Different Passive Viscoelastic Properties Between the Left and Right Ventricles in Healthy Adult Ovine

2021 ◽  
Author(s):  
Wenqiang Liu ◽  
Michael Nguyen-Truong ◽  
Matt Ahern ◽  
Kevin Labus ◽  
Christian Puttlitz ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Viscoelastic Properties ◽  
Healthy Adult ◽  
Ex Vivo ◽  
Longitudinal Direction ◽  
Mechanical Tests ◽  
Mortality And Morbidity ◽  
Linear Viscoelastic ◽  
Left And Right ◽  
Relaxation Curves

Abstract Ventricle dysfunction is the most common cause of heart failure, which leads to high mortality and morbidity. The mechanical behavior of the ventricle is critical to its physiological function. It is known that the ventricle is anisotropic and viscoelastic. However, the understanding of ventricular viscoelasticity is much less than that of its elasticity. Moreover, the left and right ventricles (LV&RV) are different in embryologic origin, anatomy, and function, but whether they distinguish in viscoelastic properties is unclear. We hypothesized that passive viscoelasticity is different between healthy LVs and RVs. Ex vivo cyclic biaxial tensile mechanical tests (1, 0.1, 0.01Hz) and stress relaxation (strain of 3, 6, 9, 12 15%) were performed for ventricles from healthy adult sheep. Outflow track direction was defined as the longitudinal direction. Hysteresis stress-strain loops and stress relaxation curves were obtained to quantify the viscoelastic properties. We found that the RV had more pronounced frequency-dependent viscoelastic changes than the LV. Under the physiological frequency (1Hz), the LV was more anisotropic in the elasticity and stiffer than the RV in both directions, whereas the RV was more anisotropic in the viscosity and more viscous than the LV in the longitudinal direction. The LV was quasi-linear viscoelastic in the longitudinal but not circumferential direction, and the RV was non-linear viscoelastic in both directions. This study is the first to investigate passive viscoelastic differences in healthy LVs and RVs, and the findings will deepen the understanding of biomechanical mechanisms of ventricular function.

scholarly journals Evaluation of Electrospun Nanofiber-Anchored Silicone for the Degenerative Intervertebral Disc

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
M. Khandaker ◽  
S. Riahanizad
Keyword(s):  
Intervertebral Disc ◽  
Viscoelastic Properties ◽  
Mechanical Stability ◽  
Ex Vivo ◽  
Electrospun Fiber ◽  
Mechanical Tests ◽  
Tissue Properties ◽  
Clinical Potential ◽  
Fiber Mesh ◽  
Mesh Anchoring

The nucleus pulposus (NP) substitution by polymeric gel is one of the promising techniques for the repair of the degenerative intervertebral disc (IVD). Silicone gel is one of the potential candidates for a NP replacement material. Electrospun fiber anchorage to silicone disc, referred as ENAS disc, may not only improve the biomechanical performances of the gel but it can also improve restoration capability of the gel, which is unknown. This study successfully produced a novel process to anchor any size and shape of NP gel with electrospun fiber mesh. Viscoelastic properties of silicone and ENAS disc were measured using standard experimental techniques and compared with the native tissue properties. Ex vivo mechanical tests were conducted on ENAS disc-implanted rabbit tails to the compare the mechanical stability between intact and ENAS implanted spines. This study found that viscoelastic properties of ENAS disc are higher than silicone disc and comparable to the viscoelastic properties of human NP. The ex vivo studies found that the ENAS disc restore the mechanical functionality of rabbit tail spine, after discectomy of native NP and replacing the NP by ENAS disc. Therefore, the PCL ENF mesh anchoring technique to a NP implant can have clinical potential.

