Silver (Ag)-doped hydroxyapatite (HAp) agglomerates containing 0.15%, 1.5% and 4.3% mole % of silver among total cations, respectively, were evaluated in vitro and in vivo to explore their potential application as a bone filler with antibacterial properties. The 0.15% Ag-doped HAp was mildly cytotoxic, whereas the 1.5% and 4.3% Ag-doped HAps were moderately cytotoxic in the standard agar overlay cytotoxicity assay. The in vivo test was carried out by implanting Ag-HAps in artificial bone defects at the periapical area of both mandibular 1 st molar of rats and no remarkable cytotoxicity was found unlike what was observed in the in vitro data. All of the implanted Ag-doped HAp particles, regardless of their Ag contents, allowed appropriated cellular proliferation and favorable bone repair without remarkable inflammatory reaction through 3 week healing periods, in spite of the mild delay in organization of fibrin and inflammatory reaction with the 4.3% Ag-doped HAp at the early healing phase. They supported well new bone formation with osteointegrative and osteoconductive properties. The results suggest that HAps doped with Ag up to 4.3 % of total cations can be applied for repair of infection-associated bony defects.
For many fatigue-critical parts of machines and structures, load history under service conditions generally involves variable amplitude loading rather than constant amplitude loading. An accurate prediction of fatigue crack propagation life under variable amplitude loading requires a thorough evaluation of load interaction effects. In this study, fatigue tests under both constant and variable amplitude loading are carried out to investigate the overload effects on fatigue crack propagation of the notched specimens. Strain distribution around the crack tip before and after a tensile overloading is measured using ESPI (Electronic Speckle Pattern Interferometry) system. The size of plastic zone is determined from the measured strain distribution. The study proposes a crack propagation prediction model that incorporates the overload effect. The overload effect factor for fatigue crack propagation life is used to characterize the load interaction effect in load spectrum. A comparative work demonstrates that the prediction by the proposed model is in good agreement with the experimental results.
In the fatigue tests of specimens, sufficiently large tensile overload included in cyclic constant amplitude loading causes the retardation in fatigue crack growth. Crack retardation remains for some period of time after the overloading. The number of cycles in the retarded crack growth has been shown to be related to the plastic zone developed due to the overload. The magnitude of the elastic-plastic zone around the crack tip of DENT(Double Edge Notched Tension) specimen after a overloading was measured by ESPI(Electronic Speckle Pattern Interferometry) system. The fatigue crack growth rate also was measured by a traveling microscope. The relationship between the measured magnitude of plastic zone and the crack growth rate was compared with the equations proposed by Wheeler. Crack growth retardation model that was characterized by crack growth length and the size of plastic zone was proposed and compared with test result. From the research, the validity of proposed model is examined on crack growth retardation, and consequently fatigue life.
Calcium metaphosphate(CMP) ceramic in the form of a macroporous block was evaluated as a bone substitute in vivo. Macroporous calcium metaphosphate ceramic blocks with a mean pore size of 250 mm were implanted into either subcutanous pouches or artificial tibial bone defects in rats, and biodegradibility, biocompatibility and osteoconductivity were analyzed, respcectively. The macroporous CMP ceramic blocks implanted into subcutanous pouches permitted ingrowth of vascularized connective tissue without an inflammatory response or a foreign body reaction for 3 weeks after implantation. In addition, there was no remarkable weight change during 3 weeks implanted in subcutanous pouches. The macroporous CMP ceramic blocks implanted into bony defects revealed a favorable connection and direct fusion of newly formed bone from local osseous margin with their framework without insertion of fibrous connective tisssue and did not evoke an inflammatory reaction. The excellent biocompatibility,osteoconductivity, biomechanical strength, and ease of handling fullfill the requirement as a promising bone substitute.
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