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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Although fatigue has been implicated in cartilage failure there are only two studies by the same author, and in both of which cartilage was tested in the direction parallel to the collagen orientation in the surface layer. In the present work articular cartilage was tested also along the perpendicular direction, being the direction in which cartilage possesses lower tensile strength. Specimens were tested under cyclic tensile load. Number of cycles at failure was recorded as well as elongation of the specimen. To date 72 specimens have been tested all from one knee joint. The number of cycles to failure ranged between two and 1.5 million. The surface and deep layers have better fatigue properties whether tested in the parallel or the perpendicular direction, while the middle layer was far weaker. Better fatigue behaviour was observed with specimens tested in parallel than in perpendicular direction to the fibres.
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PMID:Tensile fatigue behaviour of articular cartilage. 1208 82

Mechanical loading contributes to the structural deterioration of bioprosthetic heart valves. The influence of stress state during fixation may play a substantial role in their failure, linking fatigue damage caused by buckling and tension and the enzymatic degradation of glutaraldehyde-crosslinked collagen. Bovine pericardia were obtained immediately postmortem and 100 mm x 15 mm samples were cut in the base-to-apex direction. Half the samples were subjected to a uniaxial tensile stress of 250 kPa and half remained unloaded during a crosslinking treatment in 0.5% glutaraldehyde. Tissue samples were rinsed and cut into 16 mm x 4 mm test strips. Half of these strips were exposed to cyclic compressive buckling and alternating tension at 30 Hz for 20 million cycles (approx. 7.5 days) using a custom-built multi-sample fatigue system. Fatigue-damaged and non-damaged samples were subsequently incubated at 37 C for 48 hrs in: (i) Type I bacterial collagenase (20 U/ml) buffered in 0.05 M Tris, 10 mM CaCl2 2H2O (pH 7.4) or (ii) 0.05 M Tris buffer (pH 7.4) only. In both cases, the samples were loaded sinusoidally between 40 and 80 g using a previously described microtensile culture system. Tissue removed from the bath was rinsed in 0.1 M EDTA solution and mounted in a servo-hydraulic mechanical testing system (MTS). Ultimate tensile strength (UTS), maximum tissue modulus, and fracture strain were determined. The percent collagen solubilized was assessed by a colourmetric hydroxyproline assay of the enzyme bath and tissue sample. All data were analyzed by analysis of variance (ANOVA). The results confirmed the synergy between fatigue damage and collagenase proteolysis in these materials; however, there were no significant differences in this effect between simple fixation and stress-fixation up to 20 million cycles. There were significant decreases in the mechanical properties and an increase in the amount of collagen solubilized with increased exposure to fatigue cycling.
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PMID:Stress state during fixation determines susceptibility to fatigue-linked biodegradation in bioprosthetic heart valve materials. 1208 92

A silk-fiber matrix was studied as a suitable material for tissue engineering anterior cruciate ligaments (ACL). The matrix was successfully designed to match the complex and demanding mechanical requirements of a native human ACL, including adequate fatigue performance. This protein matrix supported the attachment, expansion and differentiation of adult human progenitor bone marrow stromal cells based on scanning electron microscopy, DNA quantitation and the expression of collagen types I and III and tenascin-C markers. The results support the conclusion that properly prepared silkworm fiber matrices, aside from providing unique benefits in terms of mechanical properties as well as biocompatibility and slow degradability, can provide suitable biomaterial matrices for the support of adult stem cell differentiation toward ligament lineages. These results point toward this matrix as a new option for ACL repair to overcome current limitations with synthetic and other degradable materials.
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PMID:Silk matrix for tissue engineered anterior cruciate ligaments. 1218 15

Different tendons are (i) subject to very different stresses from their muscles and (ii) differ in their susceptibility to fatigue damage. The fatigue quality of each tendon is matched to the stress it experiences, so that, in life, all tendons are similarly prone to damage. On-going damage must be routinely repaired to maintain homeostasis and prevent damage from becoming symptomatic. The discovery of major differences in fatigue quality among tendons, which had previously seemed fairly similar in their mechanical properties, raises a wide range of new questions. (A) What structural and chemical differences underlie the variations in fatigue quality? (B) What molecular structure in the tendon is damaged and how is repair organised? (C) Is fatigue quality adaptable and if so what is the trigger for adaptation? Putting these questions into context leads to an integrated review of tendon, including structure and chemistry, the turnover of proteins, the cross-linking of collagen and the response of tenocytes to load on the tendon.
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PMID:The implications of the adaptable fatigue quality of tendons for their construction, repair and function. 1248 88

