Viscoelastic Properties Of Cells Research Articles

Multi-Channel Signals in Dynamic Force-Clamp Mode of Microcantilever Sensors for Detecting Cellular Peripheral Brush.

The development of numerous diseases, such as renal cyst, cancer, and viral infection, is closely associated with the pathological changes and defects in the cellular peripheral brush. Therefore, it is necessary to develop a potential new method to detect lesions of cellular peripheral brush. Here, a piecewise linear viscoelastic constitutive model of cell is established considering the joint contribution of the peripheral brush and intra-cellular structure. By combining the Laplace transformation and its inverse transformation, and the differential method in the temporal domain and differential quadrature method (DQM) in the spatial domain, the signal interpretation models for quasi-static and dynamic signals of microcantilever are solved. The influence mechanisms of the peripheral brush on the viscoelastic properties of cells and quasi-static/dynamic signals of microcantilever are clarified. The results not only reveal that the peripheral brush has significant effects on the complex modulus of the cell and multi-channel signals of the microcantilever, but also suggest that an alternative mapping method by collecting multi-channel signals including quasi-static and higher frequency signals with more brush indexes could be potentially used to identify cancerous cells.

Unveiling the role of hydroxyapatite and hydroxyapatite/silver composite in osteoblast-like cell mineralization: An exploration through their viscoelastic properties

Mechanical properties are becoming fundamental for advancing the comprehension of cellular processes. This study addresses the relationship between viscoelastic properties and the cellular mineralization process. Osteoblast-like cells treated with an osteogenic medium were employed for this purpose. Additionally, the study explores the impact of hydroxyapatite (HA) and hydroxyapatite/silver (HA/Ag) composite on this process. AFM relaxation experiments were conducted to extract viscoelastic parameters using the Fractional Zener (FZ) and Fractional Kelvin (FK) models. Our findings revealed that the main phases of mineralization are associated with alterations in the viscoelastic properties of osteoblast-like cells. Furthermore, HA and HA/Ag treatments significantly influenced changes in the viscoelastic properties of these cells. In particular, the HA/Ag treatment demonstrated a marked enhancement in cell fluidity, suggesting a possible role of silver in accelerating the mineralization process. Moreover, the study underscores the independence observed between fluidity and stiffness, indicating that modifications in one parameter may not necessarily correspond to changes in the other. These findings shed light on the factors involved in the cellular mineralization process and emphasize the importance of using viscoelastic properties to discern the impact of treatments on cells.

Single cell mechanics analyzed by atomic force microscopy and finite element simulation

Cell mechanics plays a key role in determining physical performances and physiological functions of cells, as well as the early detection of diseases and development of biomedical engineering. In this study, we utilized a combination of atomic force microscopy (AFM) and finite element method (FEM) to compare the cellular elasticity (Young’s modulus) and viscoelasticity (stress-relaxation time) of living and fixed endothelial cells (ECs) across varying loading rates. The results showed that both mechanical properties of normal ECs are more sensitive to loading speed compared with fixed ECs. The Young’s modulus of normal endothelial cells (ECs) exhibits an increasing trend with the growing loading rate, whereas the Young’s modulus of fixed ECs is almost not affected by the loading rate. Among various viscoelastic properties of cells under varying loading rates, the long-term relaxation time, especially at a loading rate of 5 μm s−1, showed the most significant difference between living and fixed cells. This work comprehensively evaluated the effectiveness of using different mechanical properties to distinguish cells with different physiological characteristic. This research would improve our knowledge of single-cell mechanical behaviors and provide new ideas for distinguishing various types of cells by AFM-based cellular elastic and viscoelastic properties with varying loading rates.

