ceramic in a feedback loop is used to move the cantilever up and down to adjust bending of the cantilever and the applied force. (a-I) A confocal microscopy image shows the HeLa cell profile as the cell (green) is indented by a spherical bead (blue) attached to AFM cantilever. (a-II) A typical AFM force-indentation curve on cell. This curve can be fitted with an indentation model to estimate the cell elasticity. (Reprinted with permission from Ref 8. Copyright 2013 Nature Publishing Group.) (b) Optical tweezers: A small particle is stably trapped by a highly focused laser beam. The position of the optically trapped particle can be controlled by the movement of trap and small forces can be estimated from the changes in the displacement of the particle from the center of trap. (b-I, II) A tether extraction experiment involves pulling of an optically trapped bead attached to a cell membrane away from the cell. (b-II) The force-distance curve of tether extraction experiments on microglial cell. (Reprinted with permission from Ref 76. Copyright 2013 Public Library of Science.) (c) PTM: The micron or submicron beads disperse within the cytoplasm following injection into live cells. Using a high magnification objective the random spontaneous motions of the beads are captured with high spatial and temporal resolution. (c-I) 100 nm fluorescent beads injected into the cytoplasm of 3T3 fibroblasts. (c-II, III) The recorded time-dependent trajectories (c-II) of the beads are used to calculate their mean squared displacements (c-III) by which the nature of intracellular diffusion and microscopic viscoelastic properties of cellular environment can be studied. (Reprinted with permission from Ref 77. Copyright 2009 Public Library of Science.) (d) TFM: The cell is cultured onto (or within) a bead-embedded polymeric gel. Cellular contractions deform the gel and for a known gel elastic modulus the cellular traction forces can be calculated from the bead displacements. (d-I, II) Deformation vectors and traction stress field of fibroblast cultured on polyacrylamide gel were calculated by monitoring the displacement of fluorescent beads embedded in the gel. (Reprinted with permission from Ref 60. Copyright 2001 Cell Press.)

Mentions: The atomic force microscope is a high resolution surface characterization technique, that has become rapidly adopted for imaging and mechanical characterization of a range of biological samples59 (Figure 4(a)). AFM measurements utilize a micron-sized tip connected to a micro-fabricated cantilever beam to deform and interact with the sample. It is capable of probing surface topography and interaction forces with subnano-meter and pico-newton resolution. One of the most widespread uses of AFM in cell mechanics is AFM force spectroscopy to measure cellular elasticity and rheology. To extract the cell elasticity, the tip of AFM cantilever is pressed against the cell while the force and the imposed cellular deformation are monitored. Considering the tip geometry and using an appropriate contact model, the elasticity of the cell can be computed from the measured force versus indentation data.6 The success of cellular force spectroscopy measurements is in part due to the ease of the measurements, good measurement throughput and commercial systems that are readily available. Furthermore, because the levels of force and deformation can be very accurately measured over time, AFM has been applied for a variety of rheological measurements. Using a feedback loop (incorporated into most commercial systems) levels of strain and stress can be controlled over time, following indentation of the cell via AFM cantilever. Stress-relaxation and creep experiments78,79 can be readily applied and oscillatory tests71 can also be conducted to measure time-dependent cellular mechanical properties.


Cell mechanics: principles, practices, and prospects.

Moeendarbary E, Harris AR - Wiley Interdiscip Rev Syst Biol Med (2014 Sep-Oct)

