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Indentation Testing (indentation + testing)

Distribution by Scientific Domains

Polymers and Materials Science	25%

Selected Abstracts

Indentation testing of human cartilage: Sensitivity to articular surface degeneration

ARTHRITIS & RHEUMATISM, Issue 12 2003
Won C. Bae
Objective To determine, for clinical indentation testing of human articular cartilage, the effects of aging and degeneration on indentation stiffness and traditional indices of cartilage degeneration; the relationship between indentation stiffness and indices of degeneration; and the sensitivity and specificity of indentation stiffness to cartilage degeneration. Methods Osteochondral cores from femoral condyles of cadaveric human donors were harvested. Samples were distributed into experimental groups based on donor age (young [20,39 years], middle [40,59 years], and old [,60 years]), and a macroscopic articular surface appearance that was either normal or mildly degenerate, without deep erosion. Samples were analyzed for indentation stiffness, cartilage thickness, India ink staining (quantitated as the reflected light score), and Mankin-Shapiro histopathology score. Results Indentation stiffness, India ink staining, and the histopathology score each varied markedly between normal-sample and degenerate-sample groups but varied relatively little between normal samples obtained from different age groups. A decrease in indentation stiffness (softening) correlated with a decrease in the reflectance score and an increase in the overall histopathology score, especially the surface irregularity component of the histopathology score. Receiver operating characteristic analysis suggested that the indentation testing could accurately detect cartilage degeneration as indicated by macroscopic appearance, India ink staining, and histopathology score. Conclusion The indentation stiffness of the normal to mildly degenerate samples tested in this study was sensitive to mild degeneration at the articular surface and was insensitive to changes associated with normal aging or to slight variations in cartilage thickness. This suggests that indentation testing may be a useful clinical tool for the evaluation of early-stage degenerative changes in articular cartilage. [source]

Experimental Evidence for Grain-Boundary Sliding in Ultrafine-Grained Aluminum Processed by Severe Plastic Deformation,

ADVANCED MATERIALS, Issue 1 2006
Q. Chinh
Evidence for grain boundary sliding in ultrafine-grained aluminum after processing with equal channel angular pressing (ECAP) is presented (see Figure). Pure aluminum is used as a model material; depth sensing indentation testing and atomic force microscopy are used to measure the nature of the displacements around indentations for samples in an annealed and work-hardened condition, and after processing using ECAP. [source]

Spatially-localized correlation of dGEMRIC-measured GAG distribution and mechanical stiffness in the human tibial plateau

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 1 2005
Joseph T. Samosky
Abstract The concentration of glycosaminoglycan (GAG) in articular cartilage is known to be an important determinant of tissue mechanical properties based on numerous studies relating bulk GAG and mechanical properties. To date limited information exists regarding the relationship between GAG and mechanical properties on a spatially-localized basis in intact samples of native tissue. This relation can now be explored by using delayed gadolinium-enhanced MRI of cartilage (dGEMRIC,a recently available non-destructive magnetic resonance imaging method for measuring glycosaminoglycan concentration) combined with non-destructive mechanical indentation testing. In this study, three tibial plateaus from patients undergoing total knee arthroplasty were imaged by dGEMRIC. At 33,44 test locations for each tibial plateau, the load response to focal indentation was measured as an index of cartilage stiffness. Overall, a high correlation was found between the dGEMRIC index (T) and local stiffness (Pearson correlation coefficients r = 0.90, 0.64, 0.81; p < 0.0001) when the GAG at each test location was averaged over a depth of tissue comparable to that affected by the indentation. When GAG was averaged over larger depths, the correlations were generally lower. In addition, the correlations improved when the central and peripheral (submeniscal) areas of the tibial plateau were analyzed separately, suggesting that a factor other than GAG concentration is also contributing to indentation stiffness. The results demonstrate the importance of MRI in yielding spatial localization of GAG concentration in the evaluation of cartilage mechanical properties when heterogeneous samples are involved and suggest the possibility that the evaluation of mechanical properties may be improved further by adding other MRI parameters sensitive to the collagen component of cartilage. © 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source]