The linear organization of collagen fibers in tendons results in optimal stiffness and strength at low strains under tensile load. However, this organization makes repairing ruptured or lacerated tendons extremely difficult. Current suturing techniques to join split ends of tendons, while providing sufficient mechanical strength to prevent gapping, are inadequate to carry normal loads. Immobilization protocols necessary to restore tendon congruity result in scar formation at the repair site and peripheral adhesions that limit excursion. These problems are reviewed to emphasize the need for novel approaches to tendon repair, one of which is the development of biomimetic tendons. The objective of the empirical work described here was to produce biologically-based, biocompatible tendon replacements with appropriate mechanical properties to enable immediate mobilization following surgical repair. Nor-dihydroguaiaretic acid (NDGA), a di-catechol from creosote bush, caused a dose dependent increase in the material properties of reconstituted collagen fibers, achieving a 100-fold increase in strength and stiffness over untreated fibers. The maximum tensile strength of the optimized NDGA treated fibers averaged 90 MPa; the elastic modulus of these fibers averaged 580 MPa. These properties were independent of strain rates ranging from 0.60 to 600 mm/min. Fatigue tests established that neither strength nor stiffness were affected after 80 k cycles at 5% strain. Treated fibers were not cytotoxic to tendon fibroblasts. Fibroblasts attached and proliferated on NDGA treated collagen normally. NDGA-fibers did not elicit a foreign body response nor did they stimulate an immune reaction during six weeks in vivo. The fibers survived 6 weeks with little evidence of fragmentation or degradation. The polymerization scheme described here produces a fiber-reinforced NDGA-polymer with mechanical properties approaching an elastic solid. The strength, stiffness and fatigue properties of the NDGA-treated fibers are comparable to those of tendon. These fibers are biocompatible with tendon fibroblasts and elicit little rejection or antigenic response in vivo. These results indicate that NDGA polymerization may provide a viable approach for producing collagenous materials that can be used to bridge gaps in ruptured or lacerated tendons. The tendon-like properties of the NDGA-fiber would allow early mobilization after surgical repair. We predict that timely loading of parted tendons joined by this novel biomaterial will enhance mechanically driven production of neo-tendon by the colonizing fibroblasts and result in superior repair and rapid return to normal properties.
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PMID:Biomimetic approaches to tendon repair. 1248 99

The effect of creatine (Cr) supplementation on muscle function and body composition of 12 boys with Duchenne muscular dystrophy and three with Becker dystrophy was evaluated by a randomized double-blind cross-over study (3 g Cr or maltodextrin daily for 3 months, with wash-out period of 2 months). After placebo, no change was observed in maximal voluntary contraction (MVC) and resistance to fatigue, whereas total joint stiffness (TJS) was increased by approximately 25% (P < 0.05). The patients receiving Cr did not show any change in TJS, improved MVC by 15% (P = 0.02), and almost doubled their resistance to fatigue (P < 0.001). In patients still independent of a wheelchair (n = 5), bone mineral density increased by 3% (P < 0.05), and urinary excretion of collagen type I cross-linking N-telopeptide declined to about one third (P < 0.001) after Cr. No adverse effect was observed. Thus, Cr may provide some symptomatic benefit in these patients.
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PMID:Beneficial effects of creatine supplementation in dystrophic patients. 1270 81

