A unified approach to suspension cell mechanics

Mechanical profiling of cells is crucial for diagnosis and monitoring of viral and chronic diseases. In particular, the Young's modulus of cells serves as a biological fingerprint that can be assessed, e.g., by atomic force microscopy, micropipette aspiration, optical trapping and microfluidic methods. The diversity of these technologies with respect to timescale, strain rate and mechanical stress results in Young's moduli that cover orders of magnitude. Currently, it is unclear if these variations are of technical, physical or biological origin. Here, we exposed human leukaemia 60 (HL60) cells to mean hydrodynamic stress levels between 8 Pa and 800 Pa using real-time deformability cytometry. Our results follow a power law between applied stress and cellular Young's modulus and integrates seamlessly data from current state-of-the-art technologies into a unifying master curve. This renders suspension cell measurements independent from the experimental method, the timescale as well as the adhesion or suspension state. Finally, our data allows to calculate a resting Young's modulus, i.e., in the absence of an external hydrodynamic stress that is independent of measurement buffer composition and viscosity. Considering the strong need for a standardized and quantifiable approach, we believe that our data present a step towards a universal application of cell mechanical phenotyping in life sciences.