Muscle disorders such as myofibrillar myopathies and Duchenne muscular dystrophy involve mutations in key cytoskeletal proteins and lead to progressive muscle degeneration. Yet, the mechanical characterization of affected muscle cells has relied mainly on immature or non-human models. Here, we introduce a human in vitro platform based on patient-derived immortalized myoblasts differentiated into myotubes on nanogrooved substrates, which promote alignment and organotypic maturation. Using immunostaining and atomic force microscopy (AFM), we show that desmin- and dystrophin-mutated myotubes exhibit distinct morphological and mechanical phenotypes compared to wild-type myotubes. We developed an AFM stiffness pipeline to quantify cell body stiffness across myotubes of variable thickness. Desmin- and dystrophin-mutated myotubes are stiffer than controls, with desmin mutants also displaying cytoskeletal disorganization. A dynamic fatigue assay (cyclic AFM indentations over time) further revealed impaired stiffening and faster mechanical fatigue in desmin mutants, while dystrophin mutants preserved resilience. This set of results establishes a reproducible and human-relevant system to probe muscle mechanics in disease, offering a unique intermediate model between conventional immortalized lines and complex iPSC-derived tissues, and enabling future quantitative screening and translational applications.

Cell shape changes, essential for processes such as motility or division, are controlled by the actomyosin cortex that actively remodels biological membranes. Their mechanisms can be deciphered in vitro using biomimetic reconstituted systems, such as giant unilamellar vesicles (GUVs) with controlled lipid composition coupled to reconstituted actin networks. These assays allow mimicking cell shape changes in controlled biochemical and biophysical environments. However, studying the dynamics of these shape changes on statistically significant populations of GUVs with the possibility to sequentially modify the protein composition of the assay is a major experimental challenge. To address these issues, a microfluidic approach is used to immobilize several dozens of isolated GUVs and monitor membrane and actin network evolution. The loading of the chamber with GUVs and actin is first characterized. Then, the actin-induced remodeling of populations of homogeneous and phase-separated GUVs is monitored and shows that actin networks prevent the coalescence of lipid microdomains and that, in return, the number of domains affects the actin network structure. This microfluidic-based experimental strategy, thus, allows for studying actin-induced membrane deformation in vitro and can be adapted to other studies on membrane remodeling processes.

Atomic force microscopy (AFM) is the gold-standard technique to simultaneously map the morphology and viscoelastic properties of living cells. Although existing software tools, both open-source and from AFM manufacturers, can analyze cells individually, there is a growing need for fast and accessible codes to compile data from multiple cells into a single dataset. To address this, we present CellMAP, a user-friendly software tool that streamlines the batch-processing of AFM-derived topography and stiffness maps of living cells. Our analysis pipeline includes but is not limited to: flattening of the underlying substrate surface, filtering of outlier values, measurement of the cell surface and volume, and measurement of height and stiffness distributions. CellMAP can also generate a composite cell that reflects the height and stiffness properties of an entire cell population.

Cell migration profoundly influences cellular function, often resulting in adverse effects in various pathologies including cancer metastasis. Directly assessing and quantifying the nanoscale dynamics of living cell structure and mechanics has remained a challenge. At the forefront of cell movement, the flat actin modules & horbar;the lamellipodium and the lamellum & horbar;interact to propel cell migration. The lamellipodium extends from the lamellum and undergoes rapid changes within seconds, making measurement of its stiffness a persistent hurdle. In this study, we introduce the fast-quantitative imaging (fast-QI) mode, demonstrating its capability to simultaneously map both the lamellipodium and the lamellum with enhanced spatiotemporal resolution compared with the classic quantitative imaging (QI) mode. Specifically, our findings reveal nanoscale stiffness gradients in the lamellipodium at the leading edge, where it appears to be slightly thinner and significantly softer than the lamellum. Additionally, we illustrate the fast-QI mode's accuracy in generating maps of height and effective stiffness through a streamlined and efficient processing of force-distance curves. These results underscore the potential of the fast-QI mode for investigating the role of motile cell structures in mechanosensing.

The mechanical properties of living cells reflect their physiological and pathological state. In particular, cancer cells undergo cytoskeletal modifications that typically make them softer than healthy cells, a property that could be used as a diagnostic tool. However, this is challenging because cells are complex structures displaying a broad range of morphologies when cultured in standard 2D culture dishes. Here, we use adhesive micropatterns to impose the cell geometry and thus standardize the mechanics and morphologies of cancer cells, which we measure by atomic force microscopy (AFM), mechanical nanomapping, and membrane nanotube pulling. We show that micropatterning cancer cells leads to distinct morphological and mechanical changes for different cell lines. Micropatterns did not systematically lower the variability in cell elastic modulus distribution. These effects emerge from a variable cell spreading rate associated with differences in the organization of the cytoskeleton, thus providing detailed insights into the structure-mechanics relationship of cancer cells cultured on micropatterns. Combining AFM with micropatterns reveals new mechanical and morphological observables applicable to cancer cells and possibly other cell types.

