Membrane Structures - Aspects of Form-Finding Process

Force generation by actin assembly shapes cellular membranes. An experimentally constrained multiscale model shows that a minimal branched actin network is sufficient to internalize endocytic pits against membrane tension. Around 200 activated Arp2/3 complexes are required for robust internalization. A newly developed molecule-counting method determined that ~200 Arp2/3 complexes assemble at sites of clathrin-mediated endocytosis in human cells. Simulations predict that actin self-organizes into a radial branched array with growing ends oriented toward the base of the pit. Long actin filaments bend between attachment sites in the coat and the base of the pit. Elastic energy stored in bent filaments, whose presence was confirmed by cryo-electron tomography, contributes to endocytic internalization. Elevated membrane tension directs more growing filaments toward the base of the pit, increasing actin nucleation and bending for increased force production. Thus, spatially constrained actin filament assembly utilizes an adaptive mechanism enabling endocytosis under varying physical constraints.

Relevance. Recent studies show that even with damage to the structures of the triangular fibrocartilaginous complex (primary stabilizer), instability of the distal ray-elbow joint does not develop in some cases. Studies carried out by a number of authors prove that the distal interosseous membrane of the forearm can influence the stability of the joint and be a secondary stabilizer for it.
 Aim of the study. To study the variability in the structure of the distal interosseous membrane of the forearm using anatomical material and determine the effect of the distal interosseous membrane on the stability of the distal ray-elbow joint. Using ultrasound to determine the variability of the structure of the distal interosseous membrane of the forearm.
 Materials and methods. Material for our study was 10 pairs of anatomical specimens of the upper extremities. The functional viability was assessed by passive rotation of the anatomical material of the forearm. Changes in the tension of the distal interosseous membrane, its additional formations and the capsule of the distal ray-elbow joint were observed. Ultrasound was chosen as an instrumental method for visualizing the distal interosseous membrane of the forearm and its structures. In the course of this work, 30 volunteers of both sexes and different ages were examined. The study was carried out: maximum pronation (position of the sensor back) and maximum supination (position of the sensor palmar).
 Results. In the course of the anatomical study, we determined that in 6 pairs of anatomical material, the distal interosseous membrane is a thin transparent connective tissue structure. No additional formations in the form of thickening were found. In 4 pairs of preparations, which amounted to 40% of the total amount in the distal interosseous membrane, there were additional formations in the form of thickening of the membrane this is the distal oblique bundle and the distal ray-the ulnar tract. During the functional study, it was revealed that during pronation of the forearm, the distal membrane and dorsal capsule are stretched, which in turn holds the head of the ulna in the sigmoid notch of the radius. After conducting ultrasound, we determined the variability in the structure of the distal interosseous membrane of the forearm. The distal oblique bundle is visualized as a linear hyperechoic formation. Of the 30 surveyed, this formation was identified in 13 women (92.8%) and 1 man (7.1%), which in percentage terms was 43%.
 Conclusion. After conducting anatomical examination, we determined the variability in the structure of the distal interosseous membrane of the forearm in the form of the presence of thickenings the distal oblique bundle and the distal ray-ulnar tract, and determined the effect of these structures on the stability of the distal ray-elbow joint. An ultrasound scan also identified the features in the structure of the distal interosseous membrane in the form of hyperechoic formation.

Studying how the membrane modulates ion channel and transporter activity is challenging because cells actively regulate membrane properties, whereas existing in vitro systems have limitations, such as residual solvent and unphysiologically high membrane tension. Cell-sized giant unilamellar vesicles (GUVs) would be ideal for in vitro electrophysiology, but efforts to measure the membrane current of intact GUVs have been unsuccessful. In this work, two challenges for obtaining the "whole-GUV" patch-clamp configuration were identified and resolved. First, unless the patch pipette and GUV pressures are precisely matched in the GUV-attached configuration, breaking the patch membrane also ruptures the GUV. Second, GUVs shrink irreversibly because the membrane/glass adhesion creating the high-resistance seal (>1 GΩ) continuously pulls membrane into the pipette. In contrast, for cell-derived giant plasma membrane vesicles (GPMVs), breaking the patch membrane allows the GPMV contents to passivate the pipette surface, thereby dynamically blocking membrane spreading in the whole-GMPV mode. To mimic this dynamic passivation mechanism, beta-casein was encapsulated into GUVs, yielding a stable, high-resistance, whole-GUV configuration for a range of membrane compositions. Specific membrane capacitance measurements confirmed that the membranes were truly solvent-free and that membrane tension could be controlled over a physiological range. Finally, the potential for ion transport studies was tested using the model ion channel, gramicidin, and voltage-clamp fluorometry measurements were performed with a voltage-dependent fluorophore/quencher pair. Whole-GUV patch-clamping allows ion transport and other voltage-dependent processes to be studied while controlling membrane composition, tension, and shape.

