Opposing views on tensegrity as a structural framework for understanding cell mechanics

Structural response of microtubule and actin cytoskeletons to direct intracellular load

Microtubule and actin are the two major cytoskeletal polymers that form organized functional structures in the interior of eukaryotic cells. Although the structural mechanics of the cytoskeleton has been extensively studied by direct manipulations in in vitro reconstitution systems, such unambiguous characterizations inside the living cell are sparse. Here, we report a comprehensive analysis of how the microtubule and actin cytoskeletons structurally respond to direct intracellular load. Ferrofluid-based intracellular magnetic tweezers reveal rheological properties of the microtubule complex primarily determined by filamentous actin. The strain fields of the microtubule complex and actin meshwork follow the same scaling, suggesting that the two cytoskeletal systems behave as an integrated elastic body. The structural responses of single microtubules to contact and remote forces further evidence that the individual microtubules are enclosed by the elastic medium of actin. These results, directly characterizing the microtubule and actin cytoskeletons as an interacting continuum throughout the cytoplasm, serve as a cornerstone for the physical understanding of intracellular organization.

Piezoelectricity and flexoelectricity in biological cells: the role of cell structure and organelles

Living tissues experience various external forces on cells, influencing their behaviour, physiology, shape, gene expression, and destiny through interactions with their environment. Despite much research done in this area, challenges remain in our better understanding of the behaviour of the cell in response to external stimuli, including the arrangement, quantity, and shape of organelles within the cell. This study explores the electromechanical behaviour of biological cells, including organelles like microtubules, mitochondria, nuclei, and cell membranes. A two-dimensional bio-electromechanical model for two distinct cell structures has been developed to analyze the behavior of the biological cell to the external electrical and mechanical responses. The piezoelectric and flexoelectric effects have been included via multiphysics coupling for the biological cell. All the governing equations have been discretized and solved by the finite element method. It is found that the longitudinal stress is absent and only the transverse stress plays a crucial role when the mechanical load is imposed on the top side of the cell through compressive displacement. The impact of flexoelectricity is elucidated by introducing a new parameter called the maximum electric potential ratio ( V R , max ). It has been found that V R , max depends upon the orientation angle and shape of the microtubules. The magnitude of V R , max exhibit huge change when we change the shape and orientation of the organelles, which in some cases (boundary condition (BC)-3) can reach to three times of regular shape organelles. Further, the study reveals that the number of microtubules significantly impacts effective elastic and piezoelectric coefficients, affecting cell behavior based on structure, microtubule orientation, and mechanical stress direction. The insight obtained from the current study can assist in advancements in medical therapies such as tissue engineering and regenerative medicine.

In Situ Mechanics of the Cytoskeleton

Not only for man-made architecture but also for living cells, the relationship between force and structure is a fundamental properties that governs their mechanical behaviors. However, our knowledge of the mechanical properties of intracellular structures is very limited because of the lack of direct measurement methods. We established high-force intracellular magnetic tweezers that can generate calibrated forces up to 10 nN, enabling direct force measurements of the cytoskeleton. Using this method, we show that the strain field of the microtubule and actin meshwork follow the same scaling, suggesting that the two cytoskeletal systems behave as an integrated elastic body. Furthermore, quantification of structural response of single microtubules demonstrates that microtubules are enclosed by the elastic medium of filamentous actin. Our results defining the force-structure relationship of the cytoskeleton serve as a framework to understand cellular behaviors by direct intracellular mechanical measurement.

Systematic analysis of constitutive models of brain tissue materials based on compression tests

It's crucial to understand the biomechanical properties of brain tissue to comprehend the potential mechanisms of traumatic brain injury. This study, distinct from homogeneous models, integrates axonal coupling in both axial and transverse compressive experiments within a continuum mechanics framework to capture its intricate mechanical behaviors. Fresh porcine brains underwent unconfined compression at strain rates of 0.001/s and 0.1/s to 0.3 strain, allowing for a comprehensive statistical analysis of the directional, regional, and strain-rate-dependent mechanical properties of brain tissue. The established constitutive model, fitted to experimental data, delineates material parameters providing intuitive insights into the stiffness of gray/white matter isotropic matrices and neural fibers. Additionally, it predicts the mechanical performance of white matter matrix and axonal fibers under compressive loading. Results reveal that gray matter is insensitive to loading direction, exhibiting insignificant stiffness variations within regions. White matter, however, displays no significant differences in mechanical properties under axial and transverse loading, with an overall higher average stress than gray matter and a more pronounced strain-rate effect. Stress-strain curves indicate that, under axial compression, white matter axons primarily resist the load before transitioning to a matrix-dominated response. Under transverse loading, axonal fibers exhibit weaker resistance to lateral pressure. The mechanical behavior of brain tissue is highly dependent on loading rate, region, direction, and peak strain. This study, by combining experimentation with phenomenological modeling, elucidates certain phenomena, contributing valuable insights for the development of precise computational models.

From tensegrity to human organs-on-chips: implications for mechanobiology and mechanotherapeutics

The field of mechanobiology, which focuses on the key role that physical forces play in control of biological systems, has grown enormously over the past few decades. Here, I provide a brief personal perspective on the development of the tensegrity theory that contributed to the emergence of the mechanobiology field, the key role that crossing disciplines has played in its development, and how it has matured over time. I also describe how pursuing questions relating to mechanochemical transduction and mechanoregulation can lead to the creation of novel technologies and open paths for development of new therapeutic strategies for a broad range of diseases and disorders.

Valve interstitial cells under impact load, a mechanobiology study

Understanding the relationship between mechanobiology and the biosynthetic activities of the valve interstitial cells (VICs) in health and disease under severe dynamic loading conditions is of particular interest. The purpose of this study is to further understand the mechanobiology of heart valve leaflet tissue and the VICs under impact forces. Two novel computational and experimental platforms were developed to study the effect of impact load on the VICs to monitor for apoptosis. The first objective was to design and develop an apparatus to experimentally study viability (apoptosis) of the porcine heart valve leaflet tissue VICs in the aortic position under controlled impact forces. Apoptosis was assessed based on terminal transferase dUTP nick end-labelling (TUNEL) assay. The second objective was to develop a computational platform to estimate the stress and strain fields in the vicinity of VICs when the tissue experiences impact forces. A nonlinear finite element (FE) model with an anisotropic, hyperelastic and heterogeneous material model for the matrix and cells was developed. Preliminary results confirm that interstitial cells are successfully resistant to impact loads up to 30 times more than normal physiological conditions. Additionally, the structure and composition of heart valve leaflet tissue provides a mechanical shield for VICs protecting them from excessive mechanical forces such as impact loads. Although, the entire tissue may experience excessive stresses, which may lead to structural damage, the stresses around and near VICs remain consistency low. Results of this study may be used for heart valve leaflet tissue-engineering, as well as further understanding the mechanobiology of the VICs in health and disease.

