The nonlinear relationship between speed of sound and compression in articular cartilage: Measurements and modeling.
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ABSTRACT:
SUBMITTER: Mansour JM
PROVIDER: S-EPMC7493830 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The indentation test is widely used to determine the in situ biomechanical properties of articular cartilage. The mechanical parameters estimated from the test depend on the constitutive model adopted to analyze the data. Similar to most connective tissues, the solid matrix of cartilage displays different mechanical properties under tension and compression, termed tension-compression nonlinearity (TCN). In this study, cartilage was modeled as a porous elastic material with either a conewise linear elastic matrix with cubic symmetry or a solid matrix reinforced by a continuous fiber distribution. Both models are commonly used to describe the TCN of cartilage. The roles of each mechanical property in determining the indentation response of cartilage were identified by finite element simulation. Under constant loading, the equilibrium deformation of cartilage is mainly dependent on the compressive modulus, while the initial transient creep behavior is largely regulated by the tensile stiffness. More importantly, altering the permeability does not change the shape of the indentation creep curves, but introduces a parallel shift along the horizontal direction on a logarithmic time scale. Based on these findings, a highly efficient curve-fitting algorithm was designed, which can uniquely determine the three major mechanical properties of cartilage (compressive modulus, tensile modulus, and permeability) from a single indentation test. The new technique was tested on adult bovine knee cartilage and compared with results from the classic biphasic linear elastic curve-fitting program.
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Project description:A growing body of research has highlighted the role that mechanical forces play in the activation of latent TGF-? in biological tissues. In synovial joints, it has recently been demonstrated that the mechanical shearing of synovial fluid, induced during joint motion, rapidly activates a large fraction of its soluble latent TGF-? content. Based on this observation, the primary hypothesis of the current study is that the mechanical deformation of articular cartilage, induced by dynamic joint motion, can similarly activate the large stores of latent TGF-? bound to the tissue extracellular matrix (ECM). Here, devitalized deep zone articular cartilage cylindrical explants (n=84) were subjected to continuous dynamic mechanical loading (low strain: ±2% or high strain: ±7.5% at 0.5Hz) for up to 15h or maintained unloaded. TGF-? activation was measured in these samples over time while accounting for the active TGF-? that remains bound to the cartilage ECM. Results indicate that TGF-?1 is present in cartilage at high levels (68.5±20.6ng/mL) and resides predominantly in the latent form (>98% of total). Under dynamic loading, active TGF-?1 levels did not statistically increase from the initial value nor the corresponding unloaded control values for any test, indicating that physiologic dynamic compression of cartilage is unable to directly activate ECM-bound latent TGF-? via purely mechanical pathways and leading us to reject the hypothesis of this study. These results suggest that deep zone articular chondrocytes must alternatively obtain access to active TGF-? through chemical-mediated activation and further suggest that mechanical deformation is unlikely to directly activate the ECM-bound latent TGF-? of various other tissues, such as muscle, ligament, and tendon.
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Project description:SignificanceArticular cartilage exhibits a zonal architecture, comprising three distinct zones: superficial, middle, and deep. Collagen fibers, being the main solid constituent of articular cartilage, exhibit unique angular and size distribution in articular cartilage zones. There is a gap in knowledge on how the unique properties of collagen fibers across articular cartilage zones affect the scattering properties of the tissue.AimThis study hypothesizes that the structural properties of articular cartilage zones affect its scattering parameters. We provide scattering coefficient and scattering anisotropy factor of articular cartilage zones in the spectral band of 400 to 1400 nm. We enumerate the differences and similarities of the scattering properties of articular cartilage zones and provide reasoning for these observations.ApproachWe utilized collimated transmittance and integrating sphere measurements to estimate the scattering coefficients of bovine articular cartilage zones and bulk tissue. We used the relationship between the scattering coefficients to estimate the scattering anisotropy factor. Polarized light microscopy was applied to estimate the depth-wise angular distribution of collagen fibers in bovine articular cartilage.ResultsWe report that the Rayleigh scatterers contribution to the scattering coefficients, the intensity of the light scattered by the Rayleigh and Mie scatterers, and the angular distribution of collagen fibers across tissue depth are the key parameters that affect the scattering properties of articular cartilage zones and bulk tissue. Our results indicate that in the short visible region, the superficial and middle zones of articular cartilage affect the scattering properties of the tissue, whereas in the far visible and near-infrared regions, the articular cartilage deep zone determines articular cartilage scattering properties.ConclusionThis study provides scattering properties of articular cartilage zones. Such findings support future research to utilize optical simulation to estimate the penetration depth, depth-origin, and pathlength of light in articular cartilage for optical diagnosis of the tissue.
