Cells generate mechanical forces (traction forces, TFs) while interacting with the extracellular matrix or neighbouring cells. Forces are generated by both cells and extracellular matrix (ECM) and transmitted within the cell-ECM or cell-cell contacts involving focal adhesions or adherens junctions. Within more than two decades, substantial progress has been achieved in techniques that measure TFs. One of the techniques is traction force microscopy (TFM). This review discusses the TFM and its advances in measuring TFs exerted by cells (single cells and multicellular systems) at cell-ECM and cell-cell junctional intracellular interfaces. The answers to how cells sense, adapt and respond to mechanical forces unravel their role in controlling and regulating cell behaviour in normal and pathological conditions.

The standardized approach in nanoindentation measurements provides a reproducible mechanical characterization of cancer cells.

We present a new approach for the microrheological characterization of soft suspended bodies. We obtain results comparable to AFM based dynamic nanoindentation. We discuss viscoelastic and poroelastic contributions to material behavior.

This work is to study the relationship between the exposure conditions and the quality of cell imaging with soft X-ray contact microscopy (SXCM). It is a crucial step in the efficient visualization of cell structures. Three different human cell lines: DU145 prostate carcinoma cells, HCC38 breast cancer cells, and Poietics mesenchymal stem cells were used to establish the optimal exposure conditions in SXCM. The image quality depended on the soft X-ray (SXR) absorbed energy and photoresist development conditions. At lower SXR energy (200 or 400 SXR pulses), sharp cell edges, membrane projections, and cell–cell connections were visible. In contrast, higher energy (600 or 800 SXR pulses) allowed observation of the cytoskeleton and the nucleus in a cell type-dependent manner (the influence of cell thickness and internal complexity was noted).

Spheroids are of great interest in the study of cancer as they can partially mimic the tumour microenvironment, thus allowing to investigate several aspects of cell – microenvironment interactions in healthy and diseased conditions, including those pertaining to mechanobiology. Atomic Force Microscopy (AFM) is a versatile tool for studying biological samples and their mechanobiological properties. In AFM, the tip shape and dimensions determine the contact geometry between the tip and the sample and the length scales at which the mechanical properties are probed. Given the complex multiscale structure of spheroids, the choice of tip geometry and size would allow, in principle, to dissect the mechanical response of the overall system into the contributions of the constituents, from the single cell level to the cellular aggregate. In this work, we studied the mechanical properties of spheroids derived from four cell lines (A549, NHLF, HT-29, and CCD-18Co cells). Our studies revealed that using different contact geometries in the fitting procedure results in significantly different Young’s modulus values, highlighting the multiscale response of these complex cellular systems and the importance of a precise experimental design and choice of the AFM probe for the nanomechanical measurements. We observed that the location of F-actin filaments is correlated with the rigidity of the spheroids.

Cancer progression is associated with changes in cell mechanical and rheological properties that could be probed by atomic force microscopy (AFM). In this study, we applied AFM to measure elastic (by compressing the cells) and viscoelastic (by applying shear stress) properties of bladder cancers in relation to their culture morphology (in single cells, cell monolayers, and spheroids). Three different cell lines, HCV29 (non-malignant cell cancer of ureter), HT1376 (grade III bladder carcinoma), T24 (grade IV transitional cell carcinoma), were investigated. Nanoindentation measurements only differentiate between non-malignant and cancer cells, but it is difficult to distinguish between specific bladder cancers. By applying microrheological measurements, we confirm that non-malignant cells are more rigid than cancer cells but more importantly, it was possible to differentiate between two cancerous cell lines, regardless of the culture conditions. As each of them is characterized by a distinct actin filament network inside the cell, we showed that actin filaments are a key element in defining the rheological properties of spheroids originating from cells having thick actin bundles. Our results showed that HCV29 cells are more rigid than the studied cancer cells, indicating that normal cells are resistant to compressive and shear forces. Therefore, we conclude that cell mechanical and rheological properties may serve as a biophysical marker to distinguish normal and cancer cells of different malignancies.