Biological Soft Matter Laboratory Dept. of Physics, Kyushu University
Previous research
Microrheology
In order to understand how activity can control the mechanical properties
of life, it is necessary to measure both the stiffness and the degree of
(non-equilibrium) activity. We carry this out with state-of-the-art "simultaneous
active/passive microrheology".
AFM-Microrheology system
Nonequilibrium mechanics of life
Any style of life, from cells to tissues to whole organisms, is active-driven
by spontaneously generated forces. Within cells various organelles, vesicles
and lipids are found to be actively fluctuating when observed by high contrast
imaging techniques (movie 1). Cells themselves also migrate (movie 2).
Studying the strong nonequilibrium state in cells is critical for understanding
the mechanism of various cellular processes such as cell migration (movie
2), division, intracellular material production and transportation.
Recently, it has been realized that cells regulate their own properties
by their nonequilibrium activity. How much they are “alive” determines
their physical characters such as mechanical property without changing
any chemical constituents. We study this enigmatic mechanism by creating
simple model systems composed of, for instance, cytoskeleton structures,
lipid membranes and DNA.
movie1: Nonequilibrium fluctuations in a cultured cell (DIC image)
movie2: Cell migration
Inside cells, there exists a network called the cytoskeleton composed
of semi-flexible polymers such as actin, microtubules, and intermediate
filaments. The cytoskeleton provides mechanical strength to cells and facilitates
dyniamics processes by generating forces. All these are analogous to the
mechanical design of higher organisms.
Functions of the cytoskeleton (actin etc.) +motor proteins (myosin etc.)
As our body hardness and shape is determined by their associated organsm
(miscle), cell structure is determined by tissue protein called "cytoskeleton".
In our body, muscle associated with skeleton generate forces. On the othe
hand, nanometer sized molecular machine (motor protein) generate forces
with cytoskeleton in cytoplasm. Thus, cells become a out-of-equilibrium
state. Real life is too complicated for physicists to work with. We therefore
extract the most fundamental components for intracellular force generations
and reconstitute them to produce force generating gels in vitro. We call
these gels "active gels". Active gels look as if they are
alive as can be seen below (movie3, movie4).
Non -equilibrium fluctuations in non-closslinked actin/myosin gels
Force generation mechanism on actin/myosin system
Non-equilibrium fluctuations in closslinked actin/myosin gel
Coss-linked gels can support motor-generated stress (left above). We analyze
the motion of probe particles dispersed in the gel. Without motor-generated
stress, it is hard to observe such large fluctuations.
Mechano sensing
It hurts for humans to get punched (Fig . 1), and so it does for cells,
which is called "mechano-sensing". Here fibronectin-coated
colloiidal particles were adhered to a cell (movie 5), and the cell was
punched with an optical tweezers(left below). We observed release of a
second messenger,NO in response to the punches. (Fig. 2). Cells were labelled
with fluorescent NO indicator.