An Experimental and Analytical Evaluation of the Nonlinear Viscoelastic Properties of the Healing Medial Collateral Ligament in a Goat Model

2003 ◽  
Author(s):  
S. D. Abramowitch ◽  
T. D. Clineff ◽  
R. E. Debski ◽  
S. L.-Y. Woo
Keyword(s):  
Stress Relaxation ◽  
Medial Collateral Ligament ◽  
Viscoelastic Properties ◽  
Soft Tissues ◽  
Viscoelastic Behavior ◽  
Collateral Ligament ◽  
Relaxation Experiment ◽  
Nonlinear Viscoelastic ◽  
Linear Viscoelastic Behavior ◽  
Linear Viscoelastic

The medial collateral ligament (MCL) is one of the most frequently injured ligaments in the knee. Although it can heal spontaneously after rupture, laboratory studies have shown that the mechanical properties of the healing MCL remain inferior to normal for up to two years after injury (1). Additionally, the healing MCL has been shown to display increased amounts of stress relaxation and creep (2). In order to more completely describe the viscoelastic properties of healing ligaments, we propose to use the Quasi-Linear Viscoelastic (QLV) theory formulated by Fung (1972). This theory has been used to successfully describe the viscoelastic properties of many soft-tissues (3). Recently, our research center has developed an improved approach to determine the constants describing the QLV theory based on data collected from a stress relaxation experiment that utilizes a slow strain rate during loading. This approach allows for experimental errors that commonly result from fast strain rates to be avoided (ex. overshoot) (4). Therefore, the objective of this study were to use this new approach to determine the constants describing the quasi-linear viscoelastic behavior of the healing goat MCL at 12 weeks after injury.

scholarly journals The Interventricular Septum Is Biomechanically Distinct from the Ventricular Free Walls

2021 ◽  
Vol 8 (12) ◽  
pp. 216
Author(s):  
Michael Nguyen-Truong ◽  
Wenqiang Liu ◽  
Courtney Doherty ◽  
Kristen LeBar ◽  
Kevin Labus ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Constitutive Modeling ◽  
Interventricular Septum ◽  
Longitudinal Direction ◽  
Mechanical Tests ◽  
Septal Wall ◽  
New Findings ◽  
Left And Right ◽  
Heart Physiology ◽  
Pumping Function

The interventricular septum contributes to the pumping function of both ventricles. However, unlike the ventricular wall, its mechanical behavior remains largely unknown. To fill the knowledge gap, this study aims to characterize the biaxial and transmural variation of the mechanical properties of the septum and compare it to the free walls of the left and right ventricles (LV/RV). Fresh hearts were obtained from healthy, adult sheep. The septal wall was sliced along the mid-line into two septal sides and compared to the epicardial layers of the LV- and RV-free walls. Biaxial tensile mechanical tests and constitutive modeling were performed to obtain the passive mechanical properties of the LV- and RV-side of the septum and ventricular walls. We found that both sides of the septum were significantly softer than the respective ventricular walls, and that the septum presented significantly less collagen than the ventricular walls. At low strains, we observed the symmetric distribution of the fiber orientations and a similar anisotropic behavior between the LV-side and RV-side of the septum, with a stiffer material property in the longitudinal direction, rather than the circumferential direction. At high strains, both sides showed isotropic behavior. Both septal sides had similar intrinsic elasticity, as evidenced by experimental data and constitutive modeling. These new findings offer important knowledge of the biomechanics of the septum wall, which may deepen the understanding of heart physiology.

An In-Vivo Measurement and Analysis of Viscoelastic Properties of the Spinal Cord of Cats

1988 ◽  
Vol 110 (2) ◽  
pp. 115-122 ◽  
Author(s):  
Guan-Liang Chang ◽  
Tin-Kan Hung ◽  
William W. Feng
Keyword(s):  
Spinal Cord ◽  
Stress Relaxation ◽  
Viscoelastic Properties ◽  
Nonlinear Characteristics ◽  
In Vivo Measurement ◽  
Recovery Curves ◽  
Measurement And Analysis ◽  
Linear Viscoelastic ◽  
Prolonged Stress

An in-vivo experimental technique was employed to determine the linear and nonlinear characteristics of viscoelastic properties of the spinal cord of anesthetized cats. The stress relaxation and recovery curves were reproducible in a group of cat experiments. The data of linear viscoelastic properties were used to develop a power law model with Boltzmann’s convolution integral. The model was capable of predicting a prolonged stress relaxation and recovery curve. For larger deformation, the results were quantified using a nonlinear analysis of viscoelastic response of the spinal cord under the uniaxial experiment.