Bidirectional hyperelastic characterization of brain white matter tissue

Biomechanical study of brain injuries originated from mechanical damages to white matter tissue requires detailed information on mechanical characteristics of its main components, the axonal fibers and extracellular matrix, which is very limited due to practical difficulties of direct measurement. In this paper, a new theoretical framework was established based on microstructural modeling of brain white matter tissue as a soft composite for bidirectional hyperelastic characterization of its main components. First the tissue was modeled as an Ogden hyperelastic material, and its principal Cauchy stresses were formulated in the axonal and transverse directions under uniaxial and equibiaxial tension using the theory of homogenization. Upon fitting these formulae to the corresponding experimental test data, direction-dependent hyperelastic constants of the tissue were obtained. These directional properties then were used to estimate the strain energy stored in the homogenized model under each loading scenario. A new microstructural composite model of the tissue was also established using principles of composites micromechanics, in which the axonal fibers and surrounding matrix are modeled as different Ogden hyperelastic materials with unknown constants. Upon balancing the strain energies stored in the homogenized and composite models under different loading scenarios, fully coupled nonlinear equations as functions of unknown hyperelastic constants were derived, and their optimum solutions were found in a multi-parametric multi-objective optimization procedure using the response surface methodology. Finally, these solutions were implemented, in a bottom-up approach, into a micromechanical finite element model to reproduce the tissue responses under the same loadings and predict the tissue responses under unseen non-equibiaxial loadings. Results demonstrated a very good agreement between the model predictions and experimental results in both directions under different loadings. Moreover, the axonal fibers with hyperelastic characteristics stiffer than the extracellular matrix were shown to play the dominant role in directional reinforcement of the tissue.

A century of exercise physiology: key concepts in muscle cell volume regulation

Skeletal muscle cells can both gain and lose volume during periods of exercise and rest. Muscle cells do not behave as perfect osmometers because the cell volume changes are less than predicted from the change in extracellular osmolality. Therefore, there are mechanisms involved in regulating cell volume, and they are different for regulatory volume decreases and regulatory volume increases. Also, after an initial rapid change in cell volume, there is a gradual and partial recovery of cell volume that is effected by ion and water transport mechanisms. The mechanisms have been studied in non-contracting muscle cells, but remain to be fully elucidated in contracting muscle. Changes in muscle cell volume are known to affect the strength of contractile activity as well as anabolic/catabolic signaling, perhaps indicating that cell volume should be a regulated variable in skeletal muscle cells. Muscles contracting at moderate to high intensity gain intracellular volume because of increased intracellular osmolality. Concurrent increases in interstitial (extracellular) muscle volume occur from an increase in osmotically active molecules and increased vascular filtration pressure. At the same time, non-contracting muscles lose cell volume because of increased extracellular (blood) osmolality. This review provides the physiological foundations and highlights key concepts that underpin our current understanding of volume regulatory processes in skeletal muscle, beginning with consideration of osmosis more than 200 years ago and continuing through to the process of regulatory volume decrease and regulatory volume increase.

Finite element analysis of the influence of cyclic strain on cells anchored to substrates with varying properties

The response of cytoskeleton to mechanical cues plays a pivotal role in understanding several aspects of cellular growth, migration, and cell-cell and cell-matrix interactions under normal and diseased conditions. Finite element analysis (FEA) has become a powerful computational technique to study the response of cytoskeleton in the maintenance of overall cellular mechanics. With the revelation of role of external mechanical microenvironment on cell mechanics, FEA models have also been developed to simulate the effect of substrate stiffness on the mechanical properties of cancer cells. However, the models developed so far model cellular response under static mode, whereas in physiological condition, cells always experience dynamic loading conditions. To develop a more accurate model of cell-extracellular matrix (ECM) interactions, this paper models the cytoskeleton and other parts of the cell by beam and solid elements respectively, assuming spherical morphology of the cell. The stiffness and roughness of extracellular matrix were varied. Furthermore, static and dynamic sinusoidal loads were applied through a flat plate indenter on the cell along with providing sinusoidal strain at the substrate. It is observed that due to axial loading, cell reaches a plastic region, and when the sinusoidal loading is added to the axial load, the cell experiences permanent deformation. Degradation of the cytoskeleton elements and a physiologically more relevant spherical cap shape of the cell were also considered during the analysis. This study suggests that asperity topology of the substrate and indirect cyclic load can play a significant role in the shape alterations and motion of a cell.

In silico stress fibre content affects peak strain in cytoplasm and nucleus but not in the membrane for uniaxial substrate stretch

Existing in silico models for single cell mechanics feature limited representations of cytoskeletal structures that contribute substantially to the mechanics of a cell. We propose a micromechanical hierarchical approach to capture the mechanical contribution of actin stress fibres. For a cell-specific fibroblast geometry with membrane, cytoplasm and nucleus, the Mori-Tanaka homogenization method was employed to describe cytoplasmic inhomogeneities and constitutive contribution of actin stress fibres. The homogenization was implemented in a finite element model of the fibroblast attached to a substrate through focal adhesions. Strain in cell membrane, cytoplasm and nucleus due to uniaxial substrate stretch was assessed for different stress fibre volume fractions and different elastic modulus of the substrate. A considerable decrease of the peak strain with increasing stress fibre content was observed in cytoplasm and nucleus but not the membrane, whereas the peak strain in cytoplasm, nucleus and membrane increased for increasing elastic modulus of the substrate. Finite element mesh of reconstructed human fibroblast and intracellular strain distribution in cell subjected to substrate stretch.

A 2020 view of tension-based cortical morphogenesis

Brain structures change shape dramatically during development. Elucidating the mechanisms of morphogenesis provides insights relevant to understanding brain function in health and disease. The tension-based morphogenesis (TBM) hypothesis posits that mechanical tension along axons, dendrites, and glial processes contributes to many aspects of central nervous system morphogenesis. Since TBM was proposed in 1997, extensive evidence supports a role for tension in diverse cellular phenomena, but tension’s role in cortical folding has been controversial. An extensively revised version of the TBM model for cerebral cortex addresses limitations of the original model, incorporates new features, and can be tested by many experimental approaches. For cerebellar cortex, a revised model accounts for many aspects of its development and adult architecture.

