Verlag des Forschungszentrums Jülich
JUEL-4186
Cesa, Claudia Mariana
Microstructured Elastomer Films to Measure Dynamic Traction Forces of Living Animal Cells with High Spatial Resolution - Establishment of the Technique and First Results on Cardiac Myocytes
105 S., 2005
Almost all cell types are able to create mechanical forces. These forces are very
important for many cell functions like cell adhesion, cell migration or cell division.
Mechanical forces are produced in the cell mainly by the contraction of the actin-myosin
complex. In adherent cells, the actin cytoskeleton anchors to the substrate via integrins.
The linkage between integrin and the actin cytoskeleton is mediated by highly dynamic
protein complexes, known as focal contacts. Thus, mechanical forces are transmitted to the
substrates at the level of the focal contacts.
In this project a technique for measuring mechanical forces transmitted at sites of
focal adhesions based on (Balaban et al., 2001) was developed and adapted. In addition, as
a first application, forces created by single beating myocytes were measured. Cells isolated
from hearts of neonatal rat embryos were cultivated on fibronectin coated elastomers.
Upon contraction of single beating cardiac myocytes, these substrates were reversibly
deformed. Regular patterns of microstructures imprinted into the surface of the elastomer
served as markers for the deformations. The micropattern was prepared by curing the
elastomer in contact with a silicon master which exhibited the negative of the pattern of
interest. The microstructure was prepared in a silicon dioxide layer having a thickness
below 500 nm. Appropriate silicon dioxide coated silicon masters were prepared by
adapting standard techniques from semiconductor technology. The mechanical properties
of the used elastomer were carefully characterized. It was found that the material behaves
as a linear and isotropic elastic medium.
Mechanical forces exerted by cells to the substrates were measured by solving the
inverse problem of elasticity theory (Schwarz et al., 2003; Schwarz et al., 2002). In this
work, the force dipole tensor was introduced as measure of the mechanical activity of the
whole cell.
Cardiac myocytes were examined after one or two days in culture. Single beating
cells with visible focal adhesions that deformed the microstructured substrates were
selected for observation. Live cell imaging was performed using reflection interference
contrast microscopy (RICM). In this way, the sites of focal adhesions and the
microstructures could be localised by the same method.
With this optimised technique, the effect of different stiffness of the substrates on
force production (magnitude and transmission at the substrates) was also studied. Results
on substrates of five different stiffnesses are shown and discussed.
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