title: Computational modeling of shear forces and experimental validation of endothelial cell responses in an orbital well shaker system.
abstract: Vascular endothelial cells are continuously exposed to hemodynamic shear stress. Intensity and type of shear stress are highly relevant to vascular physiology and pathology. Here, we modeled shear stress distribution in a tissue culture well (R = 17.5 mm, fill volume 2 ml) under orbital translation using computational fluid dynamics with the finite element method. Free surface distribution, wall shear stress, inclination angle, drag force, and oscillatory index on the bottom surface were modeled. Obtained results predict nonuniform shear stress distribution during cycle, with higher oscillatory shear index, higher drag force values, higher circular component, and larger inclination angle of the shear stress at the periphery of the well compared with the center of the well. The oscillatory index, inclination angle, and drag force are new quantitative parameters modeled in this system, which provide a better understanding of the hydrodynamic conditions experienced and reflect the pulsatile character of blood flow in vivo. Validation experiments revealed that endothelial cells at the well periphery aligned under flow and increased Kruppel-like Factor 4 (KLF-4), cyclooxygenase-2 (COX-2) expression and endothelial nitric oxide synthase (eNOS) phosphorylation. In contrast, endothelial cells at the center of the well did not show clear directional alignment, did not induce the expression of KLF-4 and COX-2 nor increased eNOS phosphorylation. In conclusion, this improved computational modeling predicts that the orbital shaker model generates different hydrodynamic conditions at the periphery versus the center of the well eliciting divergent endothelial cell responses. The possibility of generating different hydrodynamic conditions in the same well makes this model highly attractive to study responses of distinct regions of the same endothelial monolayer to different types of shear stresses thereby better reflecting in vivo conditions.
authors.affiliation: a Department for Applied Mechanics and Automatic Control, Faculty of Engineering, Center for Bioengineering , University of Kragujevac , Sestre Janjic 6, Kragujevac 34000 , Serbia.
authors.forename: Nenad
authors.initials: N
authors.lastname: Filipovic
authors.affiliation: b Department of Medicine, Faculty of Science , University of Fribourg , Fribourg , Switzerland.
authors.forename: Kedar
authors.initials: K
authors.lastname: Ghimire
authors.affiliation: a Department for Applied Mechanics and Automatic Control, Faculty of Engineering, Center for Bioengineering , University of Kragujevac , Sestre Janjic 6, Kragujevac 34000 , Serbia.
authors.forename: Igor
authors.initials: I
authors.lastname: Saveljic
authors.affiliation: a Department for Applied Mechanics and Automatic Control, Faculty of Engineering, Center for Bioengineering , University of Kragujevac , Sestre Janjic 6, Kragujevac 34000 , Serbia.
authors.forename: Zarko
authors.initials: Z
authors.lastname: Milosevic
authors.affiliation: b Department of Medicine, Faculty of Science , University of Fribourg , Fribourg , Switzerland.
authors.forename: Curzio
authors.initials: C
authors.lastname: Ruegg
mesh_terms: D003198:Computer Simulation; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology*; D004730:Endothelium, Vascular / Q000166:cytology*; D006439:Hemodynamics; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism; D008962:Models, Theoretical; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D015203:Reproducibility of Results; D013314:Stress, Mechanical
chemical_list: C000715467:KLF4 protein, human; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human
keywords: endothelial cells; flow; modeling; orbital shaker; shear stress