scholarly journals An Agent-Based Discrete Collagen Fiber Network Model of Dynamic Traction Force-Induced Remodeling

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
James W. Reinhardt ◽  
Keith J. Gooch

Microstructural properties of extracellular matrix (ECM) promote cell and tissue homeostasis as well as contribute to the formation and progression of disease. In order to understand how microstructural properties influence the mechanical properties and traction force-induced remodeling of ECM, we developed an agent-based model that incorporates repetitively applied traction force within a discrete fiber network. An important difference between our model and similar finite element models is that by implementing more biologically realistic dynamic traction, we can explore a greater range of matrix remodeling. Here, we validated our model by reproducing qualitative trends observed in three sets of experimental data reported by others: tensile and shear testing of cell-free collagen gels, collagen remodeling around a single isolated cell, and collagen remodeling between pairs of cells. In response to tensile and shear strain, simulated acellular networks with straight fibrils exhibited biphasic stress–strain curves indicative of strain-stiffening. When fibril curvature was introduced, stress–strain curves shifted to the right, delaying the onset of strain-stiffening. Our data support the notion that strain-stiffening might occur as individual fibrils successively align along the axis of strain and become engaged in tension. In simulations with a single, contractile cell, peak collagen displacement occurred closest to the cell and decreased with increasing distance. In simulations with two cells, compaction of collagen between cells appeared inversely related to the initial distance between cells. These results for cell-populated collagen networks match in vitro findings. A demonstrable benefit of modeling is that it allows for further analysis not feasible with experimentation. Within two-cell simulations, strain energy within the collagen network measured from the final state was relatively uniform around the outer surface of cells separated by 250 μm, but became increasingly nonuniform as the distance between cells decreased. For cells separated by 75 and 100 μm, strain energy peaked in the direction toward the other cell in the region in which fibrils become highly aligned and reached a minimum adjacent to this region, not on the opposite side of the cell as might be expected. This pattern of strain energy was partly attributable to the pattern of collagen compaction, but was still present when mapping strain energy divided by collagen density. Findings like these are of interest because fibril alignment, density, and strain energy may each contribute to contact guidance during tissue morphogenesis.

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
James W. Reinhardt ◽  
Keith J. Gooch

Agent-based modeling was used to model collagen fibrils, composed of a string of nodes serially connected by links that act as Hookean springs. Bending mechanics are implemented as torsional springs that act upon each set of three serially connected nodes as a linear function of angular deflection about the central node. These fibrils were evaluated under conditions that simulated axial extension, simple three-point bending and an end-loaded cantilever. The deformation of fibrils under axial loading varied <0.001% from the analytical solution for linearly elastic fibrils. For fibrils between 100 μm and 200 μm in length experiencing small deflections, differences between simulated deflections and their analytical solutions were <1% for fibrils experiencing three-point bending and <7% for fibrils experiencing cantilever bending. When these new rules for fibril mechanics were introduced into a model that allowed for cross-linking of fibrils to form a network and the application of cell traction force, the fibrous network underwent macroscopic compaction and aligned between cells. Further, fibril density increased between cells to a greater extent than that observed macroscopically and appeared similar to matrical tracks that have been observed experimentally in cell-populated collagen gels. This behavior is consistent with observations in previous versions of the model that did not allow for the physically realistic simulation of fibril mechanics. The significance of the torsional spring constant value was then explored to determine its impact on remodeling of the simulated fibrous network. Although a stronger torsional spring constant reduced the degree of quantitative remodeling that occurred, the inclusion of torsional springs in the model was not necessary for the model to reproduce key qualitative aspects of remodeling, indicating that the presence of Hookean springs is essential for this behavior. These results suggest that traction force mediated matrix remodeling may be a robust phenomenon not limited to fibrils with a precise set of material properties.


2021 ◽  
Author(s):  
Camille Douillet ◽  
Marc Nicodeme ◽  
Loïc Hermant ◽  
Vanessa Bergeron ◽  
Fabien Guillemot ◽  
...  

