Peptide Power: Mechanistic Insights into the Effect of Mitochondria-Targeted Tetrapeptides on Membrane Electrostatics from Molecular Simulations

Mitochondrial dysfunction is implicated in nine of the ten leading causes of death in the US, yet there are no FDA-approved therapeutics to treat it. Synthetic mitochondria-targeted peptides (MTPs), including the lead compound SS-31, offer promise, as they have been shown to restore healthy mitochondrial function and treat a variety of common diseases. At the cellular level, research has shown that MTPs accumulate strongly at the inner mitochondrial membrane (IMM), slow energy sinks (e.g., proton leaks), and improve ATP production. Modulation of electrostatic fields around the IMM has been implicated as a key aspect in the mechanism of action (MoA) of these peptides; however, molecular and mechanistic details have remained elusive. In this study, we employed all-atom molecular dynamics simulations (MD) to investigate the interactions of four MTPs with lipid bilayers and calculate their effect on structural and electrostatic properties. In agreement with previous experimental findings, we observed the modulation of the membrane surface and dipole potentials by MTPs. The simulations reveal that the MTPs achieve a reduction in the dipole potential by acting to disorder both lipid head groups and water layers proximal to the bilayer surface. We also find that MTPs decrease the bilayer thickness and increase the membrane's capacitance. These changes suggest that MTPs may enhance how much potential energy can be stored across the IMM at a given transmembrane potential difference. The MTPs also displace cations away from the bilayer surface, modulating the surface potential and offering an alternative mechanism for how these MTPs reduce mitochondrial energy sinks like proton leaks and mitigate Ca2+ accumulation stress. In conclusion, this study highlights the therapeutic potential of MTPs and underlines how interactions of MTPs with lipid bilayers serve as a fundamental component of their MoA.

A scheme for realizing nonreciprocal interlayer coupling in bilayer topological systems

Nonreciprocal interlayer coupling is difficult to practically implement in bilayer non-Hermitian topological photonic systems. In this work, we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss. The similarity transformation is widely applicable, and we show its application in one- and two-dimensional bilayer topological systems as examples. The bilayer non-Hermitian system with nonreciprocal interlayer coupling, whose topological number can be defined using the gauge-smoothed Wilson loop, is topologically equivalent to the bilayer system with on-site gain/loss. We also show that the topological number of bilayer non-Hermitian C6v-typed domain-induced topological interface states can be defined in the same way as in the case of the bilayer non-Hermitian Su-Schrieffer-Heeger model. Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems. This scheme is useful for observation of non-Hermitian skin effect in three-dimensional systems.

Antibacterial self-healing bilayer dressing for epidermal sensors and accelerate wound repair

This study aimed to investigate the effect of the bilayer hydrogel as a wound dressing on the wound-healing rate. We synthesized a self-healing hydrogel with optimized formulation by introducing natural polymer (chitosan) and arginine to the hydrogel composition. We then characterized the hydrogels using FT-IR, thermal analysis, mechanical testing, and in vitro and in vivo assay. The resulting bilayer wound dressing offers a lot of desirable characteristics, including good self-healing and repeatable adhesiveness. Likewise, the conductive bilayer wound dressing could be used to analyze the patient's healthcare data in real-time as epidermal sensors. Bilayer wound dressings remarkably have broad antibacterial efficacy against Gram-positive and Gram-negative bacteria. The potential applications of this bilayer wound dressing are illustrated by detectable body movement and conductivity. The wound-healing rate of bilayer wound dressings containing chitosan and arginine was higher, but those without the aforementioned ingredients had lower wound-healing efficacy. Additionally, promoting collagen synthesis and reducing wound infection has a considerable therapeutic impact on wounds. These results could have significant implications for the development of high-performance wound dressings.

Manipulating multi-spectral slow photons in bilayer inverse opal TiO2@BiVO4 composites for highly enhanced visible light photocatalysis

Manipulation of light has been proved to be a promising strategy to increase light harvesting in solar-to-chemical energy conversion, especially in photocatalysis. Inverse opal (IO) photonic structures are highly promising for light manipulation as their periodic dielectric structures enable them to slow down light and localize it within the structure, thereby improving light harvesting and photocatalytic efficiency. However, slow photons are confined to narrow wavelength ranges and hence limit the amount of energy that can be captured through light manipulation. To address this challenge, we synthesized bilayer IO TiO₂@BiVO₄ structures that manifested two distinct stop band gap (SBG) peaks, arising from different pore sizes in each layer, with slow photons available at either edge of each SBG. In addition, we achieved precise control over the frequencies of these multi-spectral slow photons through pore size and incidence angle variations, that enabled us to tune their wavelengths to the electronic absorption of the photocatalyst for optimal light utilization in aqueous phase visible light photocatalysis. This first proof of concept involving multi-spectral slow photon utilization enabled us to achieve up to 8.5 times and 2.2 times higher photocatalytic efficiencies than the corresponding non-structured and monolayer IO photocatalysts respectively. Through this work, we have successfully and significantly improved light harvesting efficiency in slow photon-assisted photocatalysis, the principles of which can be extended to other light harvesting applications.

A double-layer smart film based on gellan gum/modified anthocyanin and sodium carboxymethyl cellulose/starch/Nisin for application in chicken breast

In order to overcome this challenge of poor stability of natural anthocyanins in intelligent packaging materials, roselle anthocyanin (RA) was first modified by acetic acid, and then a double-layer smart indication antimicrobial film was developed using modified roselle anthocyanin (MRA)-gellan gum (GG) as the inner layer and sodium carboxymethyl cellulose (CMC)-starch (ST)-Nisin as the outer layer. UV spectra revealed that acetic acid was successfully grafted onto RA, which dramatically improved their thermal stability, antioxidant capabilities, photostability, and pH stability. The bilayer films were successfully prepared, as revealed by scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction measurements. In comparison to GG-MRA and CMC-ST-Nisin films, the water content, water solubility, mechanical characteristics, water vapor barrier, oxygen barrier, and hydrophobicity of GG-MRA@CMC-ST-Nisin films were significantly enhanced. The presence of the outer layer films significantly enhanced the UV-vis light barrier, opacity, antioxidant and antibacterial properties of the inner layer films. When the films were applied to chicken breast, it was found that the indicator films not only monitored the freshness of the chicken in real-time but also that the GG-MRA film and the double-layer film were effective in extending the shelf life of the chicken by 1 and 2 days, respectively, compared to the control group.

