Fig. 1: Working principle and conceptual proof of high-frequency rheology over a continuous frequency range.

a A rounded cell (green) confined between two parallel microcantilevers. A blue laser actuates the master microcantilever while a red laser reads the motion of the slave microcantilever and measures the cell mechanical properties. b For morphological characterization the setup is combined with an optical microscope. A chamber controlling humidity, temperature, and gas atmosphere maintains cell culture conditions during the experiments. To arrange both microcantilevers in a parallel-plate assay, the slave microcantilever is mounted on a wedge. c Lumped-mass model of configuration shown in a. The motions of both microcantilevers, which have effective masses \({m}_{{\rm{m}}}\) and \({m}_{{\rm{s}}}\), are determined by transfer functions \({g}_{{\rm{m}}}(f)\) and \({g}_{{\rm{s}}}(f)\), which describe their respective coupling to their cantilever chips. Both cantilevers are coupled to each other via the transfer function of the cell \({g}_{{\rm{c}}}(f)\). d Amplitude (left) and phase (right) measurements of a rounded HeLa cell exposed to glutaraldehyde and hardening over 25 min. At 0 min, glutaraldehyde was added to the medium to a final concentration of 1% (vol/vol). e Simulation of amplitude (left) and phase (right) measurements in a lumped-mass system (inset). Microcantilevers are modeled as Kelvin–Voigt elements, the cell as a simple spring (Methods). The curves are generated for a gradual increase of the cellular spring constant.