Brownian motion of actin filaments in confining microchannels

Since the cytoskeletal protein actin is one of the principal building blocks of mammalian cells, it has recently been arousing much interest. Here, we address questions concerning the mechanical and dynamic behaviour of individual actin filaments in confining geometries which mimic the dense cytoskeletal network in eukaryotic cells. Microfluidic devices fabricated by soft photolithography in combination with fluorescence microscopy are used to manipulate, observe and characterize these biopolymers. The polymer statistics is strongly dependent on the characteristics of the surroundings such as the degree of confinement and hydrodynamical flow. Besides this, the intrinsic mechanical properties of the filaments are dominated by the persistence length and the contour length. We analyse the tangent-tangent correlation and the radial distribution function in terms of a confining potential and the contour length of the filaments. In addition, we show that hydrodynamic flow can be successfully used to apply controlled local stress on actin filaments. Our results can be surprisingly well described by a straightforward model which approximates the confining energy of the microchannels using a parabolic potential.