title: Surprisingly simple mechanical behavior of a complex embryonic tissue.
abstract: BACKGROUND
  Previous studies suggest that mechanical feedback could coordinate morphogenetic events in embryos. Furthermore, embryonic tissues have complex structure and composition and undergo large deformations during morphogenesis. Hence we expect highly non-linear and loading-rate dependent tissue mechanical properties in embryos.
  
  
  RESULTS
  We used micro-aspiration to test whether a simple linear viscoelastic model was sufficient to describe the mechanical behavior of gastrula stage Xenopus laevis embryonic tissue in vivo. We tested whether these embryonic tissues change their mechanical properties in response to mechanical stimuli but found no evidence of changes in the viscoelastic properties of the tissue in response to stress or stress application rate. We used this model to test hypotheses about the pattern of force generation during electrically induced tissue contractions. The dependence of contractions on suction pressure was most consistent with apical tension, and was inconsistent with isotropic contraction. Finally, stiffer clutches generated stronger contractions, suggesting that force generation and stiffness may be coupled in the embryo.
  
  
  CONCLUSIONS
  The mechanical behavior of a complex, active embryonic tissue can be surprisingly well described by a simple linear viscoelastic model with power law creep compliance, even at high deformations. We found no evidence of mechanical feedback in this system. Together these results show that very simple mechanical models can be useful in describing embryo mechanics.
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America. mvondass@yahoo.com
authors.forename: Michelangelo
authors.initials: M
authors.lastname: von Dassow
authors.forename: James A
authors.initials: JA
authors.lastname: Strother
authors.forename: Lance A
authors.initials: LA
authors.lastname: Davidson
mesh_terms: D000818:Animals; D015509:Developmental Biology / Q000379:methods*; D004548:Elasticity; D004625:Embryo, Nonmammalian; D005775:Gastrula / Q000502:physiology; D015233:Models, Statistical; D009024:Morphogenesis / Q000502:physiology; D009119:Muscle Contraction; D013314:Stress, Mechanical; D013499:Surface Properties; D014783:Viscosity; D014982:Xenopus laevis