HAL (Le Centre pour la Communication Scientifique Directe), 2005
ABSTRACT We implemented a pilot study in a growing animal model. The macroscopic permeability of ... more ABSTRACT We implemented a pilot study in a growing animal model. The macroscopic permeability of the vertebral endplates was measured. The influence of location, tissue maturity, and fluid flow direction was quantified. We hypothesized that the macroscopic permeability of vertebral endplate may decrease with maturity of the vertebral segment. The alternation of loading induced by the diurnal cycle generates convective flux into the vertebral segment with the dominant flow path through the vertebral endplates. The alteration of mass transport at the disc-vertebrae interface may interrupt the mechanobiologic balance, and have an effect such as degenerative changes or scoliosis. A previously validated method for measuring permeability, based on the relaxation pressure caused by a transient-flow rate was used. Three specimens were extracted from each L1 to L5 endplate. Seventy-one specimens were frozen, and 64 were stored fresh in a standard culture media. A microscopic analysis completed the biomechanical analysis. At 2, 4, and 6 months, the mean permeability (10(-14) m/N x s, flow-in/flow-out) of the central zone was respectively: 1.23/1.66, 1.03/1.29, and 0.792/1.00. Laterally, it was 1.03/1.19, 1.094/1.001, and 0.765/0.863. For all groups, cartilage endplate and growth plate were both thinner in the center of the plate. Weak differences of the vascular network were detected, except for a small increase of vascular density in the central zone. The results from this animal study showed that the central zone of the vertebral endplate was more permeable than the periphery and the flow-out permeability was up to 35% greater than the flow-in permeability. Increase of permeability with decrease of cartilage thickness was noticed within the same age group. We also found a statistically significant decrease of the macroscopic permeability correlated with the tissue maturity.
Experimental uniaxial tensile tests are carried out on circumferential samples removed from annul... more Experimental uniaxial tensile tests are carried out on circumferential samples removed from annulus tissue of pig intervertebral disks. Classical non-linear and hysteretic mechanical behaviors are observed. Using imaging techniques, the transverse dimensions of experimental samples are measured during stretching leading to the determination of both Poisson's coefficients. A large shrinkage is generally observed in the axial direction while a significant swelling is obtained in the radial direction. This emphasizes the complex coupling effects between the anisotropic fibrous structure and the viscous flow through the matrix. This communication aims at presenting an anisotropic poro-elastic model able to describe the homogenized mechanical behavior (non-linearity, hysteresis) and to retrieve microstructural characteristics (fibers reorientation, coupling with the fluid phase). This characteristic should significantly influences the cell nutrients transport from vertebrae to the disk.
HAL (Le Centre pour la Communication Scientifique Directe), 2005
ABSTRACT We implemented a pilot study in a growing animal model. The macroscopic permeability of ... more ABSTRACT We implemented a pilot study in a growing animal model. The macroscopic permeability of the vertebral endplates was measured. The influence of location, tissue maturity, and fluid flow direction was quantified. We hypothesized that the macroscopic permeability of vertebral endplate may decrease with maturity of the vertebral segment. The alternation of loading induced by the diurnal cycle generates convective flux into the vertebral segment with the dominant flow path through the vertebral endplates. The alteration of mass transport at the disc-vertebrae interface may interrupt the mechanobiologic balance, and have an effect such as degenerative changes or scoliosis. A previously validated method for measuring permeability, based on the relaxation pressure caused by a transient-flow rate was used. Three specimens were extracted from each L1 to L5 endplate. Seventy-one specimens were frozen, and 64 were stored fresh in a standard culture media. A microscopic analysis completed the biomechanical analysis. At 2, 4, and 6 months, the mean permeability (10(-14) m/N x s, flow-in/flow-out) of the central zone was respectively: 1.23/1.66, 1.03/1.29, and 0.792/1.00. Laterally, it was 1.03/1.19, 1.094/1.001, and 0.765/0.863. For all groups, cartilage endplate and growth plate were both thinner in the center of the plate. Weak differences of the vascular network were detected, except for a small increase of vascular density in the central zone. The results from this animal study showed that the central zone of the vertebral endplate was more permeable than the periphery and the flow-out permeability was up to 35% greater than the flow-in permeability. Increase of permeability with decrease of cartilage thickness was noticed within the same age group. We also found a statistically significant decrease of the macroscopic permeability correlated with the tissue maturity.
Experimental uniaxial tensile tests are carried out on circumferential samples removed from annul... more Experimental uniaxial tensile tests are carried out on circumferential samples removed from annulus tissue of pig intervertebral disks. Classical non-linear and hysteretic mechanical behaviors are observed. Using imaging techniques, the transverse dimensions of experimental samples are measured during stretching leading to the determination of both Poisson's coefficients. A large shrinkage is generally observed in the axial direction while a significant swelling is obtained in the radial direction. This emphasizes the complex coupling effects between the anisotropic fibrous structure and the viscous flow through the matrix. This communication aims at presenting an anisotropic poro-elastic model able to describe the homogenized mechanical behavior (non-linearity, hysteresis) and to retrieve microstructural characteristics (fibers reorientation, coupling with the fluid phase). This characteristic should significantly influences the cell nutrients transport from vertebrae to the disk.
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Papers by Dominique Ambard