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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 µm RBCs pass through 0.3 µm-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 µm-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 µm-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. [ABSTRACT FROM AUTHOR]

The fraction of red blood cells adopting a specific motion under low shear flow is a promising inexpensive marker for monitoring the clinical status of patients with sickle cell disease. Its high-throughput measurement relies on the video analysis of thousands of cell motions for each blood sample to eliminate a large majority of unreliable samples (out of focus or overlapping cells) and discriminate between tank-treading and flipping motion, characterizing highly and poorly deformable cells respectively. Moreover, these videos are of different durations (from 6 to more than 100 frames). We present a two-stage end-to-end machine learning pipeline able to automatically classify cell motions in videos with a high class imbalance. By extending, comparing, and combining two state-of-the-art methods, a convolutional neural network (CNN) model and a recurrent CNN, we are able to automatically discard 97% of the unreliable cell sequences (first stage) and classify highly and poorly deformable red cell sequences with 97% accuracy and an F1-score of 0.94 (second stage). Dataset and codes are publicly released for the community. [ABSTRACT FROM AUTHOR]

In this work, we compared the dynamics of motion in a linear shear flow of individual red blood cells (RBCs) from healthy and pathological donors (Sickle Cell Disease (SCD) or Sickle Cell-β-thalassemia) and of low and high densities, in a suspending medium of higher viscosity. In these conditions, at lower shear rates, biconcave discocyte-shaped RBCs present an unsteady flip-flopping motion, where the cell axis of symmetry rotates in the shear plane, rocking to and fro between an orbital angle ±ϕ observed when the cell is on its edge. We show that the evolution of ϕ depends solely on RBC density for healthy RBCs, with denser RBCs displaying lower ϕ values than the lighter ones. Typically, at a shear stress of 0.08 Pa, ϕ has values of 82 and 72° for RBCs with average densities of 1.097 and 1.115, respectively. Surprisingly, we show that SCD RBCs display the same ϕ-evolution as healthy RBCs of same density, showing that the flip-flopping behavior is unaffected by the SCD pathology. When the shear stress is increased further (above 0.1 Pa), healthy RBCs start going through a transition to a fluid-like motion, called tank-treading, where the RBC has a quasi-constant orientation relatively to the flow and the membrane rotates around the center of mass of the cell. This transition occurs at higher shear stresses (above 0.2 Pa) for denser cells. This shift toward higher stresses is even more remarkable in the case of SCD RBCs, showing that the transition to the tank-treading regime is highly dependent on the SCD pathology. Indeed, at a shear stress of 0.2 Pa, for RBCs with a density of 1.097, 100% of healthy RBCs have transited to the tank-treading regime vs. less than 50% SCD RBCs. We correlate the observed differences in dynamics to the alterations of RBC mechanical properties with regard to density and SCD pathology reported in the literature. Our results suggest that it might be possible to develop simple non-invasive assays for diagnosis purpose based on the RBC motion in shear flow and relying on this millifluidic approach. [ABSTRACT FROM AUTHOR]

Since the established correlations between mechanical properties of a piece of wood at the macroscopic scale and those of the cell wall at the submicron scale, techniques based on atomic force microscopy (AFM) have become widespread. In particular Peak Force tapping, allowing the differentiation of various layers, has become the new standard for wood cell wall's nanomechanical characterization. However, its use requires fully elastic indentation, a good knowledge of stiffness of the probe and assumes a perfect tip shape of known radius (sphere) or angle (cone). Those strong hypotheses can result in large approximations in the extracted parameters for complex, nanostructured, and stiff and viscous materials such as wood. In this work, we propose a reliable and complementary alternative based on AFM force-volume indentation by refining the Oliver and Pharr nanoindentation processing and calibration procedure for AFM cantilever and tip. The introduced area-function calibration (AFC) method allows to considerably reduce these approximations and provides semi-quantitative measurements. No prior knowledge of the tip shape and cantilever stiffness are required and viscoplasticity is investigated through a qualitative index. Indentation parameters variations are shown to impact the resulting measurements, i.e., indentation modulus, viscoplasticity index, adhesion force and energy. AFC method, applied to map regions of tension wood, provides very stable mechanical parameters characteristic of each region, which makes this method of high interest for plant cell wall studies. [ABSTRACT FROM AUTHOR]

Abstract: The development of ultrathin dielectrics for low power electronics operations, flexible and printed electronics, and field‐effect‐transistor‐based sensors is still a challenge. Here, monolayers of engineered lipids supported on silicon are reported presenting exceptional mechanical and dielectric properties. The lipid monolayers are stabilized using a simple procedure based on a two‐stage reticulation process in both their aliphatic chains and their head‐group. With a thickness lower than 3 nm, such layers are demonstrated to offer exceptional mechanical and dielectric stability with unprecedented low leakage current and dielectric strength. Surprisingly, the mechanical and dielectric pressures required to rupture/breakdown the monolayers are shown to be similar. These results suggest the presence of a strong correlation between mechanical and dielectric properties, as well as between the mechanisms of rupture and breakdown. [ABSTRACT FROM AUTHOR]

Abstract: Nanopatterned conducting polymer poly(3,4‐ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS) films are obtained using a new, facile fabrication method. In this method, an epoxy supporting layer is used to facilitate the transfer of nanopatterns from a polydimethylsiloxane mold to rigid or flexible substrates. This process overcomes several limitations that are previously introduced when using other nanopatterning techniques such as nanoimprint lithography and capillary force lithography. Two sets of nanopatterned PEDOT:PSS/Gold (Au) electrodes are fabricated with different dimensions: set 1 with 87 nm linewidth, 140 nm pitch, 30 nm depth; and set 2 with 157 nm linewidth, 280 nm pitch, 26 nm depth, respectively. The electrochemical impedance of these electrodes is measured to be lower than that of flat electrodes fabricated following the same process. These findings open the way for fabricating smaller electrodes with reduced impedance. Possible applications can be in the field of biosensing, neural recordings, and interfaces, where decreasing the contact impedance plays a key role. [ABSTRACT FROM AUTHOR]

The effect of 3-glycidoxypropyltrimethoxysilane (GOPS) content in poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) dispersions on the properties of films spun cast from these formulations is investigated. It has been found out that the concentration of GOPS has a tremendous, yet gradual impact on the electrical, electrochemical, and mechanical properties of the PEDOT:PSS/GOPS films and that there is an optimum concentration which maximizes a particular feature of the film such as its water uptake or elasticity. The benefits of aqueous stability and mechanical strength with GOPS are to be compensated by an increase in the electrochemical impedance. GOPS aids obtaining excellent mechanical integrity in aqueous media with still highly conducting properties. Moreover, active devices like organic electrochemical transistors that contain 1 wt% GOPS, which is a concentration that leads to film with high electrical conductivity with sufficient mechanical stability and softness, exhibit steady performance over three weeks. These results suggest that variations in the concentration of such an additive like GOPS can enable a facile co-optimization of electrical and mechanical properties of a conducting polymer film for in vivo bioelectronics application. [ABSTRACT FROM AUTHOR]