Investigation of the viscoelasticity of human osteosarcoma cells using a shear assay method
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Zhan Gao and Alberto M. Cuitino Department of Mechanical and Aerospace Engineering, Rutgers University, Piscataway, New Jersey 08854
Wole Soboyejoa) Princeton Institute for the Science and Technology of Materials (PRISM) and Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (Received 21 October 2005; accepted 6 April 2006)
This paper presents a shear assay method for the determination of the viscoelastic properties of biological cells. The method was applied to the measurement of the viscoelastic properties of human osteosarcoma (HOS) cells. It involves a combination of shear assay experiments and digital image correlation techniques. Following in situ observations of cell deformation during shear assay experiments, a digital image correlation (DIC) technique was used to determine the local displacement and strain fields. The creep curves were also extracted from multiple digital images that were used to extract the time dependence of local strain under constant stress conditions. The measured creep curves were well described by a generalized viscoelastic Maxwell model. The extracted elastic and viscous parameters were in good agreement with results obtained from prior studies with other techniques. The results also suggested that the nucleus is stiffer than the surrounding cytoplasm of HOS cells.
I. INTRODUCTION
The understanding of the biological responses of bone cells to mechanical loading is a subject of interest in biomaterials.1–3 One of the major mechanical stimuli that bone cells (osteoblasts and osteocytes) respond to is the deformation-generated fluid shear stress exerted by the insterstitial fluid flow through the lacunar/canalicular spaces.1,3 Shear assay experiments using a parallel-plate flow chamber have been used to study the in vitro behavior of osteoblast-like cells subjected to shear flow.1–5 Prior studies have also used the shear assay technique to explore fluid flow shear stress-induced deformation,4,6 cell adhesion,7–9 biochemical changes,2 and cell proliferation and differentiation.1,5 However, prior shear assay studies of cell mechanical properties have been limited, so far, to global elasticity measurements.6 There have, therefore, been no prior studies of the viscoelastic properties of biological cells using the shear assay method. The viscoelastic deformability of a cell is determined largely by their composite shell envelope, which is
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0235 1922 J. Mater. Res., Vol. 21, No. 8, Aug 2006 http://journals.cambridge.org Downloaded: 03 Apr 2015
composed of the lipid-protein bilayer with the associated actin cortex and by the cell cytoskeleton, which consists largely of networks of microtubules, actin, and intermediate filaments.10–12 Elastic moduli and viscosities can be used to quantify the cell viscoelasticity. To explore the viscoelastic nature of various cells, some methods such as micropipette aspiration,13 atomic force microscopy,14
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