Biorheology - Volume 41, issue 3-4

Article Type: Other

Citation: Biorheology, vol. 41, no. 3-4, pp. 153-153, 2004

Authors: Stoltz, J.F.

Article Type: Research Article

Citation: Biorheology, vol. 41, no. 3-4, pp. 155-156, 2004

Authors: Boschetti, Federica | Pennati, Giancarlo | Gervaso, Francesca | Peretti, Giuseppe M. | Dubini, Gabriele

Article Type: Research Article

Abstract: The function of articular cartilage is to support and distribute loads and to provide lubrication in the diarthrodial joints. Cartilage function is described by proper mechanical and rheological properties, strain and depth‐dependent, which are not completely assessed. Unconfined and confined compression are commonly used to evaluate the Young's modulus (E) and the aggregate modulus (HA ), respectively. The Poisson's ratio (ν) can be calculated indirectly from the equilibrium compression data, or using the biphasic indentation technique; it has recently been optically evaluated by using video microscopy during unconfined compression. The transient response of articular cartilage during confined compression depends on …its permeability k; a constant value of k can be easily identified by a simple analytical model of confined compression tests, whereas more complex models or direct measurements (permeation tests) are needed to study the permeability dependence on deformation. A poroelastic finite element model of articular cartilage was developed for this purpose. The elastic parameters (E,ν) of the model were evaluated performing unconfined compression creep tests on human articular cartilage disks, whereas k was identified from the confined test response. Our combined experimental and computational method can be used to identify the parameters that define the permeability dependence on deformation, as a function of depth from articular surface. Show more

Keywords: Femoral head, creep experiments, permeability, poroelastic model

Citation: Biorheology, vol. 41, no. 3-4, pp. 159-166, 2004

Authors: Saarakkala, Simo | Korhonen, Rami K. | Laasanen, Mikko S. | Töyräs, Juha | Rieppo, Jarno | Jurvelin, Jukka S.

Article Type: Research Article

Abstract: The compressive stiffness of an elastic material is traditionally characterized by its Young's modulus. Young's modulus of articular cartilage can be directly measured using unconfined compression geometry by assuming the cartilage to be homogeneous and isotropic. In isotropic materials, Young's modulus can also be determined acoustically by the measurement of sound speed and density of the material. In the present study, acoustic and mechanical techniques, feasible for in vivo measurements, were investigated to quantify the static and dynamic compressive stiffness of bovine articular cartilage in situ. Ultrasound reflection from the cartilage surface, as well as the dynamic modulus were determined …with the recently developed ultrasound indentation instrument and compared with the reference mechanical and ultrasound speed measurements in unconfined compression (n=72). In addition, the applicability of manual creep measurements with the ultrasound indentation instrument was evaluated both experimentally and numerically. Our experimental results indicated that the sound speed could predict 47% and 53% of the variation in the Young's modulus and dynamic modulus of cartilage, respectively. The dynamic modulus, as determined manually with the ultrasound indentation instrument, showed significant linear correlations with the reference Young's modulus (r2 =0.445, p<0.01, n=70) and dynamic modulus (r2 =0.779, p<0.01, n=70) of the cartilage. Numerical analyses indicated that the creep measurements, conducted manually with the ultrasound indentation instrument, were sensitive to changes in Young's modulus and permeability of the tissue, and were significantly influenced by the tissue thickness. We conclude that acoustic parameters, i.e. ultrasound speed and reflection, are indicative to the intrinsic mechanical properties of the articular cartilage. Ultrasound indentation instrument, when further developed, provides an applicable tool for the in vivo detection of cartilage mechano‐acoustic properties. These techniques could promote the diagnostics of osteoarthrosis. Show more

Keywords: Articular cartilage, Young's modulus, ultrasound, osteoarthrosis, finite element analysis

Citation: Biorheology, vol. 41, no. 3-4, pp. 167-179, 2004

Authors: Li, L.P. | Herzog, W.

Article Type: Research Article

Abstract: The relative importance of fluid‐dependent and fluid‐independent transient mechanical behavior in articular cartilage was examined for tensile and unconfined compression testing using a fibril reinforced model. The collagen matrix of articular cartilage was modeled as viscoelastic using a quasi‐linear viscoelastic formulation with strain‐dependent elastic modulus, while the proteoglycan matrix was considered as linearly elastic. The collagen viscoelastic properties were obtained by fitting experimental data from a tensile test. These properties were used to investigate unconfined compression testing, and the sensitivity of the properties was also explored. It was predicted that the stress relaxation observed in tensile tests was not caused …by fluid pressurization at the macroscopic level. A multi‐step tensile stress relaxation test could be approximated using a hereditary integral in which the elastic fibrillar modulus was taken to be a linear function of the fibrillar strain. Applying the same formulation to the radial fibers in unconfined compression, stress relaxation could not be simulated if fluid pressurization were absent. Collagen viscoelasticity was found to slightly weaken fluid pressurization in unconfined compression, and this effect was relatively more significant at moderate strain rates. Therefore, collagen viscoelasticity appears to play an import role in articular cartilage in tensile testing, while fluid pressurization dominates the transient mechanical behavior in compression. Collagen viscoelasticity plays a minor role in the mechanical response of cartilage in unconfined compression if significant fluid flow is present. Show more

Keywords: Cartilage mechanics, cartilage tensile properties, collagen fibril reinforcement, nonlinear biomechanics, strain rates, unconfined compression

Citation: Biorheology, vol. 41, no. 3-4, pp. 181-194, 2004

Authors: Frank, E. | Evans, R. | Lee, C. | Treppo, S. | Spector, M. | Grodzinsky, A.