Four cell mechanical measurement techniques. (a) AFM: A laser beam is reflected off the back of the cantilever and collected by photodiodes. Interactions between the tip and the sample change the bending of the cantilever and consequently the reflection path of the laser beam which is precisely measured by the photodiodes. The bending of the cantilever is converted to force using its spring constant. A piezo-electric ceramic in a feedback loop is used to move the cantilever up and down to adjust bending of the cantilever and the applied force. (a-I) A confocal microscopy image shows the HeLa cell profile as the cell (green) is indented by a spherical bead (blue) attached to AFM cantilever. (a-II) A typical AFM force-indentation curve on cell. This curve can be fitted with an indentation model to estimate the cell elasticity. (Reprinted with permission from Ref 8. Copyright 2013 Nature Publishing Group.) (b) Optical tweezers: A small particle is stably trapped by a highly focused laser beam. The position of the optically trapped particle can be controlled by the movement of trap and small forces can be estimated from the changes in the displacement of the particle from the center of trap. (b-I, II) A tether extraction experiment involves pulling of an optically trapped bead attached to a cell membrane away from the cell. (b-II) The force-distance curve of tether extraction experiments on microglial cell. (Reprinted with permission from Ref 76. Copyright 2013 Public Library of Science.) (c) PTM: The micron or submicron beads disperse within the cytoplasm following injection into live cells. Using a high magnification objective the random spontaneous motions of the beads are captured with high spatial and temporal resolution. (c-I) 100 nm fluorescent beads injected into the cytoplasm of 3T3 fibroblasts. (c-II, III) The recorded time-dependent trajectories (c-II) of the beads are used to calculate their mean squared displacements (c-III) by which the nature of intracellular diffusion and microscopic viscoelastic properties of cellular environment can be studied. (Reprinted with permission from Ref 77. Copyright 2009 Public Library of Science.) (d) TFM: The cell is cultured onto (or within) a bead-embedded polymeric gel. Cellular contractions deform the gel and for a known gel elastic modulus the cellular traction forces can be calculated from the bead displacements. (d-I, II) Deformation vectors and traction stress field of fibroblast cultured on polyacrylamide gel were calculated by monitoring the displacement of fluorescent beads embedded in the gel. (Reprinted with permission from Ref 60. Copyright 2001 Cell Press.)
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Show All Figures
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fig04: Four cell mechanical measurement techniques. (a) AFM: A laser beam is reflected off the back of the cantilever and collected by photodiodes. Interactions between the tip and the sample change the bending of the cantilever and consequently the reflection path of the laser beam which is precisely measured by the photodiodes. The bending of the cantilever is converted to force using its spring constant. A piezo-electric ceramic in a feedback loop is used to move the cantilever up and down to adjust bending of the cantilever and the applied force. (a-I) A confocal microscopy image shows the HeLa cell profile as the cell (green) is indented by a spherical bead (blue) attached to AFM cantilever. (a-II) A typical AFM force-indentation curve on cell. This curve can be fitted with an indentation model to estimate the cell elasticity. (Reprinted with permission from Ref 8. Copyright 2013 Nature Publishing Group.) (b) Optical tweezers: A small particle is stably trapped by a highly focused laser beam. The position of the optically trapped particle can be controlled by the movement of trap and small forces can be estimated from the changes in the displacement of the particle from the center of trap. (b-I, II) A tether extraction experiment involves pulling of an optically trapped bead attached to a cell membrane away from the cell. (b-II) The force-distance curve of tether extraction experiments on microglial cell. (Reprinted with permission from Ref 76. Copyright 2013 Public Library of Science.) (c) PTM: The micron or submicron beads disperse within the cytoplasm following injection into live cells. Using a high magnification objective the random spontaneous motions of the beads are captured with high spatial and temporal resolution. (c-I) 100 nm fluorescent beads injected into the cytoplasm of 3T3 fibroblasts. (c-II, III) The recorded time-dependent trajectories (c-II) of the beads are used to calculate their mean squared displacements (c-III) by which the nature of intracellular diffusion and microscopic viscoelastic properties of cellular environment can be studied. (Reprinted with permission from Ref 77. Copyright 2009 Public Library of Science.) (d) TFM: The cell is cultured onto (or within) a bead-embedded polymeric gel. Cellular contractions deform the gel and for a known gel elastic modulus the cellular traction forces can be calculated from the bead displacements. (d-I, II) Deformation vectors and traction stress field of fibroblast cultured on polyacrylamide gel were calculated by monitoring the displacement of fluorescent beads embedded in the gel. (Reprinted with permission from Ref 60. Copyright 2001 Cell Press.)
Mentions: The atomic force microscope is a high resolution surface characterization technique, that has become rapidly adopted for imaging and mechanical characterization of a range of biological samples59 (Figure 4(a)). AFM measurements utilize a micron-sized tip connected to a micro-fabricated cantilever beam to deform and interact with the sample. It is capable of probing surface topography and interaction forces with subnano-meter and pico-newton resolution. One of the most widespread uses of AFM in cell mechanics is AFM force spectroscopy to measure cellular elasticity and rheology. To extract the cell elasticity, the tip of AFM cantilever is pressed against the cell while the force and the imposed cellular deformation are monitored. Considering the tip geometry and using an appropriate contact model, the elasticity of the cell can be computed from the measured force versus indentation data.6 The success of cellular force spectroscopy measurements is in part due to the ease of the measurements, good measurement throughput and commercial systems that are readily available. Furthermore, because the levels of force and deformation can be very accurately measured over time, AFM has been applied for a variety of rheological measurements. Using a feedback loop (incorporated into most commercial systems) levels of strain and stress can be controlled over time, following indentation of the cell via AFM cantilever. Stress-relaxation and creep experiments78,79 can be readily applied and oscillatory tests71 can also be conducted to measure time-dependent cellular mechanical properties.

Bottom Line: Genetic mutations and pathogens that disrupt the cytoskeletal architecture can result in changes to cell mechanical properties such as elasticity, adhesiveness, and viscosity.Interdisciplinary research combining modern molecular biology with advanced cell mechanical characterization techniques now paves the way for furthering our fundamental understanding of cell mechanics and its role in development, physiology, and disease.We describe a generalized outline for measuring cell mechanical properties including loading protocols, tools, and data interpretation.We summarize recent advances in the field and explain how cell biomechanics research can be adopted by physicists, engineers, biologists, and clinicians alike.

View Article: PubMed Central - PubMed

Show MeSH
Related in: MedlinePlus