Local lateral contact governs shear traction of micropatterned surfaces on hydrogel substrates.

Micropatterned surfaces exhibit enhanced shear traction on soft, aqueous tissue-like materials and, thus, have the potential to advance medical technology by improving the anchoring performance of medical devices on tissue. However, the fundamental mechanism underlying the enhanced shear traction is still elusive, as previous studies focused on interactions between micropatterned surfaces and rigid substrates rather than soft substrates. Here, we present a particle tracking method to experimentally measure microscale three-dimensional (3D) deformation of a soft hydrogel in normal and shear contact with arrays of microscale pillars. The measured 3D strain and stress fields reveal that the lateral contact between each individual pillar and the deformed hydrogel substrate governs the shear response. Moreover, by comparing pillars with different cross-sectional geometries, we observe experimental evidence that the shear traction of a pillar on the hydrogel substrate is sensitive to the convex features of its leading edge in the shear direction.

Patterned enteroscopy balloon design factors influence tissue anchoring.

Balloon-assisted enteroscopy procedures allow visualization and intervention in the small intestine. These balloons anchor an endoscope and/or overtube to the small intestine, allowing endoscopists to plicate the small intestine over the overtube. This procedure can extend examination deeper into the small intestine than the length of the endoscope would allow with direct examination. However, procedures are often prolonged or incomplete due to balloon slippage. Enteroscopy balloons are pressure-limited to ensure patient safety and thus, improving anchoring without increasing pressure is essential. Patterning balloon exteriors with discrete features may enhance anchoring at the tissue-balloon interface. Here, the pattern design space is explored to determine factors that influence tissue anchoring. The anchoring ability of smooth versus balloons with patterned features is investigated by experimentally measuring a peak force required to induce slippage of an inflated balloon inside ex-vivo porcine small intestine. Stiffer materials, low aspect-ratio features, and pattern area/location on the balloons significantly increase peak force compared to smooth silicone balloons. Smooth latex balloons, used for standard enteroscopy, have the lowest peak force. This work demonstrates both a method to pattern curved surfaces and that a balloon with patterned features improves anchoring against a deformable, lubricated tissue interface.

TENSCell: Imaging of Stretch-Activated Cells Reveals Divergent Nuclear Behavior and Tension.

Mechanisms of cellular and nuclear mechanosensation are unclear, partially because of a lack of methods that can reveal dynamic processes. Here, we present a new concept for a low-cost, three-dimensionally printed device that enables high-magnification imaging of cells during stretch. We observed that nuclei of mouse embryonic skin fibroblasts underwent rapid (within minutes) and divergent responses, characterized by nuclear area expansion during 5% strain but nuclear area shrinkage during 20% strain. Only responses to low strain were dependent on calcium signaling, whereas actin inhibition abrogated all nuclear responses and increased nuclear strain transfer and DNA damage. Imaging of actin dynamics during stretch revealed similar divergent trends, with F-actin shifting away from (5% strain) or toward (20% strain) the nuclear periphery. Our findings emphasize the importance of simultaneous stimulation and data acquisition to capture mechanosensitive responses and suggest that mechanical confinement of nuclei through actin may be a protective mechanism during high mechanical stretch or loading.

Three-Dimensional Microscale Imaging and Measurement of Soft Material Contact Interfaces under Quasi-Static Normal Indentation and Shear.

Understanding the contact and friction between soft materials is vital to a wide variety of engineering applications including soft sealants and medical devices such as catheters and stents. Although the mechanisms of friction between stiff materials have been extensively studied, the mechanisms of friction between soft materials are much less understood. Time-dependent material responses, large deformations, and fluid layers at the contact interface, common in soft materials, pose new challenges toward understanding the friction between soft materials. This article aims to characterize the three-dimensional (3D) contact interfaces in soft materials under large deformations and complex contact conditions. Specifically, we introduce a microindentation and visualization (MIV) system capable of investigating soft material contact interfaces with combined normal and shear loading. When combined with a laser scanning confocal microscope, the MIV system enables the acquisition of 3D image stacks of the deformed substrate and the indenter under fixed normal and shear displacements. The 3D imaging data allows us to quantify the 3D contact profiles and correlate them with the applied normal and shear displacements. Using a spherical indenter and a hydrogel substrate as a model system, we demonstrate that the MIV system and the associated analysis techniques accurately measure the contact area under combined normal and shear loading. Although the limited speed of confocal scanning implies that this method is most suitable for quasi-static loading conditions, potential methods to increase the imaging speed and the corresponding trade-off in image resolution are discussed. The method presented here will be useful for the future investigation of soft material contact and friction involving complex surface geometries.