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1. Diffraction enhanced imaging utilizing a laser produced x-ray source

   https://doi.org/10.1063/5.0091348  

   Oliver, M.; Allen, C_H; Divol, L.; Karmiol, Z.; Landen, O_L; Ping, Y.; Wallace, R.; Schölmerich, M.; Theobald, W.; Döppner, T.; et al (September 2022, Review of Scientific Instruments)

   Image formation by Fresnel diffraction utilizes both absorption and phase-contrast to measure electron density profiles. The low spatial and spectral coherence requirements allow the technique to be performed with a laser-produced x-ray source coupled with a narrow slit. This makes it an excellent candidate for probing interfaces between materials at extreme conditions, which can only be generated at large-scale laser or pulsed power facilities. Here, we present the results from a proof-of-principle experiment demonstrating an effective ∼2 μm laser-generated source at the OMEGA Laser Facility. This was achieved using slits of 1 × 30 μm2 and 2 × 40 μm2 geometry, which were milled into 30 μm thick Ta plates. Combining these slits with a vanadium He-like 5.2 keV source created a 1D imaging system capable of micrometer-scale resolution. The principal obstacles to achieving an effective 1 μm source are the slit tilt and taper—where the use of a tapered slit is necessary to increase the alignment tolerance. We demonstrate an effective source size by imaging a 2 ± 0.2 μm radius tungsten wire. 

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2. Physical mechanisms of red blood cell splenic filtration

   https://doi.org/10.1073/pnas.2300095120  

   Moreau, Alexis; Yaya, François; Lu, Huijie; Surendranath, Anagha; Charrier, Anne; Dehapiot, Benoit; Helfer, Emmanuèle; Viallat, Annie; Peng, Zhangli (October 2023, Proceedings of the National Academy of Sciences)

   The splenic interendothelial slits fulfill the essential function of continuously filtering red blood cells (RBCs) from the bloodstream to eliminate abnormal and aged cells. To date, the process by which 8 $\mathrm{\mu }$m RBCs pass through 0.3 $\mathrm{\mu }$m-wide slits remains enigmatic. Does the slit caliber increase during RBC passage as sometimes suggested? Here, we elucidated the mechanisms that govern the RBC retention or passage dynamics in slits by combining multiscale modeling, live imaging, and microfluidic experiments on an original device with submicron-wide physiologically calibrated slits. We observed that healthy RBCs pass through 0.28 $\mathrm{\mu }$m-wide rigid slits at 37 °C. To achieve this feat, they must meet two requirements. Geometrically, their surface area-to-volume ratio must be compatible with a shape in two tether-connected equal spheres. Mechanically, the cells with a low surface area-to-volume ratio (28% of RBCs in a 0.4 $\mathrm{\mu }$m-wide slit) must locally unfold their spectrin cytoskeleton inside the slit. In contrast, activation of the mechanosensitive PIEZO1 channel is not required. The RBC transit time through the slits follows a $-$1 and $-$3 power law with in-slit pressure drop and slip width, respectively. This law is similar to that of a Newtonian fluid in a two-dimensional Poiseuille flow, showing that the dynamics of RBCs is controlled by their cytoplasmic viscosity. Altogether, our results show that filtration through submicron-wide slits is possible without further slit opening. Furthermore, our approach addresses the critical need for in vitro evaluation of splenic clearance of diseased or engineered RBCs for transfusion and drug delivery. 

