scholarly journals Increased stiffness and flow resistance of the inner wall of Schlemm’s canal in glaucomatous human eyes

2019 ◽  
Vol 116 (52) ◽  
pp. 26555-26563 ◽  
Author(s):  
Amir Vahabikashi ◽  
Ariel Gelman ◽  
Biqin Dong ◽  
Lihua Gong ◽  
Elliott D. K. Cha ◽  
...  
Keyword(s):  
Ocular Hypertension ◽  
Flow Resistance ◽  
Tissue Stiffness ◽  
Schlemm’S Canal ◽  
Force Microscopy ◽  
Schlemm's Canal ◽  
Afm Indentation ◽  
Atomic Force ◽  
Tissue Surface ◽  
Human Eyes

The cause of the elevated outflow resistance and consequent ocular hypertension characteristic of glaucoma is unknown. To investigate possible causes for this flow resistance, we used atomic force microscopy (AFM) with 10-µm spherical tips to probe the stiffness of the inner wall of Schlemm’s canal as a function of distance from the tissue surface in normal and glaucomatous postmortem human eyes, and 1-µm spherical AFM tips to probe the region immediately below the tissue surface. To localize flow resistance, perfusion and imaging methods were used to characterize the pressure drop in the immediate vicinity of the inner wall using giant vacuoles that form in Schlemm’s canal cells as micropressure sensors. Tissue stiffness increased with increasing AFM indentation depth. Tissues from glaucomatous eyes were stiffer compared with normal eyes, with greatly increased stiffness residing within ∼1 µm of the inner-wall surface. Giant vacuole size and density were similar in normal and glaucomatous eyes despite lower flow rate through the latter due to their higher flow resistance. This implied that the elevated flow resistance found in the glaucomatous eyes was localized to the same region as the increased tissue stiffness. Our findings implicate pathological changes to biophysical characteristics of Schlemm’s canal endothelia and/or their immediate underlying extracellular matrix as cause for ocular hypertension in glaucoma.

Material Property Characterization of Costal Cartilage Using AFM Indentation

2009 ◽  
Author(s):  
S. Tripathy ◽  
E. J. Berger
Keyword(s):  
Material Characterization ◽  
Costal Cartilage ◽  
Indentation Modulus ◽  
Hertz Contact ◽  
Force Microscopy ◽  
Afm Indentation ◽  
Atomic Force ◽  
Macro Scale ◽  
Property Characterization

Costal cartilage is one of the load bearing tissues of the rib cage. Literature on the material characterization of the costal cartilage is limited. Atomic force microscopy has been extremely successful in characterizing the elastic properties of articular cartilage, but no studies have been published on costal cartilage. In this study AFM indentations on human costal cartilage were performed and compared with macro scale indentation data. Spherical beaded tips of three sizes were used for the AFM indentations. The Hertz contact model for spherical indenter was used to analyze the data and obtain the Young’s modulus. The costal cartilage was found to be almost linearly elastic till 600 nm of indentation depth. It was also found that the modulus values decreased with the distance from the junction. The modulus values from macro indentations were found to be 2-fold larger than the AFM indentation modulus.

scholarly journals LIM-Nebulette Reinforces Podocyte Structural Integrity by Linking Actin and Vimentin Filaments

2020 ◽  
Vol 31 (10) ◽  
pp. 2372-2391 ◽  
Author(s):  
Xuhua Ge ◽  
Tao Zhang ◽  
Xiaoxia Yu ◽  
Alecia N. Muwonge ◽  
Nanditha Anandakrishnan ◽  
...  
Keyword(s):  
Structural Integrity ◽  
Rho Gtpase ◽  
Focal Adhesions ◽  
Super Resolution ◽  
Actin Binding ◽  
Puromycin Aminonucleoside ◽  
Force Microscopy ◽  
Afm Indentation ◽  
Atomic Force ◽  
Key Aspects

