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Abstract

Motor proteins such as kinesin are used in cells to transport intracellular cargo along defined filament paths. The constituents of the transport system (i.e., motor proteins and filaments) can be reconstructed on synthetic surfaces to serve as molecular shuttles that actively transport cargo. Microfabricated open channels have been used in the past to guide microtubules propelled by kinesin adsorbed to the surface. In an effort to better understand the mechanism by which guidance occurs, we present a quantitative measure of the transport efficiency of microtubules along straight polyurethane channels 1 mum deep. Our analysis shows that the probability of a microtubule remaining in a channel drops exponentially as a function of its travel distance and that this characteristic decay distance varies with channel width. We identify microtubule-sidewall collisions as the key event for microtubule escape from a channel and thus the determinant of guiding efficiency. To better understand the relationship between collisions and travel distance, we determine the effect of channel width on (1) the microtubule approach angle to the sidewall, (2) the collision outcome (guided or escaped), and (3) the distance traveled between collisions. Also discussed is how the physical properties of microtubules or actin filaments (i.e., length, bending stiffness, persistence length) and changes in channel geometry (width, height) can describe measured parameters.