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Biomedical subjects

V C Mow

Publications and source records attributed to V C Mow.

At least 127 records · Page 7Linked to original sources
PubMed1983

The mechanical properties of articular cartilage.

An outline of a theoretical model for the mechanical behavior of articular cartilage is presented. The model explicitly describes the pressures and flows generated in the interstitial fluid during loading and deformation. A number of experimental tests to measure the mechanical properties of cartilage are available. The interpretation of these test results in the light of this model and the important factors to consider in the design of experiments are reviewed.

Animals↗
PubMed1982

Variations in the intrinsic mechanical properties of human articular cartilage with age, degeneration, and water content.

UNLABELLED: In a series of 103 specimens from the lateral facet of the human patella, the intrinsic mechanical properties of articular cartilage were measured using a confined compression creep test. By considering the cartilage as a porous, permeable solid filed with fluid, this experimental procedure allowed the determination of the intrinsic equilibrium modulus of the cartilage matrix and its permeability to fluid flow. The intrinsic equilibrium modulus and the permeability both were highly correlated with the water content of the tissue; as water content increased, the matrix of the tissue became softer and more permeable. There was only a marginal decrease in the equilibrium modulus of the tissue with increasing age and surface degeneration. The permeability of the cartilage matrix was not significantly correlated with age or degeneration. CLINICAL RELEVANCE: We concluded that the visual or histological appearance of a cartilage specimen may be a poor indicator of its ability to function as the bearing material in the intact joint. A more reliable indicator of the functional properties of a specimen can be obtained either by direct mechanical testing or by biochemical analysis of its composition.

Adolescent↗
PubMed1981

Effects of nonlinear strain-dependent permeability and rate of compression on the stress behavior of articular cartilage.

The compressive viscoelastic behavior of articular cartilage, a fiber-reinforced, porous, permeable solid matrix filled with water, is predominately governed by the flow of the interstitial water within the tissue and its exudation across the articular surface. The fluid flow is in turn governed by the permeability of the tissue and the loading imposed upon its surface. But for articular cartilage, the permeability depends nonlinearly on the strain; k = ko exp (Me). Here, M is the nonlinear flow-limiting parameter and e is the dilatation. In this investigation, we studied the influence of M and Ro = koHA/Uh (where HA is the elastic equilibrium modulus of the solid matrix, h is the tissue's thickness and U is the rate of compression applied onto the surface via a rigid, porous, free-draining filter) on the stress history of circular plugs of cartilage specimens attached to the bone. It was found that these two parameters have profound effects on the predicted compressive stress history. For very large Ro, the fluid flow effects become negligible. For small Ro and large M, large instantaneous compressive stresses several times larger than those observed at equilibrium are predicted. This amplification of compressive stress is due to the increase of importance of the relative fluid flow effect, i.e., Ro leads to 0, and nonlinear flow-limit effect, i.e., M greater than 0. Also, the theoretical curves predict that the rate of increase of stress initially decreases (convex) and finally becomes a constant. The results of our 5 percent offset compression experiments are in good agreement with the theoretical predictions.

Biomechanical Phenomena↗
PubMed1981

The significance of electromechanical and osmotic forces in the nonequilibrium swelling behavior of articular cartilage in tension.

Studies were conducted of some of the nonequilibrium, electrolyte-activated, electromechanical and osmotic processes that can affect the tensile properties of articular cartilage. We measured changes in tensile force that were induced by altering the ionic environment of strips of cartilage held at fixed length. We compared the kinetics of changes in these macroscopically measured isometric tensile forces to theoretical estimates of the time constants that characterize the underlying physical and chemical mechanisms occurring within the cartilage specimens during the experiment. Changes in the tensile force induced by changing the bath neutral salt concentration surrounding the specimen appear to be rate-limited by the diffusion of the salt into the specimen. That is, the mechanical stress relaxation process resulting from changes in salt concentration seems to be occurring at least as rapidly as the diffusion of salt into the matrix. When the bath concentration of CaCl2 or HCl is varied, the rate of change in the resulting isometric stresses indicates that Ca++ and H+ ions are binding to the cartilage matrix macromolecules.

Animals↗
PubMed1980

The intrinsic tensile behavior of the matrix of bovine articular cartilage and its variation with age.

To study the age dependence of the uniaxial tensile behavior of bovine articular cartilage, 216 specimens of articular cartilage from the patellofemoral joint were grouped into two age categories: those from joints with growth plates present (open physes) and those from joints without growth plates (no physes). We prepared standard, dumbbell-shaped test specimens from the three ultrastructural zones of the tissue: the superficial tangential zone, the middle zone, and the deep zone. As was done in the early works of Kempson et al. and of Woo et all., we prepared specimens whose long axes were either parallel or perpendicular to the axis of the local split line on the joint surface. In these tensile tests we observed a profound difference between the two age groups in terms of the variations in the tensile properties related to the depth below the surface. With increasing distance from the articular surface, the tensile strength and stiffness increased in the open-physis group and decreased in the no-physis group. Directional dependence of the tensile response was manifested by increased stiffness and strength of the samples oriented parallel to the split-line axis when compared with the samples oriented perpendicular to it. Distortion of the initially flat, straight-sided portion of the gauge section was observed in most of the 216 specimens immediately after the application of tensile strains. This effect casts serious doubts on all previous measurements of cross-sectional dimensional changes. At present, we believe that this distortion occurs because articular cartilage is an inhomogeneous, layered material. We also observed that cartilage exudes substantial amounts of its interstitial fluid when the applied tensile strain becomes large. These two effects create serious problems in assessing the true volumetric changes and the material properties of cartilage specimens during uniaxial tension experiments.

Aging↗
PubMed1976

The permeability of articular cartilage under compressive strain and at high pressures.

The permeability of bovine articular cartilage was measured in an apparatus designed to permit this measurement while the fluid pressure gradient across the cartilage and the axial compressive strain applied to the cartilage were varied independently. For all of the pressure gradients tested the permeability of the cartilage decreased as the compressive strain increased. From previous work, it was postulated that joint lubrication is accomplished first by fluid exudation into the joint space. both at the leading edge of the moving contact area and between portions of the opposing cartilaginous surfaces, and second by imbibition of the expelled fluid back into the cartilage toward the trailing edge of the contact area caused by the "elastic" recovery of the tissue. The present work extends this model to include the condition that the permeability of cartilage is dependent on the extent to which it is deformed.

Animals↗
PubMed1975

The ultrastructure and biomechanical significance of the tidemark of articular cartilage.

Thirty specimens of human articular cartilage obtained at surgery were examined by scanning electron microscopy to determine the ultrastructure of the tidemark, the junction of the non-calcified and calcified portions of mature articular cartilage. Three distinct variations of the collagen framework of the tidemark were observed: (1) A band of randomly oriented compacted fibrils that appeared to be continuous with those of the non-calcified and calcified zones. (2) A band of flattened fibrils paralleling the undulating surface of the calcified cartilage. (3) A band of perpendicularly oriented fibrils having a distinct continuous transition between the non-calcified and calcified zones, the amount of calcified material applied about the fibrils rapidly increasing as the fibrils entered the calcified zone. The tidemark may serve to provide a tethering mechanism for the relatively flexible and perpendicularly oriented collagen fibrils of the deepest portion of the non-calcified articular cartilage and may prevent them from being sheared at their point of anchorage to the calcified zone. The undulating pattern of the tidemark affords a strong geometric pattern in providing resistance to the shearing action of articulation. Small gaps present in the tidemark may provide pathways for the passage of nutrients into the deep non-calcified zone of articular cartilage from the subchondral bone.

Biomechanical Phenomena↗