Chondrocyte viability in press-fit cryopreserved osteochondral allografts

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2004
Madhura D. Gole
Abstract The viability of chondrocytes in press-fit glycerol-preserved osteochondral allografts was compared to that in fresh autografts, after transplantation into load-bearing and non-load-bearing sites in mature sheep stifle joints. We used macroscopic grading, tonometer pen indentation testing, histology, sulfate uptake and viability as determined by confocal-microscopy to assess cartilage condition. Despite there being no statistical differences between macroscopic appearance and tonometer testing of all grafts, confocal microscopy and histology demonstrated a positive effect of load-bearing placement on cryopreserved osteochondral allografts. Allografts transplanted into load-bearing sites demonstrated superior confocal microscopy-measured chondrocyte viability (77% ± 17%SD) than those transplanted into non-load-bearing sites (25%±2%). Load-bearing effect was not seen in autografts (78%±15%), and was comparable in adjacent cartilage (83%±9%). Similarly, load-bearing allografts demonstrated histological scoring closer to that of autografts and adjacent cartilage, all of which fared significantly better than non-load-bearing allografts. Load-bearing allografts had a greater amount of fibrocartilage than autografts or adjacent cartilage but less fibrocartilage than non-load-bearing allografts. Both autografts and allografts had non-significant increases in metabolism compared to adjacent cartilage as measured by sulfate-uptake. Load-bearing placement improved chondrocyte viability of glycerol cryopreserved osteochondral allograft following a press-fit implantation. Published by Elsevier Ltd. All on behalf of orthopaedic Research Society. [source]

Effects of a cultured autologous chondrocyte-seeded type II collagen scaffold on the healing of a chondral defect in a canine model

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 2 2003
C. R. Lee
Using a previously established canine model for repair of articular cartilage defects, this study evaluated the 15-week healing of chondral defects (i.e., to the tidemark) implanted with an autologous articular chondrocyte-seeded type II collagen scaffold that had been cultured in vitro for four weeks prior to implantation. The amount and composition of the reparative tissue were compared to results from our prior studies using the same animal model in which the following groups were analyzed: defects implanted with autologous chondrocyte-seeded collagen scaffolds that had been cultured in vitro for approximately 12 h prior to implantation, defects implanted with autologous chondrocytes alone, and untreated defects. Chondrocytes, isolated from articular cartilage harvested from the left knee joint of six adult canines, were expanded in number in monolayer for three weeks, seeded into porous type II collagen scaffolds, cultured for an additional four weeks in vitro and then implanted into chondral defects in the trochlear groove of the right knee joints. The percentages of specific tissue types filling the defects were evaluated histomorphometrically and certain mechanical properties of the repair tissue were determined. The reparative tissue filled 88 ± 6% (mean ± SEM; range 70,100%) of the cross-sectional area of the original defect, with hyaline cartilage accounting for 42 ± 10% (range 7,67%) of defect area. These values were greater than those reported previously for untreated defects and defects implanted with a type II collagen scaffold seeded with autologous chondrocytes within 12 h prior to implantation. Most striking, was the decreased amount of fibrous tissue filling the defects in the current study, 5 ± 5% (range 0,26%) as compared to previous treatments. Despite this improvement, indentation testing of the repair tissue formed in this study revealed that the compressive stiffness of the repair tissue was well below (20-fold lower stiffness) that of native articular cartilage. © 2002 Orthopaedic Research Society. Published by Elsevier Science Ltd. All rights reserved. [source]

Application of Hertzian Tests to Measure Stress,Strain Characteristics of Ceramics at Elevated Temperatures

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007
Estíbaliz Sánchez-González
A new method for evaluating the elastic,plastic properties of ceramics from room temperature up to the onset of creep based on Hertzian indentation testing is proposed. Indentation stress,strain curves are compiled for representative alumina and zirconia ceramics at prescribed temperatures. Deconvolution of the indentation stress,strain curves for each material provides a measure of Young's modulus, yield stress, and work-hardening coefficient as a function of temperature, enabling construction of true stress,strain curves. The stress,strain curves flatten out with increasing temperature, in accordance with an expected increased plastic response at elevated temperatures. [source]