title: Multiscale stress-strain characterization of onion outer epidermal tissue in wet and dry states.
abstract: •
  
  
  OBJECTIVE
  Quantitative measurements of water's effects on the tension response of plant tissue will assist in understanding the regulatory mechanism underlying expansive growth. Such measurements should be multiscale in nature to account for plants' hierarchical structure.•
  
  
  METHODS
  Outer onion epidermal tissues were cut and bonded to uniaxial displacement-controlled mechanical loading devices to apply and measure the force on the sample. Fluorescent polystyrene beads (500 nm in diameter) were dispersed on the sample surface under various levels of tensile load conditions to obtain displacement maps with a confocal fluorescent microscope. The resulting strain was measured using a digital image correlation technique by tracking individual bead displacements. The applied forces were obtained by measuring the displacement of the calibrated force-sensing device. Tissue- and cell-scale mechanical properties were quantified by calculating the applied stress and the corresponding global and local strains.•
  
  
  RESULTS
  The Young's modulus values of individual cell walls of dehydrated and rehydrated samples were 3.0 ± 1.0 GPa and 0.4 ± 0.2 GPa, respectively, and are different from the Young's modulus values of the global tissue-scale dehydrated and rehydrated samples, which were 1.9 ± 0.3 GPa and 0.08 ± 0.02 GPa, respectively. Poisson's ratio increased more than 3-fold due to hydration.•
  
  
  CONCLUSIONS
  The results on global, cell-to-cell, and point-to-point mechanical property variations suggest the importance of the mechanical contribution of extracellular features including the middle lamella, cell shape, and dimension. This study shows that a multiscale investigation is essential for fundamental insights into the hierarchical deformation of biological systems.
authors.affiliation: Department of Agricultural and Biological Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 USA.
authors.forename: Keekyoung
authors.initials: K
authors.lastname: Kim
authors.affiliation: Department of Agricultural and Biological Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 USA.
authors.forename: Hojae
authors.initials: H
authors.lastname: Yi
authors.affiliation: Department of Agricultural and Biological Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 USA.
authors.forename: M Shafayet
authors.initials: MS
authors.lastname: Zamil
authors.affiliation: Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 USA.
authors.forename: M Amanul
authors.initials: MA
authors.lastname: Haque
authors.affiliation: Department of Agricultural and Biological Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 USA.
authors.forename: Virendra M
authors.initials: VM
authors.lastname: Puri
mesh_terms: D001696:Biomechanical Phenomena; D001703:Biophysics / Q000379:methods*; D055119:Elastic Modulus; D019697:Onions / Q000502:physiology*; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013718:Tensile Strength
keywords: cell wall mechanics; digital image correlation; dry and wet states; multiscale stress–strain; onion epidermal tissue; tensile testing