Dynamic ray tracing for modeling optical cell manipulation

Abstract

Current methods for predicting stress distribution on a cell surface due to optical trapping forces are based on a traditional ray optics scheme for fixed geometries. Cells are typically modeled as solid spheres as this facilitates optical force calculation. Under such applied forces however, real and non-rigid cells can deform, so assumptions inherent in traditional ray optics methods begin to break down. In this work, we implement a dynamic ray tracing technique to calculate the stress distribution on a deformable cell induced by optical trapping. Here, cells are modeled as three-dimensional elastic capsules with a discretized surface with associated hydrodynamic forces calculated using the Immersed Boundary Method. We use this approach to simulate the transient deformation of spherical, ellipsoidal and biconcave capsules due to external optical forces induced by a single diode bar optical trap for a range of optical powers.

Cell elongation via intrinsic antipodal stretching forces

“…1, this particular geometry can be generated with a single astigmatic source, whose beam axis in the x direction is focused in the z = 0 plane while remaining extended along y . To determine the resulting distribution of forces exerted on a deformable cell surface, we perform simulations modeling the optical trap as a series of discrete rays using ray-tracing methods [13–16]. …”

Optical separation of ellipsoidal particles in a uniform flow

“…35 During the ray tracing, only the refracted ray was traced because the reflectance is small under the condition of small difference in refractive indices on both sides of the interface, i.e., biological matters. 5,6,20,21 The optical force per unit volume on each nodal point was calculated by…”

“…The optical force on the particle much smaller than the wavelength was obtained by the Rayleigh dipole approximation, 16 while that on the particle much larger than the wavelength was calculated by the ray optics method. 5,6,12,[17][18][19][20][21][22] For the optical force on the particle with arbitrary size including the intermediate one, the generalized Lorenz-Mie theory was employed. 23,24 Among these methods, the ray optics method is relatively simple, and covers the size range of most blood cells, i.e., red blood cell and white blood cell.…”

“…The fluid flow and particle motion were separately solved using different methods and were coupled using the penalty immersed boundary method (pIBM) developed by Huang et al 34 Optical force calculations were conducted using the ray optics method containing the ray-triangle intersection method, i.e., the dynamic ray tracing method. 20,21 The oblate spheroidal particles were considered, and their separation was characterized according to the lateral migration distances obtained for various aspect ratios. In our previous study, it was shown that an initially inclined ellipsoidal particle could rotate with horizontal movement during levitation by the optical force.…”

Using GPUs for Realtime Prediction of Optical Forces on Microsphere Ensembles

“…Sraj et al [19] used dynamic ray tracing to deduce the optical force on the surface of the deformable cell from which they calculate stress distribution. Rather than using the rigid spheres as an approximated shape of the cell, they perform force calculation on the actual cell.…”