Abstract Fibroblasts and myofibroblasts play a central role in skin homeostasis through dermal organization and maintenance. Nonetheless, the dynamic interactions between (myo)fibroblasts and the extracellular matrix (ECM) remain poorly exploited in skin repair strategies. Indeed, there is still an unmet need for soft tissue models allowing to study the spatial-temporal remodeling properties of (myo)fibroblasts. In vivo, wound healing studies in animals are limited by species specificity. In vitro, most models rely on collagen gels reorganized by randomly distributed fibroblasts. But biofabrication technologies have significantly evolved over the past ten years. High-resolution bioprinting now allows to investigate various cellular micropatterns and the emergent tissue organizations over time. In order to harness the full dynamic properties of cells and active biomaterials, it is essential to consider “time” as the 4th dimension in soft tissue design. Following this 4D bioprinting approach, we aimed to develop a novel model that could replicate fibroblast dynamic remodeling in vitro. For this purpose, (myo)fibroblasts were patterned on collagen gels with laser-assisted bioprinting (LAB) to study the generated matrix deformations and reorganizations. First, distinct populations, mainly composed of fibroblasts or myofibroblasts, were established in vitro to account for the variety of fibroblastic remodeling properties. Then, LAB was used to organize both populations on collagen gels in even isotropic patterns with high resolution, high density and high viability. With maturation, bioprinted patterns of fibroblasts and myofibroblasts reorganized into dispersed or aggregated cells, respectively. Stress-release contraction assays revealed that these phenotype-specific pattern maturations were associated with distinct lattice tension states. The two populations were then patterned in anisotropic rows in order to direct the cell-generated deformations and to orient global matrix remodeling. Only maturation of anisotropic fibroblast patterns, but not myofibroblasts, resulted in collagen anisotropic reorganizations both at tissue-scale, with lattice contraction, and at microscale, with embedded microbead displacements. Following a 4D bioprinting approach, LAB patterning enabled to elicit and orient the dynamic matrix remodeling mechanisms of distinct fibroblastic populations and organizations on collagen. For future studies, this method provides a new versatile tool to investigate in vitro dermal organizations and properties, processes of remodeling in healing, and new treatment opportunities.


2021 ◽  
Author(s):  
Bashar Emon ◽  
M Saddam H Joy ◽  
M Taher A Saif

Abstract Cell-matrix interactions, mediated by cellular force and matrix remodeling, result in a dynamic reciprocity that drives numerous biological processes and disease progression. Currently, there is no available method for direct quantification cell traction force and matrix remodeling in 3D matrices as a function of time. To address this long-standing need, we recently developed a high-resolution microfabricated sensor1 that measures cell force, tissue-stiffness and can apply mechanical stimulation to the tissue. Here the tissue self-assembles and self-integrates with the sensor. With primary fibroblasts, cancer cells and neurons, we demonstrated the feasibility of the sensor by measuring single/multiple cell force with a resolution of 1 nN, and tissue stiffness1 due to matrix remodeling by the cells. The sensor can be translated into a high-throughput system for clinical assays such as patient-specific drug and phenotypic screening. In this paper, we present the detailed protocol for manufacturing the sensors, preparing experimental setup, developing assays with different tissues, and for imaging and analyzing the data.


2016 ◽  
Vol 113 (11) ◽  
pp. 2898-2903 ◽  
Author(s):  
David A. Stout ◽  
Eyal Bar-Kochba ◽  
Jonathan B. Estrada ◽  
Jennet Toyjanova ◽  
Haneesh Kesari ◽  
...  

Mechanobiology relates cellular processes to mechanical signals, such as determining the effect of variations in matrix stiffness with cell tractions. Cell traction recorded via traction force microscopy (TFM) commonly takes place on materials such as polyacrylamide- and polyethylene glycol-based gels. Such experiments remain limited in physiological relevance because cells natively migrate within complex tissue microenvironments that are spatially heterogeneous and hierarchical. Yet, TFM requires determination of the matrix constitutive law (stress–strain relationship), which is not always readily available. In addition, the currently achievable displacement resolution limits the accuracy of TFM for relatively small cells. To overcome these limitations, and increase the physiological relevance of in vitro experimental design, we present a new approach and a set of associated biomechanical signatures that are based purely on measurements of the matrix's displacements without requiring any knowledge of its constitutive laws. We show that our mean deformation metrics (MDM) approach can provide significant biophysical information without the need to explicitly determine cell tractions. In the process of demonstrating the use of our MDM approach, we succeeded in expanding the capability of our displacement measurement technique such that it can now measure the 3D deformations around relatively small cells (∼10 micrometers), such as neutrophils. Furthermore, we also report previously unseen deformation patterns generated by motile neutrophils in 3D collagen gels.


2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Claire McLeod ◽  
John Higgins ◽  
Yekaterina Miroshnikova ◽  
Rachel Liu ◽  
Aliesha Garrett ◽  
...  

The formation of microvascular networks (MVNs) is influenced by many aspects of the microenvironment, including soluble and insoluble biochemical factors and the biophysical properties of the surrounding matrix. It has also become clear that a dynamic and reciprocal interaction between the matrix and cells influences cell behavior. In particular, local matrix remodeling may play a role in driving cellular behaviors, such as MVN formation. In order to explore the role of matrix remodeling, an in vitro model of MVN formation involving suspending human umbilical vein endothelial cells within collagen hydrogels was used. The resulting cell and matrix morphology were microscopically observed and quantitative metrics of MVN formation and collagen gathering were applied to the resulting images. The macroscopic compaction of collagen gels correlates with the extent of MVN formation in gels of different stiffness values, with compaction preceding elongation leading to MVN formation. Furthermore, the microscopic analysis of collagen between cells at early timepoints demonstrates the alignment and gathering of collagen between individual adjacent cells. The results presented are consistent with the hypothesis that endothelial cells need to gather and align collagen between them as an early step in MVN formation.


2019 ◽  
Author(s):  
Leeya Engel ◽  
Guido Gaietta ◽  
Liam P. Dow ◽  
Mark F. Swift ◽  
Gaspard Pardon ◽  
...  