Effect of Induced Incomplete Ossification of the Humeral Condyle on Ex Vivo Humeral Condylar Biomechanics

2020 ◽  
Author(s):  
Logan M. Scheuermann ◽  
Michael G. Conzemius
Keyword(s):  
Mechanical Testing ◽  
Study Design ◽  
Ex Vivo ◽  
Peak Load ◽  
Testing System ◽  
Condylar Fracture ◽  
Naturally Occurring ◽  
Left And Right ◽  
Condylar Fractures ◽  
Humeral Condyle

Abstract Objective The aim of this study was to investigate the effects of an induced incomplete ossification of the humeral condyle (IOHC) lesion on ex vivo canine humeral condylar biomechanics. Study Design Nine paired cadaveric elbows were collected from mature dogs weighing between 20 and 25 kg. Left and right limbs were randomized to IOHC or normal groups. Limbs were prepared for mechanical testing; ligaments were preserved and an IOHC lesion was created. Elbows were potted, positioned into a biomaterials testing system at an angle of 135 degrees and axially loaded to failure at a rate of 30 mm/minute. Results Induced IOHC lesions reduced peak load (p = 0.02) when compared with an intact humerus. There was no difference between stiffness (p = 0.36) of intact humeri or humeri with an induced IOHC lesion. An induced IOHC lesion increased (p = 0.012) the probability of intracondylar fracture under load. Conclusion Cadaveric humeri are weakened by the creation of an intracondylar osteotomy and fractures secondary to induced IOHC are similar to spontaneous humeral condylar fractures. These findings support the hypothesis that naturally occurring IOHC weakens the humeral condyle and may predispose to humeral condylar fracture.

scholarly journals Viscoelastic Properties of Cell Structures Manufactured Using a Photo-Curable Additive Technology—PJM

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1895
Author(s):  
Tomasz Kozior ◽  
Czesław Kundera
Keyword(s):  
Viscoelastic Properties ◽  
Cellular Structure ◽  
Material Selection ◽  
Cellular Structures ◽  
Test Results ◽  
Additive Technology ◽  
Polymer Resin ◽  
Cell Structures ◽  
Relaxation Curves ◽  
The Impact

This research paper reviews the test results involving viscoelastic properties of cellular structure models made with the PolyJet Matrix—PJM additive technology. The designed test specimens were of complex cellular structure and made of three various photo-curable polymer resin types. Materials were selected taking into account the so-called “soft” and “tough” material groups. Compressive stress relaxation tests were conducted in accordance with the recommendations of standard ISO 3384, and the impact of the geometric structure shape and material selection on viscoelastic properties, as well as the most favorable geometric variants of the tested cellular structure models were determined. Mathematica and Origin software was used to conduct a statistical analysis of the test results and determine five-parameter functions approximating relaxation curves. The most favorable rheological was adopted and its mean parameters determined, which enables to match both printed model materials and their geometry in the future, to make a component with a specific rheological response. Furthermore, the test results indicated that there was a possibility of modelling cellular structures within the PJM technology, using support material as well.

Preparation, Characterization and Processing of PCL/PHO Blends by 3D Bioplotting

2020 ◽  
Vol 35 (5) ◽  
pp. 458-470
Author(s):  
S. Gopi ◽  
B. A. Ramsay ◽  
J. A. Ramsay ◽  
M. Kontopoulou
Keyword(s):  
Viscoelastic Properties ◽  
Biomedical Applications ◽  
Synergistic Effects ◽  
Thermal And Mechanical Properties ◽  
Flow Properties ◽  
Immiscible Blends ◽  
Melt Compounding ◽  
Linear Viscoelastic ◽  
Matrix Morphology ◽  
Good Flow