Mechanical tension along the length of axons, dendrites, and glial processes has been proposed as a major contributor to morphogenesis throughout the nervous system [D. C. Van Essen, Nature 385, 313–318 (1997)]. Tension-based morphogenesis (TBM) is a conceptually simple and general hypothesis based on physical forces that help shape all living things. Moreover, if each axon and dendrite strive to shorten while preserving connectivity, aggregate wiring length would remain low. TBM can explain key aspects of how the cerebral and cerebellar cortices remain thin, expand in surface area, and acquire their distinctive folds. This article reviews progress since 1997 relevant to TBM and other candidate morphogenetic mechanisms. At a cellular level, studies of diverse cell types in vitro and in vivo demonstrate that tension plays a major role in many developmental events. At a tissue level, I propose a differential expansion sandwich plus (DES+) revision to the original TBM model for cerebral cortical expansion and folding. It invokes tangential tension and “sulcal zipping” forces along the outer cortical margin as well as tension in the white matter core, together competing against radially biased tension in the cortical gray matter. Evidence for and against the DES+ model is discussed, and experiments are proposed to address key tenets of the DES+ model. For cerebellar cortex, a cerebellar multilayer sandwich (CMS) model is proposed that can account for many distinctive features, including its unique, accordion-like folding in the adult, and experiments are proposed to address its specific tenets.

The Hypothesis of Biotensegrity and D. D. Palmer's Hypothesis on Tone: A Discussion of Their Alignment

OBJECTIVE

The purpose of this article is to compare D. D. Palmer's hypothesis of tone with the modern hypothesis of biotensegrity.

DISCUSSION

Although researchers have been using the hypothesis of biotensegrity for over 40 years to explain the mechanics of movement within biological systems, it has experienced revived support in the last 25 years. Biotensegrity as a concept is applied at the molecular, cellular, tissue, and organ levels, revealing a different understanding of the architecture of biological organisms. Biotensegrity offers a way of exploring the human body in the field of functional anatomy. The model has become popular among bodywork and movement practitioners, as it recognizes the wholeness of the human body. D. D. Palmer used tone to explain the origin of disease; biotensegrity, instead, explains why certain diseases may develop.

CONCLUSION

The concept of tone hypothesized by D. D. Palmer is different from the modern concept of biotensegrity. Although biotensegrity offers a different way of seeing how the human body functions, using it as a theoretical framework to explain the effects of manual therapies such as chiropractic may be premature. The use of the biotensegrity hypothesis requires further research and investigation before application in clinical settings.

Elastic Tethers Between Separating Anaphase Chromosomes Regulate the Poleward Speeds of the Attached Chromosomes in Crane-Fly Spermatocytes

Elastic "tethers" connect separating anaphase chromosomes in most (or all) animal cells. We tested whether tethers are involved in coordinating movements of separating anaphase chromosomes in crane-fly spermatocytes. In these cells the coupled movements of separating chromosomes become uncoupled after the tethers are severed by laser microbeam irradiation of the interzone region between the chromosomes (Sheykhani et al., 2017). While this strongly suggests that tethers are involved with coordinating the poleward chromosome movements, the experiments are open to another interpretation: laser irradiations that cut the tethers also might damage something else in the interzone, and those non-tether components might regulate chromosome movements. In the experiments reported herein we distinguish between those two possibilities by disabling the tethers without cutting the interzone. We cut the arms from individual chromosomes, thereby severing the mechanical connection between separating chromosomes, disconnecting them, without damaging components in the interzone. Disabling tethers in this way uncoupled the movements of the separating chromosomes. We thus conclude that tethers are involved in regulating the speeds of separating anaphase chromosomes in crane-fly spermatocytes.

Structural and mechanical remodeling of the cytoskeleton maintains tensional homeostasis in 3D microtissues under acute dynamic stretch

When stretched, cells cultured on 2D substrates share a universal softening and fluidization response that arises from poorly understood remodeling of well-conserved cytoskeletal elements. It is known, however, that the structure and distribution of the cytoskeleton is profoundly influenced by the dimensionality of a cell's environment. Therefore, in this study we aimed to determine whether cells cultured in a 3D matrix share this softening behavior and to link it to cytoskeletal remodeling. To achieve this, we developed a high-throughput approach to measure the dynamic mechanical properties of cells and allow for sub-cellular imaging within physiologically relevant 3D microtissues. We found that fibroblast, smooth muscle and skeletal muscle microtissues strain softened but did not fluidize, and upon loading cessation, they regained their initial mechanical properties. Furthermore, microtissue prestress decreased with the strain amplitude to maintain a constant mean tension. This adaptation under an auxotonic condition resulted in lengthening. A filamentous actin cytoskeleton was required, and responses were mirrored by changes to actin remodeling rates and visual evidence of stretch-induced actin depolymerization. Our new approach for assessing cell mechanics has linked behaviors seen in 2D cultures to a 3D matrix, and connected remodeling of the cytoskeleton to homeostatic mechanical regulation of tissues.

Probing the Membrane Vibration of Single Living Cells by Using Nanopipettes

The vibration of a cell membrane plays a key role in the regulation of cell shape and the behavior of cells. However, most existing approaches for the measurement of cell vibration require either exogenous modification or sophisticated techniques, and the main challenge lies in developing methods that can monitor membrane vibration of living cells directly. Herein, a noninvasive strategy based on ultrasmall quartz nanopipettes is introduced. With a tip size of less than 100 nm, nanopipettes can be spatially controlled for precision targeting of a specific location on the membrane of single living cells. Surprisingly, by employing a constant voltage, stable cyclic oscillations are observed from the continuous current versus time traces. The time-domain current can be decomposed into two basic waves: the high-frequency one indicates the local membrane vibration driven by the electro-osmotic flow from the nanopipette, whereas the low-frequency one indicates the natural frequency of the whole cell. This provides a simple but reliable method to test local and global membrane vibration of single living cells simultaneously with little damage, which provides a tool for the quantification of drugs, disease, or mutations of the cell structure.

