Cells have amazing mechanisms to modify their surroundings by applying traction forces. They can also quickly adapt to changes in the mechanical properties of their environment. Mimicking of these cellular mechanisms in adaptive materials depends on a detailed understanding of the underlying cellular processes.
Hydrogel-based traction force microscopy (TFM) and PDMS-based micropillar arrays are common techniques to collect further insight into cellular traction forces.
In TFM, cells are placed on a soft matrix that contains fluorescent nanoparticles. The displacement of these nanoparticles is used to determine cellular traction forces. In PDMS-based micropillar arrays, the deflection of the micropillars upon cell adhesion is a measure of the bending forces applied by the cells.
Unfortunately, both techniques suffer from a lack of precision. On the one hand, micropillar arrays can only be used for in-plane displacement measurements On the other hand, the resolution of TFM highly depends on the substrate stiffness. Moreover, the position of the fluorescent nanoparticles that monitor substrate deformations influences its optical resolution. Finally, the analysis of the 3D substrate deformations is extremely time-consuming. So, quantitative and high-throughput local cell force measurements in- and out-of-plane are strongly needed.
In consequence, a novel strategy to measure 3D cell traction forces is presented here using 2D NiTi microsensor arrays. They have been designed based on finite element method (FEM) and fabricated by thin film photolithography in collaboration with Rodrigo Lima de Miranda/Acquandas GmbH. Within the simulations, the deformations of the inner contact point of the sensors were analyzed as a function of the applied force that mimic 3D cell traction forces in the nN region. The x-, y-, z-deflection of the elastic cantilever arrays is optically read-out and will be directly correlated to the normal and shear traction forces of the cell.