A microstructured fiber with defined borosilicate regions to produce a radial micronozzle array for nanoelectrospray ionization

This work highlights the possibility of using microstructured fibres with predefined doped regions to produce functional microstructures at a fibre facet with differential chemical etching. A specially designed silica microstructured fibre (MSF) that possesses specific boron-doped silica regions was fabricated for the purpose of generating a radial micronozzle array. The MSF was drawn from a preform comprising pure silica capillaries surrounded by boron-doped silica rods. Different etching rates of the boron-doped and silica regions at the fiber facet produces raised nozzles where the silica capillaries were placed. Fabrication parameters were explored in relation to the fidelity and protrusion length of the nozzle. Using etching alone, the nozzle protrusion length was limited, and the inner diameter of the channels in the array is expanded. However with the addition of a protective water counter flow, nozzle protrusion is increased to 60 μm with a limited increase in hole diameter. The radial micronozzle array generated nine individual electrosprays which were characterized using spray current measurements and related to theoretical prediction. Signal enhancement for the higher charge state ions for two peptides showed a substantial signal enhancement compared to conventional emitter technology.Y. Fu, S. Morency, K. Bachus, D. Simon, T. Hutama, G. T. T. Gibson, Y. Messaddeq and R. D. Oleschu

Projection Effect Errors in Biomaterials and Bone Research

Micoradiography and backscattered electron (BSE) imaging are techniques used to investigate the morphologic, histometric, and mineral content changes at the bone/biomaterials interface. Investigators have shown that the superimposition of multiple tissue layers can cause errors with both the morphologic observations and the histometric measurements of bone. The objective of this study was to document errors in the bone mineral content measurements associated with overlapping tissues. Using a digital image analysis system, microradiographic and BSE images from canine cortical and cancellous bone were captured and analyzed. The results of this study showed that microradiography had more projection effect errors associated with the morphology and histometry. The BSE technique provided substantially better resolution of the bone morphology and showed significantly more (p$0.05) bone surface perimeter than the microradiographic technique. Contrary to the literature, the BSE images did not show less bone area than the microradiographic images of the identical regions. This discrepancy was explained by projection effect errors and over penetration artifacts of the X-ray beam. Unique to this study was the documentation that microradiography has inherent projection effect errors associated with mineral content measurements. The SSE images had significantly more (p$0.05) graylevels present than the microradiographic images. Due to the limited tissue overlap, the BSE images provide excellent morphologic resolution, accurate bone histometry and the ability to accurately measure the mineral content of cortical and cancellous bone at a microscopic level

Stereoscopic Analysis of Trabecular Bone Orientation in Proximal Human Tibias

The three-dimensional orientation of trabeculae is a key factor in determining the load carrying capabilities of cancellous bone. Previous biomechanical studies have shown that proximal tibias resected parallel to the articulating surface are stronger and stiffer than the contralateral tibias resected perpendicular to the long axis of the bone. However, morphologic evidence was not provided to help explain the mechanical differences. To determine the orientation of the trabeculae in the medial condyle for both parallel cut and perpendicular cut specimens, a scanning electron microscope and stereoscopic techniques were used. Data showed that tibias cut parallel to the articular surface had trabeculae oriented nearly vertical with a mean angle of 4.5° ± 14.7° (range, 0° to 56.3°). The contralateral tibias cut perpendicular to the long axis of the tibia had trabeculae oriented at a mean angle of 36.0° ± 12.2° (range, 16.1° to 67.4 °) from vertical. The differences between the two resection techniques were shown to be significant (p s. 0.01) using an Analysis of Variance. This study provided morphologic evidence to explain why previous specimens cut parallel to the articular surface had stronger and stiffer cancellous bone than the contralateral specimens cut perpendicular to the long axis of the tibia. This information is important in understanding the load carrying capabilities of cancellous bone and how it may be applied to improving the clinical results of primary total knee arthroplasty

Reproducible Method for Calibrating the Backscattered Electron Signal for Quantitative Assessment of Mineral Content in Bone

Backscattered electron (BSE) imaging shows promise for orthopaedic and bone research. BSE images of bone may be captured on-line directly from the scanning electron microscope (SEM), and then analyzed to produce a backscattered electron profile (BSEP), a modified image graylevel histogram which is representative of the mineral content in bone. The goals of this work were 1) develop a reproducible graylevel calibration technique for bone specimens, and 2) determine a conservative time interval during which SEM operating conditions would remain stable. Calibration standards containing pure aluminum and pure magnesium wires were placed in the SEM with human cancellous bone. Baseline imaging conditions were first established by adjusting the SEM until the bone image displayed good resolution and graylevel separation between regions of different mineral content. Microscope brightness and contrast controls were randomly changed to initiate the new operating conditions of another imaging session, and graylevel values from the calibration metals were used to readjust the microscope back to baseline operating conditions. Weighted mean graylevel values of the BSEPs from calibration trials were compared to those of the baseline. Data showed that bone images could be reproduced within 1.2 percent. It was also concluded that our equipment required calibration checks at 20 minute intervals

Functional trade-offs in the limb bones of dogs selected for running versus fighting

The physical demands of rapid and economical running differ from the demands of fighting in ways that may prevent the simultaneous evolution of optimal performance in these two behaviors. Here, we test an hypothesis of functional trade-off in limb bones by measuring mechanical properties of limb bones in two breeds of domestic dog (Canis lupus familiaris L.) that have undergone intense artificial selection for running (greyhound) and fighting (pit bull) performance. The bones were loaded to fracture in three-point static bending. To correct for the effect of shear, we estimated the shear stress in the cross section and added energy due to shear stress to the tensile energy. The proximal limb bones of the pit bulls differed from those of the greyhounds in having relatively larger second moments of area of mid-diaphyseal cross sections and in having more circular cross-sectional shape. The pit bulls exhibited lower stresses at yield, had lower elastic moduli and failed at much higher levels of work. The stiffness of the tissue of the humerus, radius, femur and tibia was 1.5-2.4-fold greater in the greyhounds than in the pit bulls. These bones from the pit bulls absorbed 1.9-2.6-fold more energy before failure than did those of the greyhounds. These differences between breeds were not observed in the long bones of the feet, metacarpals and metatarsals. Nevertheless, the results of this analysis suggest that selection for high-speed running is associated with the evolution of relatively stiff, brittle limb bones, whereas selection for fighting performance leads to the evolution of limb bones with relatively high resistance to failure.Keywords: Aggression, Greyhound, Locomotion, Pit bull, Bone mechanical properties, Canis lupus familiari