Force Distributions in Biopolymer Networks

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Intracellular biopolymer networks perform many essential functions for living cells. They stabilize the architecture of cells, facilitate directed transport by forming tracks for molecular motors, and enable cell motility. Most of these networks show a highly nonlinear mechanical response that is well studied on the macroscopic scale; however little is known experimentally about how specific properties of the individual filaments and the network architecture contribute to the nonlinearity. In this project a method will be developed for simultaneously visualizing the network architecture and the distribution of forces through the network, without and with an external load. Networks will be imaged with a recently developed 3D scanning probe microscope based on optical tweezers that use a small colloidal particle as a sensor. As the size of the particle is significantly smaller than the typical mesh size of the network, it can diffuse freely through the network. Thermal forces which drive the motion of the particle provide a natural position scanner. The particle position is followed by a 3D position sensor with nanometer precision and megahertz bandwidth. The network structure and force distribution are extracted from 3D position histograms of the particle. This project will provide experimental insight into how biopolymer networks obtain highly nonlinear mechanical properties from the mechanics of individual filaments and how these networks distribute forces. Researchers in the field will be able to refine their models and/or develop new ones. The broader impact resulting from the proposed activity will be the development of a novel microscopic technique for imaging the nanoscopic architecture and force distributions in biopolymer networks. Students will be trained in recently developed 3D scanning probe microscopy. The data will be important for health related research and engineering of novel materials. Additionally, the project is ideal for integrating research and education for undergraduate, and graduate students in an interdisciplinary field.