Accelular nanofibrous bilayer scaffold intrapenetrated with polydopamine network and implemented into a full-thickness wound of a white-pig model affects inflammation and healing process

Treatment of complete loss of skin thickness requires expensive cellular materials and limited skin grafts used as temporary coverage. This paper presents an acellular bilayer scaffold modified with polydopamine (PDA), which is designed to mimic a missing dermis and a basement membrane (BM). The alternate dermis is made from freeze-dried collagen and chitosan (Coll/Chit) or collagen and a calcium salt of oxidized cellulose (Coll/CaOC). Alternate BM is made from electrospun gelatin (Gel), polycaprolactone (PCL), and CaOC. Morphological and mechanical analyzes have shown that PDA significantly improved the elasticity and strength of collagen microfibrils, which favorably affected swelling capacity and porosity. PDA significantly supported and maintained metabolic activity, proliferation, and viability of the murine fibroblast cell lines. The in vivo experiment carried out in a domestic Large white pig model resulted in the expression of pro-inflammatory cytokines in the first 1-2 weeks, giving the idea that PDA and/or CaOC trigger the early stages of inflammation. Otherwise, in later stages, PDA caused a reduction in inflammation with the expression of the anti-inflammatory molecule IL10 and the transforming growth factor β (TGFβ1), which could support the formation of fibroblasts. Similarities in treatment with native porcine skin suggested that the bilayer can be used as an implant for full-thickness skin wounds and thus eliminate the use of skin grafts.

Notes on molecular fragmentation and parameter settings for a dissipative particle dynamics study of a C(10)E(4)/water mixture with lamellar bilayer formation

The influence of molecular fragmentation and parameter settings on a mesoscopic dissipative particle dynamics (DPD) simulation of lamellar bilayer formation for a C₁₀E₄/water mixture is studied. A "bottom-up" decomposition of C₁₀E₄ into the smallest fragment molecules (particles) that satisfy chemical intuition leads to convincing simulation results which agree with experimental findings for bilayer formation and thickness. For integration of the equations of motion Shardlow's S1 scheme proves to be a favorable choice with best overall performance. Increasing the integration time steps above the common setting of 0.04 DPD units leads to increasingly unphysical temperature drifts, but also to increasingly rapid formation of bilayer superstructures without significantly distorted particle distributions up to an integration time step of 0.12. A scaling of the mutual particle-particle repulsions that guide the dynamics has negligible influence within a considerable range of values but exhibits apparent lower thresholds beyond which a simulation fails. Repulsion parameter scaling and molecular particle decomposition show a mutual dependence. For mapping of concentrations to molecule numbers in the simulation box particle volume scaling should be taken into account. A repulsion parameter morphing investigation suggests to not overstretch repulsion parameter accuracy considerations.

Helical Bilayer Nonbenzenoid Nanographene Bearing a [10]Helicene with Two Embedded Heptagons

The precision synthesis of helical bilayer nanographenes (NGs) with new topology is of substantial interest because of their exotic physicochemical properties. However, helical bilayer NGs bearing non-hexagonal rings remain synthetically challenging. Here we present the efficient synthesis of the first helical bilayer nonbenzenoid nanographene (HBNG1) from a tailor-made azulene-embedded precursor, which contains a novel [10]helicene backbone with two embedded heptagons. Single-crystal X-ray analysis reveals its highly twisted bilayer geometry with a record small interlayer distance of 3.2 Å among the reported helical bilayer NGs. Notably, the close interlayer distance between the two layers offers intramolecular through-space conjugation as revealed by in situ spectroelectrochemistry studies together with DFT simulations. Furthermore, the chiroptical properties of the P/M enantiomers of HBNG1 are also evaluated by circular dichroism and circularly polarized luminescence.

Tuning the shell structure of peptide nanotubes with sodium tartrate: From monolayer to bilayer

Though the function of peptide based nanotubes are well correlated with its shape and size, controlling the dimensions of nanotubes still remains a great challenge in the field of peptide self-assembly. Here, we demonstrated that the shell structure of nanotubes formed by a bola peptide Ac-KI₃VK-NH₂ (KI₃VK, in which K, I, and V are abbreviations of lysine, isoleucine, and valine) can be regulated by mixing it with the salt sodium tartrate (STA). The ratio of KI₃VK and STA had a great impact on shell structure of the nanotubes. Bilayer nanotubes can be constructed when the molar ratio of KI₃VK and STA was less than 1:2. Both the two hydroxyls and the negative charges carried by STA were proved to play important roles in the bilayer nanotubes formation. Observations of different intermediates provided obvious evidence for the varied pathway of the bilayer nanotubes formation. Based on these experimental results, the possible mechanism for bilayer nanotubes formation was proposed. Such a study provides a simple and effective way for regulating the shell structure of the nanotubes and may expand their applications in different fields.

A novel multifunctional bilayer scaffold based on chitosan nanofiber/alginate-gelatin methacrylate hydrogel for full-thickness wound healing

Due to their lack of multifunctionality, the majority of traditional wound dressings do not support all the clinical requirements. Bilayer wound dressings with multifunctional properties can be attractive for effective skin regeneration. In the present study, we designed a multifunctional bilayer scaffold containing Chitosan-Polycaprolactone (PC) nanofiber and tannic acid (TA) reinforced methacrylate gelatin (GM)/alginate (Al) hydrogel (GM/Al/TA). PC nanofibers were coated with GM/Al/TA hydrogel to obtain a bilayer nanocomposite scaffold (Bi-TA). The GM/Al/TA hydrogel layer of Bi-TA showed antibacterial, free radical scavenging, and biocompatibility properties. Also, PC nanofiber acted as a barrier for preventing bacterial invasion and moisture loss of the hydrogel layer. The wound healing performance of the Bi-TA scaffold was investigated via a full-thickness wound model. In addition, the histopathological and immunohistochemical (IHC) stainings of transforming growth factor-β1(TGF-β1) and tumor necrosis factor-α (TNF-α) were assessed. The results indicated an enhanced wound closure rate, effective collagen deposition, quick re-epithelialization, more skin appendages, and replacement of defect area with normal skin tissue by Bi-TA scaffold compared to other groups. Additionally, the regulation of TGF-β1 and TNF-α was observed by Bi-TA dressing. Overall, the Bi-TA with appropriate structural and multifunctional properties can be an excellent candidate for developing effective dressings for wound healing applications.

