Flexible fiber-optic endoscopes provide a solution for imaging at depths beyond the reach of conventional microscopes. Current endoscopes require focusing and/or scanning mechanisms at the distal end, which limit miniaturization, frame-rate, and field of view. Alternative wavefront-shaping based lensless solutions are extremely sensitive to fiber-bending. We present a lensless, bend-insensitive, single-shot imaging approach based on speckle-correlations in fiber bundles that does not require wavefront shaping. Our approach computationally retrieves the target image by analyzing a single camera frame, exploiting phase information that is inherently preserved in propagation through convnetional fiber bundles. Unlike conventional fiber-based imaging, planar objects can be imaged at variable working distances, the resulting image is unpixelated and diffraction-limited, and miniaturization is limited only by the fiber diameter.

We report on the elastocapillary deformation of flexible microfibers in contact with liquid droplets. A fiber is observed to bend more as the size of the contacting droplet is increased. At a critical droplet size, proportional to the bending elastocapillary length, the fiber is seen to spontaneously wind around the droplet. To rationalize these observations, we invoke a minimal model based on elastic beam theory, and find agreement with experimental data. Further energetic considerations provide a consistent prediction for the winding criterion.Wetting of liquids on fibrous materials is central to a wide variety of natural and industrial phenomena such as the coalescence of wet hairs [1,2], the drying of textiles [3], the altered mechanical properties of dewy spider silk [4][5][6], the defense mechanism of a species of beetle [7], and the bundling of carbon nanotubes and nanowires during processing [8][9][10][11]. In some of these examples, the fibers are sufficiently flexible that capillary forces induce large-scale deformations -a phenomenon also observed in other geometries such as a drop contacting a flexible solid strip [12]. The bending elastocapillary length L BC = E r 3 /γ is the natural length scale that emerges when balancing elastic bending and capillarity, where E is the Young's modulus of the fiber, r is the fiber radius, and γ is the liquid-air surface tension [1,14]. A slender structure is significantly deformed by capillary forces if the length scale over which these forces act is larger than L BC [1]. To understand the wetting of fibers, several model experiments have been carried out, focusing on droplets between slender flexible structures, where material stiffness and geometry dictate the final wetting configuration [1,[15][16][17][18].Despite its simplicity, even the problem of a single droplet atop an undeformable cylinder is interesting as there are two possible equilibrium states: an axisymmetric "barrel" configuration and a non-axisymmetric "clamshell" [19][20][21][22][23]. It is then not surprising that the case of a flexible fiber interacting with a liquid is a rich subject of study, showcasing complexity and stunning examples of self-assembly [1,5,6,[24][25][26]. In a series of beautiful experiments, droplets were placed on taut elastomeric fibers, and reached the barrel configuration [5,6]. With reduced tension, capillary forces cause the fiber to buckle inside the droplet if the radius of the latter exceeds roughly L BC . As the fiber is slackened, it coils inside the droplet which acts as a windlass to maintain tension. However, for a smaller droplet-to-fiber radius ratio, or for less-wettable conditions, the clam-shell configuration may be more favourable than the barrel [23]. In such a case, a soft fiber may instead wind around the surface of a droplet without experiencing a buckling transition [1]. As argued by Roman and Bico, the reduction in surface energy upon winding exceeds the bending penalty if the droplet radius is larger than ∼ L BC . This is reminiscent of DNA molecul...

When a soft hydrogel sphere is placed on a rigid hydrophilic substrate, it undergoes arrested spreading by forming an axisymmetric foot near the contact line, while conserving its global spherical shape. In contrast, liquid water (that constitutes greater than 90% of the hydrogel's volume) spreads into a thin film on the same surface. We study systematically this elastowetting of gel spheres on substrates of different surface energies and find that their contact angle increases as the work of adhesion between the gel and the substrate decreases, as one would observe for drops of pure water-albeit being larger than in the latter case. This difference in the contact angles of gel and water appears to be due to the elastic shear stresses that develop in the gel and oppose its spreading. Indeed, by increasing the elastic modulus of the gel spheres, we find that their contact angle also increases. In addition, the length of the contact foot increases with the work of adhesion and sphere size, while it decreases when the elastic modulus of the gel is increased. We discuss those experimental results in light of a minimal analysis based on energy minimization, volume conservation, and scaling arguments.