ABSTRACTCryogenic electron tomography is the highest resolution tool available for structural analysis of macromolecular organization inside cells. Micropatterning of extracellular matrix (ECM) proteins is an established in vitro cell culture technique used to control cell shape. Recent traction force microscopy studies have shown correlation between cell morphology and the regulation of force transmission. However, it remains unknown how cells sustain increased strain energy states and localized stresses at the supramolecular level. Here, we report a technology to enable direct observation of mesoscale organization in epithelial cells under morphological modulation, using a maskless protein photopatterning method to confine cells to ECM micropatterns on electron microscopy substrates. These micropatterned cell culture substrates can be used in mechanobiology research to correlate changes in nanometer-scale organization at cell-cell and cell-ECM contacts to strain energy states and traction stress distribution in the cell.


2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Elizabeth J. Wright ◽  
Nigel W. Hodson ◽  
Michael J. Sherratt ◽  
Moustapha Kassem ◽  
Andrew L. Lewis ◽  
...  

Background.Mesenchymal stem cells (MSCs) and glucagon-like peptide-1 (GLP-1) are being tested as treatment strategies for myocardial infarction (MI); however, their mechanisms in the heart are not fully understood.Methods.We examined the effects of MSCs, either native, or engineered to secrete a GLP-1 fusion protein (MSCs ± GLP-1), on human cardiomyocyte apoptosisin vitro. The effect on cardiac remodeling when encapsulated in alginate beads (CellBeads-MSC and CellBeads-MSC + GLP-1) was also evaluated in a pig MI model, whereby pigs were treated with Empty Beads, CellBeads-MSC, or CellBeads-MSC + GLP-1 and sacrificed at one or four weeks following MI.Results.MSC + GLP-1 conditioned media demonstrated antiapoptotic effects on ischaemic human cardiomyocytesin vitro.In vivo,qRT-PCR revealed large changes in the expression of several genes involved in extracellular matrix remodeling, which were altered following MSC ± GLP treatment. After four weeks, infarcted areas were imaged using atomic force microscopy, demonstrating significant alterations between groups in the structure of collagen fibrils and resulting scar.Conclusions.These data demonstrate that MSCs ± GLP-1 exhibit modulatory effects on healing post-MI, affecting both apoptosis and collagen scar formation. These data support the premise that both MSCs and GLP-1 could be beneficial in MI treatment.


Author(s):  
Zhenhua Hu ◽  
Dimitris Metaxas ◽  
Leon Axel

Mechanical properties of the myocardium have been investigated intensively in the past four decades. Due to the non-linearity and history dependence of myocardial deformation, many complex strain energy functions have been used to describe the stress-strain relationship in the myocardium. These functions are good at fitting in-vitro experimental data from myocardial stretch testing into strain energy functions. However, it is difficult to model in-vivo myocardium by using strain energy functions. In a previous paper [1], we have implemented a transversely anisotropic material model to estimate in-vivo strain and stress in the myocardium. In this work, the fiber orientation is updated at each time step from the end of diastole to the end of systole; the stiffness matrix is recalculated using the current fiber orientation. We also extend our model to include residual ventricular stresses and time-dependent blood pressure in the ventricular cavities.


1990 ◽  
Vol 1 (3) ◽  
pp. 278-285
Author(s):  
R Mangoo-Karim ◽  
J J Grantham

Renal cysts develop from microscopic tubules and may enlarge progressively several thousandfold. Sustained epithelial proliferation, intracavitary fluid accumulation, and extracellular matrix remodeling are central elements in a multistep process that leads to the formation and enlargement of cysts. MDCK cells suspended within medium-hydrated collagen gels grow to form spherical, monolayered, fluid-filled cysts that enlarge steadily. Vasopressin and other agents that increase intracellular levels of cAMP stimulate the rate of MDCK cyst growth and net fluid/solute secretion when added to defined medium in vitro. In this model, net fluid secretion is the only means by which fluid can accumulate within the cyst cavity. We used this cyst-forming line of epithelial cells to evaluate several membrane transport properties that are important in the coupled movements of solute and water in the process of secretory fluid transport. Individual cysts were microdissected from collagen gels, held by a micropipet in a thermostated chamber, and examined at a high magnification by video microscopy. Transepithelial water flow was initiated by rapidly exchanging the bath medium with hyperosmotic solutions. Net water flux, Jv, determined from the initial rate of decrease in cyst diameter, was proportionate to the transmembrane osmotic gradient of NaCl or raffinose; the reflection coefficient for NaCl was indistinguishable from 1.0. Osmotic water permeability (cm3/cm2/osm/min x 10(-6)) was 739 +/- 99 (N = 11) in medium augmented by an NaCl concentration of 100 mosmol/kg. Hydraulic conductivity (Pt), estimated in control cysts, was 6.8 +/- 0.9 microns/s, a value similar to that of medullary and cortical thick ascending limbs of Henle.(ABSTRACT TRUNCATED AT 250 WORDS)


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