Twisted bilayer arsenene sheets as a chemical sensor for toluene and M-xylene vapours - A DFT investigation

2D (two-dimensional) materials are emerging in today's world. Among the 2D materials, arsenene sheets are prominently used as chemical and biosensors. In the present work, the twisted bilayer arsenene sheets (TB-AsNS) are used to adsorb toluene and M-xylene vapours. Moreover, the band gap of pristine TB-AsNS is calculated to be 0.437 eV. Besides, the surface adsorption of toluene and M-xylene vapours modify the electronic properties of TB-AsNS noticed from the band structure, density of states, and electron density difference diagrams. The surface assimilation of target toluene and M-xylene on TB-AsNS falls in the physisorption regime facilitating the adsorption and desorption of molecules. Also, the charge transfer analysis infers that TB-AsNS acts as acceptor and target molecules play as donors. The findings support that TB-AsNS can be used as a sensing medium towards M-xylene and toluene.

Reconstitution of Detergent-Solubilized Membrane Proteins into Proteoliposomes and Nanodiscs for Functional and Structural Studies

Reconstitution of detergent-solubilized membrane proteins into phospholipid bilayers allows for functional and structural studies under close-to-native conditions that greatly support protein stability and function. Here we outline the detailed steps for membrane protein reconstitution to result in proteoliposomes and nanodiscs. Reconstitution can be achieved via a number of different strategies. The protocols for preparation of proteoliposomes use detergent removal via dialysis or via nonpolar polystyrene beads, or a mixture of the two methods. In this chapter, the protocols for nanodiscs apply polystyrene beads only. Proteoliposome preparation methods allow for substantial control of the lipid-to-protein ratio, from minimal amounts of phospholipid to high concentrations, type of phospholipid, and mixtures of phospholipids. In addition, dialysis affords a fairly large degree of control and variation of parameters such as rate of reconstitution, temperature, buffer conditions, and proteoliposome size. For the nanodisc approach, which is highly advantageous for ensuring equal access to both membrane sides of the protein as well as fast reconstitution of only a single membrane protein into a well-defined bilayer environment in each nanodisc, the protocols outline how a number of these parameters are more restricted in comparison to the proteoliposome protocols.

A new elastic characterization method for anisotropic bilayer specimens via Bayesian resonant ultrasound spectroscopy

A novel nondestructive method for complete elastic characterization of substrate-coating bilayer specimens with distinct anisotropic layers via resonant ultrasound spectroscopy (RUS) and Bayesian inversion is developed here. Bayesian formulations of the RUS inversion problem-of quantifying elastic properties given a measured list of resonance frequencies recorded from a single, typically small, precisely fabricated, macroscopically homogeneous, linear-elastic specimen-are a recent development. Here we report the first Bayesian formulation of the bilayer problem, and through a series of practical examples, demonstrate novel parameter estimation capabilities of our open-source CmdStan-RUS code. Finding specimen geometry and the number of resonance modes used for inversion strongly govern the ability to retrieve individual elastic moduli. The concept of "invertability" is explored for a range of relevant geometries using virtual specimens that resemble experimental bilayers of plasma sprayed ceramic coatings on single crystal metallic substrates. A range of Bayesian posterior evaluation methods are addressed, particularly considering the large computational cost of the bilayer forward model. Laplace approximation methods are thus developed and implemented for bilayer geometry design space modeling and expedient estimates of parameter uncertainties. Ideal specimen design, different noise models, the influence of prior distributions, dual-likelihood fits incorporating measurements of the bare substrate, and how Bayesian RUS methods differ from traditional RUS optimization are discussed.

Effect of thermal gradient on structural relaxation and characterization of thermal stresses in dental porcelains - A finite element study

Zirconia-based materials veneered with glassy porcelain have become the material of choice for both dentists and their patients. This restoration material is now extensively used in clinical practice for the following reasons: material closely resembles tooth appearance, biofunctionality, biocompatibility and affordability. However, premature clinical failures due to the combination of subsurface flaws and tensile stresses within porcelains raise a concern about their reliability and integrity. This study evaluates structural relaxation in dental porcelain to form a suitable explanation for subsurface tensile stresses. Finite Element Method (FEM) is used for this analysis. User material subroutines, UEXPAN, and UTRS, were developed and integrated into a finite element solver to study the effects of structural relaxation on thermal stresses in veneer during final heat treatment. The predictions of the model were validated through qualitative and quantitave means. A validated model was used for Finite Element Analysis (FEA). Faster cooling rates and high veneer thickness predicted high subsurface tensile stresses due to ineffective structural relaxation. Slow cooling rates and lower veneer thickness showed desired compressive stresses in subsurface areas with visible structural relaxation. This work, emphasizing structural relaxation in veneering dental porcelain, provides a way forward for effective designing of dental restorations. Accordingly, it is useful to tailor the desired stress state for extended life in veneered dental porcelains on zirconia frameworks.

Insertion and activation of functional Bacteriorhodopsin in a floating bilayer

The proton pump transmembrane protein bacteriorhodopsin was successfully incorporated into planar floating lipid bilayers in gel and fluid phases, by applying a detergent-mediated incorporation method. The method was optimized on single supported bilayers by using quartz crystal microbalance, atomic force and fluorescence microscopy techniques. Neutron and X-ray reflectometry were used on both single and floating bilayers with the aim of determining the structure and composition of this membrane-protein system before and after protein reconstitution at sub-nanometer resolution. Lipid bilayer integrity and protein activity were preserved upon the reconstitution process. Reversible structural modifications of the membrane, induced by the bacteriorhodopsin functional activity triggered by visible light, were observed and characterized at the nanoscale.

Ag@MOF-loaded chitosan nanoparticle and polyvinyl alcohol/sodium alginate/chitosan bilayer dressing for wound healing applications

In this paper, Ag-Metal-organic framework loaded chitosan nanoparticles (0.1%Ag@MOF/1.5%CSNPs) and polyvinyl alcohol/sodium alginate/chitosan (PACS) were used as the upper and lower layers to successfully prepare a bilayer composite dressing for wound healing. The performance of bilayer dressing was evaluated. The lower layer (PACS) had uniform pore size distribution, good water retention, swelling, water vapor permeability, and biocompatibility while PACS had almost no antibacterial activity. The upper layer (Ag@MOF/CSNPs) possessed excellent antibacterial activity and poor biocompatibility. As the upper layer, it can avoid direct contact with the skin and inhibit microbial invasion. In addition, the bilayer can adhere to a large number of red blood cells and platelets, promoting blood coagulation and cell proliferation. Ag@MOF, CSNPs, Ag@MOF/CSNPs and bilayer showed antibacterial activity in ascending order, due to the synergistic antibacterial action of the upper and lower layer. In vivo evaluation showed that both bilayer and PACS could significantly accelerate the wound healing, and the bilayer dressing showed more complete re-epithelialization with less inflammatory cells. In summary, this new bilayer composite is an ideal dressing for accelerating wound healing.

