Numerical model for the deformation of nucleated cells by optical stretchers

Ihab Sraj, Joshua Francois, David W M Marr and Charles D Eggleton

In this paper, we seek to numerically study the deformation of nucleated cells by single diode-laser bar optical stretchers. We employ a recently developed computational model, the dynamic ray-tracing method, to determine the force distribution induced by optical stretchers on a cell encapsulating a nucleus of different optical properties. These optical forces are shape dependent and can deform real non-rigid objects; thus resulting in dynamically changing distributions with cell and nucleus deformation. A Chinese hamster ovary (CHO) cell is a common biological cell that is of interest to the biomedical community because of its use in recombinant protein therapeutics and is an example of a nucleated cell. To this end, we model CHO cells as two concentric three-dimensional elastic capsules immersed in a fluid where the hydrodynamic forces are calculated using the immersed boundary method. We vary the inner capsule size to simulate different nucleus sizes. Our results show that the presence of a nucleus has a major effect on the force distribution on the cell surface and consequently on its net deformation. Scattering and gradient forces are reported for different nucleus sizes and the effect of nucleus size on the cell deformation is discussed quantitatively.

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