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1. 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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2. Developing a platform for Fresnel diffractive radiography with 1 μ m spatial resolution at the National Ignition Facility

   https://doi.org/10.1063/5.0101890  

   Schoelmerich, M. O.; Döppner, T.; Allen, C. H.; Divol, L.; Oliver, M.; Haden, D.; Biener, M.; Crippen, J.; Delora-Ellefson, J.; Ferguson, B.; et al (January 2023, Review of Scientific Instruments)

   An x-ray Fresnel diffractive radiography platform was designed for use at the National Ignition Facility. It will enable measurements of micron-scale changes in the density gradients across an interface between isochorically heated warm dense matter materials, the evolution of which is driven primarily through thermal conductivity and mutual diffusion. We use 4.75 keV Ti K-shell x-ray emission to heat a 1000 μm diameter plastic cylinder, with a central 30 μm diameter channel filled with liquid D 2 , up to 8 eV. This leads to a cylindrical implosion of the liquid D 2 column, compressing it to ∼2.3 g/cm 3 . After pressure equilibration, the location of the D 2 /plastic interface remains steady for several nanoseconds, which enables us to track density gradient changes across the material interface with high precision. For radiography, we use Cu He- α x rays at 8.3 keV. Using a slit aperture of only 1 μm width increases the spatial coherence of the source, giving rise to significant diffraction features in the radiography signal, in addition to the refraction enhancement, which further increases its sensitivity to density scale length changes at the D 2 /plastic interface. 

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3. Modelling planar kirigami metamaterials as generalized elastic continua

   https://doi.org/10.1098/rspa.2022.0665  

   Zheng, Y.; Niloy, I.; Tobasco, I.; Celli, P.; Plucinsky, P. (April 2023, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   Kirigami metamaterials dramatically change their shape through a coordinated motion of nearly rigid panels and flexible slits. Here, we study a model system for mechanism-based planar kirigami featuring periodic patterns of quadrilateral panels and rhombi slits, with the goal of predicting their engineering scale response to a broad range of loads. We develop a generalized continuum model based on the kirigami’s effective (cell-averaged) nonlinear deformation, along with its slit actuation and gradients thereof. The model accounts for three sources of elasticity: a strong preference for the effective fields to match those of a local mechanism, inter-panel stresses arising from gradients in slit actuation, and distributed hinge bending. We provide a finite-element formulation of this model and implement it using the commercial software Abaqus. Simulations of the model agree quantitatively with experiments across designs and loading conditions. 

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4. Slit-Robo signaling supports motor neuron avoidance of the spinal cord midline through DCC antagonism and other mechanisms

   https://doi.org/10.3389/fcell.2025.1563403  

   Nickerson, Kelsey R; Sammoura, Ferass M; Zhou, Yonghong; Jaworski, Alexander (April 2025, Frontiers in Cell and Developmental Biology)

   Axon pathfinding and neuronal migration are orchestrated by attractive and repulsive guidance cues. In the mouse spinal cord, repulsion from Slit proteins through Robo family receptors and attraction to Netrin-1, mediated by the receptor DCC, control many aspects of neural circuit formation. This includes motor neuron wiring, where Robos help prevent both motor neuron cell bodies and axons from aberrantly crossing the spinal cord midline. These functions had been ascribed to Robo signaling being required to counter DCC-mediated attraction to Netrin-1 at the midline, either by mediating repulsion from midline-derived Slits or by silencing DCC signaling. However, the role of DCC in promoting motor neuron and axon midline crossing had not been directly tested. Here, we usedin vivomouse genetics andin vitroaxon turning assays to further explore the interplay between Slit and Netrin signaling in motor neuron migration and axon guidance relative to the midline. We find that DCC is a major driver of midline crossing by motor axons, but not motor neuron cell bodies, whenRobo1andRobo2are knocked out. Further,in vitroresults indicate that Netrin-1 attracts motor axons and that Slits can modulate the chemotropic response to Netrin-1, converting it from attraction to repulsion. Our findings indicate that Robo signaling allows both motor neuron cell bodies and axons to avoid the midline, but that only motor axons require this pathway to antagonize DCC-dependent midline attraction, which likely involves a combination of mediating Slit repulsion and directly influencing Netrin-DCC signaling output. 

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5. Quantum mechanical double slit for molecular scattering

   https://doi.org/10.1126/science.abl4143  

   Zhou, Haowen; Perreault, William E.; Mukherjee, Nandini; Zare, Richard N. (November 2021, Science)

   Interference observed in a double-slit experiment most conclusively demonstrates the wave properties of particles. We construct a quantum mechanical double-slit interferometer by rovibrationally exciting molecular deuterium (D 2 ) in a biaxial ( v = 2, j = 2) state using Stark-induced adiabatic Raman passage, where v and j represent the vibrational and rotational quantum numbers, respectively. In D 2 ( v = 2, j = 2) → D 2 ( v = 2, j ′ = 0) rotational relaxation via a cold collision with ground state helium, the two coherently coupled bond axis orientations in the biaxial state act as two slits that generate two indistinguishable quantum mechanical pathways connecting initial and final states of the colliding system. The interference disappears when we decouple the two orientations of the bond axis by separately constructing the uniaxial states of D 2 , unequivocally establishing the double-slit action of the biaxial state. This double slit opens new possibilities in the coherent control of molecular collisions. 

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