Molecular dynamics simulations of membrane deformation induced by amphiphilic helices of Epsin,Sar1p,and Arf1

The N-terminal amphiphilic helices of proteins Epsin, Sarlp, and Arfl play a critical role in initiating membrane deformation. The interactions of these amphiphilic helices with the lipid membranes are investigated in this study by combining the all-atom and coarse-grained simulations. In the all-atom simulations, the amphiphilic helices of Epsin and Sarlp are found to have a shallower insertion depth into the membrane than the amphiphilic helix of Arfl, but remarkably, the amphiphilic helices of Epsin and Sat lp induce higher asymmetry in the lipid packing between the two monolayers of the membrane. The insertion depth of amphiphilic helix into the membrane is determined not only by the overall hydrophobicity but also by the specific distributions of polar and non-polar residues along the helix. To directly compare their ability to deform the membrane, the coarse-grained simulations are performed to investigate the membrane deformation under the insertion of multiple helices.

Influenza Viral Membrane Deformation Due to Refolding of HA-Protein:Two-dimensional Model and Analysis

In this paper we study influenza viral membrane deformation related to the refolding of Hemagglutinin(HA)protein.The focus of the paper is to understand membrane deformation and budding due to experimentally observed linear HA-protein clusters,which have not been mathematically studied before.The viral membrane is modeled as a two dimensional incompressible lipid bilayer with bending rigidity.For tensionless membranes,we derive an analytical solution while for membrane under tension we solve the problem numerically.Our solution for tensionless membranes shows that the height of membrane deformation increases monotonically with the bending moment exerted by HA-proteins and attains its maximum when the size of the protein cluster reaches a critical value.Our results also show that the hypothesis of dimple formation proposed in the literature is valid in the two dimensional setting.Our comparative study of axisymmetric HA-clusters and linear HA-clusters reveals that the linear HA-clusters are not favorable to provide a sufficient energy required to overcome an energy barrier for a successful fusion,despite their capability to cause membrane deformation and budding.

Estimation of biophysical properties of cell exposed to electric field

Excitable media,such as cells,can be polarized and magnetized in the presence of an external electromagnetic field.In fact,distinct geometric deformation can be induced by the external electromagnetic field,and also the capacitance of the membrane of cell can be changed to pump the field energy.Furthermore,the distribution of ion concentration inside and outside the cell can also be greatly adjusted.Based on the theory of bio-electromagnetism,the distribution of field energy and intracellular and extracellular ion concentrations in a single shell cell can be estimated in the case with or without external electric field.Also,the dependence of shape of cell on the applied electronic field is calculated.From the viewpoint of physics,the involvement of external electric field will change the gradient distribution of field energy blocked by the membrane.And the intracellular and extracellular ion concentration show a certain difference in generating timevarying membrane potential in the presence of electric field.When a constant electric field is applied to the cell,distinct geometric deformation is induced,and the cell triggers a transition from prolate to spherical and then to oblate ellipsoid shape.It is found that the critical frequency in the applied electric field for triggering the distinct transition from prolate to oblate ellipsoid shape obtains smaller value when larger dielectric constant of the cell membrane and intracellular medium,and smaller conductivity for the intracellular medium are used.Furthermore,the effect of cell deformation is estimated by analyzing the capacitance per unit area,the density of field energy,and the change of ion concentration on one side of cell membrane.The intensity of external applied electric field is further increased to detect the change of ion concentration.And the biophysical effect in the cell is discussed.So the deformation effect of cells in electric field should be considered when regulating and preventing harm to normal neural activities occurs in a nervous system.

COUPLING COMPUTATION OF THE FLOW FIELD AND THE LARGE DEFORMATION OF MEMBRANE STRUCTURE OF STRATOSPHERE AIRSHIPS

In this article, the mathematical model of the coupling of the three-dimensional fluid flow and the large deformation of membrane structure is established. The fluid-structure coupling interaction is simulated using the computational codes developed by the authors. By analyzing the interactions of membrane and flow field, the aeroelasticity of the airship is detailed. All the results are adopted in the focused study of the stratosphere airship in trimmed state.

The critical pressure for driving a red blood cell through a contracting microfluidic channel

When a red blood cell （RBC） is driven by a pressure gradient through a microfluidic channel, its passage or blockage provides a measure of the rigidity of the cell. This has been developed as a means to separate RBCs according to their mechanical properties, which are known to change with pathological conditions such as malaria infection. In this study, we use numerical simulations to establish a quantitative connection between the minimum pressure needed to drive an RBC through a contracting microfluidic channel and the rigidity of the cell membrane. This provides the basis for designing such devices and interpreting the experimental data.

Research on Gliding Aerodynamic Effect of Deformable Membrane Wing for a Robotic Flying Squirrel

Inspired by creatures with membrane to obtain ultra-high gliding ability, this paper presents a robotic flying squirrel （a novel gliding robot） characterized as membrane wing and active membrane deformation. For deep understanding of membrane wing and gliding mechanism from a robotic system perspective, a simplified blocking aerodynamic model of the deformable membrane wing and CFD simulation are finished. In addition, a physical prototype is developed and wind tunnel experiments are carried out. The results show that the proposed membrane wing is able to support the gliding action of the robot. Meanwhile, factors including geometry characteristics, material property and wind speed are considered in the experiments to investigate the aerodynamic effects of the deformable membrane wing deeply. As a typical characteristic of robotic flying squirrel, deformation modes of the membrane wing not only affect the gliding ability, but also directly determine the effects of the posture adjustment. Moreover, different deformation modes of membrane wing are illustrated to explore the possible effects of active membrane deformation on the gliding performance. The results indicate that the deformation modes have a significant impact on posture adjustment, which reinforces the rationality of flying squirrel＇s gliding strategy and provides valuable information on prototype optimal design and control strategy in the actual gliding process.

Fabrication of Microporous Membranes from Melt Extruded Polypropylene Precursor Films via Stretching: Effect of Annealing

In this work, the effects of annealing conditions on the microstructure of polypropylene（PP） precursor films and further on the porous structure and permeability of stretched membranes were investigated. Combinations of WAXD, FTIR, DSC and DMA results clearly showed the crystalline orientation and crystallinity of the precursor film increased with annealing temperature, while the molecular chain entanglements in the amorphous phase decreased. Changes in the deformation behavior suggested more lamellar separation occurred for the films annealed at higher temperatures. Surface morphologies of the membranes examined by SEM revealed more pore number and uniform porous structure as the annealing temperature increased. In accordance with the SEM results, the permeability of the membranes increased with annealing temperature. On the other hand, it was found that 10 min was almost enough for the annealing process to obtain the microporous membranes with an optimal permeability.