Toughening mechanisms based on the presence of collagen fibrils have long been proposed for mineralized biological tissues like bone and dentin; however, no direct evidence for their precise role has ever been provided. Furthermore, although the anisotropy of mechanical properties of dentin with respect to orientation has been suggested in the literature, accurate measurements to support the effect of orientation on the fracture toughness of dentin are not available. To address these issues, the in vitro fracture toughness of dentin, extracted from elephant tusk, has been characterized using fatigue-precracked compact-tension specimens tested in Hank's balanced salt solution at ambient temperature, with fracture paths perpendicular and parallel to the tubule orientations (and orientations in between) specifically being evaluated. It was found that the fracture toughness was lower where cracking occurred in the plane of the collagen fibers, as compared to crack paths perpendicular to the fibers. The origins of this effect on the toughness of dentin are discussed primarily in terms of the salient toughening mechanisms active in this material; specifically, the role of crack bridging, both from uncracked ligaments and by individual collagen fibrils, is considered. Estimates for the contributions from each of these mechanisms are provided from theoretical models available in the literature.
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PMID:Effect of orientation on the in vitro fracture toughness of dentin: the role of toughening mechanisms. 1283 91

Adhesion, spreading, proliferation, and collagen matrix production of human bone marrow stromal cells (BMSCs) on an RGD-modified silk matrix was studied. Anterior cruciate ligament fibroblasts (ACLFs) were used as a control cell source. Scanning electron microscopy (SEM) and MTT analyses demonstrated that the modified silk matrices support improved BMSC and ACLF attachment and show higher cell density over 14 days in culture when compared with the non-RGD-modified matrices. Collagen type I transcript levels (at day 7) and content (at day 14) was significantly higher on the RGD-modified substrate than on the nonmodified group. The ability of RGD-coupled silk matrices to support BMSC attachment, which leads to higher cell density and collagen matrix production in vitro, combined with mechanical, fatigue, and biocompatibility properties of the silk protein matrix, suggest potential for use of this biomaterial for tissue engineering.
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PMID:Human bone marrow stromal cell and ligament fibroblast responses on RGD-modified silk fibers. 1456 98

This study aims at the mechanism of foveola formation in bovine trabecular bone under fatigue process and its relation with biomechanical pathogenesis of senile osteoporosis. The scanning electron microscope equipped with fatigue stage was used to observe fatigue micro injury accumulation of cancellous bone. The massive foveola formation in the laminal bone of vertical trabeculae was found in the tensile fatigue test. There existed the collagen avulsion in the foveola. The massive foveola formation was also observed in the lamina bone of the horizontal trabeculae in the compressive fatigue test. The bone collagen fibers were protracted, debound with hydroxyapatite crystal, and then avulsed under tensile and bending stresses. Finally the retraction of the avulsed collagen fibers brought on the massive formation of foveolae in lamina bone. The mechanical capacity of bone also declined greatly. We infer that the direct mineralization of avulsed collagen and foveola in lamina bone would be one of the main processes of self repair in vivo, which brings on the increase in fragility and stiffness of trabeculae of senile osteoporotic bone along with the agelong accumulation of collagen fatigue injury and foveola formation in the lamina bone.
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PMID:[Prospect of the foveola formation in the bovine trabecular bone under fatigue process]. 1502 64

The role of eosinophilia in connective tissue diseases and the relationship between symptoms of rheumatic disease and eosinophilia have not been clearly established. The purpose of the present study was to explore the prevalence of eosinophilia in rheumatologic disease and determine its relationship to the symptoms. One thousand patients who applied to our rheumatology outpatient clinic between 2001 and 2002 were prospectively studied. The upper limit of normal blood eosinophil numbers was determined as 500 cells/microl of blood. A detailed history was obtained from all patients and careful physical examination was done. A negative correlation was observed between eosinophilia and dryness of the mouth, vitiligo, and fatigue (P < 0.05). Nonsteroidal anti-inflammatory drug usage correlated positively with eosinophilia, which was also statistically meaningful (P < 0.05). Twenty-six of our patients with fibromyalgia (n = 293), three of our subjects with rheumatoid arthritis who were using methotrexate (n = 182), 15 of whom who were not on methotrexate therapy, and one of the 26 with vasculitis had eosinophilia, which was not statistically significant (P > 0.05). None of the patients with scleroderma (n = 12) had eosinophilia. Eleven of the patients with gout had eosinophilia, and only one of them was using allopurinol. We conclude that eosinophilia can be seen in various rheumatologic conditions but, as corticosteroids are one of the most common medications used in collagen tissue diseases, the eosinophil numbers found may be lower than expected and eosinophilia may be more frequent than reported.
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PMID:Eosinophilia in rheumatologic diseases: a prospective study of 1000 cases. 1506 29


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