Now showing 1 - 10 of 12
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    Analysis on the effect of eye globe diameters on the biomechanics of posterior ocular tissues during horizontal adduction
    (01-08-2022)
    Goyal, Arsh
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    Swaminathan, Ramakrishnan
    In this work, an attempt has been made to analyze the influence of pathological changes in eye globe dimensions towards the mechanical responses of optic nerve head tissues during eye adductions. For this study, a 3D baseline model geometry of posterior ocular tissues has been constructed. The eye globe diameters of the model are modified to mimic the changes in ocular globe morphology in control, glaucoma, myopia and glaucoma with myopia conditions. Adductions are simulated for each modified model as the rotation of the globe from 1ºto 10ºin steps of 1º. von Mises strain in lamina cribrosa (LC) and posterior displacement of LC are estimated. Results show that strains developed in LC and its posterior displacement are higher in diseased eyes compared to healthy eyes. It appears that eyes with higher axial length and globe anisotropy are more susceptible to optic nerve head damage. This study might be extended to assess the progression of glaucomatous optic neuropathy.
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    Anisotropic 3D confinement of MCF-7 cells induces directed cell-migration and viscoelastic anisotropy of cell-membrane
    (01-01-2023)
    Edwin, Privita Edwina Rayappan George
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    Kumar, Sumeet
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    Roy, Srestha
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    Tumor-associated collagen signature-3 (TACS-3) is a prognostic indicator for breast cancer survival. It is characterized by highly organized, parallel bundles of collagen fibers oriented perpendicular to the tumor boundary, serving as directional, confining channels for cancer cell invasion. Here we design a TACS-3-mimetic anisotropic, confined collagen I matrix and examine the relation between anisotropy of matrix, directed cellular migration, and anisotropy of cell membrane-the first direct contact between TACS-3 and cell-using Michigan Cancer Foundation-7 (MCF-7) cells as cancer-model. Using unidirectional freezing, we generated ∼50 μm-wide channels filled with collagen I. Optical tweezer (OT) microrheology shows that anisotropic confinement increases collagen viscoelasticity by two orders of magnitude, and the elastic modulus is significantly greater along the direction of anisotropic confinement compared to that along the orthogonal direction, thus establishing matrix anisotropy. Furthermore, MCF-7 cells embedded in anisotropic collagen I, exhibit directionality in cellular morphology and migration. Finally, using customized OT to trap polystyrene probes bound to cell-membrane (and not to ECM) of either free cells or cells under anisotropic confinement, we quantified the effect of matrix anisotropy on membrane viscoelasticity, both in-plane and out-of-plane, vis-à-vis the membrane. Both bulk and viscous modulus of cell-membrane of MCF-7 cells exhibit significant anisotropy under anisotropic confinement. Moreover, the cell membrane of MCF-7 cells under anisotropic confinement is significantly softer (both in-plane and out-of-plane moduli) despite their local environment being five times stiffer than free cells. In order to test if the coupling between anisotropy of extracellular matrix and anisotropy of cell-membrane is regulated by cell-cytoskeleton, actin cytoskeleton was depolymerized for both free and confined cells. Results show that cell membrane viscoelasticity of confined MCF-7 cells is unaffected by actin de-polymerization, in contrast to free cells. Together, these findings suggest that anisotropy of ECM induces directed migration and correlates with anisotropy of cell-membrane viscoelasticity of the MCF-7 cells in an actin-independent manner.
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    Detection of sub-degree angular fluctuations of the local cell membrane slope using optical tweezers
    (28-08-2020)
    Vaippully, Rahul
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    Ramanujan, Vaibavi
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    Normal thermal fluctuations of the cell membrane have been studied extensively using high resolution microscopy and focused light, particularly at the peripheral regions of a cell. We use a single probe particle attached non-specifically to the cell-membrane to determine that the power spectral density is proportional to (frequency)-5/3 in the range of 5 Hz to 1 kHz. We also use a new technique to simultaneously ascertain the slope fluctuations of the membrane by relying upon the determination of pitch motion of the birefringent probe particle trapped in linearly polarized optical tweezers. In the process, we also develop the technique to identify pitch rotation to a high resolution using optical tweezers. We find that the power spectrum of slope fluctuations is proportional to (frequency)-1, which we also explain theoretically. We find that we can extract parameters like bending rigidity directly from the coefficient of the power spectrum particularly at high frequencies, instead of being convoluted with other parameters, thereby improving the accuracy of estimation. We anticipate this technique for determination of the pitch angle in spherical particles to high resolution as a starting point for many interesting studies using the optical tweezers. This journal is
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    Thermodynamically-consistent constitutive modeling of aligned Silk fibroin sponges: Theory and application to uniaxial compression
    (01-05-2018)
    Panda, Debojyoti
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    Konar, Subhajit
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    Arockiarajan, A.