Nonlinear mechanics of soft composites: hyperelastic characterization of white matter tissue components

This paper presents a bi-directional closed-form analytical solution, in the framework of nonlinear soft composites mechanics, for top-down hyperelastic characterization of brain white matter tissue components, based on the directional homogenized responses of the tissue in the axial and transverse directions. The white matter is considered as a transversely isotropic neo-Hookean composite made of unidirectional distribution of axonal fibers within the extracellular matrix. First, two homogenization formulations are derived for the homogenized axial and transverse shear moduli of the tissue, based on definition of the strain energy density function. Next, the rule of mixtures and Hashin-Shtrikman theories are used to derive two coupled nonlinear equations which correlates the tissue shear moduli to these of its components. Closed-form solutions for shear moduli of the components are then obtained by solving these equations simultaneously. In order to validate the hyperelastic characteristics of components obtained in previous step, they are used in a bottom-up approach in a micromechanical model of the tissue with the aim of predicting the directional homogenized responses of the tissue. Comparison of model predictions with the experimental test results reported for corona radiata and corpus callosum white matter structures reveals very good agreements with the experimental results in both directions. The model predictions are also in good agreement with the analytical solution obtained by the iterated homogenization technique. Results indicate that axonal fibers are almost ten times stiffer than the extracellular matrix under large deformations.

Viscoelasticity of single cells-from subcellular to cellular level

This review deals with insights into complex cellular structures and processes obtained by measuring viscoelastic impedances of the cell envelope and the cytoplasm by colloidal bead microrheometry. I first introduce a mechanical cell model that allows us to understand their unique ability of mechanical self-stabilization by actin microtubule crosstalk. In the second part, I show how cell movements can be driven by pulsatile or propagating solitary actin gelatin waves (SAGW) that are generated on nascent adhesion domains by logistically controlled membrane recruitment of functional proteins by electrostatic-hydrophobic forces. The global polarization of cell migration is guided by actin-microtubule crosstalk that is mediated by the Ca⁺⁺ and strain-sensitive supramolecular scaffolding protein IQGAP. In the third part, I introduce the traction force microscopy as a tool to measure the forces between somatic cells and the tissue ´Here I show, how absolute values of viscoelastic impedances of the composite cell envelope can be obtained by deformation field mapping techniques. In the fourth part, it is shown how the dynamic mechanical properties of the active viscoplastic cytoplasmic space can be evaluated using colloidal beads as phantom endosomes. Separate measurements of velocity distributions of directed and random motions of phantom endosomes, yield local values of transport forces, viscosities and life times of directed motion along microtubules. The last part deals with biomimetic experiments allowing us to quantitatively evaluate the mechanical properties of passive and active actin networks on the basis of the percolation theory of gelation.

A three-dimensional micromechanical model of brain white matter with histology-informed probabilistic distribution of axonal fibers

This paper presents a three-dimensional micromechanical model of brain white matter tissue as a transversely isotropic soft composite described by the generalized Ogden hyperelastic model. The embedded element technique, with corrected stiffness redundancy in large deformations, was used for the embedment of a histology-informed probabilistic distribution of the axonal fibers in the extracellular matrix. The model was linked to a multi-objective, multi-parametric optimization algorithm, using the response surface methodology, for characterization of material properties of the axonal fibers and extracellular matrix in an inverse finite element analysis. The optimum hyperelastic characteristics of the tissue constituents, obtained based on the axonal and transverse direction test results of the corona radiata tissue samples, indicated that the axonal fibers were almost thirteen times stiffer than the extracellular matrix under large deformations. Simulation of the same tissue under a different loading condition, as well as that of another white matter tissue, i.e., the corpus callosum, in the axonal and transverse directions, using the optimized hyperelastic characteristics revealed tissue responses very close to those of the experiments. The results of the model at the sub-tissue level indicated that the stress concentrations were considerably large around the small axons, which might contribute into the brain injury.

Structural Rearrangements in CHO Cells After Disruption of Individual Cytoskeletal Elements and Plasma Membrane

Cellular structural integrity is provided primarily by the cytoskeleton, which comprises microtubules, actin filaments, and intermediate filaments. The plasma membrane has been also recognized as a mediator of physical forces, yet its contribution to the structural integrity of the cell as a whole is less clear. In order to investigate the relationship between the plasma membrane and the cytoskeleton, we selectively disrupted the plasma membrane and each of the cytoskeletal elements in Chinese hamster ovary cells and assessed subsequent changes in cellular structural integrity. Confocal microscopy was used to visualize cytoskeletal rearrangements, and optical tweezers were utilized to quantify membrane tether extraction. We found that cholesterol depletion from the plasma membrane resulted in rearrangements of all cytoskeletal elements. Conversely, the state of the plasma membrane, as assessed by tether extraction, was affected by disruption of any of the cytoskeletal elements, including microtubules and intermediate filaments, which are located mainly in the cell interior. The results demonstrate that, besides the cytoskeleton, the plasma membrane is an important contributor to cellular integrity, possibly by acting as an essential framework for cytoskeletal anchoring. In agreement with the tensegrity model of cell mechanics, our results support the notion of the cell as a prestressed structure.

Transient Pinning and Pulling: A Mechanism for Bending Microtubules

Microtubules have a persistence length of the order of millimeters in vitro, but inside cells they bend over length scales of microns. It has been proposed that polymerization forces bend microtubules in the vicinity of the cell boundary or other obstacles, yet bends develop even when microtubules are polymerizing freely, unaffected by obstacles and cell boundaries. How these bends are formed remains unclear. By tracking the motions of microtubules marked by photobleaching, we found that in LLC-PK1 epithelial cells local bends develop primarily by plus-end directed transport of portions of the microtubule contour towards stationary locations (termed pinning points) along the length of the microtubule. The pinning points were transient in nature, and their eventual release allowed the bends to relax. The directionality of the transport as well as the overall incidence of local bends decreased when dynein was inhibited, while myosin inhibition had no observable effect. This suggests that dynein generates a tangential force that bends microtubules against stationary pinning points. Simulations of microtubule motion and polymerization accounting for filament mechanics and dynein forces predict the development of bends of size and shape similar to those observed in cells. Furthermore, simulations show that dynein-generated bends at a pinning point near the plus end can cause a persistent rotation of the tip consistent with the observation that bend formation near the tip can change the direction of microtubule growth. Collectively, these results suggest a simple physical mechanism for the bending of growing microtubules by dynein forces accumulating at pinning points.