Membrane nanotubes are continuously assembled and disassembled by the cell to generate and dispatch transport vesicles, for instance, in endocytosis. While these processes crucially involve the ill-understood local mechanics of the nanotube, existing micromanipulation assays only give access to its global mechanical properties. Here we develop a new platform to study this local mechanics using atomic force microscopy (AFM). On a single coverslip we quickly generate millions of substrate-bound nanotubes, out of which dozens can be imaged by AFM in a single experiment. A full theoretical description of the AFM tip-membrane interaction allows us to accurately relate AFM measurements of the nanotube heights, widths, and rigidities to the membrane bending rigidity and tension, thus demonstrating our assay as an accurate probe of nanotube mechanics. We reveal a universal relationship between nanotube height and rigidity, which is unaffected by the specific conditions of attachment to the substrate. Moreover, we show that the parabolic shape of force-displacement curves results from thermal fluctuations of the membrane that collides intermittently with the AFM tip. We also show that membrane nanotubes can exhibit high resilience against extreme lateral compression. Finally, we mimic in vivo actin polymerization on nanotubes and use AFM to assess the induced changes in nanotube physical properties. Our assay may help unravel the local mechanics of membrane-protein interactions, including membrane remodeling in nanotube scission and vesicle formation.

We use single-cell force spectroscopy to compare elasticity, adhesion, and tether extrusion on four breast cancer cell lines with an increasing invasive potential. We perform cell attachment/detachment experiments either on fibronectin or on another cell using an atomic force microscope. Our study on the membrane tether formation from cancer cells show that they are easier to extrude from aggressive invasive cells. Measured elastic modulus values confirm that more invasive cells are softer. Moreover, the adhesion force increases with the invasive potential. Our results provide a mechanical signature of breast cancer cells that correlates with their invasivity.

Cyclic depth-sensing nanoindentation tests are carried out to unravel the effect of monolithic and multilayer thin coatings on load-bearing capacity and stress distribution in the coating-Zr-based metallic glass systems. Thin films of TiN, CrN, and Ti/TiN multilayer, having thickness of 300 nm, are deposited on Zr 60 Ni 10 Cu 20 Al 10 and Zr 50 Cu 40 Al 10 metallic glasses by RF sputtering technique. Strain softening occurs over several cycles in Zr-based metallic glasses, CrN, and TiN films as evidenced by a disparity between the unloading and reloading sequences. However, the cyclic nanoindentation of Ti/TiN multilayer coating results in a hysteresis loop in the load-depth profiles, and this event depends on the number of cycles and the loading rates. AFM and SEM characterization of remnant imprints revealed microcraks and crack-like shear bands in nanocoatings and Zr-based metallic glasses, respectively. Based on shear-fracture driven plastic flow of the coatings, a modified cavity model is used to determine the shear stress evolution as a function of penetration depth. The finite-element simulations predicted the stress distribution beneath the indenter and are well consistent with the evolving trend of shear stress obtained from experiments.

Ti/TiN multilayer and monolithic TiN nanocoatings have been deposited on Zr-based metallic glass substrates by means of RF sputtering technique at room temperature. Nanoindentation and nanoscratch tests are used to characterise the mechanical and tribological properties of coated samples. In addition, a Vickers indentation tests and scanning electron microscopy observation have been carried out to explore the deformation mechanism. When coated with the TiN and Ti/TiN multilayers, Zr60Ni10Cu20Al10 bulk metallic glass shows a significant enhancement of both apparent hardness and elastic modulus with a decrease of the friction coefficient. The Vickers indentation shows a fragile behaviour of TiN coatings compared to the Ti/TiN multilayer one. Based on Bhowmick model description, experimental nanoindentation approach is taken to determine the variation of shear stress as function of the penetration depth. It is found that the shear stress developed in the TiN coatings is higher than that observed in the Ti/TiN multilayer. A correlation between finite-element analysis results and experimental data has been proposed. The monolithic or multilayer type of coatings is found to have an influence on the stress and plastic deformation distributions.

Des essais de nanoindentation instrumenté pour des chargements monotones et cycliques sur deux verres métalliques massifs (VMM) à base Zirconium ont été réalisés à température ambiante et avec une vitesse de chargement qui varie de 250 à 2500 μN/s. Nous avons trouvé que les chargements cycliques induisent un adoucissement qui semble être dépendant du nombre de cycles et du taux de chargement. L’effet de la vitesse de chargement a été comparé avec des essais effectués sur des échantillons du verre métallique à base Zirconium revêtus par des films de TiN et de CrN. La déformation inélastique dans le verre métallique à base Zirconium a été étudiée en analysant par microscopie à force atomique les empreintes résultantes des essais de nanoindentation. Le mécanisme de volume libre est proposé pour l’interprétation quantitative de ces observations.