Building Synthetic Transmembrane Peptide Pores

Membrane protein pores have demonstrated applications in nanopore technology. Previous studies have mostly focused on β-barrel protein pores, whereas α-helix-based transmembrane protein pores are rarely explored in nanopore applications. Here, we developed a synthetic transmembrane peptide pore built entirely from short synthetic α-helical peptides. We examined the formation of a stable uniform ion-selective pore in single-channel electrical recordings. Furthermore, we show that cyclodextrins (CDs) block the peptide pores and determine the kinetics of CD binding and translocation. We suggest that such designed synthetic transmembrane pores will be useful for several applications in biotechnology, including stochastic sensing.

Atomic Force Microscopy Reveals Membrane Protein Activity at the Single Molecule Level

Atomic force microscopy has emerged as a valuable complementary technique in membrane structural biology. The apparatus is capable of probing individual membrane proteins in fluid lipid bilayers at room temperature with spatial resolution at the molecular length scale. Protein conformational dynamics are accessible over a range of biologically relevant timescales. This chapter presents methodology our group uses to achieve robust AFM image data of the General Secretory system, the primary pathway of protein export from the cytoplasm to the periplasm of E. coli. Emphasis is given to measuring and maintaining biochemical activity and to objective AFM image processing methods. For example, the biochemical assays can be used to determine chemomechanical coupling efficiency of surface adsorbed translocases. The Hessian blob algorithm and its extension to nonlocalized linear features, the line detection algorithm, provide automated feature delineations. Many of the methods discussed here can be applied to other membrane protein systems of interest.

Influence of the second layer on geometry and spectral properties of doped two-dimensional hexagonal boron nitride

Influence of the additional layer of hexagonal boron nitride (h-BN) on structure, energetics, and electronic spectra of a layer doped with magnesium, silicon, phosphorus, aluminum, or carbon atoms has been examined by theoretical methods. The h-BN layers are modeled as BN clusters of over thirty atoms with the defect in the center. The calculations show that atom positions undergo some modifications in the presence of the second layer, which in several cases lead to significant changes in electronic spectra, like (i) modifications of the character of some states from local excitation to a partial charge transfer; (ii) redshift of the majority of lowest excitations; (iii) absence or appearance of new states in comparison with the monolayers. For instance, a zero-intensity excitation below 4 eV for the carbon atom in place of boron transforms into a dipole-allowed one in the presence of the second layer. A comparison of the interaction energies of doped and undoped clusters shows a strong dependence of the stabilizing of destabilizing effect on the dopant atom, the replaced atom, and in some cases also on the stacking type (AA’ or AB). The stabilization energy per BN pair, calculated for two undoped clusters, is equal to − 31 and − 28 meV for the AA’ and AB stacking, respectively, thus confirming a larger stability of the AA’ stacking for the h-BN case.

Development and characterisation of bilayered periosteum-inspired composite membranes based on sodium alginate-hydroxyapatite nanoparticles

BACKGROUND AND AIM

Membranes for guided bone regeneration should have a mechanical structure and a chemical composition suitable for mimicking biological structures. In this work, we pursue the development of periosteum-inspired bilayered membranes obtained by crosslinking alginate with different amounts of nanohydroxyapatite.

EXPERIMENTS

Alginate-nanohydroxyapatite interaction was studied by rheology and infrared spectroscopy measurements. The membranes were characterized regarding their tensile strength, degradation and surface morphology. Finally, cell cultures were performed on each side of the membranes.

FINDINGS

The ionic bonding between alginate polysaccharide networks and nanohydroxyapatite was proven, and had a clear effect in the strength and microstructure of the hydrogels. Distinct surface characteristics were achieved on each side of the membranes, resulting in a highly porous fibrous side and a mineral-rich side with higher roughness and lower porosity. Moreover, the effect of amount of nanohydroxyapatite was reflected in a decrease of the membranes' plasticity and an increment of degradation rate. Finally, it was proved that osteoblast-like cells proliferated and differentiated on the mineral-rich side, specially when a higher amount of nanohydroxyapatite was used, whereas fibroblasts-like cells were able to proliferate on the fibrous side. These periosteum-inspired membranes are promising biomaterials for guided tissue regeneration applications.

A DFT study of Janus structure of S and Se in HfSSe layered as a promising candidate for electronic devices

The transition-metal dichalcogenides are presently being intensively researched because of their unique optoelectronic properties. Further, the success of TMDs in all areas of science without exception has opened the street to find other two-dimensional materials. Based on density functional theory, we study the vibrational and electronic properties of the mixed-phase of S and Se in HfSSe system, i.e, HfSSe monolayer and HfSSe/HfSSe bilayer. In this framework, our systems are full dynamically stable, which shown by their phonon dispersion. Also, we found that the HfSSe (heterolayer) monolayer is an indirect semiconductor (0.63 eV with BLYP), while the HfSSe (alternating) monolayer is a direct semiconductor (0.753 eV with BLYP). Our AA, AB, AA', and AB' of HfSSe/HfSSe (heterolayer) bilayer are indirect band gaps in a range 0.361-0.830 eV, which are promising candidates for electronic devices as field-effect transistors, photodetectors, and other optoelectronics. Nevertheless, HfSSe/HfSSe (alternating) bilayer is a direct bandgap semiconductor with a value of 0.671 eV, when vdW is used.

Methylene volumes in monoglyceride bilayers are larger than in liquid alkanes

The densities as a function of temperature of four fully hydrated saturated monoglycerides with even chain lengths ranging from eight to fourteen were determined by vibrating tube densitometry and their phase transition temperatures were determined by differential scanning calorimetry (DSC). We find the volume of a methylene group in a monoglyceride bilayer is 2% larger than in liquid alkanes at physiological temperatures, similar to the methylene group volumes found in phosphatidylcholine (PC) bilayers. Additionally, we carefully consider the traditional method of calculating component volumes from experimental data and note potential difficulties in this approach. In the literature, the ratio of terminal methyl volume (CH₃) to methylene (CH₂) volumes is typically assumed to be 2. By analysis of literature alkane data, we find this ratio actually ranges from 1.9 to 2.3 for temperatures ranging from 0 °C to 100 °C. For a rough sense of scale, we note that to effect a 2% reduction in volume requires of order 200 atmospheres of pressure, and pressures of this magnitude are biologically relevant. For instance, this amount of pressure is sufficient to reverse the effect of anesthesia. The component volumes obtained are an important parameter used for determining the structure of lipid bilayers and for molecular dynamics simulations.