Elastic properties of epithelial cells probed by atomic force microscopy

Cellular mechanics plays a crucial role in many biological processes such as cell migration, cell growth, embryogenesis, and oncogenesis. Epithelia respond to environmental cues comprising biochemical and physical stimuli through defined changes in cell elasticity. For instance, cells can differentiate between certain properties such as viscoelasticity or topography of substrates by adapting their own elasticity and shape. A living cell is a complex viscoelastic body that not only exhibits a shell architecture composed of a membrane attached to a cytoskeleton cortex but also generates contractile forces through its actomyosin network. Here we review cellular mechanics of single cells in the context of epithelial cell layers responding to chemical and physical stimuli. This article is part of a Special Issue entitled: Mechanobiology.

X-ray radiation promotes the metastatic potential of tongue squamous cell carcinoma cells via modulation of biomechanical and cytoskeletal properties

This study investigated the metastatic potential of tongue squamous cell carcinoma (TSCC) cells after X-ray irradiation as well as radiation-induced changes in the biomechanical properties and cytoskeletal structure that are relevant to metastasis. Tca-8113 TSCC cells were X-ray-irradiated at increasing doses (0, 1, 2, or 4 Gy), and 24 h later, migration was evaluated with the wound healing and transwell migration assays, while invasion was assessed with the Matrigel invasion assay. Confocal and atomic force microscopy were used to examine changes in the structure of the actin cytoskeleton and Young's modulus (cell stiffness), respectively. X-ray radiation induced dose-dependent increases in invasive and migratory potentials of cells relative to unirradiated control cells (p < 0.05). The Young's modulus of irradiated cells was decreased by radiation exposure (p < 0.05), which was accompanied by alterations in the integrity and organization of the cytoskeletal network, as evidenced by a decrease in the signal intensity of actin fibers (p < 0.05). X-ray irradiation enhanced migration and invasiveness in Tca-8113 TSCC cells by altering their biomechanical properties and the organization of the actin cytoskeleton. A biomechanics-based analysis can provide an additional platform for assessing tumor response to radiation and optimization of cancer therapies.

The Application of Tensegrity Massage in a Professionally Active Musician - Case Report

PURPOSE

The purpose of our study was to present options for the application of tensegrity massage to manage pain caused by the overload of soft tissues in musicians.

DESIGN

Tensegrity massage was applied to a 34-year-old male violinist.

METHODS

The methodology included a correct positioning and tensegrity massage with individually designed procedure.

FINDINGS

After therapy, the patient achieved complete pain relief, and relaxation of muscles in the shoulder girdle and free part of the upper arm. The analgesic effect lasted for 6 months after the end of therapy.

CONCLUSIONS

Massage is an effective method in eliminating pain caused by the overload of soft tissues. If used regularly before physical effort, it can prevent muscle overload.

CLINICAL RELEVANCE

The presented massage procedure is an effective therapy in pain caused by the overload of soft tissues in musicians and it can be one of the elements of complex physiotherapy in active musicians.

Tensegrity, cellular biophysics, and the mechanics of living systems

The recent convergence between physics and biology has led many physicists to enter the fields of cell and developmental biology. One of the most exciting areas of interest has been the emerging field of mechanobiology that centers on how cells control their mechanical properties, and how physical forces regulate cellular biochemical responses, a process that is known as mechanotransduction. In this article, we review the central role that tensegrity (tensional integrity) architecture, which depends on tensile prestress for its mechanical stability, plays in biology. We describe how tensional prestress is a critical governor of cell mechanics and function, and how use of tensegrity by cells contributes to mechanotransduction. Theoretical tensegrity models are also described that predict both quantitative and qualitative behaviors of living cells, and these theoretical descriptions are placed in context of other physical models of the cell. In addition, we describe how tensegrity is used at multiple size scales in the hierarchy of life—from individual molecules to whole living organisms—to both stabilize three-dimensional form and to channel forces from the macroscale to the nanoscale, thereby facilitating mechanochemical conversion at the molecular level.

A multi-structural single cell model of force-induced interactions of cytoskeletal components

Several computational models based on experimental techniques and theories have been proposed to describe cytoskeleton (CSK) mechanics. Tensegrity is a prominent model for force generation, but it cannot predict mechanics of individual CSK components, nor explain the discrepancies from the different single cell stimulating techniques studies combined with cytoskeleton-disruptors. A new numerical concept that defines a multi-structural 3D finite element (FE) model of a single-adherent cell is proposed to investigate the biophysical and biochemical differences of the mechanical role of each cytoskeleton component under loading. The model includes prestressed actin bundles and microtubule within cytoplasm and nucleus surrounded by the actin cortex. We performed numerical simulations of atomic force microscopy (AFM) experiments by subjecting the cell model to compressive loads. The numerical role of the CSK components was corroborated with AFM force measurements on U2OS-osteosarcoma cells and NIH-3T3 fibroblasts exposed to different cytoskeleton-disrupting drugs. Computational simulation showed that actin cortex and microtubules are the major components targeted in resisting compression. This is a new numerical tool that explains the specific role of the cortex and overcomes the difficulty of isolating this component from other networks in vitro. This illustrates that a combination of cytoskeletal structures with their own properties is necessary for a complete description of cellular mechanics.

Novel role for vinculin in ventricular myocyte mechanics and dysfunction

Vinculin (Vcl) plays a key structural role in ventricular myocytes that, when disrupted, can lead to contractile dysfunction and dilated cardiomyopathy. To investigate the role of Vcl in myocyte and myocardial function, cardiomyocyte-specific Vcl knockout mice (cVclKO) and littermate control wild-type mice were studied with transmission electron microscopy (TEM) and in vivo magnetic resonance imaging (MRI) tagging before the onset of global ventricular dysfunction. MRI revealed significantly decreased systolic strains transverse to the myofiber axis in vivo, but no changes along the muscle fibers or in fiber tension in papillary muscles from heterozygous global Vcl null mice. Myofilament lattice spacing from TEM was significantly greater in cVclKO versus wild-type hearts fixed in the unloaded state. AFM in Vcl heterozygous null mouse myocytes showed a significant decrease in membrane cortical stiffness. A multiscale computational model of ventricular mechanics incorporating cross-bridge geometry and lattice mechanics showed that increased transverse systolic stiffness due to increased lattice spacing may explain the systolic wall strains associated with Vcl deficiency, before the onset of ventricular dysfunction. Loss of cardiac myocyte Vcl may decrease systolic transverse strains in vivo by decreasing membrane cortical tension, which decreases transverse compression of the lattice thereby increasing interfilament spacing and stress transverse to the myofibers.

A historical to present-day account of efforts to answer the question: "what puts the brakes on mammalian hair cell regeneration?"

