Abstract
We developed force clamp force mapping (FCFM), an atomic force microscopy (AFM) technique for measuring the viscoelastic creep behavior of live cells with sub-micrometer spatial resolution. FCFM combines force-distance curves with an added force clamp phase during tip-sample contact. From the creep behavior measured during the force clamp phase, quantitative viscoelastic sample properties are extracted. We validate FCFM on soft polyacrylamide gels. We find that the creep behavior of living cells conforms to a power-law material model. By recording short (50-60 ms) force clamp measurements in rapid succession, we generate, for the first time, two-dimensional maps of power-law exponent and modulus scaling parameter. Although these maps reveal large spatial variations of both parameters across the cell surface, we obtain robust mean values from the several hundreds of measurements performed on each cell. Measurements on mouse embryonic fibroblasts show that the mean power-law exponents and the mean modulus scaling parameters differ greatly among individual cells, but both parameters are highly correlated: stiffer cells consistently show a smaller power-law exponent. This correlation allows us to distinguish between wild-type cells and cells that lack vinculin, a dominant protein of the focal adhesion complex, even though the mean values of viscoelastic properties between wildtype and knockout cells did not differ significantly. Therefore, FCFM spatially resolves viscoelastic sample properties and can uncover subtle mechanical signatures of proteins in living cells.
Highlights
In order to quantify the mechanical properties of live cells, a myriad of different rheological instruments and methods have been developed
We developed force clamp force mapping (FCFM) as a novel atomic force microscopy (AFM) technique
FCFM is based on force mapping (FM), an AFM imaging mode used to determine the local elastic properties of a sample by recording force–distance curves
Summary
In order to quantify the mechanical properties of live cells, a myriad of different rheological instruments and methods have been developed. Examples are micropipette manipulation,[11] magnetic bead microrheometry,[12] intracellular microrheology,[13] the optical stretcher,[14] and atomic force microscopy (AFM).[15] With these techniques, local variations in the viscoelastic power-law parameters between individual positions have been observed.[16,17,18,19,20,21,22,23] AFM combines the capabilities of high-resolution imaging with quantitative mechanical probing. It has been used to record spatially resolved maps of viscoelastic properties of live cells, but using purely elastic material models or spring-dashpot type viscoelastic material models only.[24,25,26,27] Neither AFM nor other methods have yet been used to spatially map viscoelastic powerlaw parameters
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