Cholesterol transfer at the plasma membrane

Cholesterol homeostasis is of central importance for life. Therefore, cells have developed a divergent set of pathways to meet their cholesterol needs. In this review, we focus on the direct transfer of cholesterol from lipoprotein particles to the cell membrane. More molecular details on the transfer of lipoprotein-derived lipids were gained by recent studies using phospholipid bilayers. While amphiphilic lipids are transferred right after contact of the lipoprotein particle with the membrane, the transfer of core lipids is restricted. Amphiphilic lipid transfer gains special importance in genetic diseases impairing lipoprotein metabolism like familial hypercholesterolemia. Taken together, these data indicate that there is a constant exchange of amphiphilic lipids between lipoprotein particles and the cell membrane.

A biradical-tagged phospholipid as a polarizing agent for solid-state MAS Dynamic Nuclear Polarization NMR of membrane proteins

A novel Dynamic Nuclear Polarization (DNP) NMR polarizing agent ToSMTSL-PTE representing a phospholipid with a biradical TOTAPOL tethered to the polar head group has been synthesized, characterized, and employed to enhance solid-state Nuclear Magnetic Resonance (SSNMR) signal of a lipid-reconstituted integral membrane protein proteorhodopsin (PR). A matrix-free PR formulation for DNP improved the absolute sensitivity of NMR signal by a factor of ca. 4 compared to a conventional preparation with TOTAPOL dispersed in a glassy glycerol/water matrix. DNP enhancements measured at 400 MHz/263 GHz and 600 MHz/395 GHz showed a strong field dependence but remained moderate at both fields, and comparable to those obtained for PR covalently modified with ToSMTSL. Additional continuous wave (CW) X-band electron paramagnetic resonance (EPR) experiments with ToSMTSL-PTE in solutions and in lipid bilayers revealed that an unfavorable conformational change of the linker connecting mononitroxides could be one of the reasons for moderate DNP enhancements. Further, differential scanning calorimetry (DSC) and CW EPR experiments indicated an inhomogeneous distribution and/or a possibility of a partial aggregation of ToSMTSL-PTE in DMPC:DMPA bilayers when the concentration of the polarizing agent was increased to 20 mol% to maximize the DNP enhancement. Thus, conformational changes and an inhomogeneous distribution of the lipid-based biradicals in lipid bilayers emerged as important factors to consider for further development of this matrix-free approach for DNP of membrane proteins.

Calcium-induced transformation of cardiolipin nanodisks

Miniature membranes comprised of tetramyristoylcardiolipin (CL) and apolipoprotein (apo) A-I, termed nanodisks (ND), are stable, aqueous soluble, reconstituted high density lipoproteins. When CL ND, but not dimyristoylphosphatidylcholine (PC) ND, were incubated with CaCl₂, a concentration dependent increase in sample turbidity occurred, consistent with CL undergoing a bilayer to non-bilayer transition. To assess the cation specificity of this reaction, CL ND were incubated with various mono- and divalent cations. Whereas monovalent cations had no discernable effect, MgCl₂ and SrCl₂ induced a response similar to CaCl₂. When ND were formulated using different weight ratios of CL and PC, those possessing 100% CL or 75% CL remained susceptible to CaCl₂ induced sample turbidity development while ND possessing 50% CL displayed reduced susceptibility. ND comprised of 25% CL and 75% PC were unaffected by CaCl₂ under these conditions. SDS PAGE analysis of insoluble material generated by incubation of CL ND with CaCl₂ revealed that nearly all apoA-I was recovered in the insoluble fraction along with CL. One h after addition of EDTA to CaCl₂-treated CL ND, sample clarity was restored. Collectively, the data are consistent with a model wherein Ca²⁺ forms a bidentate interaction with anionic phosphates in the polar head group of CL. As phosphate group repositioning occurs to maximize Ca²⁺ binding, CL acyl chains reposition, accentuating the conical shape of CL to an extent that is incompatible with the ND bilayer structure.

Thermal induced deflection of a porcelain-zirconia bilayer: Influence of cooling rate

OBJECTIVE

To determine the thermal expansion of a porcelain (VM9) and tetragonal zirconia (Y-TZP) as well as the deflection upon re-heating and cooling of a bilayer fabricated from these two materials after slow and rapid cooling during initial fabrication.

METHODS

The coefficient of thermal expansion (CTE) of bulk porcelain and Y-TZP as well as bilayer beam deflection was measured with a novel non-contact optical dilatometer. The influence of cooling rate during initial fabrication of the porcelain-zirconia bilayer and the bulk porcelain during subsequent heating and cooling is investigated. Specimens were heated to 900°C in the dilatometer, well in excess of the glass transition temperature (T_g) and softening temperature (T_s) of the porcelain.

RESULTS

The thermal expansion of the porcelain above T_g exhibits a threefold increase in CTE over that observed below T_g. Observations of the bilayer deflection reflect the difference in the CTE of the component materials and enable T_g and T_s temperatures for the porcelain to be estimated. Initial cooling rate of the porcelain and porcelain-YTZP bilayer was found to have a profound influence on the subsequent response to slow reheating and cooling as well as the resultant residual deflection.

SIGNIFICANCE

The estimation of the residual stress and potential for chipping of porcelain-zirconia dental restorative systems should not be based solely on thermal expansion data measured below T_g.

EPR Techniques to Probe Insertion and Conformation of Spin-Labeled Proteins in Lipid Bilayers

Electron paramagnetic resonance (EPR) spectroscopy of spin-labeled membrane proteins is a valuable biophysical technique to study structural details and conformational transitions of proteins close to their physiological environment, for example, in liposomes, membrane bilayers, and nanodiscs. Unlike in nuclear magnetic resonance (NMR) spectroscopy, having only one or few specific side chains labeled at a time with paramagnetic probes makes the size of the object under investigation irrelevant in terms of technique sensitivity. As a drawback, extensive site-directed mutagenesis is required in order to analyze the properties of the protein under investigation. EPR can provide detailed information on side chain dynamics of large membrane proteins or protein complexes embedded in membranes with an exquisite sensitivity for flexible regions and on water accessibility profiles across the membrane bilayer. Moreover, distances between the two spin-labeled side chains in membrane proteins can be detected with high precision at cryogenic temperatures. The application of EPR to membrane proteins still presents some challenges in terms of sample preparation, sensitivity and data interpretation, thus it is difficult to give ready-to-go methodological recipes. However, new technological developments (arbitrary waveform generators) and new spin labels spectroscopically orthogonal to nitroxides increased the range of applicability from in vitro toward in-cell EPR experiments. This chapter is an updated version of the one published in the first edition of the book and describes the state of the art in the application of nitroxide-based site-directed spin labeling EPR to membrane proteins, addressing new tools such as arbitrary waveform generators and spectroscopically orthogonal labels, such as Gd(III)-based labels. We will present challenges in sample preparation and data analysis for functional and structural membrane protein studies using site-directed spin labeling techniques and give experimental details on EPR techniques providing information on side chain dynamics and water accessibility using nitroxide probes. An updated optimal Q-band DEER setup for nitroxide probes will be described, and its extension to gadolinium-containing samples will be addressed.

