title: Characterizing microscale biological samples under tensile loading: stress-strain behavior of cell wall fragment of onion outer epidermis.
abstract: OBJECTIVE
  The results of published studies investigating the tissue-scale mechanical properties of plant cell walls are confounded by the unknown contributions of the middle lamella and the shape and size of each cell. However, due to their microscale size, cell walls have not yet been characterized at the wall fragment level under tensile loading. It is imperative to understand the stress-strain behavior of cell wall fragments to relate the wall's mechanical properties to its architecture. •
  
  
  METHODS
  This study reports a novel method used to characterize wall fragments under tensile loading. Cell wall fragments from onion outer epidermal peels were cut to the desired size (15 × 5 µm) using the focused ion beam milling technique, and these fragments were manipulated onto a microelectromechanical system (MEMS) tensile testing device. The stress-strain behavior of the wall fragments both in the major and minor growth directions were characterized in vacuo. •
  
  
  RESULTS
  The measured mean modulus, fracture strength, and fracture strain in the major growth direction were 3.7 ± 0.8 GPa, 95.5 ± 24.1 MPa, and 3.0 ± 0.5%, respectively. The corresponding properties along the minor growth direction were 4.9 ± 1.2 GPa, 159 ± 48.4 MPa, and 3.8 ± 0.5%, respectively. •
  
  
  CONCLUSIONS
  The fracture strength and fracture strain were significantly different along the major and minor growth directions, the wall fragment level modulus of elasticity anisotropy for a dehydrated cell wall was 1.23, suggesting a limited anisotropy of the cell wall itself compared with tissue-scale results.
authors.affiliation: Department of Agricultural and Biological Engineering, 235 Agricultural Engineering Building, Penn State University, University Park, PA 16802, USA. msz126@psu.edu
authors.forename: M S
authors.initials: MS
authors.lastname: Zamil
authors.forename: Hojae
authors.initials: H
authors.lastname: Yi
authors.forename: M A
authors.initials: MA
authors.lastname: Haque
authors.forename: Virendra M
authors.initials: VM
authors.lastname: Puri
mesh_terms: D001696:Biomechanical Phenomena; D002473:Cell Wall / Q000502:physiology* / Q000648:ultrastructure*; D055724:Electrophysiological Phenomena; D019697:Onions / Q000166:cytology*; D019441:Plant Epidermis / Q000502:physiology / Q000648:ultrastructure*
keywords: MEMS; fragment level; mechanical properties; plant cell wall; tensile test