    Microstructurally-aligned Silk fibroin sponges have emerged as a viable candidate for replicating the anisotropic fibrous microarchitecture that is encountered in several functional tissues in vivo. But for the material to reach its full potential in terms of its application in biomimetic soft tissue constructs or scaffolds, a complete understanding and quantification of its nonlinear viscoelastic response in the finite strain regime is needed. To address this gap from the mechanical modeling perspective, an anisotropic, nonlinear, viscoelastic model is developed within a thermodynamic framework in this study, to capture the macroscopic response of these sponges in a phenomenological manner. The rate-type constitutive equations that are developed in the process are subsequently applied for the case of uniaxial compression, and satisfactorily corroborated against the results from finite strain viscoelastic characterization experiments done on hydrated Silk fibroin sponges under uniaxial compression for different constituent material concentrations of the sponges ranging from 1 w/v % - 4 w/v %.
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    Morphology and cellular-traction of fibroblasts on 2D silk-fibroin hydrogel substrates
    (01-01-2022)
    Edwin, Privita Edwina Rayappan George
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    Rajagopalan, Neeraj Raghuraman
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    Development of clinically amenable bio-implants with silk-fibroin (SF) necessitates characterization of cellular-traction generated between cells and the substrate. However, studies on the biomechanical response of cells on SF substrates are limited. In this study, we prepared SF hydrogels of varying compliance (SF30 and SF50) and varying surface-ligands (derivatized with poly-L-lysine (PLL) or Arg-Gly-Asp (RGD) peptide). Subsequently, NIH-3T3 fibroblast cells were grown on these substrates, and the morphological changes was examined. It was observed that the increase in SF stiffness from 0.7 kPa to 3.1 kPa decreased nucleus-to-cytoplasm area-ratio and increased asymmetricity along the major-axis of cells. Moreover, while functionalization of SF with RGD induced increase in cell-area and circularity, functionalization with PLL did not cause any change. Next, using traction-force-microscopy (TFM), we quantified 2D cell-traction for NIH-3T3 cells cultured on SF hydrogels. Cells plated on SF50 hydrogel exhibited significantly high traction stress as compared to SF30; change of functionalization did not show significant change. Also, protrusion traction stress was found to be greater than nuclear traction stress. Put together, our results suggest that surface-stiffness of SF-hydrogel, rather than nature of surface-ligand, regulates both cellular morphology and cellular traction stresses.
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    Comparison of translational and rotational modes towards passive rheology of the cytoplasm of MCF-7 cells using optical tweezers
    (09-01-2023)
    Roy, Srestha
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    Vaippully, Rahul
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    Lokesh, Muruga
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    Nalupurackal, Gokul
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    Edwina, Privita
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    A colloidal particle placed inside the cell cytoplasm is enmeshed within a network of cytoskeletal fibres immersed in the cytosolic fluid. The translational mode is believed to yield different rheological parameters than the rotational mode, given that these modes stretch the fibers differently. We compare the parameters for Michigan Cancer Foundation-7 (MCF-7) cells in this manuscript and find that the results are well comparable to each other. At low values of 0 Hz viscosity, the rotational and translational viscoelasticity matches well. However, discrepancies appear at higher values which may indicate that the cytoskeletal modes involved in rotation and translation of the particle are getting invoked. We also show that the 0 Hz viscosity increases as the cell ages under the conditions of constant room temperature of 25°C on the sample chamber.
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    Synthesis and viscoelastic characterization of microstructurally aligned Silk fibroin sponges
    (01-07-2017)
    Panda, Debojyoti
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    Konar, Subhajit
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    Arockiarajan, A.
    Silk fibroin (SF) is a model candidate for use in tissue engineering and regenerative medicine owing to its bio-compatible mechanochemical properties. Despite numerous advances made in the fabrication of various biomimetic substrates using SF, relatively few clinical applications have been designed, primarily due to the lack of complete understanding of its constitutive properties. Here we fabricate microstructurally aligned SF sponge using the unidirectional freezing technique wherein a novel solvent-processing technique involving Acetic acid is employed, which obviates the post-treatment of the sponges to induce their water-stability. Subsequently, we quantify the anisotropic, viscoelastic response of the bulk SF sponge samples by performing a series of mechanical tests under uniaxial compression over a wide range of strain rates. Results for these uniaxial compression tests in the finite strain regime through ramp strain and ramp-relaxation loading histories applied over two orders of strain rate magnitude show that microstructural anisotropy is directly manifested in the bulk viscoelastic solid-like response. Furthermore, the experiments reveal a high degree of volume compressibility of the sponges during deformation, and also evince for their remarkable strain recovery capacity under large compressive strains during strain recovery tests. Finally, in order to predict the bulk viscoelastic material properties of the fabricated and pre-characterized SF sponges, a finite strain kinematics-based, nonlinear, continuum model developed within a thermodynamically-consistent framework in a parallel investigation, was successfully employed to capture the viscoelastic solid-like, transversely isotropic, and compressible response of the sponges macroscopically.