Quantitative Analysis of Structure and Dynamics in AFM Images of Lipid Membranes

AFM is now established as a powerful and direct technique for studying lipid membranes, and is highly complementary with other techniques. It is the only method for direct imaging and mechanical probing of lipid phase structure in a liquid environment down to the nanometer level. In order to understand the structure, function, and interactions of membranes at this level, we must be able to reliably and quantitatively measure the AFM images. Here we describe the methods used to process and analyze AFM images of phase-separated supported lipid bilayers . This initially takes a static approach, where we simply quantify the % of domain area, number of domains, and morphology, and quantify how many images must be taken to obtain reliable statistics. We then look at dynamics, describing the methods we use to study the nanometer scale motion of the domain perimeter as observed using Fast Scan AFM, and hence extract a quantitative line tension.

Tunable Electric Properties of Bilayer α-GeTe with Different Interlayer Distances and External Electric Fields

Based on first-principle calculations, the stability, electronic structure, optical absorption, and modulated electronic properties by different interlayer distances or by external electric fields of bilayer α-GeTe are systemically investigated. Results show that van der Waals (vdW) bilayer α-GeTe has an indirect band structure with the gap value of 0.610 eV, and α-GeTe has attractively efficient light harvesting. Interestingly, along with the decrease of interlayer distances, the band gap of bilayer α-GeTe decreases linearly, due to the enhancement of interlayer vdW interaction. In addition, band gap transition is originated from the electric field-induced near free-electron gas (NFEG) under the application of positive electrical fields. However, when the negative electric fields are applied, there is no NFEG. On account of these characteristics of bilayer α-GeTe, a possible data storage device has been designed. These results indicate that bilayer α-GeTe has a potential to work in new electronic and optoelectronic devices.

The influence of the essential oil extracted from hops on monolayers and bilayers imitating plant pathogen bacteria membranes

Many plant-derived compounds possess antimicrobial, antioxidant and even anticancer activities. Therefore, they are considered as substances that can be used instead of synthetic compounds in various applications. In this work, the essential oil from hop cones was extracted and analyzed, and then its effects on model bacteria membranes were studied to verify whether the hop essential oils could be used as ecological pesticides. The experiments involved surface pressure-area measurements, penetration studies and Brewster angle microscopy (BAM) imaging of lipid monolayers as well as hydrodynamic diameter, zeta potential, steady-state fluorescence anisotropy and Cryo-Transmission Electron Microscopy (cryo-TEM) measurements of liposomes. Finally the bactericidal tests on plant pathogen bacteria Pseudomonas syringae pv. lachrymans PCM 1410 were performed. The obtained results showed that the components of the essential oils from hop cones incorporate into lipid monolayers and bilayers and alter their fluidity. However, the observed effect is determined by the system composition, its condensation and the oil concentration. Interestingly, at a given dose, the effect of the essential oil on membranes was found to stabilize. Moreover, BAM images proved that hop oil prevents the formation of a large fraction of a condensed phase at the interface. Both the studies on model membranes as well as the in vitro tests allow one to conclude that the hop essential oil could likely be considered as the candidate to be used in agriculture as a natural pesticide.

Disruptive effect of tocopherol oxalate on DPPC liposome structure: DSC, SAXS, and fluorescence anisotropy studies

α-Tocopherol oxalate (TO), a tocopherol ester derivative, was investigated for its effect on the structural changes of fully hydrated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes, as a function of concentration and temperature, by applying differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), and DPH fluorescence anisotropy methods. The DSC and DPH anisotropy data indicated that TO embedded into DPPC membrane lowered the enthalpy (ΔH_m) and temperature (T_m) of the main phase transition as well its cooperativity. Fluidization of the membrane at a lowered temperature was accompanied by formation of mixed structures of tocopherol-enriched domains. SAXS studies showed the formation of various ordered structures in DPPC gel-phase during incorporation of TO into the bilayer, as evidenced by the existence of lamellar phases with repeat distances (d) of 6.13 and 6.87 nm, assigned to TO-enriched domains and a lamellar, liquid-ordered DPPC phase with d = 8.45 nm at increasing TO concentrations with lowering and broadening of the Bragg peaks, and diffuse scattering, characteristic of a fluid L_α phase, were observed. In DPPC fluid-phase, the increasing presence of TO at low concentrations resulted in the appearance of a liquid-ordered phase with repeat d = 6.9 nm coexistent with a lamellar structure with d = 9.2 nm, assigned to liquid-disordered structures. An increasing repeat distance observed with raising the TO amount in the DPPC bilayer evolved from an increasing interlamellar water layer of increasing thickness. Presence of TO facilitated penetration of water molecules into the acyl chain region which decreased van der Waals interactions in the bilayer. The DSC, SAXS, and fluorescence anisotropy data established that TO exhibited pronounced disruptive activity in DPPC membranes compared to α-tocopherol. The driving force of the observed action was attributed to electrostatic and dipole interactions of the acidic moiety with the polar head group of phospholipids in the interface region of the bilayer.

A Raman spectroscopy study on the effects of intermolecular hydrogen bonding on water molecules absorbed by borosilicate glass surface

The structural forms of water/deuterated water molecules located on the surface of borosilicate capillaries have been first investigated in this study on the basis of the Raman spectral data obtained at different temperatures and under atmospheric pressure for molecules in bulk and also for molecules absorbed by borosilicate glass surface. The strongest two fundamental bands locating at 3063cm^-1 (2438cm^-1) in the recorded Raman spectra are assigned here to the OH (OD) bond stretching vibrations and they are compared with the corresponding bands observed at 3124cm^-1 (2325cm^-1) in the Raman spectrum of ice Ih. Our spectroscopic observations have indicated that the structure of water and deuterated water molecules on borosilicate surface is similar to that of ice Ih (hexagonal phase of ice). These observations have also indicated that water molecules locate on the borosilicate surface so as to construct a bilayer structure and that strong and weak intermolecular hydrogen bonds are formed between water/deuterated molecules and silanol groups on borosilicate surface. In accordance with these findings, water and deuterated water molecules at the interface of capillary have a higher melting temperature.

