Compression of the intervertebral disc with combined flexion and torsion

Bovine caudal motion segments were used to investigate the loss of load-bearing ability under both quasi-static and cyclic loading. 80 motion segments dissected from 41 bovine tails were subjected to quasi-static and cyclic compression...

Rupture of intervertebral disc under internal pressurization

Bovine caudal motion segments were used to investigate the intrinsic failure strenght of the intect intervertebral disc under internal hydrostatic pressure...

Fatigue damage of human tendons.

The study was designed to examine the effects of partial fatigue on specific mechanical parameters which characterise human tendons in vitro. Specimens prepared from 12 intact Extensor digitorum longus tendons of the foot were subjected to partial fatigue, equivalent to 25% of the median fatigue life, by a cyclic square tension-tension stress waveform at the physiological frequency of 4 Hz. The maximum stress was set at a value corresponding to 20% of the calculated ultimate tensile strength (UTS) of 100 MPa. The minimum stress was set at 1% of the UTS. Dynamic characterisation was performed at stress levels of 10% and 20% of the UTS prior to and following partial mechanical fatigue. Subsequent quasi-static tests were performed on some of the specimens. Comparative analysis of the damage ratios (DRs) of quasi-static and dynamic mechanical parameters suggested the use of the DR for dynamic tensile modulus as a good indicator of damage inflicted by mechanical fatigue. Such an approach might be used for an in vivo assessment of tendon damage.

Collagen arrangement in hepatic granuloma in mice infected with Schistosoma mansoni: dependence on fiber radiation centers.

The collagen structure of isolated and in situ liver granuloma from Swiss Webster mice infected with Schistosoma mansoni was sequentially and three-dimensionally analyzed during different times of infection (early acute, acute, transitional acute-chronic, and chronic phases) by laser scanning confocal microscopy and electron scanning variable vacuum microscopy. The initial granuloma structure is characterized by vascular collagen residues and by anchorage points (or fiber radiation centers), from where collagenous fibers are angularly shed and self-assembled. During the exudative-productive stage, the self-assembly of these fibers minimizes energy and mass through continuous tension and focal compression. The curvature or angles between collagen fibers probably depends on the fibroblastic or myofibroblastic organization of stress fibers. Gradually, the loose unstable lattice of the exudative-productive stage transforms into a highly packed and stable architecture as a result of progressive compactness. The three-dimensional architecture of granulomas provides increased tissue integrity, efficient distribution of soluble compounds and a haptotactic background to the cells.

Collagen arrangement in hepatic granuloma in mice infected with Schistosoma mansoni: dependence on fiber radiation centers

The collagen structure of isolated and in situ liver granuloma from Swiss Webster mice infected with Schistosoma mansoni was sequentially and three-dimensionally analyzed during different times of infection (early acute, acute, transitional acute-chronic, and chronic phases) by laser scanning confocal microscopy and electron scanning variable vacuum microscopy. The initial granuloma structure is characterized by vascular collagen residues and by anchorage points (or fiber radiation centers), from where collagenous fibers are angularly shed and self-assembled. During the exudative-productive stage, the self-assembly of these fibers minimizes energy and mass through continuous tension and focal compression. The curvature or angles between collagen fibers probably depends on the fibroblastic or myofibroblastic organization of stress fibers. Gradually, the loose unstable lattice of the exudative-productive stage transforms into a highly packed and stable architecture as a result of progressive compactness. The three-dimensional architecture of granulomas provides increased tissue integrity, efficient distribution of soluble compounds and a haptotactic background to the cells

Histoarchitecture of schistosomal granuloma development and involution: morphogenetic and biomechanical approaches.

The authors present morphogenetic and biomechanical approaches on the concept of the Schistosoma mansoni granulomas, considering them as organoid structures that depend on cellular adhesion and sorting, forming rearrangement into hierarchical concentric layers, creating tension-dependent structures, aiming to acquire round form, since this is the minimal energy form, in which opposing forces pull in equally from all directions and are in balance. From the morphogenetic point of view, the granulomas function as little organs, presenting maturative and involutional stages in their development with final disappearance (pre-granulomatous stages, subdivided in: weakly and/or initial reactive and exudative; granulomatous stages: exudative-productive, productive and involutional). A model for the development of granulomas was suggested, according to the following stages: encapsulating, focal histolysis, fiber production, orientation and compacting and involution and disintegration. The authors concluded that schistosomal granuloma is not a tangled web of individual cells and fibers, but an organized structure composed by host and parasite components, which is not formed to attack the miracidia, but functions as an hybrid interface between two different phylogenetic beings.

In vitro fatigue of human tendons.

The purpose of this study was to determine the fatigue behaviour of human tendons in vitro. The testing was accomplished with the use of specially designed grips and the local measurement of tendon cross-sectional area. Ninety specimens prepared from Extensor digitorum longus (EDL) tendons of the foot were subjected to a cyclic square tension-tension stress waveform at physiological frequencies. The maximum tensile stress was normalised to values corresponding to prescribed levels between 10% and 90% of the calculated ultimate tensile strength (UTS) of 100 MPa. The minimum stress was set at 1% of the UTS. A replication of 10 specimens per stress level allowed the use of statistical models for the distribution of fatigue life. Results followed a linear model, of form S = 101.3 - 14.8 log(N), relating the normalised stress to the median number of cycles to failure, therefore suggesting the absence of an endurance limit. The Weibull distribution was found to describe adequately the probability of failure at each stress level. A model which takes into account in vivo healing was proposed. This model was able to explain the presence of intact tendons throughout the lifetime of an individual.