Modelling the structural response of an eukaryotic cell in the optical
stretcher
R Ananthakrishnan,
Jochen Guck,
F Wottawah,
S Schinkinger,
B Lincoln,
M Romeyke,
J Kas
CURRENT SCIENCE
88
(9)
1434-1440
(2005)
The cytoskeleton of an eukaryotic cell is a composite polymer material with unique structural (mechanical) properties. To investigate the role of individual cytoskeletal polymers in the deformation response of a cell to an external force (stress), we created two structural models - a thick shell model for the actin cortex, and a three-layered model for the whole cell. These structural models for a cell are based on data obtained by deforming suspended cells, where each cell is stretched between two counter-propagating laser beams using an optical stretcher. Our models, with the data, suggest that the outer actin cortex is the main determinant of the structural response of the cell.
Characterizing single suspended cells by optorheology
F Wottawah,
S Schinkinger,
B Lincoln,
S Ebert,
K Muller,
F Sauer,
K Travis,
Jochen Guck
The measurement of the mechanical properties of individual cells has received much attention in recent years. In this paper we describe the application of optically induced forces with an optical stretcher to perform step-stress experiments on individual suspended fibroblasts. The conversion from creep-compliance to frequency-dependent complex shear modulus reveals characteristic viscoelastic signatures of the underlying cytoskeleton and its dynamic molecular properties. Both normal and cancerous fibroblasts display a single stress relaxation time in the observed time and frequency space that can be related to the transient binding of actin crosslinking proteins. In addition, shear modulus and steady-state viscosity of the shell-like actin cortex as the main module resisting small deformations are extracted. These values in combination with insight into the cells' architecture are used to explain their different deformability. This difference can then be exploited to distinguish normal from cancerous cells. The nature of the optical stretcher as an optical trap allows easy incorporation in a microfluidic system with automatic trapping and alignment of the cells, and thus a high measurement throughput. This carries the potential for using the microfluidic optical stretcher to investigate cellular processes involving the cytoskeleton and to diagnose diseases related to cytoskeletal alterations. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Optical rheology of biological cells
F Wottawah,
S Schinkinger,
B Lincoln,
R Ananthakrishnan,
M Romeyke,
Jochen Guck,
J Kas
A step stress deforming suspended cells causes a passive relaxation, due to a transiently cross-linked isotropic actin cortex underlying the cellular membrane. The fluid-to-solid transition occurs at a relaxation time coinciding with unbinding times of actin cross-linking proteins. Elastic contributions from slowly relaxing entangled filaments are negligible. The symmetric geometry of suspended cells ensures minimal statistical variability in their viscoelastic properties in contrast with adherent cells and thus is defining for different cell types. Mechanical stimuli on time scales of minutes trigger active structural responses.
Optical deformability as an inherent cell marker for testing malignant
transformation and metastatic competence
Jochen Guck,
S Schinkinger,
B Lincoln,
F Wottawah,
S Ebert,
M Romeyke,
D Lenz,
HM Erickson,
R Ananthakrishnan, et al.
The relationship between the mechanical properties of cells and their molecular architecture has been the focus of extensive research for decades. The cytoskeleton, an internal polymer network, in particular determines a cell's mechanical strength and morphology. This cytoskeleton evolves during the normal differentiation of cells, is involved in many cellular functions, and is characteristically altered in many diseases, including cancer. Here we examine this hypothesized link between function and elasticity, enabling the distinction between different cells, by using a microfluidic optical stretcher, a two-beam laser trap optimized to serially deform single suspended cells by optically induced surface forces. In contrast to previous cell elasticity measurement techniques, statistically relevant numbers of single cells can be measured in rapid succession through microfluidic delivery, without any modi. cation or contact. We find that optical deformability is sensitive enough to monitor the subtle changes during the progression of mouse fibroblasts and human breast epithelial cells from normal to cancerous and even metastatic state. The surprisingly low numbers of cells required for this distinction reflect the tight regulation of the cytoskeleton by the cell. This suggests using optical deformability as an inherent cell marker for basic cell biological investigation and diagnosis of disease.
Contact
Cell Physics Division Prof. Vahid Sandoghdar Acting Division Head
Max Planck Institute for the Science of Light Staudtstr. 2 91058 Erlangen, Germany