Hearing and balance deficits often affect humans and other mammals permanently, because their ears stop producing hair cells within a few days after birth. But production occurs throughout life in the ears of sharks, bony fish, amphibians, reptiles, and birds allowing them to replace lost hair cells and quickly recover after temporarily experiencing the kinds of sensory deficits that are irreversible for mammals. Since the mid 1970s, researchers have been asking what puts the brakes on hair cell regeneration in mammals. Here we evaluate the headway that has been made and assess current evidence for alternative mechanistic hypotheses that have been proposed to account for the limits to hair cell regeneration in mammals.

Computational aspects in mechanical modeling of the articular cartilage tissue

This review focuses on the modeling of articular cartilage (at the tissue level), chondrocyte mechanobiology (at the cell level) and a combination of both in a multiscale computation scheme. The primary objective is to evaluate the advantages and disadvantages of conventional models implemented to study the mechanics of the articular cartilage tissue and chondrocytes. From monophasic material models as the simplest form to more complicated multiscale theories, these approaches have been frequently used to model articular cartilage and have contributed significantly to modeling joint mechanics, addressing and resolving numerous issues regarding cartilage mechanics and function. It should be noted that attentiveness is important when using different modeling approaches, as the choice of the model limits the applications available. In this review, we discuss the conventional models applicable to some of the mechanical aspects of articular cartilage such as lubrication, swelling pressure and chondrocyte mechanics and address some of the issues associated with the current modeling approaches. We then suggest future pathways for a more realistic modeling strategy as applied for the simulation of the mechanics of the cartilage tissue using multiscale and parallelized finite element method.

Effective treatment of edema and endothelial barrier dysfunction with imatinib

BACKGROUND

Tissue edema and endothelial barrier dysfunction as observed in sepsis and acute lung injury carry high morbidity and mortality, but currently lack specific therapy. In a recent case report, we described fast resolution of pulmonary edema on treatment with the tyrosine kinase inhibitor imatinib through an unknown mechanism. Here, we explored the effect of imatinib on endothelial barrier dysfunction and edema formation.

METHODS AND RESULTS

We evaluated the effect of imatinib on endothelial barrier function in vitro and in vivo. In human macro- and microvascular endothelial monolayers, imatinib attenuated endothelial barrier dysfunction induced by thrombin and histamine. Small interfering RNA knock-downs of the imatinib-sensitive kinases revealed that imatinib attenuates endothelial barrier dysfunction via inhibition of Abl-related gene kinase (Arg/Abl2), a previously unknown mediator of endothelial barrier dysfunction. Indeed, Arg was activated by endothelial stimulation with thrombin, histamine, and vascular endothelial growth factor. Imatinib limited Arg-mediated endothelial barrier dysfunction by enhancing Rac1 activity and enforcing adhesion of endothelial cells to the extracellular matrix. Using mouse models of vascular leakage as proof-of-concept, we found that pretreatment with imatinib protected against vascular endothelial growth factor-induced vascular leakage in the skin, and effectively prevented edema formation in the lungs. In a murine model of sepsis, imatinib treatment (6 hours and 18 hours after induction of sepsis) attenuated vascular leakage in the kidneys and the lungs (24 hours after induction of sepsis).

CONCLUSIONS

Thus, imatinib prevents endothelial barrier dysfunction and edema formation via inhibition of Arg. These findings identify imatinib as a promising approach to permeability edema and indicate Arg as novel target for edema treatment.

ELECTROHYDRODYNAMIC PROCESSING OF CALCIUM PHOSPHATES: COATING AND PATTERNING FOR MEDICAL IMPLANTS

Hydroxyapatite (HA)-coated metallic prostheses, which combine the osteoconductivity of HA and high strength of metallic alloys, have been increasingly the choice of joint replacement prostheses by surgeons as the general population lives longer. Surface modification of metallic implant surfaces is one of the key focal points to implantation technology. In addition to material chemistry, surface topography has been found to positively impact cellular response and is able to enhance the life time of the implant. Recently, a new technique, template-assisted electrohydrodynamic atomization (TAEA) spraying, developed using the principles of electrohydrodynamic atomization spraying, which is an electrically driven jet-based deposition method, is of considerable interest in surface topography formation. The process offers the attractive advantages of compatibility with micro-fabrication technology and versatility in pattern specification for advanced implant designs. This technology incorporates nanosized calcium phosphate to mimic the size and chemical composition of bone mineral in a micrometer-dimension pattern configuration to guide cellular responses. In vitro studies showed that both pillar and track nano Silicon-substituted HA (SiHA) patterns were able to encourage the attachment and growth of osteoblast cells, the track patterns provided the favourite surface for the initial cell attachment while a fast cell proliferation rate was found on the pillar pattern from day 1 to day 5 in comparison with that of a SiHA-coated surface. The alignment of actin cytoskeleton of osteoblast cells matched the orientation of the entire cell. The shear peel strength of the patterned interlocking nano-HA coating was found to be at least an order of magnitude higher than the conventional HA coating. Therefore, TAEA offers great potential for producing new coatings with a tailored surface topography, on both the micro- and nano-scale in a more cost effective way to enhance the performance of medical implants.

APPLICATION OF BIOMECHANICS TO TISSUE ENGINEERING: A PERSONAL VIEW

Cellular biomechanics is an area of study that is receiving more attention as time progresses. The response of cells to their mechanical environment, including biomechanical stimuli, has far-reaching ramifications for the area of tissue engineering, especially for tissues designed to withstand mechanical loading (e.g. bone, cartilage, tendons and ligaments, and arteries). The effects of mechanical stimuli on cells are only recently being examined, and the potential role of mechanical stimuli in tissue engineering is still one that is largely ignored in the design of tissue engineering scaffolds. The relationship of mechanical properties of scaffolds or of mechanical stimuli to cell behavior is complex, but vital to the development of the field. Also, understanding the complex interplay of form and environment on cells involves an increase in our knowledge of how cells react to their total environment including mechanical stimuli and material properties. In order to improve tissue engineering outcomes, a nexus must be developed between the mechanical, biochemical, and biological studies of cellular behavior, in the context of extremely complex systems.