Multiscale molecular dynamics simulations of lipid interactions with P-glycoprotein in a complex membrane

P-glycoprotein (P-gp) can transport a wide range of very different hydrophobic organic molecules across the membrane. Its ability to extrude molecules from the cell creates delivery problems for drugs that target proteins in the central nervous system (CNS) and also causes drug-resistance in many forms of cancer. Whether a drug will be susceptible to export by P-gp is difficult to predict and currently this is usually assessed with empirical and/or animal models. Thus, there is a need to better understand how P-gp works at the molecular level in order to fulfil the 3Rs: Refinement, reduction and replacement of animals in research. As structural information increasingly becomes available, our understanding at the molecular level improves. Proteins like P-gp are however very dynamic entities and thus one of the most appropriate ways to study them is with molecular dynamics simulations, especially as this can capture the influence of the surrounding environment. Recent parameterization developments have meant that it is now possible to simulate lipid bilayers that more closely resemble in vivo membranes in terms of their composition. In this report we construct a complex lipid bilayer that mimics the composition of brain epithelial cells and examine the interactions of it with P-gp. We find that the negatively charged phosphatidylserine lipids in the inner leaflet of the membrane tend to form an annulus around P-gp. We also observed the interaction of cholesterol with three distinct areas of the P-gp. Potential of mean force (PMF) calculations suggest that a crevice between transmembrane helices 10 and 12 has particularly favourable interaction energy for cholesterol.

Membrane interactions of ionic liquids and imidazolium salts

Room-temperature ionic liquids (RTILs) have attracted considerable attention in recent years due to their versatile properties such as negligible volatility, inflammability, high extractive selectivity and thermal stability. In general, RTILs are organic salts with a melting point below ~100 °C determined by the asymmetry of at least one of their ions. Due to their amphiphilic character, strong interactions with biological materials can be expected. However, rising attention has appeared towards their similarity and interaction with biomolecules. By employing structural modifications, the biochemical properties of RTILs can be designed to mimic lipid structures and to tune their hydrophobicity towards a lipophilic behavior. This is evident for the interaction with lipid-membranes where some of these compounds present membrane-disturbing effects or cellular toxicity. Moreover, they can form micelles or lipid-like bilayer structures by themselves. Both aspects, cellular effects and membrane-forming capacities, of a novel class of lipophilic imidazolium salts will be discussed.

Enhanced Performance of a Monolayer MoS2/WSe2 Heterojunction as a Photoelectrochemical Cathode

Transition-metal dichalcogenide (TMD) semiconductors have attracted interest as photoelectrochemical (PEC) electrodes due to their novel band-gap structures, optoelectronic properties, and photocatalytic activities. However, the photo-harvesting efficiency still requires improvement. In this study, A TMD stacked heterojunction structure was adopted to further enhance the performance of the PEC cathode. A P-type WSe₂ and an N-type MoS₂ monolayer were stacked layer-by-layer to build a ultrathin vertical heterojunction using a micro-fabrication method. In situ measurement was employed to characterize the intrinsic PEC performance on a single-sheet heterostructure. Benefitting from its built-in electric field and type II band alignment, the MoS₂/WSe₂ bilayer heterojunction exhibited exceptional photocatalytic activity and a high incident photo-to-current conversion efficiency (IPCE). Comparing with the monolayer WSe₂ cathode, the PEC current and the IPCE of the bilayer heterojunction increased by a factor of 5.6 and enhanced 50%, respectively. The intriguing performance renders the MoS₂/WSe₂ heterojunction attractive for application in high-performance PEC water splitting.

Novel bilayer wound dressing composed of SIS membrane with SIS cryogel enhanced wound healing process

Full-thickness skin damage is a server issue and sometimes even dangerous to life. Many researches have been done toward full-thickness wound dressing. In this study, we demonstrated a facile and one-step procedure of SIS bilayer wound dressing. The top layer could protect the wound from bacterial infection and provide a moist environment suitable for wound healing, while the cryogel layer could promote cell proliferation. The SIS bilayer wound dressing has sufficient mechanical properties to protect wound from second damage and can maintain a moist environment for cell proliferation and migration at wound site. Bacterial permeation testing demonstrated that the bilayer scaffold had high efficiency in blocking bacteria at the wound site. In vivo tests and qRT-PCR results revealed that the bilayer group possessed a higher tendency toward keratinocyte proliferation and migration. The SIS bilayer has a high potential to use as full-thickness wound dressing.

Novel bilayer dissolving microneedle arrays with concentrated PLGA nano-microparticles for targeted intradermal delivery: Proof of concept

Polymeric microneedle (MN) arrays continue to receive growing attention due to their ability to bypass the skin's stratum corneum barrier in a minimally-invasive fashion and achieve enhanced transdermal drug delivery and "targeted" intradermal vaccine administration. In this research work, we fabricated biodegradable bilayer MN arrays containing nano - microparticles for targeted and sustained intradermal drug delivery. For this study, model drug (vitamin D₃, VD₃)-loaded PLGA nano- and microparticles (NMP) were prepared by a single emulsion solvent evaporation method with 72.8% encapsulation of VD₃. The prepared NMP were directly mixed 20% w/v poly(vinyl pyrrolidone) (PVP) gel, with the mixture filled into laser engineered micromoulds by high-speed centrifugation (30min) to concentrate NMP into MN shafts. The particle size of PLGA NMP ranged from 300nm to 3.5μm and they retained their particle size after moulding of bilayer MN arrays. The relatively wide particle size distribution of PLGA NMP was shown to be important in producing a compact structure in bilayer conical, as well as pyramidal, MN, as confirmed by scanning electron microscopy. The drug release profile from PLGA NMP was tri-phasic, being sustained over 5days. The height of bilayer MN arrays was influenced by the weight ratio of NMP and 20% w/v PVP. Good mechanical and insertion profiles (into a skin simulant and excised neonatal porcine skin) were confirmed by texture analysis and optical coherence tomography, respectively. Ex vivo intradermal neonatal porcine skin penetration of VD₃ NMP from bilayer MN was quantitatively analysed after cryostatic skin sectioning, with 74.2±9.18% of VD₃ loading delivered intradermally. The two-stage novel processing strategy developed here provides a simple and easy method for localising particulate delivery systems into dissolving MN. Such systems may serve as promising means for controlled transdermal delivery and targeted intradermal administration.

