Digital image correlation (DIC) is of vital importance in the field of experimental mechanics, yet producing suitable DIC patterns for demanding in-situ (micro) mechanical tests remains challenging, especially for ultrafine patterns, despite the large number of patterning techniques reported in the literature. Therefore, we propose a simple, flexible, one-step technique (only requiring a conventional physical vapour deposition machine) to obtain scalable, high-quality, robust DIC patterns, suitable for a range of microscopic techniques, by deposition of a low-melting temperature solder alloy in the so-called island growth mode, without elevating the substrate temperature. Proof of principle is shown by (near-)room temperature deposition of InSn patterns, yielding highly dense, homogeneous DIC patterns over large areas with a feature size that can be tuned from as small as~10 nm to~2 μm and with control over the feature shape and density by changing the deposition parameters. Pattern optimisation, in terms of feature size, density, and contrast, is demonstrated for imaging with atomic force microscopy, scanning electron microscopy, optical profilometry, and optical microscopy. Moreover, the performance of the InSn DIC patterns and their robustness to large deformations is validated in two challenging case studies of in-situ micromechanical testing: (a) self-adaptive isogeometric digital height correlation of optical surface height profiles of a coarse, bimodal InSn pattern providing microscopic 3D deformation fields (illustrated for delamination of Al stretchable interconnects on a PI substrate) and (b) DIC on scanning electron microscopy images of a much finer InSn pattern allowing quantification of high strains near fracture locations (illustrated for rupture of a polycrystalline Fe foil). As such, the high controllability, performance, and scalability of the DIC patterns, created by island growth of a solder alloy, offer a promising step towards more routine DIC-based in-situ micromechanical testing.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

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Contractile stress generation by adherent cells is largely determined by the interplay of forces within their cytoskeleton. It is known that actin stress fibers, connected to focal adhesions, provide contractile stress generation, while microtubules and intermediate filaments provide cells compressive stiffness. Recent studies have shown the importance of the interplay between the stress fibers and the intermediate filament vimentin. Therefore, the effect of the interplay between the stress fibers and vimentin on stress generation was quantified in this study. We hypothesized that net stress generation comprises the stress fiber contraction combined with the vimentin resistance. We expected an increased net stress in vimentin knockout (VimKO) mouse embryonic fibroblasts (MEFs) compared to their wild-type (vimentin wild-type (VimWT)) counterparts, due to the decreased resistance against stress fiber contractility. To test this, the net stress generation by VimKO and VimWT MEFs was determined using the thin film method combined with sample-specific finite element modeling. Additionally, focal adhesion and stress fiber organization were examined via immunofluorescent staining. Net stress generation of VimKO MEFs was three-fold higher compared to VimWT MEFs. No differences in focal adhesion size or stress fiber organization and orientation were found between the two cell types. This suggests that the increased net stress generation in VimKO MEFs was caused by the absence of the resistance that vimentin provides against stress fiber contraction. Taken together, these data suggest that vimentin resists the stress fiber contractility, as hypothesized, thus indicating the importance of vimentin in regulating cellular stress generation by adherent cells.

Confocal microscopy allows quantitative surface roughness analysis and 3-dimensional reconstruction of human corneal lamellae. Femtosecond-laser photodisruption at 60 kHz results in rougher surfaces compared with mechanical dissection. The motor-driven linear microkeratome allows single-pass dissection of ultrathin endothelial lamellae with a standard deviation ≤20 μm.

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