A micro-opto-acousto-fluidic chip for single cell mechanics evaluation

The rapid development of microfluidic circuits and lab-on-chip devices for cell studies opened new perspectives for cellular biology, in particular for the biophysics and biomechanics of single cells. At the state of the art, a lot of attention is being paid to the possible integration of optical and acoustic actuators within microfluidic system because they both provide a contactless way for cell manipulation and analysis; additionally, they both offer other advantages such as rapid actuation, programmable capability and simple operation. In this work we exploit a microfluidic setup, combining optical and acoustic actuators, to perform cell mechanics characterization in terms of both cellular optical deformability (OD) and acoustic compressibility (AC). The OD and AC measurements reliability is obtained thanks to a precise determination of many parameters, as culture medium refractive index, viscosity and density, laser beam waist values and cell size, which are required for a proper estimation of cellular OD and AC. Cellular OD values are obtained by cell optical stretching procedure [1] while AC values are derived by fitting the cell acoustophoretic trajectory [2]. We apply this technique to measure the OD and AC of two human breast cancer cell populations, MCF7 and MDA, which are characterized by different metastatic potential. These two measurements are firstly performed separately and the results are reported in Fig.1. It can be seen that the two cell lines have similar cell size distribution, however, MDA shows both higher optical deformation and higher acoustic compressibility than MCF7, which is in good agreement with literature and can be associated with its elevated metastatic nature and stronger migratory ability. Afterwards, combined measurements of these two parameters were directly carried out on the same cell and it is found that there is no clear relationship between them in each cell sample, i.e., higher compressibility does not imply higher optical deformability [3]. Furthermore, we demonstrated that these two measurements do not affect each other. In conclusion, the chip presented here, together with the proposed measurement protocols, constitute a step forward in the characterization of cellular mechanical properties and thus in the possible identification of cells with specific biological properties. Additionally, we will present the experimental results of the currently on-going experiments showing the impact of drugs treatments on tumour-cells mechanical properties.