Ionic strength tunes yeast viscoelasticity and promotes trace-level cell detection

Dynamically controlling cell-material interactions has a strong potential for advancing many cell-based technologies, including cell detection and cell sorting systems. To this end, fundamental studies that provide insights into how cells respond biologically to physico-chemical cues are necessary. Studies show that biological responses, such as cytoskeletal reorganization alter the overall viscoelastic properties of cells. Here, we monitored, in real time, and non-invasively, the evolution of the viscoelastic properties of yeast cells as a function of medium ionic strength (IS). Measurements were performed on SiO2-coated sensor surfaces using the quartz crystal microbalance with dissipation monitoring (QCM-D). Our results indicate that, for every adhesion phase, the cell stiffness decreases with increasing IS. This trend was consistent across the various cell concentrations studied. In terms of cell-substrate interactions, we show that a high IS promotes cell adhesion for all cell concentrations, including ultra-low concentrations. Our results also show that while the adhesion signal decreases with cell concentration for each IS, only temporal and close to noise-level adhesion signals were measured in ion-free medium irrespective of the cell concentration. We also show that cell adhesion rates are higher in physiological ionic strengths compared to cells in higher ionic strengths. Finally, from a cell detection perspective, the results reveal that for very low cell concentrations, large signal enhancements can be achieved by measuring the same concentration in a higher ionic strength. This result also applies for measurements on gold surfaces; thus, we suggest ionic tuning as a strategy for promoting trace-level cell detection in biosensors and cell sorting applications.

Actin cytoskeletal structure and the statistical variations of the mechanical properties of non-tumorigenic breast and triple-negative breast cancer cells

This paper presents the results of a study of the actin cytoskeletal structures and the statistical variations in the actin fluorescence intensities and viscoelastic properties of non-tumorigenic breast cells and triple-negative breast cancer cells at different stages of tumor progression. The variation in the actin content of the cell cytoskeletal structures is shown to be consistent with the viscoelastic properties of the cell as it progresses from non-tumorigenic to more metastatic states. The corresponding viscoelastic properties of the nuclei and the cytoplasm (Young's moduli, viscosities, and relaxation times) of the cells are also measured using Digital Image Correlation (DIC) and shear assay techniques. These properties are shown to exhibit statistical variations that are well characterized by normal distributions. The changes in the mean properties of individual cancer cells are tested using Fisher pairwise comparisons and the analysis of variance (ANOVA). The implications of the results are then discussed for the development of shear assay techniques and mechanical biomarkers for the detection of triple-negative breast cancer at different stages of tumor progression.

A QCM-D sensing strategy for investigating the real-time effects of oxidative stress on the viscoelastic properties of pre-osteoblast cells

Oxidative stress results from an imbalance in the cellular redox state which can cause damage to the cell cytoskeleton and morphology, thereby affecting cell viscoelasticity. In this study, we introduce a quartz crystal microbalance with dissipation (QCM-D) sensing strategy that enables the real-time assessment of the changes in the viscoelastic properties of an MC3T3 cell monolayer in response to oxidative stress. This was successfully achieved by tracking the changes in energy dissipation (ΔD-response) caused by the interaction of H2O2 with the cell monolayer adhered to a poly-d-lysine-coated polystyrene quartz sensor. While a return to baseline values of the ΔD-response was obtained at 325 min (recovery point) after the incubation of cells with 25 μM H2O2, higher concentrations (50 μM-10 mM) exhibited no recovery. We successfully validated using scanning electron, atomic force and fluorescence microscopy that at the recovery point the cell morphology recovered from 25 μM H2O2 exposure, whereas, higher concentrations (50 μM-10 mM) resulted in the shrinkage of the cytoskeleton, alteration in cell morphology, and decrease in cell density due to apoptosis/necrosis, supported by a cell viability assay. Finally, total antioxidant capacity assay (TAC) confirmed that while cells’ metabolic state recovered from 25 μM H2O2 treatment, higher H2O2 concentrations led to a decline in the TAC. Altogether, these results showed that the viscoelastic properties of cells can be used to investigate cell recovery from oxidative stress, which may allow us to distinguish oxidative eustress from distress. Overall, we have demonstrated that QCM-D is a viable tool for measuring the effects of oxidative stress on the viscoelastic properties of MC3T3 cells.