Cyclic nanoindentation tests were carried out to study the influence of the chromium nitride thin films on the mechanical properties of Zr‐based metallic glass. Chromium nitride thin coatings have been deposited on Zr50Cu40Al10 metallic glass substrate by RF sputtering. The deposition process was done at room temperature under nitrogen reactive gas using a metallic chromium target. The CrN films have a thickness of 300 nm. Several cyclic nanoindentation measurements were conducted on CrN films and Zr50Cu40Al10 metallic glass substrate samples at various loading rate values. We have found that the coated metallic glass sample shows high mechanical properties such as hardness and reduced elastic modulus. Cyclic nanoindentation results show a hardening behaviour for these CrN coatings. Moreover, the CrN coated on Zr‐based metallic glass was found to have a high value of resistance to crack propagation, as being analysed through the SEM pictures of the residual Vickers indentation impressions.

The influence of the size of crystalline regions on mechanical properties of irradiated oxides has been studied using magnesium aluminate spinel MgAl2O4. The samples characterized by different dimensions of crystalline domains, from sintered ceramics with grains of few micrometers in size up to single crystals, were used in the experiments. The samples were irradiated at room temperature with 320keV Ar2+ ions up to fluences reaching 5×1016cm−2. Nanomechanical properties were measured by using a nanoindentation technique and the resistance to crack formation by measurement of the total crack lengths made by Vickers indenter. The results revealed: correlation of nanohardness with accumulated damage, radiation-induced hardness increase in grain-boundary region and significant improvement of material resistance to crack formation.

The influence of the size of crystalline regions on mechanical properties of irradiated oxides has been studied using a magnesium aluminate spine! MgAl2O4. The samples characterized by different dimensions of crystalline domains, varying from sintered ceramics with grains of few micrometers in size up to single crystals, were used in the experiments. The samples were irradiated at room temperature with 320 keV Ar2+ ions up to fluences reaching 5 x 10(16) cm(-2). Nanomechanical properties (nanohardness and Young's modulus) were measured by using a nanoindentation technique and the resistance to crack formation by measurement of the total crack lengths made by the Vickers indenter. The results revealed several effects: correlation of nanohardness evolution with the level of accumulated damage, radiation-induced hardness increase in grain-boundary region and significant improvement of material resistance to crack formation. This last effect is especially surprising as the typical depth of cracks formed by Vickers indenter in unirradiated material exceeds several tens of micrometers, i.e. is more than hundred times larger than the thickness of the modified layer.

Monotonic and cyclic nanoindentation tests were carried out on Zr50Cu40Al10 bulk metallic glass (BMG) at loading rates ranging from 250 to 2500 mu N/s and at ambient temperature. We found that cyclic loadings induced a mechanical softening which appears to be dependent on the number of cycles and the loading rates. The effect of loading rates was compared with the same nanoindentation tests on specimens of Zr-based metallic glass coated with CrN and TiN films. The inelastic deformation on Zr-based metallic glass was studied by analysing the remnant indent morphology using atomic force microscopy. A free-volume mechanism was proposed for interpreting these observations quantitatively.

The in-plane penetration depth of Sr0.88La0.12CuO2+x thin films at various doping obtained from oxygen reduction has been measured, using ac-susceptibility measurements. For the higher doping samples, the superfluid density deviates strongly from the s-wave behavior, suggesting, in analogy with other electron-doped cuprates, a contribution from a nodal hole pocket, or a small gap on the Fermi surface such as an anisotropic s-wave order parameter. The low value of the superfluid densities, likely due to a strong doping-induced disorder, places the superconducting transition of our samples in the phase-fluctuation regime.

Introduction of nucleic acids into cells is an important biotechnology research field which also holds great promise for therapeutic applications. One of the key steps in the gene delivery process is compaction of DNA into nanometric particles. The study of DNA condensing properties of three linear cationic triblock copolymers poly(ethylenimine-b-propylene glycol-b-ethylenimine), namely, LPEI(50)-PPG(36)-LPEI(50), LPEI(19)-PPG(36)-LPEI(19), and LPEI(14)-PPG(68)-LPEI(14), indicates that proper DNA condensation is driven by both the charge and the size of the respective cationic hydrophilic linear polyethylenimine (LPEI) and neutral hydrophobic poly(propylene glycol) (PPG) parts. Atomic force microscopy was used to investigate the interactions of the triblock copolymers with plasmid DNA at the single molecule level and to enlighten the mechanism involved in DNA condensation.

The effects of grain size on the nanomechanical properties of Ar-irradiated magnesium-aluminate spinels was studied. Spinel single crystals and ceramics of different grain size varying from ∼1μm up to few tens of micrometers were used in the experiments. The measurements were performed in both grain centers and grain boundaries and point to rapidly disappearing differences between bulk and boundaries in irradiated ceramics. The stress-induced hardening has been observed as well. This last effect depends on the grain size of the irradiated material and may serve as an indicator of the stress evolution in the irradiated samples.