Remodeling in Cell-Seeded Fibrin Gels: Changes in Composition, Organization, and Planar Biaxial Mechanical Behavior

2009 ◽  
Author(s):  
Edward A. Sander ◽  
Sandra L. Johnson ◽  
Victor H. Barocas ◽  
Robert T. Tranquillo
Keyword(s):  
Aspect Ratio ◽  
Stress Field ◽  
Mechanical Behavior ◽  
The Other ◽  
Fibrin Gel ◽  
Fiber Alignment ◽  
Mechanical Environment ◽  
Heterogeneous Sample ◽  
Fibrin Gels ◽  
Stress Environment

Engineered tissues are necessary to replace diseased and damaged tissues incapable of healing on their own. One method employed to produce them involves cell entrapment in a fibrin gel constrained by specially designed molds [1]. As the cells compact and remodel the gel, the combination of mold constraints and cell tractions produces fiber alignment similar to native tissues [2]. One potentially important factor in the remodeling outcome is the local mechanical environment that develops during the compaction and remodeling process. It is well established that the global stress environment leads to changes in remodeling in an isotropic sample [3], but we do not know the effect of local variations in stress field in a heterogeneous sample. To begin to assess the local mechanical environment’s role, we examined the remodeling process in cross-shaped Teflon molds (cruciforms). In this experiment, two mold geometries with differing channel widths were examined: a 1:1 aspect ratio in which the both axes possessed 8 mm wide channels, and a 1:0.5 aspect ratio in which one axis had 8 mm wide channels and the other 4 mm wide channels (fig. 1).

scholarly journals Planar Biaxial Mechanical Behavior of Bioartificial Tissues Possessing Prescribed Fiber Alignment

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Choon-Sik Jhun ◽  
Michael C. Evans ◽  
Victor H. Barocas ◽  
Robert T. Tranquillo
Keyword(s):  
Aspect Ratio ◽  
Mechanical Behavior ◽  
Mechanical Response ◽  
Great Influence ◽  
Mechanical Anisotropy ◽  
Fiber Direction ◽  
Modulus Ratio ◽  
Biaxial Testing ◽  
Fiber Alignment ◽  
Aspect Ratios

Though it is widely accepted that fiber alignment has a great influence on the mechanical anisotropy of tissues, a systematic study of the influence of fiber alignment on the macroscopic mechanical behavior by native tissues is precluded due to their predefined microstructure and heterogeneity. Such a study is possible using collagen-based bioartificial tissues that allow for alignment to be prescribed during their fabrication. To generate a systemic variation of strength of fiber alignment, we made cruciform tissue constructs in Teflon molds that had arms of different aspect ratios. We implemented our anisotropic biphasic theory of tissue-equivalent mechanics to simulate the compaction by finite element analysis. Prior to tensile testing, the construct geometry was standardized by cutting test samples with a 1:1 cruciform punch after releasing constructs from the molds. Planar biaxial testing was performed on these samples, after stretching them to their in-mold dimensions to recover in-mold alignment, to observe the macroscopic mechanical response with simultaneous fiber alignment imaging using a polarimetry system. We found that the strength of fiber alignment of the samples prior to release from the molds linearly increased with anisotropy of the mold. In testing after release, modulus ratio (modulus in fiber direction/modulus in normal direction) was greater as the initial strength of fiber alignment increased, that is, as the aspect ratio increased. We also found that the fiber alignment strength and modulus ratio increased in a hyperbolic fashion with stretching for a sample of given aspect ratio.

Fibroblast-Mediated Fiber Realignment in Fibrin Gels

2013 ◽  
Author(s):  
Aribet M. De Jesus ◽  
Maziar Aghvami ◽  
Edward A. Sander
Keyword(s):  
Time Lapse ◽  
Dermal Fibroblasts ◽  
Initial Alignment ◽  
Fibrin Gel ◽  
Traction Forces ◽  
Fiber Alignment ◽  
Fibrin Gels ◽  
Mechanical Constraints ◽  
Ecm Proteins ◽  
Cell Traction

When fibroblasts are added to a fibrin gel, the cells rapidly compact the gel and produce a fiber alignment pattern that depends in part on the cell traction forces, gel geometry, and gel mechanical constraints [1]. Over time the fibrin is digested and replaced with cell synthesized collagen and other extracellular matrix (ECM) proteins that follow the initial alignment pattern of the gel [2]. This remodeling process proceeds in a complex and integrated manner that is influenced by the mechanical environment [3]. In order to better understand fibroblast-fibrin interactions and the remodeling process, we obtained time-lapse images of the development of fiber alignment between clusters of dermal fibroblasts (i.e., explants) in a fibrin gel. The experimental results were then compared to a model that incorporated the effects of traction forces on ECM reorganization.