Hybrid polymer/lipid vesicles: Influence of polymer architecture and molar mass on line tension

Lipid packing in cellular membranes has a direct effect on membrane tension and microviscosity, and plays a central role in cellular adaptation, homeostasis and disease. According to conventional mechanical descriptions, viscosity and tension are directly interconnected, with increased tension leading to decreased membrane microviscosity. However, the intricate molecular interactions that combine to build the structure and function of a cell membrane suggest a more complex relationship between these parameters. In this work, a viscosity-sensitive fluorophore (‘molecular rotor’) is used to map changes in microviscosity in model membranes under conditions of osmotic stress. Our results suggest that the relationship between membrane tension and microviscosity is strongly influenced by the bilayer's lipid composition. In particular, we show that the effects of increasing tension are minimised for membranes that exhibit liquid disordered (Ld) – liquid ordered (Lo) phase coexistence; while, surprisingly, membranes in pure gel and Lo phases exhibit a negative compressibility behaviour, i.e. they soften upon compression.

Existing Eurocodes Applied to a Membrane Structure

Organelles are surrounded by membranes with a distinct lipid and protein composition. While it is well established that lipids affect protein functioning and vice versa, it has been only recently suggested that elevated membrane protein concentrations may affect the shape and organization of membranes. We therefore analyzed the effects of high chloroplast envelope protein concentrations on membrane structures using an in vivo approach with protoplasts. Transient expression of outer envelope proteins or protein domains such as CHUP1-TM–GFP, outer envelope protein of 7 kDa–GFP, or outer envelope protein of 24 kDa–GFP at high levels led to the formation of punctate, circular, and tubular membrane protrusions. Expression of inner membrane proteins such as translocase of inner chloroplast membrane 20, isoform II (Tic20-II)–GFP led to membrane protrusions including invaginations. Using increasing amounts of DNA for transfection, we could show that the frequency, size, and intensity of these protrusions increased with protein concentration. The membrane deformations were absent after cycloheximide treatment. Co-expression of CHUP1-TM–Cherry and Tic20-II–GFP led to membrane protrusions of various shapes and sizes including some stromule-like structures, for which several functions have been proposed. Interestingly, some structures seemed to contain both proteins, while others seem to contain one protein exclusively, indicating that outer and inner envelope dynamics might be regulated independently. While it was more difficult to investigate the effects of high expression levels of membrane proteins on mitochondrial membrane shapes using confocal imaging, it was striking that the expression of the outer membrane protein Tom20 led to more elongate mitochondria. We discuss that the effect of protein concentrations on membrane structure is possibly caused by an imbalance in the lipid to protein ratio and may be involved in a signaling pathway regulating membrane biogenesis. Finally, the observed phenomenon provides a valuable experimental approach to investigate the relationship between lipid synthesis and membrane protein expression in future studies.

This paper describes an improvement of the membrane structure of MEMS piezoresistive(PZR) pressure sensor. Finite element method (FEM) is applied to design and optimize the property of PZR the membrane structure and piezoresistors stress analysis is performed under the rated pressure. An equation that transfers the simulation stress data into output voltage is proposed in this paper according to the Wheatstone bridge principle and piezoresisitive effect in silicon. In order to achieve better sensor performance, several kinds of output voltage curve of the membrane structure were contrasted to obtain a suitable membrane structure. The design parameters of the pressure sensor include membrane size and shape and the location of piezoresistance. After that the pressure-output characteristic, the nonlinear error of the optimization sensor and the mechanical stability were analyzed. The results confirmed that the optimization structure has good sensitivity and linearity. It is a kind of high stability, high sensitivity, and low linear error of MEMS PZR pressure sensor.