BackgroundMaintenance of the intricate interdigitating morphology of podocytes is crucial for glomerular filtration. One of the key aspects of specialized podocyte morphology is the segregation and organization of distinct cytoskeletal filaments into different subcellular components, for which the exact mechanisms remain poorly understood.MethodsCells from rats, mice, and humans were used to describe the cytoskeletal configuration underlying podocyte structure. Screening the time-dependent proteomic changes in the rat puromycin aminonucleoside–induced nephropathy model correlated the actin-binding protein LIM-nebulette strongly with glomerular function. Single-cell RNA sequencing and immunogold labeling were used to determine Nebl expression specificity in podocytes. Automated high-content imaging, super-resolution microscopy, atomic force microscopy (AFM), live-cell imaging of calcium, and measurement of motility and adhesion dynamics characterized the physiologic role of LIM-nebulette in podocytes.ResultsNebl knockout mice have increased susceptibility to adriamycin-induced nephropathy and display morphologic, cytoskeletal, and focal adhesion abnormalities with altered calcium dynamics, motility, and Rho GTPase activity. LIM-nebulette expression is decreased in diabetic nephropathy and FSGS patients at both the transcript and protein level. In mice, rats, and humans, LIM-nebulette expression is localized to primary, secondary, and tertiary processes of podocytes, where it colocalizes with focal adhesions as well as with vimentin fibers. LIM-nebulette shRNA knockdown in immortalized human podocytes leads to dysregulation of vimentin filament organization and reduced cellular elasticity as measured by AFM indentation.ConclusionsLIM-nebulette is a multifunctional cytoskeletal protein that is critical in the maintenance of podocyte structural integrity through active reorganization of focal adhesions, the actin cytoskeleton, and intermediate filaments.

Analysis of Indentation: Implications for Measuring Mechanical Properties With Atomic Force Microscopy

1999 ◽  
Vol 121 (5) ◽  
pp. 462-471 ◽  
Author(s):  
K. D. Costa ◽  
F. C. P. Yin
Keyword(s):  
Indentation Depth ◽  
Constitutive Law ◽  
Elastic Materials ◽  
Force Microscopy ◽  
Linear Elastic ◽  
Afm Indentation ◽  
Atomic Force ◽  
Afm Probe ◽  
Nonlinear Elastic ◽  
Indenter Geometry

Indentation using the atomic force microscope (AFM) has potential to measure detailed micromechanical properties of soft biological samples. However, interpretation of the results is complicated by the tapered shape of the AFM probe tip, and its small size relative to the depth of indentation. Finite element models (FEMs) were used to examine effects of indentation depth, tip geometry, and material nonlinearity and heterogeneity on the finite indentation response. Widely applied infinitesimal strain models agreed with FEM results for linear elastic materials, but yielded substantial errors in the estimated properties for nonlinear elastic materials. By accounting for the indenter geometry to compute an apparent elastic modulus as a function of indentation depth, nonlinearity and heterogeneity of material properties may be identified. Furthermore, combined finite indentation and biaxial stretch may reveal the specific functional form of the constitutive law—a requirement for quantitative estimates of material constants to be extracted from AFM indentation data.

scholarly journals Simultaneous in vivo time-lapse stiffness mapping and fluorescence imaging of developing tissue

2018 ◽  
Author(s):  
Amelia J. Thompson ◽  
Iva K. Pillai ◽  
Ivan B. Dimov ◽  
Christine E. Holt ◽  
Kristian Franze
Keyword(s):  
Fluorescence Imaging ◽  
Temporal Dynamics ◽  
Time Lapse ◽  
Tissue Mechanics ◽  
Tissue Stiffness ◽  
Time Resolved ◽  
Force Microscopy ◽  
Atomic Force ◽  
Spatio Temporal

AbstractTissue mechanics is important for development; however, the spatio-temporal dynamics of in vivo tissue stiffness is still poorly understood. We here developed tiv-AFM, combining time-lapse in vivo atomic force microscopy with upright fluorescence imaging of embryonic tissue, to show that in the developing Xenopus brain, a stiffness gradient evolves over time because of differential cell proliferation. Subsequently, axons turn to follow this gradient, underpinning the importance of time-resolved mechanics measurements.

scholarly journals Cortical cell stiffness is independent of substrate mechanics

2019 ◽  
Author(s):  
Johannes Rheinlaender ◽  
Andrea Dimitracopoulos ◽  
Bernhard Wallmeyer ◽  
Nils M. Kronenberg ◽  
Kevin J. Chalut ◽  
...  
Keyword(s):  
Cortical Cell ◽  
Cell Stiffness ◽  
Soft Substrate ◽  
Hertz Model ◽  
Force Microscopy ◽  
Afm Indentation ◽  
Atomic Force ◽  
Cell Substrate ◽  
Substrate Model ◽  
Cellular Property