Short-term effects of X-ray on viscoelastic properties of epithelial cells.

Examining the effects of ionizing radiation on the living cell is significant due to its usage in recent centuries. Investigations into the long- and short-term effects of ionizing radiation began simultaneously with its discovery. Previous studies were done on the effects of radiation on cell DNA or the biochemical cycle based on the electromagnetic radiation wavelength, intensity, and exposure time. Considering some dependent parameters like cell communication, the differentiation and the mechanical interactions of intercellular environment, and cell mechanical properties, the effects of ionizing radiation on the viscoelastic properties of cells seem to be important. The current research investigated the short-term biomechanical effects of ionizing radiation and examined the mechanical properties of cells using magnetic tweezer cytometry with nanomagnetic particles. To evaluate these effects, cells were incubated with nanomagnetic particles and then separated into controlled and irradiated groups. A 3 mGy cm2 X-ray was radiated to the irradiated group for 0.02 s. The dishes of both groups were inserted into magnetic tweezer cytometry for applying a magnetic force pulse, and the cell membrane displacement was detected by an image processing system. The creep response of the membrane was determined for viscoelastic model curve fitting. The frequency responses of the model for both groups were calculated. The results showed that radiation could decrease cell extensibility from 0.084 ± 0.001 to 0.019 ± 0.001 µm and change the storage and loss modulus as the indicator of the viscoelastic property of the material. This research explains that radiation could affect cellular mechanical properties.

Viscoelastic properties of cells: Modeling and identification by atomic force microscopy

Identification of mechanical properties of cells has previously been shown to have a great potential and effectiveness on medical diagnosis. As a result, it has gathered increasing interest of researchers over the recent years. Atomic force microscopy has become one of the prime technologies for obtaining such properties. Traditionally, local variations in elasticity has been obtained by mapping contact force during sample indentation to static Hertzian contact models. More recently, multiharmonic methods have allowed for both viscous and elastic measurements of soft samples. In this article, a new technique is presented based on dynamic modeling and identification of the sample. Essentially, the measured signals are mapped to the sample properties of the model in a least-square sense. This approach allows for easy extensibility beyond pure viscoelastic measurements. Furthermore, an iterative modeling approach can be used to best describe the measured data. The technique can be operated in either dynamic indentation viscoelastic mode, or scanning viscoelastic mode. First, a dynamic, viscoelastic model of the sample is presented. Then, the parameter identification method is described, showing exponential convergence of the parameters. A simulation study demonstrates the effectiveness of the approach in both modes of operation.

Simvastatin Treatment Modulates Mechanically-Induced Injury and Inflammation in Respiratory Epithelial Cells.

Mechanical forces in the respiratory system, including surface tension forces during airway reopening and high transmural pressures, can result in epithelial cell injury, barrier disruption and inflammation. In this study, we investigated if a clinically relevant pharmaceutical agent, Simvastatin, could mitigate mechanically induced injury and inflammation in respiratory epithelia. Pulmonary alveolar epithelial cells (A549) were exposed to either cyclic airway reopening forces or oscillatory transmural pressure in vitro and treated with a wide range of Simvastatin concentrations. Simvastatin induced reversible depolymerization of the actin cytoskeleton and a statistically significant reduction the cell's elastic modulus. However, Simvastatin treatment did not result in an appreciable change in the cell's viscoelastic properties. Simvastatin treated cells did exhibit a reduced height-to-width aspect ratio and these changes in cell morphology resulted in a significant decrease in epithelial cell injury during airway reopening. Interestingly, although very high concentrations (25-50µM) of Simvastatin resulted in dramatically less IL-6 and IL-8 pro-inflammatory cytokine secretion, 2.5µM Simvastatin did not reduce the total amount of pro-inflammatory cytokines secreted during mechanical stimulation. These results indicate that although Simvastatin treatment may be useful in reducing cell injury during airway reopening, elevated local concentrations of Simvastatin might be needed to reduce mechanically-induced injury and inflammation in respiratory epithelia.