Form-finding analysis and optimization of cable membrane structure based on iterative correction of tension process

We construct a family of Hermitian metrics on the Hopf surface S 3 × S 1 \mathbb {S}^3\times \mathbb {S}^1 , whose fundamental classes represent distinct cohomology classes in the Aeppli cohomology group. These metrics are locally conformally Kähler. Among the toric fibres of π : S 3 × S 1 → C P 1 \pi :\mathbb {S}^3\times \mathbb {S}^1\to \mathbb {C} P^1 two of them are stable minimal surfaces and each of the two has a neighbourhood so that fibres therein are given by stable harmonic maps from 2-torus and outside, far away from the two tori, there are unstable harmonic ones that are also unstable minimal surfaces. A similar result is true for S 2 n − 1 × S 1 \mathbb {S}^{2n-1}\times \mathbb {S}^{1} .

Bayesian neural networks for uncertainty quantification in data-driven materials modeling

Summary With the advent of Ensemble methods for Assisted History Matching of reservoir models, it has become increasingly common to use initial ensembles of reservoir models consisting of a fixed (certain) grid geometry and variable (uncertain) 3D facies distributions and 3D petro-physical property distributions conditional upon facies. In such process, 3D facies realizations are often derived by modifying facies boundary locations around certain known 3D features (often from seismic interpretation). In the context of a fixed grid, distributions of petro-physical parameters are biased because all the models in the initial ensemble are such that facies boundaries are located at grid boundary locations; in reality, the facies boundary can be located anywhere, and the petro-physical properties of cells containing facies boundaries differ from strictly facies-dependent statistics. The bias results, typically, in excessive variance of petro-physical parameters in initial ensembles in cells which possibly belong to different facies. Such variance bias has detrimental consequences on iterative inversion processes, incrementally introducing a cumulative error on the match term. A 3D Facies Boundary Filter has been developed to statistically correct this bias over ensembles of initial models. The filter relies on the construction of a refined grid and simple averaging of petro-physical properties and is based on a hypothesis of piecewise linearity of facies boundaries between cell centres. In any ensemble approach, a filtered ensemble would be used to compute unbiased updates and such updates applied upon un-filtered ensembles. The filter helps obtain better matched models (closer to initial ensemble and/or, in synthetic cases, the truth) and ultimately determines better performance forecast. The bias will be illustrated through a simple 1D example, a 3D synthetic dataset and a real 3D field model. The principle of the filter will be detailed. The impact of the filter on the petro-physical statistics will be illustrated as well as its impact within the context of EnKF Assisted History Match.

This paper presents a simple damage-gradient based elastoplastic model with non linear isotropic hardening in order to regularize the associated initial and boundary value problem (IBVP). Using the total energy equivalence hypothesis, fully coupled constitutive equations are used to describe the non local damage induced softening leading to a mesh independent solution. An additional partial differential equation governing the evolution of the non local isotropic damage is added to the classical equilibrium equations and associated weak forms derived. This leads to discretized IBVP governed by two algebric systems. The first one, associated with equilibrium equations, is highly non linear and can be solved by an iterative Newton Raphson method. The second one, related to the non local damage, is a linear algebric system and can be solved directly to compute the non local damage variable at each load increment. Two fields, linear interpolation triangular element with additional degree of freedom is terms of the non local damage variable is constructed. The non local damage variable is then transferred from mesh nodes to the quadrature (or Gauss) points to affect strongly the elastoplastic behavior. Two simple 2D examples are worked out in order to investigate the ability of proposed approach to deliver a mesh independent solution in the softening stage.

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In this paper we present a new, direct computational method for calculating the complex thermal transfer impedances between two separate locations of a given physical structure aimed at the implementation into a field-solver based on the SUNRED (SUccessive Node REDuction) algorithm. We tested the method with a simple 2D example containing 125 internal nodes. For testing the proposed new calculation method multiple combinations of Dirichlet and Neumann type boundary conditions were applied. Also, different types of thermal loads such as prescribed unit-step change in dissipation or temperature were assumed (for time domain transient analysis). The test case was also studied with the assumption of sinusoidal dissipation. Results obtained by the proposed new calculation method and results obtained by conventional simulations differ less than the uncertainty of the traditional solution method. The good agreement enables us to use the balanced truncation method to reduce the order of the transfer functions with low computational cost.