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DOI

Abstract

Although the role of the primary cilium as a sensory organelle in epithelial cells has been elucidated significantly over the past decade, the function of primary cilia in connective tissue cells has been studied less extensively. Primary cilia have been implicated as mechanotransducers in connective tissues, but the mechanisms by which the cells sense loads and convert them to biochemical signals for tissue formation and adaptation are poorly understood. Before hypotheses regarding the function of the primary cilium in connective tissue cells can be tested, methods for quantitation of incidence as well as three-dimensional visualization of primary cilia with respect to the extracellular matrix (ECM) are needed. The objective of this study was to develop a rapid method for visualizing primary cilia in their native ECM in a wide range of connective tissues. Whole-mount immunohistochemical and multiphoton microscopy techniques were developed to simultaneously image primary cilia, cell nuclei, and collagen and their relationships to each other in situ. Axonemes of primary cilia projecting into the ECM were successfully visualized in thick sections of growth plate cartilage, tendon, ligament, meniscus, intervertebral disc, and perichondrium. These methodologies will allow analysis of the incidence and three-dimensional orientation of primary cilia and enable investigation of the role of primary cilia in normal and pathological growth and adaptation in a variety of musculoskeletal tissues. Anat Rec, 291:1062–1073, 2008. © 2008 Wiley-Liss, Inc.

Keywords

Small cracks; Biaxial stress; Fatigue crack growth

Fig 7 from The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology
Volume 291, Issue 9, pages 1062-1073, 25 AUG 2008 DOI: 10.1002/ar.20665
http://onlinelibrary.wiley.com/doi/10.1002/ar.20665/full#fig7

DOI

Abstract

Cancellous bone plays a crucial structural role in the skeleton, yet little is known about the microstructure-mechanical property relationships of the tissue at the microscale. Cancellous tissue is characterized by a microstructure consisting of layers interspaced with transition zones with different proportions of collagen and mineral. In this study, the quasistatic and dynamic mechanical properties of lamellar and interlamellar tissue in human vertebrae were assessed with nanoindentation, and the collagen content and organization were characterized with second harmonic generation microscopy. Lamellar tissue was 35% stiffer, 25% harder, and had a 13% lower loss tangent relative to interlamellar tissue. The stiff, hard lamellae corresponded to areas of highly ordered, collagen-rich material, with a relatively low loss tangent, whereas the compliant, soft interlamellar regions corresponded to areas of disordered or collagen-poor material. These data suggest an important role for collagen in the tissue-level mechanical properties of bone.

Keywords

Bone; Hardness; Microstructure

DOI

Abstract

The effects of two key experimental parameters on the measured nanomechanical properties of lamellar and interlamellar tissue were examined in dehydrated rabbit cancellous bone. An anhydrous sample preparation protocol was developed to maintain surface integrity and produce RMS surface roughnesses ∼10 nm (5 × 5-μm² area). The effects of surface roughness and maximum nanoindentation load on the measured mechanical properties were examined in two samples of differing surface roughness using maximum loads ranging from 250 to 3000 μN. As the ratio of indentation depth to surface roughness decreased below ∼3:1, the variability in material properties increased substantially. At low loads, the indentation modulus of the lamellar bone was ∼20% greater than that of the interlamellar bone, while at high loads the measured properties of both layers converged to an intermediate value. Relatively shallow indentations made on smooth surfaces revealed significant differences in the properties of lamellar and interlamellar bone that support microstructural observations that lamellar bone is more mineralized than interlamellar bone. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2006.

Keywords

cancellous bone; nanoindentation; mechanical properties; surface roughness; sample preparation

DOI

Abstract

Previous studies of the growth of small fatigue cracks in aluminum alloy 7075-T6 are reviewed to compare observed behavior and explanations for that behavior. The results of small crack growth tests conducted in this work are then reported. Crack growth was monitored periodically between initial crack sizes of approximately 10 μm to final sizes of approximately 0.5 mm in rotating bending and plate specimens subjected to fully-reversed cycling. Both longitudinal and transverse stress components were present in the central region of the plate specimens, while rotating bending specimens experienced nearly uniaxial cyclic stress. Specimens were taken from rolled 7075-T651 with a pancake microstructure. Tests were conducted at a number of different strain amplitudes. Small cracks grew faster than large cracks for the same stress intensity range ΔK, as expected from previous research by others. When compared on the basis of ΔK, growth rates in the plate specimens varied from being little different than those in rotating bending specimens to approximately four times higher, depending on strain amplitude. The growth rates of cracks at different locations around the circumference of the rotating bending specimens varied little, in spite of the different microstructural orientations of the different locations. In both plate and rotating bending tests, some cracks exhibited marked decelerations and accelerations in growth rate, while others did not. For those cracks that did not exhibit such oscillations in growth rate plus those cracks that had grown large enough for such oscillations to have subsided, growth rates were found to be proportional to crack size and to amplitude of maximum shear strain to a power of approximately 4.5. Growth rate data from both rotating bending and plate specimens were well correlated by that strain parameter.

Keywords

Small cracks; Biaxial stress; Fatigue crack growth