Mechanical Properties of Re-constituted Actin Networks at an Oil/Water Interface Determined by Microrheology
Ershov, D.S. ; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
Soft Matter 8 (2012). - ISSN 1744-683X - p. 5896 - 5903.
particle-tracking microrheology - cytoskeletal protein networks - micropipette aspiration - myosin-filaments - molecular motors - polymer networks - living cells - cortex - microscopy - membranes
There have been various attempts to investigate the mechanical properties of the actin cortex in cells, but the factors that control them remain poorly understood. To make progress, we develop a reconstituted model of the actin cortex that mimics its structure. We attach actin filaments to lipids lining the surface of an oil droplet using biotin–streptavidin bonds. In this way we can form a thin actin network that can be visualized and studied by confocal microscopy. Our approach allows incorporation of different actin-binding and motor proteins into this 2D network and characterization of their effect on its mechanical properties in a quantitative way. To study the viscoelasticity of the network, we use passive particle tracking microrheology, which allows storage and loss moduli to be extracted from the mean square displacement of tracer particles. We show that adding cross-linkers to the cortex increases its elasticity by several orders of magnitude and addition of myosin in the presence of ATP results in a strong and rapid stiffening of the network. This approach opens up a variety of possibilities to study viscoelastic properties of the actin cortex in vitro, allowing incorporation of any protein of interest into the system.
Shape-Memory Effects in Biopolymer Networks with Collagen-Like Transient Nodes
Skrzeszewska, P.J. ; Jong, L.N. ; Wolf, F.A. de; Stuart, M.A.C. ; Gucht, J. van der - \ 2011
Biomacromolecules 12 (2011)6. - ISSN 1525-7797 - p. 2285 - 2292.
polymer networks - triblock copolymers - hydrogels - proteins - release
In this article we study shape-memory behavior of hydrogels, formed by biodegradable and biocompatible recombinant telechelic polypeptides, with collagen-like end blocks and a random coil-like middle block. The programmed shape of these hydrogels was achieved by chemical cross-linking of lysine residues present in the random coil. This led to soft networks, which can be stretched up to 200% and “pinned” in a temporary shape by lowering the temperature and allowing the collagen-like end blocks to assemble into physical nodes. The deformed shape of the hydrogel can be maintained, at room temperature, for several days, or relaxed within a few minutes upon heating to 50 °C or higher. The presented hydrogels could return to their programmed shape even after several thermomechanical cycles, indicating that they remember the programmed shape. The kinetics of shape recovery at different temperatures was studied in more detail and analyzed using a mechanical model composed of two springs and a dashpot.