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The effect of moisture content on the mechanical properties of a seed shell (1995)

Williamson, L. ; Lucas, P.

Springer

Journal of materials science 30 (1995), S. 162-166

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ISSN: 1573-4803

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract The mechanical properties of the seed shells of the African mongongo nut, Schinziophyton rautenenii (Euphorbiaceae), were measured by compressive C-ring tests in an air-dry condition and also after soaking in distilled water. Young's modulus was found to be about 5 GPa and the fracture strength was 40–50 MPa, for both conditions. However, fracture toughness was affected significantly by moisture content. The critical stress intensity factor, K IC, of air-dried specimens was 27% greater and the work of fracture, R, 69% greater than those of wet specimens. This difference corresponded well with microscopic observations of the complexity of the fracture surface. Viewed either by scanning electron microscopy or confocal microscopy, cracks in the wet shell deviated neatly around individual fibres, while cracks in air-dried shells either crossed individual fibres or ran obliquely across the outer layers of the secondary cell wall leaving a feathered appearance. It is proposed that the increase in toughness of shells which would be obtained from air-drying may help protect embryonic seed tissues from predation by larger animals (e.g. vertebrates such as rodents) after abcission from the parent plant.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00352145

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Mesenchymal stem cells reside within the connective tissues of many organs (1995)

Young, H. E. ; Mancini, M. L. ; Wright, R. P. ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

Developmental Dynamics 202 (1995), S. 137-144

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ISSN: 1058-8388

Keywords: Mesenchymal stem cells ; Progenitor cells ; Pluripotent cells ; Muscle ; Fat ; Cartilage ; Bone ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: Previous studies have noted the presence of mesenchymal stem cells located within the connective tissue matrices of avian skeletal muscle, dermis, and heart. In these studies, clonal analysis coupled with dexamethasone treatment revealed the presence of multiple populations of stem cells composed of both lineage-committed progenitor mesenchymal stem cells and lineage-uncommitted pluripotent mesenchymal stem cells. The present study was undertaken to assess the distribution of these stem cells in the connective tissues throughout various regions of the body. Day 11 chick embryos were divided into 26 separate regions. Heart, limb skeletal muscle, and limb dermis were included as control tissues. Cells were harvested enzymatically and grown using conditions optimal for the isolation, cryopreservation, and propagation of avian mesenchymal stem cells. Cell aliquots were plated, incubated with various concentrations of dexamethasone, and examined for differentiated phenotypes. Four recurring phenotypes appeared in dexamethasone-treated stem cells: skeletal muscle myotubes, fat cells, cartilage nodules, and bone nodules. These results suggest that progenitor mesenchymal stem cells and putative pluripotent mesenchymal stem cells with the potential to form at least four tissues of mesodermal origin have a widespread distribution throughout the body, being located within the connective tissue compartments of many organs and organ systems. © 1995 Wiley-Liss, Inc.

Additional Material: 2 Ill.