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D. Zeng, T. Juzkiw, C. R. Ethier, M. Johnson; Estimating Young’s Modulus of Schlemm’s Canal Endothelial Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2074.
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© ARVO (1962-2015); The Authors (2016-present)
To present a method for quantifying the elastic modulus (Young’s modulus) of Schlemm's canal (SC) endothelial cells using finite element models combined with magneto-cytometry.
4.5 µm diameter paramagnetic beads (Dynal Biotech) coated with RGD peptide were bound to sub-confluent SC cells in culture and pulled by a magnetic force of known magnitude applied through a micro-needle (ARVO 2005, Abstract 1346). Finite element models (ABAQUS Inc.) were created to calculate bead displacements, using a generic SC cellular geometry based on phase-contrast and confocal images. SC cells were modeled as linearly elastic materials, and the experimental data was fitted to determine a best estimate of cellular Young’s modulus. The direction of the magnetic pulling force, the bead embedding angle (related to bead-cell contact area), and the distance between the bead and the culture dish surface were parametrically varied using the finite element models to evaluate their influence on cellular elastic modulus.
Three SC cells with beads bound to the peripheral cytoplasmic region were pulled by a magnetic force of 800 pN for 4 seconds. Cells demonstrated visco-elastic responses to the applied mechanical load with bead displacements ranging from 0.1 µm to 0.4 µm. We focused on estimating bounds for Young’s modulus by examining the initial and long-term elastic response of the cells. Based on the initial elastic response of the SC cells, with thick cytoplasm and a small embedding angle, the upper bound of Young’s modulus was 7730±1130 Pa, while the lower bound of 133±50 Pa was obtained from the long-term elastic response of the cells, with a large embedding angle and small bead-to-dish gap. Estimates of the elastic modulus were strongly affected by embedding angle and bead-to-dish distance, while the pulling direction had little influence.
The bounds of Young’s modulus obtained in this study are within previously published ranges of Young’s modulus for endothelial cells. Combining finite element modeling with magnetic bead pulling cytometry is a viable approach for quantifying SC cells’ elastic properties, provided that the embedding angle and cytoplasm thickness are measured accurately. Future work includes improvement on these measurements, as well as extension of the finite element models to incorporate visco-elastic properties of the cells.
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