Mechanical microscopy of cancer cells: TGF-ß induced epithelial to mesenchymal transition corresponds to low intracellular viscosity in cancer cells.

Viscosity is an essential parameter that regulates bio-molecular reaction rates of diffusion-driven cellular processes. Hence, abnormal viscosity levels are often associated with various diseases and malfunctions like cancer. For this reason, monitoring intracellular viscosity becomes vital. While several approaches have been developed for in vitro and in vivo measurement of viscosity, analysis of intracellular viscosity in live cells has not yet been well realized. Our research introduces a novel, natural frequency-based, non-invasive method to determine the intracellular viscosity in cells. This method can not only efficiently analyze the differences in intracellular viscosity post modulation with molecules like PEG or glucose but is sensitive enough to distinguish the difference in intra-cellular viscosity among various cancer cell lines such as Huh-7, MCF-7, and MDAMB-231. Interestingly, TGF-ß a cytokine reported to induce epithelial to mesenchymal transition (EMT), a feature associated with cancer invasiveness resulted in reduced viscosity of cancer cells, as captured through our method. To corroborate our findings with existing methods of analysis, we analyzed intra-cellular viscosity with a previously described viscosity-sensitive molecular rotor-based fluorophore-TPSII. In parity with our position sensing device (PSD)-based approach, an increase in fluorescence intensity was observed with viscosity enhancers, while, TGF-ß exposure resulted in its reduction in the cells studied. This is the first study of its kind that attempts to characterize differences in intracellular viscosity using a novel, non-invasive PSD-based method.

Modulating the Mechanical Resonance of Huh-7 Cells Based on Elasticity of Adhesion Proteins.

The atomic force microscope (AFM) has been used in cell biology for a decade. AFM is a unique tool for investigating the viscoelastic characteristics of live cells in culture and mapping the spatial distribution of mechanical properties, giving an indirect signal of the underlying cytoskeleton and cell organelles. Although several experimental and numerical studies were conducted to analyze the mechanical properties of the cells. We established the non-invasive Position Sensing Device (PSD) technique to evaluate the resonance behavior of the Huh-7 cells. This technique results in the natural frequency of the cells. Obtained experimental frequencies were compared with the numerical AFM modeling. Most of the numerical analysis were based on the assumed shape and geometry. In this study, we propose a new method for numerical AFM characterization of Huh-7 cells to estimate its mechanical behavior. We capture the actual image and geometry of the trypsinized Huh-7 cells. These real images are then used for numerical modeling. The natural frequency of the cells was evaluated and found to be in the range of 24 kHz. Furthermore, the impact of focal adhesion (FA's) stiffness on the fundamental frequency of the Huh-7 cells was investigated. There has been a 6.5 times increase in the natural frequency of the Huh-7 cells on increasing the FA's stiffness from 5 pN/nm to 500 pN/nm. This indicates that the mechanical behavior of FA's leads to change the resonance behavior of the Huh-7 cell. Hence FA's are the key element in controlling the dynamics of the cell. These measurements can enhance our understanding of normal and pathological cell mechanics and potentially improve disease etiology, diagnosis, and therapy choices. The proposed technique and numerical approach are further useful in selecting the target therapies parameters (frequency) and evaluating of mechanical properties of the cells.

Modelling the Effect of Geometry and Loading on Mechanical Response of SARS-CoV-2.

In recent times, coronavirus (SARS-CoV-2) becomes a pandemic disease across the globe. This virus affects the severe acute respiratory system that causes a type of pneumonia, which results in an outbreak in Wuhan, China, and then in whole global countries. The virus possesses a complex structure and varied in composition along with its geometrical shape and size. Contributions of the lipid and protein components of a virus to the influenza viral envelope's mechanical properties are still unknown. In this work, the virus is modeled like the SARS-CoV-2 and surrounded with spikes made up of S glycoproteins, and numerical analysis was made to predict its mechanical behavior while resting on the substrate. The static and viscoelastic response of the virus was carried out in a finite element (FE) commercial software Ansys. The impact of changing viral envelope thickness on SARS-CoV-2 and bald virus stiffness was investigated. The viscoelastic analysis shows the increase in the deformation and stress with an increase in the pressure. The static analysis predicts the lower stiffness for SARS-CoV-2 compared to bald virion and increases with the increase in the envelop thickness. This study is useful for analyzing the effect of geometry and mechanical properties on the mechanical response of SARS-CoV-2.