Abstract Blends of polycaprolactone (PCL) and poly(3-hydroxyoctanoate) P(3HO) were prepared by melt compounding. These immiscible blends exhibited droplet-matrix morphology at compositions up to 30 wt% P(3HO). Even though the addition of amorphous P(3HO) decreased the crystallinity of PCL, the crystallization temperature of the blends increased by 6 to 7 8C. Blends containing up to 30 wt% P(3HO) had higher crystallization rates, and lower crystallization half-times compared to neat PCL. The viscosity of PCL decreased upon addition of P(3HO), making the blends suitable for processing using a 3D bioplotter. Compositions with 10 to 30 wt% P(3HO) were ideal for processing, because of their improved crystallization kinetics, reduced stickiness and good flow properties. Estimation of the interfacial tension by fitting the Palierne model to the linear viscoelastic properties of the blends revealed good compatibility, which gave rise to synergistic effects in the thermal and mechanical properties. The fibres prepared by 3D bioplotting maintained droplet matrix morphology, with finer particle size than the original compounded material. In addition to favourable viscosity and thermal properties, the extruded fibres containing 30 wt% P(3HO) had comparable modulus to the neat PCL, while exhibiting good ductility. These blends may be suitable alternatives to PCL for biomedical applications, because they provide a range of crystallinities, crystallization rates and viscosities.

Study of effect of waste tire rubber which is a recycling material in production of laminated veneer lumber (LVL) boards

2021 ◽  
pp. 147776062110194
Author(s):  
Kadir Özkaya ◽  
Taner Dizel ◽  
Hasan Özgür Imirzi
Keyword(s):  
Environmental Problem ◽  
Forest Products ◽  
Longitudinal Direction ◽  
Mechanical Tests ◽  
Pinus Silvestris ◽  
Forest Products Industry ◽  
Scotch Pine ◽  
Laminated Veneer Lumber ◽  
Waste Tire ◽  
Different Types

The amount of waste produced by people increases with the increasing population in the world. Especially non-recyclable wastes have become a major environmental problem. Waste tires that emerge as car demands of people increase are one of the non-recyclable wastes. In this study, the usage possibilities of powder rubbers obtained from waste car tires were examined in the production of laminated veneer lumber (LVL) boards, which are preferred as furniture and decoration material in the forest products industry. For this, three different tree species (Scotch Pine— Pinus silvestris L., Oriental Beech— Fagus orientalis L., Stinking Juniper— Juniperus foetidissima Wild.) and two different types of glue (UF and PVAc glues) were used. Waste tire rubbers (WTR) were mixed into the glue in different proportions (0%, 10%, 20%, 30%). Physical (full dry and equilibrium moisture density, contraction in the transversal and longitudinal direction) and mechanical tests (MoR, MoE, bonding resistance) were performed on the LVL samples prepared. According to the results obtained, it has been seen that the mixtures of 10% and 20% WTR increase the LVL resistance. An eco-friendly building material has been obtained by using WTR produced from waste car tires in production of LVL.

STRESS RELAXATION OF MAGNETORHEOLOGICAL FLUIDS

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2655-2661
Author(s):  
W. H. LI ◽  
G. CHEN ◽  
S. H. YEO ◽  
H. DU
Keyword(s):  
Stress Relaxation ◽  
Viscoelastic Model ◽  
Relaxation Modulus ◽  
Damping Function ◽  
Mr Fluids ◽  
Large Step ◽  
Linear Viscoelastic ◽  
Predicted Values ◽  
Two Parameters ◽  
Step Strain

In this paper, the experimental and modeling study and analysis of the stress relaxation characteristics of magnetorheological (MR) fluids under step shear are presented. The experiments are carried out using a rheometer with parallel-plate geometry. The applied strain varies from 0.01% to 100%, covering both the pre-yield and post-yield regimes. The effects of step strain, field strength, and temperature on the stress modulus are addressed. For small step strain ranges, the stress relaxation modulus G(t,γ) is independent of step strain, where MR fluids behave as linear viscoelastic solids. For large step strain ranges, the stress relaxation modulus decreases gradually with increasing step strain. Morever, the stress relaxation modulus G(t,γ) was found to obey time-strain factorability. That is, G(t,γ) can be represented as the product of a linear stress relaxation G(t) and a strain-dependent damping function h(γ). The linear stress relaxation modulus is represented as a three-parameter solid viscoelastic model, and the damping function h(γ) has a sigmoidal form with two parameters. The comparison between the experimental results and the model-predicted values indicates that this model can accurately describe the relaxation behavior of MR fluids under step strains.

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