Driver’s Drowsiness Detection Using Dlib and IOT

2020 ◽  
Vol 10 ◽  
Author(s):  
Prasanna Lakshmi Kompalli ◽  
Padma Vallakati ◽  
Ganapathi Raju Nadimpalli ◽  
Vinod Mahesh Jain ◽  
Samuel Annepogu
Keyword(s):  
Aspect Ratio ◽  
The Other ◽  
Human Intervention ◽  
Road Accidents ◽  
Online Content ◽  
Facial Landmarks ◽  
Drowsiness Detection ◽  
Rear Part ◽  
Cause Of Deaths ◽  
Published Paper

Background: Road accidents are major cause of deaths worldwide. This is enormously due to fatigue, drowsiness and microsleep of the drivers. This don’t just risk the life of driver and copassengers but also a great threat to the vehicles and humans moving around that vehicle. Methods: Research, online content and previously published paper related to drowsiness are reviewed. Using the facial landmarks DAT file, the prototype will locate and get the eye coordinates and it will calculate Eye Aspect Ratio (EAR). The EAR indicates whether the driver is drowsy or not based on the result various sensors gets activated such as Alarm generator, LED Indicators, LCD message scroll, message sent to owner and engine gets locked. Results: The prototype is able to locate eyes in the frame and detect whether the person is sleepy or not. Whenever the person is feeling drowsy alarm gets generated in the cabinet on further if the person is feeling drowsy, LED indicators will start glowing, messaging will be scrolling at the rear part of vehicle so that other vehicles and humans gets cautioned and vehicle slows down and engine gets locked. Conclusion: This prototype will help in reduction of road accidents due to human intervention. It is not only helpful to the person who install it in their vehicles but also for the other vehicles and humans moving around it.

Modeling the Large Deformation and Microstructure Evolution of Nonwoven Polymer Fiber Networks

2018 ◽  
Vol 86 (1) ◽  
Author(s):  
Mang Zhang ◽  
Yuli Chen ◽  
Fu-pen Chiang ◽  
Pelagia Irene Gouma ◽  
Lifeng Wang
Keyword(s):  
Mechanical Properties ◽  
Aspect Ratio ◽  
Mechanical Behavior ◽  
Large Deformation ◽  
Biological Tissues ◽  
High Porosity ◽  
Polymer Fiber ◽  
Fiber Networks ◽  
Fiber Aspect Ratio ◽  
Network Microstructure

The electrospinning process enables the fabrication of randomly distributed nonwoven polymer fiber networks with high surface area and high porosity, making them ideal candidates for multifunctional materials. The mechanics of nonwoven networks has been well established for elastic deformations. However, the mechanical properties of the polymer fibrous networks with large deformation are largely unexplored, while understanding their elastic and plastic mechanical properties at different fiber volume fractions, fiber aspect ratio, and constituent material properties is essential in the design of various polymer fibrous networks. In this paper, a representative volume element (RVE) based finite element model with long fibers is developed to emulate the randomly distributed nonwoven fibrous network microstructure, enabling us to systematically investigate the mechanics and large deformation behavior of random nonwoven networks. The results show that the network volume fraction, the fiber aspect ratio, and the fiber curliness have significant influences on the effective stiffness, effective yield strength, and the postyield behavior of the resulting fiber mats under both tension and shear loads. This study reveals the relation between the macroscopic mechanical behavior and the local randomly distributed network microstructure deformation mechanism of the nonwoven fiber network. The model presented here can also be applied to capture the mechanical behavior of other complex nonwoven network systems, like carbon nanotube networks, biological tissues, and artificial engineering networks.

Effect of Specimen Geometry on the Predicted Mechanical Behavior of Polyethylene Pipe Material

2014 ◽  
Author(s):  
Tarek M. A. A. El-Bagory ◽  
Tawfeeq A. R. Alkanhal ◽  
Maher Y. A. Younan
Keyword(s):  
Mechanical Behavior ◽  
Longitudinal Direction ◽  
Primary Objective ◽  
The Other ◽  
Pipe Material ◽  
Ring Specimen ◽  
Design Data ◽  
Practical Applications ◽  
Other Hand ◽  
Gauge Section

