Synchronized Heterogeneous Indentation and Stress Relaxation Behavior of Articular Cartilage Upon Macroscopic Compression: A Preliminary Study

2014 ◽  
Author(s):  
Jiayue Shen ◽  
Wenting Gu ◽  
Xavier-lewis Palmer ◽  
Siqi Guo ◽  
Zhili Hao
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Viscoelastic Behavior ◽  
Relaxation Modulus ◽  
Relaxation Behavior ◽  
Indentation Modulus ◽  
Cartilage Sample ◽  
Stress Relaxation Behavior ◽  
Bovine Articular Cartilage ◽  
Preliminary Study

By using a newly-developed experimental technique that is enabled by a polymer-based microfluidic device for detecting distributed normal loads, a preliminary study is presented on the synchronized heterogeneous indentation and stress relaxation behavior of articular cartilage upon macroscopic compression. In a measurement, a rigid cylinder probe is employed to exert macroscopic indentation or step input to a cartilage sample on the device. Consequently, the synchronized heterogeneous viscoelastic behavior of the sample translates to distributed normal loads acting on the device and is captured by the device. While the macroscopic load acting on a sample is recorded by a load cell, the deflections of a sample along its length are captured by the device. Thus, the measured results essentially are the load-deflection relations of a sample along its length. Full-thickness lapine and bovine articular cartilage samples are prepared and measured. A thorough data analysis is implemented on the recorded data for extracting their instant and relaxed indentation modulus, as well as Young’s relaxation modulus.

Targeted Loss of Proteoglycans Results in Changes of Frequency-Dependent Viscoelastic Behavior of the Intact Articular Cartilage

2012 ◽  
Author(s):  
Simon Y. Tang ◽  
Tamara Alliston
Keyword(s):  
Articular Cartilage ◽  
Mechanical Behavior ◽  
Viscoelastic Behavior ◽  
Enzymatic Digestion ◽  
Cartilage Tissue ◽  
Indentation Modulus ◽  
Frequency Dependent ◽  
Bovine Articular Cartilage ◽  
Before And After ◽  
Tan Δ

Cartilage is a multi-phasic, viscoelastic material that derives its mechanical behavior of its primary constituents including collagen, proteoglycans, and water. The complex mechanical function of cartilage depends critically on the composition and balance of these constituents. We sought to determine the effects of proteoglycan loss on both the time- and frequency-dependent mechanical behavior of articular cartilage. Using cathepsin d, an enzyme that specifically cleaves proteoglycans, we assessed the in situ mechanical behavior of intact bovine articular cartilage before and after enzymatic digestion using microindentation over loading frequencies ranging between 0.5 hz to 20 hz. The loss of proteoglycans does not affect the elastic components of mechanical behavior (indentation modulus; p = 0.67), but have significant consequences on the viscoelastic components (tan δ; p<0.001). Moreover, the changes in the viscoelastic mechanical behavior are more pronounced at higher loading frequencies (p<0.001). Taken together, these results suggest that proteoglycans are critical for providing dynamic stability for the cartilage tissue.

The Stress-Relaxation Behavior of Rice as a Function of Time, Moisture and Temperature

2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Pan Wang ◽  
Li-jun Wang ◽  
Dong Li ◽  
Zhi-gang Huang ◽  
Benu Adhikari ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Moisture Content ◽  
Master Curve ◽  
Superposition Principle ◽  
Relaxation Modulus ◽  
Maxwell Model ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Linear Viscoelastic ◽  
Single Rice

Abstract: Stress-relaxation behavior of single rice kernel was studied using a dynamic mechanical analyzer (DMA) in compression mode. The relaxation modulus was measured in a moisture content range of 12–30 % on dry basis (d.b.) and a temperature range of 25–80°C. A constant stain value of 1 % (within the linear viscoelastic range) was selected during the stress-relaxation tests. The relaxation modulus was found to decrease as the temperature and moisture increased. A master curve of relaxation modulus as a function of temperature and moisture content was generated using the time–moisture–temperature superposition principle. Results showed that the generalized Maxwell model satisfactorily fitted the experimental data of the stress-relaxation behavior and the master curve of relaxation modulus (R2> 0.997). By shifting the temperature curves horizontally, the activation energy of the stress relaxation was obtained which significantly decreased with increase in the moisture content.

Tensile Stress Relaxation of Thermosetting Polyurethane Solid and Foam

2010 ◽  
Author(s):  
Bipul Barua ◽  
Mrinal C. Saha
Keyword(s):  
Stress Relaxation ◽  
Rectangular Cross Section ◽  
Tensile Force ◽  
Relaxation Modulus ◽  
Relaxation Behavior ◽  
Characteristic Relaxation Time ◽  
Foam Formation ◽  
Stress Relaxation Behavior ◽  
Different Temperatures ◽  
Cure Temperature

Stress relaxation behavior of thermosetting polyurethane (PU) solid and foam were investigated in tensile mode using a dynamic mechanical analyzer (DMA). PU solid samples were manufactured in a closed mold under compression to avoid any foam formation, whilst the foam samples were manufactured inside a woven using a silicone mold. Effects of cure and the post-cure temperature were also investigated on the stress relaxation behavior. Samples in the form of rectangular cross-section were subjected to a predetermined amount tensile strain and the tensile force was recorded as a function of time. Relaxation modulus was determined for different temperatures up to near the glass transition temperature. It was found that the viscous part becomes dominant with increasing test temperature. The experimental data was precisely modeled using a generalized Maxwell’s model and the characteristic relaxation time was identified with the corresponding relaxation process. Although the stress relaxation behavior of PU solid and PU foams were found similar at room temperature, the relaxation behavior of the foam was found to be influenced by the cell morphology at higher temperature.

