Modulus Of Articular Cartilage Research Articles

Approaching the compressive modulus of articular cartilage through naturally derived cartilage matrix

Approaching the compressive modulus of articular cartilage through naturally derived cartilage matrix

The study on the mechanical characteristics of articular cartilage in simulated microgravity

The microgravity environment of a long-term space flight may induce acute changes in an astronaut’s musculo-skeletal systems. This study explores the effects of simulated microgravity on the mechanical characteristics of articular cartilage. Six rats underwent tail suspension for 14 days and six additional rats were kept under normal earth gravity as controls. Swelling strains were measured using high-frequency ultrasound in all cartilage samples subject to osmotic loading. Site-specific swelling strain data were used in a triphasic theoretical model of cartilage swelling to determine the uniaxial modulus of the cartilage solid matrix. No severe surface irregularities were found in the cartilage samples obtained from the control or tail-suspended groups. For the tail-suspended group, the thickness of the cartilage at a specified site, as determined by ultrasound echo, showed a minor decrease. The uniaxial modulus of articular cartilage at the specified site decreased significantly, from (6.31 ± 3.37)MPa to (5.05 ± 2.98)MPa (p < 0.05). The histology-stained image of a cartilage sample also showed a reduced number of chondrocytes and decreased degree of matrix staining. These results demonstrated that the 14 d simulated microgravity induced significant effects on the mechanical characteristics of articular cartilage. This study is the first attempt to explore the effects of simulated microgravity on the mechanical characteristics of articular cartilage using an osmotic loading method and a triphasic model. The conclusions may provide reference information for manned space flights and a better understanding of the effects of microgravity on the skeletal system.

Effect of tip geometry of atomic force microscope on mechanical responses of bovine articular cartilage and agarose gel

The objective of this study is to investigate the effect of different Atomic Force Microscope (AFM) tip geometries (sharp-conical and spherical tips) on the microscale Young’s modulus of bovine articular cartilage and agarose gel that is calculated by the method of the average point-wise modulus. The measurements of the microscale Young’s moduli of 3% agarose gel under a conical AFM tip (20.9±4.9 kPa) and under a spherical AFM tip (17.5±3.0 kPa), averaged over an indentation depth of 600 nm, were comparable. However, the microscale Young’s moduli of articular cartilage, as measured with a conical AFM tip (116.9±62.9 kPa), were significantly higher than the corresponding values under a spherical AFM tip (30.9±14.3 kPa). The results of the current study suggest that the AFM tip geometry affects the microscale measurements of the mechanical properties on the surfaces of biological materials. The findings of the study can help to elucidate more accurately the microscale mechanical properties on the surface layers of diverse biological materials including tissue-engineered cartilages with different material characteristics.

Mechanical properties of bovine articular cartilage under microscale indentation loading from atomic force microscopy.

Atomic force microscopy (AFM) techniques have been increasingly used for investigating the mechanical properties of articular cartilage. According to the previous studies reporting the microscale Young's modulus under AFM indentation tests, the Hertz contact model has been employed with a sharp conical tip indenter. However, the non-linear microscale behaviour of articular cartilage could not be resolved by the standardized Hertz analysis using small and sharp atomic force microscope tips. Therefore, the objective of this study was to evaluate the microscale Young's modulus of articular cartilage more accurately through a non-Hertzian approach with a spherical tip of 5 microm diameter, and to characterize its microscale mechanical behaviour. This methodology adopted in the present study was proved by the consistent values between the microscale (2 per cent, about 9.3 kPa; 3 per cent, about 17.5kPa) and macroscale (2 per cent, about 8.3kPa; 3 per cent, about 18.3kPa) Young's moduli for 2 per cent and 3 per cent agarose gel (n = 100). Therefore, the microscale Young's modulus evaluated in this study is representative of more accurate measurements of cartilage stiffness at the 600 nm deformation level and corresponds to approximately 30.9 kPa (n = 100). Furthermore, on this level of the microscale deformation, articular cartilage showed depth-dependent and frequency-independent behaviour under AFM indentation loading. These findings reveal the microscale mechanical behaviour of articular cartilage more accurately and can be employed further to design microscale structures of chondrocyte-seeded scaffolds and tissue-engineered cartilage by evaluating their microscale properties.

Collagen network primarily controls Poisson's ratio of bovine articular cartilage in compression

The equilibrium Young's modulus of articular cartilage is known to be primarily determined by proteoglycans (PGs). However, the relation between the Poisson's ratio and the composition and structure of articular cartilage is more unclear. In this study, we determined Young's modulus and Poisson's ratio of bovine articular cartilage in unconfined compression. Subsequently, the same samples, taken from bovine knee (femoral, patellar and tibial cartilage) and shoulder (humeral cartilage) joints, were processed for quantitative microscopic analysis of PGs, collagen content, and collagen architecture. The Young's modulus, Poisson's ratio, PG content (estimated with optical density measurements), collagen content, and birefringence showed significant topographical variation (p < 0.05) among the test sites. Experimentally the Young's modulus was strongly determined by the tissue PG content (r = 0.86, p < 0.05). Poisson's ratio revealed a significant negative linear correlation (r = -0.59, p < 0.05) with the collagen content, as assessed by the Fourier transform infrared imaging. Finite element analyses, conducted using a fibril reinforced biphasic model, indicated that the mechanical properties of the collagen network strongly affected the Poisson's ratio. We conclude that Poisson's ratio of articular cartilage is primarily controlled by the content and organization of the collagen network.

Estimation of the Young's modulus of articular cartilage using an arthroscopic indentation instrument and ultrasonic measurement of tissue thickness

We evaluated whether the use of cartilage thickness measurement would improve the ability of the arthroscopic indentation technique to estimate the intrinsic stiffness of articular cartilage. First, cartilage thickness and ultrasound reflection from the surface of bovine humeral head were registered in situ using a high-frequency ultrasound probe. Subsequently, cartilage was indented in situ at the sites of the ultrasound measurements using arthroscopic instruments with plane-ended and spherical-ended indenters. Finally, full-thickness cartilage disks ( n=30) were extracted from the indented sites (thickness=799–1654 μm) and the equilibrium Young's modulus was determined with a material testing device in unconfined compression geometry. We applied analytical and numerical indentation models for the theoretical correction of experimental indentation measurements. An aspect-ratio (the ratio of indenter radius to cartilage thickness) correction improved the correlation of the indenter force with the equilibrium Young's modulus from r 2=0.488 to r 2=0.642–0.648 ( n=30) for the plane-ended indenter (diameter=1.000 mm, height=0.300 mm) and from r 2=0.654 to r 2=0.684–0.692 ( n=30) for the spherical-ended indenter (diameter=0.500 mm, height=0.100 mm), depending on the indentation model used for the correction. The linear correlation between the ultrasound reflection and the Young's modulus was r 2=0.400 ( n=30). These results suggest that with large indenters, knowledge of the cartilage thickness improves the reliability of the indentation measurements, especially in pathological situations where cartilage thickness may be significantly lower than normal. Ultrasound measurements also provide diagnostically important information about cartilage thickness as well as knowledge of the integrity of the superficial zone of cartilage.