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Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Nov;82(5 Pt 1):051923. Epub 2010 Nov 17.

Comparison of Brownian-dynamics-based estimates of polymer tension with direct force measurements.

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Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Towne Building, 220 S. 33rd St., Philadelphia, Pennsylvania 19104-6315, USA.


With the aid of brownian dynamics models, it is possible to estimate polymer tension by monitoring polymers' transverse thermal fluctuations. To assess the precision of the approach, brownian dynamics-based tension estimates were compared with the force applied to rhodamine-phalloidin labeled actin filaments bound to polymer beads and suspended between two optical traps. The transverse thermal fluctuations of each filament were monitored with a CCD camera, and the images were analyzed to obtain the filament's transverse displacement variance as a function of position along the filament, the filament's tension, and the camera's exposure time. A linear Brownian dynamics model was used to estimate the filament's tension. The estimated force was compared and agreed within 30% (when the tension <0.1 pN ) and 70% (when the tension <1 pN ) with the applied trap force. In addition, the paper presents concise asymptotic expressions for the mechanical compliance of a system consisting of a filament attached tangentially to bead handles (dumbbell system). The techniques described here can be used for noncontact estimates of polymers' and fibers' tension.

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