Desmin, Mechanics and Myofibrillar Myopathies

The cytoskeleton plays a central role in transmitting and generating mechanical forces through the cell. It is composed of three interconnected networks, actin, microtubules and intermediate filaments (IF). Desmin belongs to the type III IF, specifically expressed in muscles. Desmin is essential to maintain the integrity and functioning of muscles. More than fifty mutations have been identified in the gene encoding desmin leading to rare diseases belonging to MyoFibrillar Myopathy group (MFM). These pathologies are mainly characterized by aggregates formation in muscle tissue, associated with misorganizations of the contractile apparatus. Moreover patients progressively develop muscle weakness. Currently, pathophysiology and molecular defects of MFMs remain largely unknown, and no treatments are available.In this context, the aim of our study is to clarify whether desmin mutations implicated in MFMs plays a role at early stage of expression, by impairing the properties of pre-muscular cells, the myoblasts. First we have studied the formation of desmin aggregates in living myoblasts over-expressing for 24h wild-type (WT) or different mutant desmins. We show that each mutant has a specific impact on the desmin network organization. Second we have performed mechanical measurements on C2C12 cells, focusing on the E413K mutant, which induces a large desmin network disorganization associated with important aggregate formation: we have compared the mechanical properties of WT-cells, C2C12 over-expressing desmin-WT-GFP and C2C12 overexpressing mutated desmin E413K-GFP. Visco-elastic properties of cells have been evaluated by using two custom-made set-ups, optical tweezers and a single-cell rheometer: we show that the 3 cells types share the same visco-elastic behaviour. Finally, we have investigated the impact of mutated desmin on the contractility of myoblasts, and we demonstrate that E413K-mutation significantly decreases cell contraction abilities specifically for cells with desmin aggregates, while aggregates of WT-desmin do no induce the same effect.

Viscoelastic Properties of Vascular Endothelial Cells Exposed to Uniaxial Stretch

Vascular endothelial cells (VECs) that line the interior of blood vessels are continually stretched as the vessel walls expand and contract. It is widely accepted that VECs will remodel themselves in response to this mechanical stimuli, leading to changes in cell function. Few studies, however, have analyzed the mechanical properties of these cells under stretch. We hypothesize that uniaxial stretch will cause an anisotropic realignment of actin filaments, and a change in the viscoelastic properties of the cell. To test this hypothesis, VECs were grown on a thin, transparent membrane mounted on a microscope. The membrane was stretched, consequently stretching the cells. Time-lapse sequences of the cells were taken every hour with a time resolution of 10 Hz. The random trajectories of intracellular endogenous particles were tracked using in-house algorithms. Using a novel particle tracking microrheology formulation, that takes into account the anisotropic nature of the cytoplasm, these trajectories were analyzed and the mechanical properties of VECs subjected to various stretching conditions were calculated and compared.

Dynamic cell adhesion and viscoelastic signatures distinguish normal from malignant human mammary cells using quartz crystal microbalance

During transformation of a normal cell to a cell capable of forming a cancerous growth, cellular morphology, the cytoskeleton, and focal contacts undergo significant changes. These changes should be capable of being characterized via real-time monitoring of the dynamic cell adhesion process and viscoelastic properties of cells. Here, we describe use of the quartz crystal microbalance (QCM) to distinguish the dynamic cell adhesion signatures of human normal (HMEC) versus malignant (MCF-7) mammary epithelial cells. The significantly reduced QCM responses (changes in frequency [Δ f] and motional resistance Δ R) of MCF-7 cells compared with those of HMECs mirror the cancer cells’ morphological features as observed via optical microscope. We analyzed the initial 2-h cell adhesion kinetics, suggesting cell–cell cooperativity for HMECs and no or weak cell–cell interactions for MCF-7 cells. We propose that changes of the Δ R/Δ f ratio, which we term the cell viscoelastic index ( CVI), reflect the establishment of cytoskeleton structure and dynamic viscoelastic properties of living cells. The CVI decreases significantly on initiation of cell to surface interactions as cells establish their cytoskeletal structures. During the cell adhesion process, MCF-7 cells were consistently softer, exhibiting up to a 2.5-fold smaller CVI when compared with HMECs.