Article Type: Research Article

Citation: Biorheology, vol. 41, no. 3-4, pp. 195-202, 2004

Authors: Verteramo, A. | Seedhom, B.B.

Article Type: Research Article

Abstract: The aims of this study were: (i) to investigate the variation in the tensile properties of articular cartilage with depth through cartilage thickness and fibre orientation; (ii) to determine the effect of strain rate on tensile properties of articular cartilage. Materials and method: All experimental work was performed on cartilage specimens taken from two bovine knee joints. Osteochondral plugs 12 mm in diameter were harvested with a special reamer from the femur and the tibial plateaux of each knee. Slices (0.2 mm thick), of articular cartilage were cut from the plug with a microtome. The predominant orientation of the …collagen fibres on the cartilage surface was determined using the pinpricking technique. Each specimen used for the tensile test was cut, so as to produce a dumbbell shape, with a gauge length of 6 mm. Uniaxial tensile tests were performed on each specimen in order to determine the tensile Young's modulus, and ultimate tensile strength (UTS). In this investigation, these tensile tests were carried out at different strain rate: 1, 20, 50 and 70%/sec. Results: As regards the zonal properties, it was found that tensile stiffness was greater in the superficial layer than in deep layer. However, a few specimens from the deep layer displayed similar or greater stiffness compared to the superficial layer. With respect to the directional properties, the specimens oriented parallel to the predominant alignment of collagen, were stiffer than those, which were perpendicular to it in each layer. However, only the results regarding the deep layer can be considered statistically significant. In regard to the variation of modulus with the strain‐rate, the results showed that there is no significant increase of the modulus with increasing strain rate from 20 to 50% per second. However, at 70% per second, articular cartilage stiffness considerably increased by up to one order of magnitude greater than that determined at lower strain rates in both the superficial and deep layer. Moreover, the UTS of cartilage specimens tested at 70% per second showed a significant rise, reaching values of four to five times that of those measured at 1, 20 or 50% per second. Conclusion: The steep increases in both the stiffness and ultimate tensile strength of cartilage at high strain rates point to the existence in cartilage of a mechanism for its protection from damage by stresses arising in trauma, which are usually applied at high rates. This mechanism needs to be elucidated. The reduced anisotropy found in the present study pointed out that collagen is likely to be less organized in bovine cartilage than in the human and therefore, a study of its ultra‐structure would be appropriate. Show more

Citation: Biorheology, vol. 41, no. 3-4, pp. 203-213, 2004

Authors: Moyne, Christian | Murad, Márcio A.

Article Type: Research Article

Abstract: The equations governing the electro‐chemo‐hydro‐mechanical processes in cartilage are derived using the periodic homogenization technique. First the equations at the microscale are recalled. Then the homogenization technique is applied to propagate the physics to the macroscale. The results of this work and of the thermodynamical approach used by various authors are finally compared.

Citation: Biorheology, vol. 41, no. 3-4, pp. 215-222, 2004

Authors: Kelly, Terri‐Ann N. | Wang, Christopher C.‐B. | Mauck, Robert L. | Ateshian, Gerard A. | Hung, Clark T.

Article Type: Research Article

Abstract: Chondrocytes embedded in agarose and subjected to dynamic deformational loading produce a functional matrix with time in culture, but there is usually a delay in the development of significant differences compared to free swelling. In this study, we hypothesized that the initial presence of a cell‐associated matrix would expedite construct development in response to dynamic deformational loading. Seeded samples with enzymatically isolated chondrocytes and chondrons (the chondrocyte and its pericellular matrix) and examined the effects of seeding density and dynamic loading on the development of tissue properties. At 60 million/ml, dynamic loading significantly augmented the development of material properties in …chondrocyte‐ and chondron‐seeded constructs. Biochemical content and histological analysis indicated that the deposition of GAG, link protein and collagens are affected by the pre‐existing cell‐associated matrix of the chondron‐seeded samples. The pericellular matrix associated with the chondrons did not expedite the development of material properties in response to deformational loading, disproving our hypothesis. The relative concentration and distribution of matrix proteins may play a major role in the disparate responses observed for the chondrocyte‐ and chondron‐seeded cultures. In further support of these findings, culturing chondrocytes in agarose for two weeks prior to the application of deformational loading also did not exhibit expedited construct development. Show more

Keywords: Chondron, functional tissue engineering, material properties, collagens, link protein, glycosaminoglycans

Citation: Biorheology, vol. 41, no. 3-4, pp. 223-237, 2004

Authors: An, Kai‐Nan | Sun, Yu‐Long | Luo, Zong‐Ping

Article Type: Research Article

Abstract: The hierarchical organization of the connective tissue, more specifically, the musculoskeletal soft tissue, has been extensively studied. With advancements in experimental methodology, investigation of the structure–function relationship has provided more insight into how the mechanical integrity of the tissue is created. Such information is essential in the linking the macroscopic loading environment of the tissue to the microscopic level of the tissue to be experienced by the cell. The flexibility and elastic modulus of gross connective tissue, the fascicle, the fiber and then the collagen molecule are compared based on the data available in the literature.

Keywords: Flexibility, elastic modulus, type I collagen, tendon, fascicle, connective tissue

Citation: Biorheology, vol. 41, no. 3-4, pp. 239-246, 2004