Computational modeling of epithelial tissues

There is an extensive literature on the computational modeling of epithelial tissues at all levels from subcellular to whole tissue. This review concentrates on behavior at the individual cell to whole tissue level, and particularly on organizational aspects, and provides an indication of where information from other areas, such as the modeling of angiogenesis, is relevant. The skin, and the lining of all of the body cavities (lung, gut, cervix, bladder etc) are epithelial tissues, which in a topological sense are the boundary between inside and outside the body. They are thin sheets of cells (usually of the order of 0.5 mm thick) without extracellular matrix, have a relatively simple structure, and contain few types of cells. They have important barrier, secretory and transport functions, which are essential for the maintenance of life, so homeostasis and wound healing are important aspects of the behavior of epithelial tissues. Carcinomas originate in epithelial tissues.There are essentially two approaches to modeling tissues--to start at the level of the tissue (i.e., a length scale of the order of 1 mm) and develop generalized equations for behavior (a continuum approach); or to start at the level of the cell (i.e., a length scale of the order of 10 µm) and develop tissue behavior as an emergent property of cellular behavior (an individual-based approach). As will be seen, these are not mutually exclusive approaches, and they come in a variety of flavors.

Stress transmission within the cell

An outstanding problem in cell biology is how cells sense mechanical forces and how those forces affect cellular functions. During past decades, it has become evident that the deformable cytoskeleton (CSK), an intracellular network of various filamentous biopolymers, provides a physical basis for transducing mechanical signals into biochemical responses. To understand how mechanical forces regulate cellular functions, it is necessary to first understand how the CSK develops mechanical stresses in response to applied forces, and how those stresses are propagated through the CSK where various signaling molecules are immobilized. New experimental techniques have been developed to quantify cytoskeletal mechanics, which together with new computational approaches have given rise to new theories and models for describing mechanics of living cells. In this article, we discuss current understanding of cell biomechanics by focusing on the biophysical mechanisms that are responsible for the development and transmission of mechanical stresses in the cell and their effect on cellular functions. We compare and contrast various theories and models of cytoskeletal mechanics, emphasizing common mechanisms that those theories are built upon, while not ignoring irreconcilable differences. We highlight most recent advances in the understanding of mechanotransduction in the cytoplasm of living cells and the central role of the cytoskeletal prestress in propagating mechanical forces along the cytoskeletal filaments to activate cytoplasmic enzymes. It is anticipated that advances in cell mechanics will help developing novel therapeutics to treat pulmonary diseases like asthma, pulmonary fibrosis, and chronic obstructive pulmonary disease.

Atomic force microscopy in mechanobiology: measuring microelastic heterogeneity of living cells

Recent findings clearly demonstrate that cells feel mechanical forces, and respond by altering their -phenotype and modulating their mechanical environment. Atomic force microscope (AFM) indentation can be used to mechanically stimulate cells and quantitatively characterize their elastic properties, providing critical information for understanding their mechanobiological behavior. This review focuses on the experimental and computational aspects of AFM indentation in relation to cell biomechanics and pathophysiology. Key aspects of the indentation protocol (including preparation of substrates, selection of indentation parameters, methods for contact point detection, and further post-processing of data) are covered. Historical perspectives on AFM as a mechanical testing tool as well as studies of cell mechanics and physiology are also highlighted.

Complexity of the tensegrity structure for dynamic energy and force distribution of cytoskeleton during cell spreading

Cytoskeleton plays important roles in intracellular force equilibrium and extracellular force transmission from/to attaching substrate through focal adhesions (FAs). Numerical simulations of intracellular force distribution to describe dynamic cell behaviors are still limited. The tensegrity structure comprises tension-supporting cables and compression-supporting struts that represent the actin filament and microtubule respectively, and has many features consistent with living cells. To simulate the dynamics of intracellular force distribution and total stored energy during cell spreading, the present study employed different complexities of the tensegrity structures by using octahedron tensegrity (OT) and cuboctahedron tensegrity (COT). The spreading was simulated by assigning specific connection nodes for radial displacement and attachment to substrate to form FAs. The traction force on each FA was estimated by summarizing the force carried in sounding cytoskeletal elements. The OT structure consisted of 24 cables and 6 struts and had limitations soon after the beginning of spreading by declining energy stored in struts indicating the abolishment of compression in microtubules. The COT structure, double the amount of cables and struts than the OT structure, provided sufficient spreading area and expressed similar features with documented cell behaviors. The traction force pointed inward on peripheral FAs in the spread out COT structure. The complex structure in COT provided further investigation of various FA number during different spreading stages. Before the middle phase of spreading (half of maximum spreading area), cell attachment with 8 FAs obtained minimized cytoskeletal energy. The maximum number of 12 FAs in the COT structure was required to achieve further spreading. The stored energy in actin filaments increased as cells spread out, while the energy stored in microtubules increased at initial spreading, peaked in middle phase, and then declined as cells reached maximum spreading. The dynamic flows of energy in struts imply that microtubules contribute to structure stabilization.

Force propagation and force generation in cells

Determining how forces are produced by and propagated through the cytoskeleton (CSK) of the cell is of great interest as dynamic processes of the CSK are intimately correlated with many molecular signaling pathways. We are presenting a novel approach for integrating measurements on cell elasticity, transcellular force propagation, and cellular force generation to obtain a comprehensive description of dynamic and mechanical properties of the CSK under force loading. This approach uses a combination of scanning force microscopy (SFM) and Total Internal Reflection Fluorescence (TIRF) microscopy. We apply well-defined loading schemes onto the apical cell membrane of fibroblasts using the SFM and simultaneously use TIRF microscopy to image the topography of the basal cell membrane. The locally distinct changes of shape and depth of the cytoskeletal imprints onto the basal membrane are interpreted as results of force propagation through the cytoplasm. This observation provides evidence for the tensegrity model and demonstrates the usefulness of our approach that does not depend on potentially disturbing marker compounds. We confirm that the actin network greatly determines cell stiffness and represents the substrate that mediates force transduction through the cytoplasm of the cell. The latter is an essential feature of tensegrity. Most importantly, our new finding that, both intact actin and microtubule networks are required for enabling the cell to produce work, can only be understood within the framework of the tensegrity model. We also provide, for the first time, a direct measurement of the cell's mechanical power output under compression at two femtowatts.