Non-contact force sensing for real-time stressing of biological cells

Mechanical force sensing is an important and integral component in the study of the viscoelastic properties of biological cells. In this study, a vision-based non-contact force sensing technique for real-time stressing of biological cells by a vision-guided robotic micromanipulation system is introduced. The system is capable of providing real-time external mechanical stressing on biological cells with a predefined profile and estimating the cell membrane deformation using the proposed cell strain model. One of the phenomena manifesting the viscoelastic properties of cells is the gradual reduction of reaction force in the compressive stress under cyclic loading. The applied force with respect to the cell membrane strain and the number of stressing cycles is modelled and validated by different zebrafish embryos. The experimental results show that the proposed force model can estimate the reaction force of cell membrane with the average maximum error of 10.07%.

Influence of power-law rheology on cell injury during microbubble flows

The reopening of fluid-occluded pulmonary airways generates microbubble flows which impart complex hydrodynamic stresses to the epithelial cells lining airway walls. In this study we used boundary element solutions and finite element techniques to investigate how cell rheology influences the deformation and injury of cells during microbubble flows. An optimized Prony-Dirichlet series was used to model the cells' power-law rheology (PLR) and results were compared with a Maxwell fluid model. Results indicate that membrane strain and the risk for cell injury decreases with increasing channel height and bubble speed. In addition, the Maxwell and PLR models both indicate that increased viscous damping results in less cellular deformation/injury. However, only the PLR model was consistent with the experimental observation that cell injury is not a function of stress exposure duration. Correlation of our models with experimental observations therefore highlights the importance of using PLR in computational models of cell mechanics/deformation. These computational models also indicate that altering the cell's viscoelastic properties may be a clinically relevant way to mitigate microbubble-induced cell injury.

Comparison of analytical and inverse finite element approaches to estimate cell viscoelastic properties by micropipette aspiration

The viscoelastic properties of cells are important in predicting cell deformation under mechanical loading and may reflect cell phenotype or pathological transition. Previous studies have demonstrated that viscoelastic parameters estimated by finite element (FE) analyses of micropipette aspiration (MA) data differ from those estimated by the analytical half-space model. However, it is unclear whether these differences are statistically significant, as previous studies have been based on average cell properties or parametric analyses that do not reflect the inherent experimental and biological variability of real experimental data. To determine whether cell material parameters estimated by the half-space model are significantly different from those predicted by the FE method, we implemented an inverse FE method to estimate the viscoelastic parameters of a population of primary porcine aortic valve interstitial cells tested by MA. We found that inherent differences between the analytical and inverse FE estimation methods resulted in statistically significant differences in individual cell properties. However, in cases with small pipette to cell radius ratios and short loading periods, model-dependent differences were masked by experimental and cell-to-cell variability. Analytical models that account for finite cell-size and loading rate further relaxed the experimental conditions for which accurate cell material parameter estimates could be obtained. These data provide practical guidelines for analysis of MA data that account for the wide range of conditions encountered in typical experiments.

Biofunctional Magnetic Tweezers

MATERIALS SCIENCE The viscoelastic properties of cells and intracellular transport forces have been studied with micrometer-sized transducers that can handle relatively large forces (tens of nanonewtons). Abdelghani-Jacquin et al. have made magnetic cobalt and iron particles more cell-friendly by plating them with gold in a spontaneous electrodeless reaction to produce a uniform coating. Using thiol chemistry, they then functionalized the particles either by attaching biomolecules directly or by adding a polymer cushion formed of polysaccharides. These beads were used as magnetic tweezers to characterize the local viscoelastic properties of a soft biopolymer film, which showed a purely elastic response when a pulsed magnetic force was applied. They also measured the lateral stiffness, which is related to the shear elastic modulus. — MSL Langmuir 17 , 2129 (2001).