title: Comparison of stresses on homogeneous spheroids in the optical stretcher computed with geometrical optics and generalized Lorenz-Mie theory.
abstract: We present two electromagnetic frameworks to compare the surface stresses on spheroidal particles in the optical stretcher (a dual-beam laser trap that can be used to capture and deform biological cells). The first model is based on geometrical optics (GO) and limited in its applicability to particles that are much greater than the incident wavelength. The second framework is more sophisticated and hinges on the generalized Lorenz-Mie theory (GLMT). Despite the difference in complexity between both theories, the stress profiles computed with GO and GLMT are in good agreement with each other (relative errors are on the order of 1-10%). Both models predict a diminishing of the stresses for larger wavelengths and a strong increase of the stresses for shorter laser-cell distances. Results indicate that surface stresses on a spheroid with an aspect ratio of 1.2 hardly differ from the stresses on a sphere of similar size. Knowledge of the surface stresses and whether or not they redistribute during the stretching process is of crucial importance in real-time applications of the stretcher that aim to discern the viscoelastic properties of cells for purposes of cell characterization, sorting, and medical diagnostics.
authors.affiliation: Sector for Biological and Soft Systems, Department of Physics, Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, UK. lars.boyde@cantab.net
authors.forename: Lars
authors.initials: L
authors.lastname: Boyde
authors.forename: Andrew
authors.initials: A
authors.lastname: Ekpenyong
authors.forename: Graeme
authors.initials: G
authors.lastname: Whyte
authors.forename: Jochen
authors.initials: J
authors.lastname: Guck
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D008863:Microspheres; D008962:Models, Theoretical; D052898:Optical Tweezers; D011829:Radiation Dosage; D013314:Stress, Mechanical