A sub-cellular viscoelastic model for cell population mechanics

Understanding the biomechanical properties and the effect of biomechanical force on epithelial cells is key to understanding how epithelial cells form uniquely shaped structures in two or three-dimensional space. Nevertheless, with the limitations and challenges posed by biological experiments at this scale, it becomes advantageous to use mathematical and 'in silico' (computational) models as an alternate solution. This paper introduces a single-cell-based model representing the cross section of a typical tissue. Each cell in this model is an individual unit containing several sub-cellular elements, such as the elastic plasma membrane, enclosed viscoelastic elements that play the role of cytoskeleton, and the viscoelastic elements of the cell nucleus. The cell membrane is divided into segments where each segment (or point) incorporates the cell's interaction and communication with other cells and its environment. The model is capable of simulating how cells cooperate and contribute to the overall structure and function of a particular tissue; it mimics many aspects of cellular behavior such as cell growth, division, apoptosis and polarization. The model allows for investigation of the biomechanical properties of cells, cell-cell interactions, effect of environment on cellular clusters, and how individual cells work together and contribute to the structure and function of a particular tissue. To evaluate the current approach in modeling different topologies of growing tissues in distinct biochemical conditions of the surrounding media, we model several key cellular phenomena, namely monolayer cell culture, effects of adhesion intensity, growth of epithelial cell through interaction with extra-cellular matrix (ECM), effects of a gap in the ECM, tensegrity and tissue morphogenesis and formation of hollow epithelial acini. The proposed computational model enables one to isolate the effects of biomechanical properties of individual cells and the communication between cells and their microenvironment while simultaneously allowing for the formation of clusters or sheets of cells that act together as one complex tissue.

Anterograde microtubule transport drives microtubule bending in LLC-PK1 epithelial cells

Microtubules (MTs) have been proposed to act mechanically as compressive struts that resist both actomyosin contractile forces and their own polymerization forces to mechanically stabilize cell shape. To identify the origin of MT bending, we directly observed MT bending and F-actin transport dynamics in the periphery of LLC-PK1 epithelial cells. We found that F-actin is nearly stationary in these cells even as MTs are deformed, demonstrating that MT bending is not driven by actomyosin contractility. Furthermore, the inhibition of myosin II activity through the use of blebbistatin results in microtubules that are still dynamically bending. In addition, as determined by fluorescent speckle microscopy, MT polymerization rarely results, if ever, in bending. We suppressed dynamic instability using nocodazole, and we observed no qualitative change in the MT bending dynamics. Bending most often results from anterograde transport of proximal portions of the MT toward a nearly stationary distal tip. Interestingly, we found that in an in vitro kinesin-MT gliding assay, MTs buckle in a similar manner. To make quantitative comparisons, we measured curvature distributions of observed MTs and found that the in vivo and in vitro curvature distributions agree quantitatively. In addition, the measured MT curvature distribution is not Gaussian, as expected for a thermally driven semiflexible polymer, indicating that thermal forces play a minor role in MT bending. We conclude that many of the known mechanisms of MT deformation, such as polymerization and acto-myosin contractility, play an inconsequential role in mediating MT bending in LLC-PK1 cells and that MT-based molecular motors likely generate most of the strain energy stored in the MT lattice. The results argue against models in which MTs play a major mechanical role in LLC-PK1 cells and instead favor a model in which mechanical forces control the spatial distribution of the MT array.

Elasticity mapping of pore-suspending native cell membranes

The mechanics of cellular membranes are governed by a non-equilibrium composite framework consisting of the semiflexible filamentous cytoskeleton and extracellular matrix proteins linked to the lipid bilayer. While elasticity information of plasma membranes has mainly been obtained from whole cell analysis, techniques that allow addressing local mechanical properties of cell membranes are desirable to learn how their lipid and protein composition is reflected in the elastic behavior on local length scales. Introduced here is an approach based on basolateral membranes of polar epithelial Madin-Darby canine kidney (MDCK) II cells, prepared on a highly ordered porous substrate that allows elastic mapping on a submicrometer-length scale. A strong correlation between the density of actin filaments and the measured membrane elasticity is found. Spatially resolved indentation experiments carried out with atomic force and fluorescence microscope permit relation of the supramolecular structure to the elasticity of cellular membranes. It is shown that the elastic response of the pore spanning cell membranes is governed by local bending modules rather than lateral tension.

Modulation of cellular mechanics during osteogenic differentiation of human mesenchymal stem cells

Recognition of the growing role of human mesenchymal stem cells (hMSC) in tissue engineering and regenerative medicine requires a thorough understanding of intracellular biochemical and biophysical processes that may direct the cell's commitment to a particular lineage. In this study, we characterized the distinct biomechanical properties of hMSCs, including the average Young's modulus determined by atomic force microscopy (3.2 +/- 1.4 kPa for hMSC vs. 1.7 +/- 1.0 kPa for fully differentiated osteoblasts), and the average membrane tether length measured with laser optical tweezers (10.6 +/- 1.1 microm for stem cells, and 4.0 +/- 1.1 microm for osteoblasts). These differences in cell elasticity and membrane mechanics result primarily from differential actin cytoskeleton organization in these two cell types, whereas microtubules did not appear to affect the cellular mechanics. The membrane-cytoskeleton linker proteins may contribute to a stronger interaction of the plasma membrane with F-actins and shorter membrane tether length in osteoblasts than in stem cells. Actin depolymerization or ATP depletion caused a two- to threefold increase in the membrane tether length in osteoblasts, but had essentially no effect on the stem-cell membrane tethers. Actin remodeling in the course of a 10-day osteogenic differentiation of hMSC mediates the temporally correlated dynamical changes in cell elasticity and membrane mechanics. For example, after a 10-day culture in osteogenic medium, hMSC mechanical characteristics were comparable to those of mature bone cells. Based on quantitative characterization of the actin cytoskeleton remodeling during osteodifferentiation, we postulate that the actin cytoskeleton plays a pivotal role in determining the hMSC mechanical properties and modulation of cellular mechanics at the early stage of stem-cell osteodifferentiation.

Constitutive material modeling of cell: a micromechanics approach

The variations in mechanical properties of cells obtained from experimental and theoretical studies can be overcome only through the development of a sound mathematical framework correlating the derived mechanical property with the cellular structure. Such a formulation accounting for the inhomogeneity of the cytoplasm due to stress fibers and actin cortex is developed in this work. The proposed model is developed using the Mori-Tanaka method of homogenization by treating the cell as a fiber-reinforced composite medium satisfying the continuum hypothesis. The validation of the constitutive model using finite element analysis on atomic force microscopy (AFM) and magnetic twisting cytometry (MTC) has been carried out and is found to yield good correlation with reported experimental results. It is observed from the study that as the volume fraction of the stress fiber increases, the stiffness of the cell increases and it alters the force displacement behavior for the AFM and MTC experiments. Through this model, we have also been able to find the stress fiber as a likely cause of the differences in the derived mechanical property from the AFM and MTC experiments. The correlation of the mechanical behavior of the cell with the cell composition, as obtained through this study, is an important observation in cell mechanics.