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Project description:Objective: To examine the changes in tibial plateau cartilage in relation to body mass index (BMI) in patients with end-stage osteoarthritis (OA). Design: Knees were obtained from 23 OA patients (3 non-obese, 20 obese) at the time of total knee replacement. RNA prepared from cartilage was probed for differentially expressed (DE) gene transcripts using RNA microarrays and validated via real-time PCR. Differences with regard to age, sex, and between medial and lateral compartments were also queried. Results: Microarrays revealed that numerous transcripts were significantly DE between non-obese and obese patients (≥1.5-fold) using pooled and separate data from medial and lateral compartments. Correlation analyses showed that 706 transcripts (459 positively, 247 negatively) were significantly correlated with BMI. Among these, HS3ST6, HSD17B12, and FAM26F were positively correlated while STAC3, PRSS21, and EDA were negatively correlated. Differentially correlated transcripts represented important biological processes e.g. cellular metabolic processes, anatomical structure morphogenesis and cellular response to growth factors. Although age and sex had some effect on transcript expression, most intriguing results were observed for comparison between medial and lateral compartments. Transcripts (MMP13, CLEC3A, MATN3, EPYC, SCARNA5, COL2A1) elevated in the medial compartment represented skeletal system development, cartilage development, collagen and proteoglycan metabolism, and extracellular matrix organization. Likewise, transcripts (SELE, CTSS, VSIG4, F13A1, and STEAP4) repressed in medial compartment represented host immune response, cell migration, wound healing, cell proliferation and response to cytokines. PCR data confirmed expression of DE transcripts. Conclusions: This study supports molecular interaction between obesity and OA and implies that BMI is an important determinant of transcript-level changes in cartilage.
2017-05-03 | GSE98460 | GEO
Project description:The pericellular matrix (PCM) is a narrow region of tissue that completely surrounds chondrocytes in articular cartilage. Previous theoretical models of the "chondron" (the PCM with enclosed cells) suggest that the structure and properties of the PCM may significantly influence the mechanical environment of the chondrocyte. The objective of this study was to quantify changes in the three-dimensional (3D) morphology of the chondron in situ at different magnitudes of compression applied to the cartilage extracellular matrix. Fluorescence immunolabeling for type-VI collagen was used to identify the boundaries of the cell and PCM, and confocal microscopy was used to form 3D images of chondrons from superficial, middle, and deep zone cartilage in explants compressed to 0%, 10%, 30%, and 50% surface-to-surface strain. Lagrangian tissue strain, determined locally using texture correlation, was highly inhomogeneous and revealed depth-dependent compressive stiffness and Poisson's ratio of the extracellular matrix. Compression significantly decreased cell and chondron height and volume, depending on the zone and magnitude of compression. In the superficial zone, cellular-level strains were always lower than tissue-level strains. In the middle and deep zones, however, tissue strains below 25% were amplified at the cellular level, while tissue strains above 25% were decreased at the cellular level. These findings are consistent with previous theoretical models of the chondron, suggesting that the PCM can serve as either a protective layer for the chondrocyte or a transducer that amplifies strain, such that cellular-level strains are more homogenous throughout the tissue depth despite large inhomogeneities in local ECM strains.
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Project description:Articular cartilage in knee joint can be anatomically divided into different regions: medial and lateral condyles of femur; patellar groove of femur; medial and lateral plateaus of tibia covered or uncovered by meniscus. The stress-strain curves of cartilage in uniaxially unconfined compression demonstrate strain rate dependency and exhibit distinct topographical variation among these seven regions. The femoral cartilage is stiffer than the tibial cartilage, and the cartilage in femoral groove is stiffest in the knee joint. Compared with the uncovered area, the area covered with meniscus shows the stiffer properties. To investigate the origin of differences in macroscopic mechanical properties, histological analysis of cartilage in seven regions are conducted. The differences are discussed in terms of the cartilage structure, composition content and distribution. Furthermore, the commonly used constitutive models for biological tissues, namely Fung, Ogden and Gent models, are employed to fit the experimental data, and Fung and Ogden models are found to be qualified in representing the stiffening effect of strain rate.
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