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3. Pneumatic Soft Actuators With Kirigami Skins

   https://doi.org/10.3389/frobt.2021.749051  

   Khosravi, Hesameddin; Iannucci, Steven M.; Li, Suyi (September 2021, Frontiers in Robotics and AI)

   Soft pneumatic actuators have become indispensable for many robotic applications due to their reliability, safety, and design flexibility. However, the currently available actuator designs can be challenging to fabricate, requiring labor-intensive and time-consuming processes like reinforcing fiber wrapping and elastomer curing. To address this issue, we propose to use simple-to-fabricate kirigami skins—plastic sleeves with carefully arranged slit cuts—to construct pneumatic actuators with pre-programmable motion capabilities. Such kirigami skin, wrapped outside a cylindrical balloon, can transform the volumetric expansion from pneumatic pressure into anisotropic stretching and shearing, creating a combination of axial extension and twisting in the actuator. Moreover, the kirigami skin exhibits out-of-plane buckling near the slit cut, which enables high stretchability. To capture such complex deformations, we formulate and experimentally validates a new kinematics model to uncover the linkage between the kirigami cutting pattern design and the actuator’s motion characteristics. This model uses a virtual fold and rigid-facet assumption to simplify the motion analysis without sacrificing accuracy. Moreover, we tested the pressure-stroke performance and elastoplastic behaviors of the kirigami-skinned actuator to establish an operation protocol for repeatable performance. Analytical and experimental parametric analysis shows that one can effectively pre-program the actuator’s motion performance, with considerable freedom, simply by adjusting the angle and length of the slit cuts. The results of this study can establish the design and analysis framework for a new family of kirigami-skinned pneumatic actuators for many robotic applications. 

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4. Pneumatic Extension Actuators With Kirigami Skins

   https://doi.org/10.1115/SMASIS2020-2219  

   Iannucci, Steven; Li, Suyi (September 2020, ASME 2020 Conference on Smart Materials, Adaptive Structures and Intelligent Systems)

   null (Ed.)

   Soft pneumatic actuators have found many applications in robotics and adaptive structures. Traditionally, these actuators are constructed by wrapping layers of reinforcing helical fibers around an elastomeric tube. This approach is versatile and robust, but it suffers from a critical disadvantage: cumbersome fabrication procedures. Wrapping long helical filaments around a cylindrical tube requires expensive equipment or excessive manual labor. To address this issue, we propose a new approach towards designing and constructing pneumatic actuators by exploiting the principle of kirigami, the ancient art of paper cutting. More specifically, we use “kirigami skins” — plastic sleeves with carefully arranged slit cuts — to replace the reinforcing helical fibers. This paper presents an initial investigation on a set of linear extension actuators featuring kirigami skins with a uniform array of cross-shaped, orthogonal cuts. When under internal pressurization, the rectangular-shaped facets defined by these cuts can rotate and induce the desired extension motion. Through extensive experiments, we analyze the elastic and plastic deformations of these kirigami skins alone under tension. The results show strongly nonlinear behaviors involving both in-plane facet rotation the out-of-plane buckling. Such a deformation pattern offers valuable insights into the actuator’s performance under pressure. Moreover, both the deformation characteristics and actuation performance are “programmable” by tailoring the cut geometry. This study lays down the foundation for constructing more capable Kirigami-skinned soft actuators that can achieve sophisticated motions. 

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5. Kirigami Oscillators: Nonlinear Free and Forced Responses

   https://doi.org/10.21203/rs.3.rs-5283451/v1  

   Danzi, Francesco; Taoh, Hongcheng; Silva, Christian; Gibert, James (October 2024, Research Square)

   Abstract Inspired by the ancient Japanese art of kirigami, slitted plastic sheets, termed kirigami springs, were designed, fabricated, and characterized, utilizing the quasi-mechanism behavior of various slit patterns. Quasi-static tension tests determined the spring stiffness, and experimental transient responses were analyzed to infer system damping. A system of two parallel-connected kirigami springs, attached to a mass oscillating on a smooth track, was modeled as a 1 DOF Helmholtz-Duffing oscillator with nonlinear damping. The system's free and forced responses were compared to experimental and numerical results using asymptotically valid solutions derived via the Method of Multiple Time Scales. This approach provides an unprecedented degree of programmability in the constitutive relations for nonlinear oscillators and is straightforward to implement. 

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