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1. Bending Stability of Corrugated Tubes With Anisotropic Frustum Shells

   https://doi.org/10.1115/1.4053267  

   Wo, Zhongyuan ; Filipov, Evgueni T. ( April 2022 , Journal of Applied Mechanics)

   Abstract Thin-walled corrugated tubes that have a bending multistability, such as the bendy straw, allow for variable orientations over the tube length. Compared to the long history of corrugated tubes in practical applications, the mechanics of the bending stability and how it is affected by the cross sections and other geometric parameters remain unknown. To explore the geometry-driven bending stabilities, we used several tools, including a reduced-order simulation package, a simplified linkage model, and physical prototypes. We found the bending stability of a circular two-unit corrugated tube is dependent on the longitudinal geometry and the stiffness of the crease lines that connect separate frusta. Thinner shells, steeper cones, and weaker creases are required to achieve bending bi-stability. We then explored how the bending stability changes as the cross section becomes elongated or distorted with concavity. We found the bending bi-stability is favored by deep and convex cross sections, while wider cross sections with a large concavity remain mono-stable. The different geometries influence the amounts of stretching and bending energy associated with bending the tube. The stretching energy has a bi-stable profile and can allow for a stable bent configuration, but it is counteracted by the bending energy which increases monotonically.more »The findings from this work can enable informed design of corrugated tube systems with desired bending stability behavior.« less
2. An untethered isoperimetric soft robot

   https://doi.org/10.1126/scirobotics.aaz0492  

   Usevitch, Nathan S. ; Hammond, Zachary M. ; Schwager, Mac ; Okamura, Allison M. ; Hawkes, Elliot W. ; Follmer, Sean ( March 2020 , Science Robotics)

   For robots to be useful for real-world applications, they must be safe around humans, be adaptable to their environment, and operate in an untethered manner. Soft robots could potentially meet these requirements; however, existing soft robotic architectures are limited by their ability to scale to human sizes and operate at these scales without a tether to transmit power or pressurized air from an external source. Here, we report an untethered, inflated robotic truss, composed of thin-walled inflatable tubes, capable of shape change by continuously relocating its joints, while its total edge length remains constant. Specifically, a set of identical roller modules each pinch the tube to create an effective joint that separates two edges, and modules can be connected to form complex structures. Driving a roller module along a tube changes the overall shape, lengthening one edge and shortening another, while the total edge length and hence fluid volume remain constant. This isoperimetric behavior allows the robot to operate without compressing air or requiring a tether. Our concept brings together advantages from three distinct types of robots—soft, collective, and truss-based—while overcoming certain limitations of each. Our robots are robust and safe, like soft robots, but not limited by a tether;more »are modular, like collective robots, but not limited by complex subunits; and are shape-changing, like truss robots, but not limited by rigid linear actuators. We demonstrate two-dimensional (2D) robots capable of shape change and a human-scale 3D robot capable of punctuated rolling locomotion and manipulation, all constructed with the same modular rollers and operating without a tether.« less
3. ON THE DEPLOYMENT OF MULTISTABLE KRESLING ORIGAMI-INSPIRED STRUCTURES

   https://doi.org/10.1115/DETC2019-97427  

   Kidambi, Narayanan ; and Wang, K.W. ( August 2019 , ASME section IX)

   Origami designs have attracted significant attention from researchers seeking to develop new types of deployable structures due to their ability to undergo large and complex yet predictable shape changes. The Kresling pattern, which is based on a natural accumulation of folds and creases during the twistbuckling of a thin-walled cylinder, offers a great example for the design of deployable systems that expand uniaxially into tubes or booms. However, much remains to be understood regarding the characteristics of Kresling-based deployable systems, and their dynamics during the deployment process remain largely unexplored. Hence this research investigates the deployment of Kresling origami-inspired structures, employing a full sixdegree- of-freedom truss-based model to study their dynamics under different conditions. Results show that tuning the initial rotation angle of a structure gives rise to several qualitatively distinct mechanical properties and stability characteristics, each of which has different implications for the design of the deployable systems. Dynamic analyses reveal the robustness of Kresling structures to out-of-axis perturbations while remaining compliant in the axial direction. These findings suggest that Kresling-based designs can form the basis for the development of new types of deployable structures and systems with tunable performance.
4. Modeling membrane nanotube morphology: the role of heterogeneity in composition and material properties

   https://doi.org/10.1038/s41598-020-59221-x  

   Alimohamadi, Haleh ; Ovryn, Ben ; Rangamani, Padmini ( February 2020 , Scientific Reports)

   Membrane nanotubes are dynamic structures that may connect cells over long distances. Nanotubes are typically thin cylindrical tubes, but they may occasionally have a beaded architecture along the tube. In this paper, we study the role of membrane mechanics in governing the architecture of these tubes and show that the formation of bead-like structures along the nanotubes can result from local heterogeneities in the membrane either due to protein aggregation or due to membrane composition. We present numerical results that predict how membrane properties, protein density, and local tension compete to create a phase space that governs the morphology of a nanotube. We also find that there exists a discontinuity in the energy that impedes two beads from fusing. These results suggest that the membrane-protein interaction, membrane composition, and membrane tension closely govern the tube radius, number of beads, and the bead morphology.
5. An ion mobility mass spectrometer coupled with a cryogenic ion trap for recording electronic spectra of charged, isomer-selected clusters

   https://doi.org/10.1063/5.0085680  

   Buntine, Jack T. ; Carrascosa, Eduardo ; Bull, James N. ; Jacovella, Ugo ; Cotter, Mariah I. ; Watkins, Patrick ; Liu, Chang ; Scholz, Michael S. ; Adamson, Brian D. ; Marlton, Samuel J. P. ; et al ( April 2022 , Review of Scientific Instruments)

   Infrared and electronic spectra are indispensable for understanding the structural and energetic properties of charged molecules and clusters in the gas phase. However, the presence of isomers can potentially complicate the interpretation of spectra, even if the target molecules or clusters are mass-selected beforehand. Here, we describe an instrument for spectroscopically characterizing charged molecular clusters that have been selected according to both their isomeric form and their mass-to-charge ratio. Cluster ions generated by laser ablation of a solid sample are selected according to their collision cross sections with helium buffer gas using a drift tube ion mobility spectrometer and their mass-to-charge ratio using a quadrupole mass filter. The mobility- and mass-selected target ions are introduced into a cryogenically cooled, three-dimensional quadrupole ion trap where they are thermalized through inelastic collisions with an inert buffer gas (He or He/N₂mixture). Spectra of the molecular ions are obtained by tagging them with inert atoms or molecules (Ne and N₂), which are dislodged following resonant excitation of an electronic transition, or by photodissociating the cluster itself following absorption of one or more photons. An electronic spectrum is generated by monitoring the charged photofragment yield as a function of wavelength. The capacity of the instrumentmore »is illustrated with the resonance-enhanced photodissociation action spectra of carbon clusters ([Formula: see text]) and polyacetylene cations (HC_{2 n}H⁺) that have been selected according to the mass-to-charge ratio and collision cross section with He buffer gas and of mass-selected [Formula: see text] and Au₂Ag⁺clusters.

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