AbstractCortical stiffness is an important cellular property that changes during migration, adhesion, and growth. Previous atomic force microscopy (AFM) indentation measurements of cells cultured on deformable substrates suggested that cells adapt their stiffness to that of their surroundings. Here we show that the force applied by AFM onto cells results in a significant deformation of the underlying substrate if it is softer than the cells. This ‘soft substrate effect’ leads to an underestimation of a cell’s elastic modulus when analyzing data using a standard Hertz model, as confirmed by finite element modelling (FEM) and AFM measurements of calibrated polyacrylamide beads, microglial cells, and fibroblasts. To account for this substrate deformation, we developed the ‘composite cell-substrate model’ (CoCS model). Correcting for the substrate indentation revealed that cortical cell stiffness is largely independent of substrate mechanics, which has significant implications for our interpretation of many physiological and pathological processes.

scholarly journals Predicting local tissue mechanics using immunohistochemistry

2018 ◽  
Author(s):  
David E. Koser ◽  
Emad Moeendarbary ◽  
Stefanie Kuerten ◽  
Kristian Franze
Keyword(s):  
Nervous Tissue ◽  
Tissue Mechanics ◽  
Tissue Stiffness ◽  
Force Microscopy ◽  
Local Tissue ◽  
Atomic Force ◽  
Local Stiffness ◽  
Sophisticated Technology

AbstractLocal tissue stiffness provides an important signal to which cells respond in vivo. However, assessing tissue mechanics is currently challenging and requires sophisticated technology. We here developed a model quantitatively predicting nervous tissue stiffness heterogeneities at cellular resolution based on cell density, myelin and GFAP fluorescence intensities. These histological parameters were identified by a correlation analysis of atomic force microscopy-based elasticity maps of spinal cord sections and immunohistochemical stainings. Our model provides a simple tool to estimate local stiffness distributions in nervous tissue, and it can easily be expanded to other tissue types, thus paving the way for studies of the role of mechanical signals in development and pathology.

Measuring Viscoelasticity of Soft Samples Using Atomic Force Microscopy

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
S. Tripathy ◽  
E. J. Berger
Keyword(s):  
Atomic Force Microscopy ◽  
Soft Tissues ◽  
Relaxation Times ◽  
Indentation Test ◽  
Strain History ◽  
Force Microscopy ◽  
Afm Indentation ◽  
Atomic Force ◽  
Dependent Part ◽  
Soft Samples

Relaxation indentation experiments using atomic force microscopy (AFM) are used to obtain viscoelastic material properties of soft samples. The quasilinear viscoelastic (QLV) model formulated by Fung (1972, “Stress Strain History Relations of Soft Tissues in Simple Elongation,” in Biomechanics, Its Foundation and Objectives, Prentice-Hall, Englewood Cliffs, NJ, pp. 181–207) for uniaxial compression data was modified for the indentation test data in this study. Hertz contact mechanics was used for the instantaneous deformation, and a reduced relaxation function based on continuous spectrum is used for the time-dependent part in the model. The modified QLV indentation model presents a novel method to obtain viscoelastic properties from indentation data independent of relaxation times of the test. The major objective of the present study is to develop the QLV indentation model and implement the model on AFM indentation data for 1% agarose gel and a viscoelastic polymer using spherical indenter.

An Atomic Force Microscopy Indentation Study of Biomaterial Properties

2005 ◽  
Author(s):  
E. J. Berger ◽  
S. Tripathy ◽  
K. Vemaganti ◽  
Y. M. Kolambkar ◽  
H. X. You ◽  
...  
Keyword(s):  
Atomic Force Microscopy ◽  
Soft Materials ◽  
Data Interpretation ◽  
Close Relative ◽  
Small Scale ◽  
Force Microscopy ◽  
Afm Indentation ◽  
Atomic Force ◽  
Biomechanical Investigation ◽  
Series Type

Atomic force microscopy (AFM) is a powerful and increasingly common modality of biomechanical investigation, including imaging, force spectroscopy, and microrheology. AFM indentation of biomaterials requires use of a contact model for data interpretation and material property extraction, and a large segment of the scientific community uses the Hertz model or a close relative for small-scale indentation of thin, soft materials in high strain applications. We present experimental results and analytical/numerical modeling which lead to two main conclusions: (i) Hertzian mechanics are useful in a surprisingly large parameter range, including scenarios in which the underlying assumptions are seemingly violated, and (ii) the Hertz solution serves as a useful base from which power-series type solutions can be derived for a variety of non-Hertzian effects.

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