The primary objective of the present paper is to depict the mechanical behavior of high density polyethylene, (HDPE), pipes under different loading conditions with different specimen geometries to provide the designer with reliable design data relevant to practical applications. Therefore, it is necessary to study the effect of strain rate, ring configuration, and grip or fixture type on the mechanical behavior of dumb-bell-shaped, (DBS), and ring specimens made from HDPE pipe material. DBS and ring specimens are cut from the pipe in longitudinally, and circumferential (transverse) direction respectively. On the other hand, the ring specimen configuration is classified into two types; full ring, (FR), and notched ring, (NR) (equal double notch from two sides of notched ring specimen) specimens according to ASTM D 2290-12 standard. Tensile tests are conducted on specimens cut out from the pipe with thickness 10 mm at different crosshead speeds (10–1000 mm/min), and ambient temperature, Ta = 20 °C to investigate the mechanical properties of DBS, and ring specimens. In the case of test specimens taken from longitudinal direction from the pipe a necking phenomenon before failure appears at different locations along the gauge section. On the other hand, the fracture of NR specimens occurs at one notched side. The results demonstrated that the NR specimen has higher yield stress than DBS, and FR specimens at all crosshead speeds. The present experimental work reveals that the crosshead speed has a significant effect on the mechanical behavior of both DBS, and ring specimens. The fixture type plays an important role in the mechanical behavior for both FR and NR specimens at all crosshead speeds.

The magnetic flux and self-inductivity of a thick toroidal current

2007 ◽  
Vol 73 (5) ◽  
pp. 741-756 ◽  
Author(s):  
TOMISLAV ŽIC ◽  
BOJAN VRŠNAK ◽  
MARINA SKENDER
Keyword(s):  
Aspect Ratio ◽  
Magnetic Flux ◽  
Magnetic Energy ◽  
The Other ◽  
Poloidal Field ◽  
Other Hand ◽  
Radial Profiles ◽  
Internal Flux ◽  
The Difference ◽  
Better Than

AbstractWe investigate numerically the magnetic flux and self-inductivity of a toroidal current I of arbitrary aspect ratio (R0/r0 = 1/η, where R0 and r0 are the major and the minor torus radii, respectively). The total flux Ψ is represented by the sum of the flux outside the torus envelope (Ψo) and the internal flux within the torus body (Ψi). Analogously, the total inductivity is expressed as L = Lo + Li. The outside self-inductivity is determined directly from the magnetic flux Ψo, utilizing Ψo = LoI. On the other hand, the internal inductivity is evaluated as the magnetic energy contained in the poloidal field. The calculations are performed for three different radial profiles of the current density, j(r).It is found that Ψo(η) and Lo (η) depend only very weakly on the form of j(r). On the other hand, Ψi and Li do not depend on η, but depend on the form of j(r). In the range 0.02 ≲ η ≲ 0.5, the numerical values of Lo can be very well fitted by the function of the form Lofit1(η) = −A log(η) − B. Such a relation is analogous to that for a slender torus, although the coefficients are different. For η ≲ 0.01 the slender-torus approximation (Lo*) matches the numerical results better than our function Lofit1, whereas for thicker tori, Lofit1 becomes more appropriate. It is shown that, beyond η ≳ 0.1, the departure of the slender-torus analytical expression from the numerical values becomes greater than 10%, and the difference becomes larger than 100% at η 0.55. In the range η 0.5, the numerical values of Lo can be very well expressed by the function Lofit2(η)=c1 (1 − η)c2. Furthermore, since the internal flux and inductivity become larger than that outside the envelope, Ψi and Li become larger than Ψo and Lo. The total inductivity Ltotfit = Lofit + Li, calculated by appropriately employing our functions Lofit1 and Lofit2, never deviates by more than 1% from the numerically determined values of Ltot.

scholarly journals Fibrin regulates neutrophil migration in response to interleukin 8, leukotriene B4, tumor necrosis factor, and formyl-methionyl-leucyl-phenylalanine.

1995 ◽  
Vol 181 (5) ◽  
pp. 1763-1772 ◽  
Author(s):  
J D Loike ◽  
J el Khoury ◽  
L Cao ◽  
C P Richards ◽  
H Rascoff ◽  
...  
Keyword(s):  
Extracellular Matrix ◽  
Polyethylene Glycol ◽  
Tumor Necrosis Factor ◽  
Tumor Necrosis ◽  
Leukotriene B4 ◽  
Interleukin 8 ◽  
Matrix Proteins ◽  
Fibrin Gel ◽  
Fibrin Gels ◽  
Necrosis Factor