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    Measurement of viscoelastic properties of the cellular cytoplasm using optically trapped Brownian probes
    (12-03-2020)
    Vaippully, Rahul
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    Ramanujan, Vaibavi
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    Measurement of the viscoelastic properties of a cell using microscopic tracer particles has been complicated given that the medium viscosity is dependent upon the size of the measurement probe leading to reliability issues. Further, a technique for direct calibration of optically trapped particles in vivo has been elusive due to the frequency dependence and spatial inhomogeneity of the cytoplasmic viscosity, and the requirement of accurate knowledge of the medium refractive index. Here, we employ a recent extension of Jeffery's model of viscoelasticity in the microscopic domain to fit the passive motional power spectra of micrometer-sized optically trapped particles embedded in a viscoelastic medium. We find excellent agreement between the 0 Hz viscosity in MCF7 cells and the typical values of viscosity in literature, between 2 to 16 mPa sec expected for the typical concentration of proteins inside the cytoplasmic solvent. This bypasses the dependence on probe size by relying upon small thermal displacements. Our measurements of the relaxation time also match values reported with magnetic tweezers, at about 0.1 s. Finally, we calibrate the optical tweezers and demonstrate the efficacy of the technique to the study of in vivo translational motion.
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    Collagen-I/silk-fibroin biocomposite exhibits microscalar confinement of cells and induces anisotropic morphology and migration of embedded fibroblasts
    (01-07-2020)
    Konar, Subhajit
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    Edwina, Privita
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    Ramanujam, Vaibavi
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    Arockiarajan, Arunachalakasi
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    Microstructural anisotropy of tumor-associated matrix correlates with invasion of cancer cells into the surrounding matrix during metastasis. Here, we report the fabrication and characterization of a three-dimensional (3D) silk-fibroin/collagen-I bio-composite based cell-culture model that exhibits microstructural and biochemical anisotropy. Using RGD-deficient silk-fibroin fibers to confine collagen-I gelation, we develop a silk-fibroin/collagen-I (SFC) bio-composite in a one-step process allowing control over the microstructural and biochemical anisotropy and the pore-size. Two forms of the SFC bio-composite are reported: a sandwich (Sfc) configuration amenable to live-cell microscopy and an unsupported membrane (Mfc) for use as a scaffold. Both microscalar and macroscalar mechanical properties of the SFC bio-composite are characterized using atomic force microscope (AFM)-based indentation and tensile-testing. We find that the modulus of stiffness of both Sfc and Mfc can be controlled and falls in the physiological range of 5–20 kPa. Furthermore, the modulus of stiffness of Mfc exhibits a ~200% increase in axial direction of microstructure, as compared to lateral direction. This implies a highly anisotropic mechanical stiffness of the microenvironment. Live-cell morphology and migration studies show that both the morphology and the migration of NIH-3 T3 fibroblasts is anisotropic and correlates with microstructural anisotropy. Our results show that SFC bio-composite permits proliferation of cells in both Sfc and Mfc configuration, promotes cell-migration along the major axis of anisotropy and together with morphological and migration data, suggest a potential application of both the composite configurations as a biomimetic scaffold for tissue engineering applications.
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    Investigation of magnetoelectric properties and biocompatibility of CoFe2O4-BaTiO3 core-shell nanoparticles for biomedical applications
    (28-10-2017)
    Rao, Badari Narayana
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    Kaviraj, P.
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    Vaibavi, S. R.
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    Kumar, Amit
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    Arockiarajan, A.
    The CoFe2O4-BaTiO3 core-shell (CFO@BTO) nanocomposites have been synthesized, and a particular volume fraction of 15% CoFe2O4-85% BaTiO3 has been studied for its magnetic, ferroelectric, and magnetoelectric properties. The optimization of synthesis conditions showed that a temperature of at least 800 °C is required to obtain pure phase BaTiO3, whereas for the tetragonality to be visible in the x-ray diffraction (XRD) pattern, BaTiO3 needed to be sintered to at least 1050 °C. Even though the CFO@BTO composite began to react at the interface at 1050 °C and a small amount of the secondary phase was observed in the XRD pattern, the ferroelectric and magnetic properties were found to be not affected. Upon treating the living epithelial cells with either CFO@BTO or BTO nanoparticles, no toxicity was observed for up to 7 days. Together, these results establish the potential for the use of CFO@BTO nanoparticles in biomedical applications.