Tensile Stress Relaxation Behavior of Thermosetting Polyurethane Solid and Foams: Experiment and Model Prediction

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Bipul Barua ◽  
Mrinal C. Saha
Keyword(s):  
Stress Relaxation ◽  
Rectangular Cross Section ◽  
Tensile Force ◽  
Relaxation Modulus ◽  
Exponential Model ◽  
Relaxation Behavior ◽  
Foam Formation ◽  
Stress Relaxation Behavior ◽  
Stretched Exponential ◽  
Stretched Exponential Model

Stress relaxation behavior of thermosetting polyurethane (PU) solid and foams were investigated in tensile mode using a dynamic mechanical analyzer (DMA). PU solid samples were manufactured in a closed mold to avoid any foam formation, whilst PU foam samples were manufactured inside a woven using a silicone mold. Samples with rectangular cross-section were subjected to a predetermined amount of tensile strain and the tensile force was recorded as a function of time. Relaxation modulus was determined for different temperatures up to near the glass transition temperature. It was found that the viscous part becomes more dominant with increasing test temperature. Although the stress relaxation behavior of PU solid and foam were found similar at lower temperature, the relaxation behavior of the foam was influenced by the cellular structure especially at higher temperature due to the combination of gas expansion and cell wall softening. Different stress relaxation models such as Maxwell model, Burgers model, Generalized Maxwell (GM) model, and Stretched exponential model were employed to predict the relaxation behavior of PU solid and foams. It was found that the GM model (with three or more elements) and the Stretched exponential model were in good agreement with the experimental data in predicting the stress relaxation behavior of both solid and foams. The predicted relaxation time and equilibrium modulus were found to decrease with increase in temperature.

scholarly journals Comparison of Compressive Stress-Relaxation Behavior in Osteoarthritic (ICRS Graded) Human Articular Cartilage

2017 ◽  
Author(s):  
Rajesh Kumar ◽  
David M. Pierce ◽  
Vidar Isaksen ◽  
Catharina de Lange Davies ◽  
Jon O. Drogset ◽  
...  
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Computational Models ◽  
Articular Surface ◽  
Significant Loss ◽  
Relaxation Behavior ◽  
Human Articular Cartilage ◽  
Osteoarthritic Cartilage ◽  
Human Cartilage ◽  
Stress Relaxation Behavior

Osteoarthritis (OA) is a common joint disorder found mostly in elderly people. The role of mechanical behavior in the progression of OA is complex and remains unclear. The stress-relaxation behavior of human articular cartilage in clinically defined osteoarthritic stages may have importance in diagnosis and prognosis of OA. In this study we investigated differences in the biomechanical responses among human cartilage of ICRS grades I, II and III using polymer dynamics theory. We collected 24 explants of human articular cartilage (eight each of ICRS grade I, II and III) and acquired stress-relaxation data applying a continuous load on the articular surface of each cartilage explant for 1180 s. We observed a significant decrease in Young&rsquo;s modulus, stress-relaxation time, and stretching exponent in advanced stages of OA (ICRS grade III). The stretch exponential model indicated that significant loss in hyaluronic acid polymer might be the reason for the loss of proteoglycan in advanced OA. This work encourages further biomechanical modelling of osteoarthritic cartilage utilizing these data as input parameters to enhance the fidelity of computational models aimed at revealing how mechanical behaviors play a role in pathogenesis of OA.

Stress Relaxation Measurement of Agar Using a Polymer-Based Microfluidic Device

2013 ◽  
Author(s):  
Jiayue Shen ◽  
Peng Cheng ◽  
Wenting Gu ◽  
Michael Stacey ◽  
Zhili Hao
Keyword(s):  
Stress Relaxation ◽  
Microfluidic Device ◽  
Series Representation ◽  
Relaxation Modulus ◽  
Soft Materials ◽  
Maxwell Model ◽  
Relaxation Behavior ◽  
Relaxation Measurement ◽  
Stress Relaxation Behavior ◽  
Prony Series Representation

In light of the significance of the viscoelastic property of agar to cell-based tissue engineering, this paper presents the stress relaxation measurement of agar using a polymer-based microfluidic device. Comprised of a single polymer rectangular microstructure and a set of electrolyte-enabled distributed transducers, this device is capable of detecting continuous distributed static and dynamic loads. In the measurement, an agar specimen is placed on the device and a rigid probe is utilized to press the specimen against the device with a step displacement input. Consequently, the stress relaxation behavior of the specimen translates to time-dependent continuous distributed loads acting on the device and is further registered as discrete resistance changes by the device. Two agar specimens of 1% and 3% in concentration, respectively, are measured using this device; and the data analysis is conducted on the measured results to extract Young’s relaxation modulus, which is further expressed by a Prony-series representation of the Maxwell model with two exponential terms. The results demonstrate the feasibility of using this device to measure the stress relaxation behavior of soft materials.

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