We have examined the capacity of four different chemoattractants/cytokines to promote directed migration of polymorphonuclear leukocytes (PMN) through three-dimensional gels composed of extracellular matrix proteins. About 20% of PMN migrated through fibrin gels and plasma clots in response to a gradient of interleukin 8 (IL-8) or leukotriene B4 (LTB4). In contrast, < 0.3% of PMN migrated through fibrin gels in response to a gradient of tumor necrosis factor alpha (TNF) or formyl-methionyl-leucyl-phenylalanine (FMLP). All four chemoattractants stimulated PMN to migrate through gels composed of collagen IV or of basement membrane proteins (Matrigel), or through filters to which fibronectin or fibrinogen had been adsorbed. PMN stimulated with TNF or FMLP adhered and formed zones of close apposition to fibrin, as measured by the exclusion of a 10-kD rhodamine-polyethylene glycol probe from the contact zones between PMN and the underlying fibrin gel. By this measure, IL-8- or LTB4-treated PMN adhered loosely to fibrin, since 10 kD rhodamine-polyethylene glycol permeated into the contact zones between these cells and the underlying fibrin gel. PMN stimulated with FMLP and IL-8, or FMLP and LTB4, exhibited very little migration through fibrin gels, and three times as many of these cells excluded 10 kD rhodamine-polyethylene glycol from their zones of contact with fibrin as PMN stimulated with IL-8 or LTB4 alone. These results show that PMN chemotaxis is regulated by both the nature of the chemoattractant and the composition of the extracellular matrix; they suggest that certain combinations of chemoattractants and matrix proteins may limit leukocyte movements and promote their localization in specific tissues in vivo.

Experimental Study for Proximity Rule of Multiple Flaws for Ductile Fracture

2004 ◽  
Author(s):  
Katsumasa Miyazaki ◽  
Kunio Hasegawa ◽  
Takeshi Shimamura
Keyword(s):  
Aspect Ratio ◽  
Ductile Fracture ◽  
Fracture Behavior ◽  
Maximum Load ◽  
Tensile Tests ◽  
Fracture Pattern ◽  
The Other ◽  
Plastic Collapse ◽  
Intensity Factors ◽  
Class 1

The proximity rule of multiple flaws in ASME B&PV Code Section XI 2003 addenda was mainly determined by the evaluation of stress intensity factors from the viewpoint of brittle fracture. Since the austenitic steel and carbon steel for class 1 piping shows a ductile manner in fracture, a new proximity rule for ductile fracture is required. To understand the fracture behavior of multiple flaws, tensile tests, using flat plate specimens made of Type 304SS with twin flaws, were conducted. When the shapes of twin flaws were semi-circular with aspect ratio, a/l = 0.5, the effect of the space of multiple flaws on maximum load is clear. On the other hand, the effect of flaw spacing on maximum load was insignificant for flat multiple flaws with 0.167 in a/l. The effect of space of multiple flaws, aspect ratio of multiple flaws on ductile fracture pattern was discussed. Finally, the proximity rule for plastic collapse was proposed in this paper.

Collagen Network Architecture Varies Between Pure Collagen and Collagen-Fibrin Co-Gels

2012 ◽  
Author(s):  
Victor K. Lai ◽  
Allan M. Kerandi ◽  
Spencer P. Lake ◽  
Robert T. Tranquillo ◽  
Victor H. Barocas
Keyword(s):  
Mechanical Behavior ◽  
Network Architecture ◽  
Rational Design ◽  
Structural Integrity ◽  
Collagen Network ◽  
Fibrin Gel ◽  
Ecm Proteins ◽  
Fibrin Networks ◽  
Pure Collagen ◽  
Function Relationship

Naturally-occurring extracellular matrix (ECM) proteins, e.g. collagen I and fibrin, play an important role in tissues, conferring structural integrity and providing a biochemical environment for eliciting important cellular responses (e.g. migration). Tissue engineers use a variety of matrix polymers as initial scaffolds for seeding cells, sometimes in combination with one another (e.g. collagen-fibrin [1]). For example, our group fabricates arterial tissue equivalents (TEs) by seeding cells in a fibrin gel, which is gradually degraded over time and replaced by cell-produced collagen [2]. While the structure and mechanics of individual ECM proteins have been studied extensively, how multiple fibrillar networks interact to confer overall mechanical behavior remains poorly understood. Narrowing this gap in knowledge of scaffolds comprising multiple fibril networks is crucial in allowing for more rational design in tissue engineering, as cells react differently according to their mechanical environments. For collagen-fibrin networks in particular, early efforts in elucidating interactions between these two fibril networks in co-gels have proven inconclusive due to inconsistent findings from various groups. Recent modeling efforts by our group have shown that simple “series” and “parallel” type interactions provide bounds for the mechanical behavior of collagen-fibrin co-gels [3]. In addition, experiments on pure collagen and fibrin vs. their respective networks from collagen-fibrin co-gels after digestion showed slight differences in mechanical behavior [4]. These previous studies have focused on the composition-function relationship between collagen and fibrin. The objective of the current work is to explore how collagen network architecture changes in the presence of the fibrin network in collagen-fibrin co-gels, thereby providing an added dimension to our understanding of collagen-fibrin systems by elucidating structure-composition-function relationships between collagen and fibrin.

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