Multiscale molecular dynamics simulations of lipid interactions with P-glycoprotein in a complex membrane

P-glycoprotein (P-gp) can transport a wide range of very different hydrophobic organic molecules across the membrane. Its ability to extrude molecules from the cell creates delivery problems for drugs that target proteins in the central nervous system (CNS) and also causes drug-resistance in many forms of cancer. Whether a drug will be susceptible to export by P-gp is difficult to predict and currently this is usually assessed with empirical and/or animal models. Thus, there is a need to better understand how P-gp works at the molecular level in order to fulfil the 3Rs: Refinement, reduction and replacement of animals in research. As structural information increasingly becomes available, our understanding at the molecular level improves. Proteins like P-gp are however very dynamic entities and thus one of the most appropriate ways to study them is with molecular dynamics simulations, especially as this can capture the influence of the surrounding environment. Recent parameterization developments have meant that it is now possible to simulate lipid bilayers that more closely resemble in vivo membranes in terms of their composition. In this report we construct a complex lipid bilayer that mimics the composition of brain epithelial cells and examine the interactions of it with P-gp. We find that the negatively charged phosphatidylserine lipids in the inner leaflet of the membrane tend to form an annulus around P-gp. We also observed the interaction of cholesterol with three distinct areas of the P-gp. Potential of mean force (PMF) calculations suggest that a crevice between transmembrane helices 10 and 12 has particularly favourable interaction energy for cholesterol.

Electrospun vein grafts with high cell infiltration for vascular tissue engineering

Demand is increasing for functional small-diameter vascular grafts (diameter<6mm) for clinical arterial replacement. In the present study, we develop a bilayer poly(ε-caprolactone, PCL) fibrous vascular graft consisting of a thin internal layer made of longitudinally aligned fibers and a relatively thick highly porous external layer. The internal layer provides a scaffold with the necessary mechanical strength and enhances the growth of endothelial cells, whereas the external layer enhances cell motility through the scaffold bulk. The biocompatibility and biological performance of bilayer fibrous scaffolds are evaluated by in vivo experiments, molecular biology, and histology studies. Our bilayer scaffolds demonstrate much better fiber alignment and higher porosity than do normal electrospun vascular grafts with randomly distributed fibers. The results suggest that the proposed grafts can overcome limitations owing to the inadequate porosity, small pores, and poor cell infiltration of scaffolds fabricated by conventional electrospinning. The unique structure of bilayer scaffolds is satisfactory and promotes cell proliferation, collagen-fiber deposition, and ingrowth of smooth muscle cells and endothelial cells in vivo. The results of this study illustrate the strong potential of such bilayer fibrous scaffolds for vascular tissue engineering and regeneration.

SSM-Based Electrophysiology for Transporter Research

Functional characterization of transport proteins using conventional electrophysiology can be challenging, especially for low turnover transporters or transporters from bacteria and intracellular compartments. Solid-supported membrane (SSM)-based electrophysiology is a sensitive and cell-free assay technique for the characterization of electrogenic membrane proteins. Purified proteins reconstituted into proteoliposomes or membrane vesicles from cell culture or native tissues are adsorbed to the sensor holding an SSM. A substrate or a ligand is applied via rapid solution exchange. The electrogenic transporter activity charges the sensor, which is recorded as a transient current. The high stability of the SSM allows cumulative measurements on the same sensor using different experimental conditions. This allows the determination of kinetic properties including EC₅₀, IC₅₀, K_m, K_D, and rate constants of electrogenic reactions. About 100 different transporters have been measured so far using this technique, among them symporters, exchangers, uniporters, ATP-, redox-, and light-driven ion pumps, as well as receptors and ion channels. Different instruments apply this technique: the laboratory setups use a closed flow-through arrangement, while the commercially available SURFE²R N1 resembles a pipetting robot. For drug screening purposes high-throughput systems, such as the SURFE²R 96SE enable the simultaneous measurement of up to 96 sensors.

Applications of NMR to membrane proteins

Membrane proteins present a challenge for structural biology. In this article, we review some of the recent developments that advance the application of NMR to membrane proteins, with emphasis on structural studies in detergent-free, lipid bilayer samples that resemble the native environment. NMR spectroscopy is not only ideally suited for structure determination of membrane proteins in hydrated lipid bilayer membranes, but also highly complementary to the other principal techniques based on X-ray and electron diffraction. Recent advances in NMR instrumentation, spectroscopic methods, computational methods, and sample preparations are driving exciting new efforts in membrane protein structural biology.

Lower Eyelid Reconstruction

Lower eyelid defects are common, and a systematic approach to reconstruction of the lower eyelid is required. Attention to the bilaminar eyelid anatomy and canthal support structures, with efforts to maintain functionally important structures, such as the lacrimal canalicular system, is vital to appropriate lower eyelid reconstruction. Techniques of advancement and rotation flaps and grafting of skin and mucosa are mainstays of lower eyelid reconstruction. An appropriate armamentarium of techniques allows for optimal surgical results.

ZnO Nanoparticles/Reduced Graphene Oxide Bilayer Thin Films for Improved NH3-Sensing Performances at Room Temperature

ZnO nanoparticles and graphene oxide (GO) thin film were deposited on gold interdigital electrodes (IDEs) in sequence via simple spraying process, which was further restored to ZnO/reduced graphene oxide (rGO) bilayer thin film by the thermal reduction treatment and employed for ammonia (NH3) detection at room temperature. rGO was identified by UV-vis absorption spectra and X-ray photoelectron spectroscope (XPS) analyses, and the adhesion between ZnO nanoparticles and rGO nanosheets might also be formed. The NH3-sensing performances of pure rGO film and ZnO/rGO bilayer films with different sprayed GO amounts were compared. The results showed that ZnO/rGO film sensors exhibited enhanced response properties, and the optimal GO amount of 1.5 ml was achieved. Furthermore, the optimal ZnO/rGO film sensor showed an excellent reversibility and fast response/recovery rate within the detection range of 10-50 ppm. Meanwhile, the sensor also displayed good repeatability and selectivity to NH3. However, the interference of water molecules on the prepared sensor is non-ignorable; some techniques should be researched to eliminate the effect of moisture in the further work. The remarkably enhanced NH3-sensing characteristics were speculated to be attributed to both the supporting role of ZnO nanoparticles film and accumulation heterojunction at the interface between ZnO and rGO. Thus, the proposed ZnO/rGO bilayer thin film sensor might give a promise for high-performance NH3-sensing applications.

Spongy bilayer dressing composed of chitosan-Ag nanoparticles and chitosan-Bletilla striata polysaccharide for wound healing applications

The purpose of this study was to develop a promising wound dressing. Though chitosan cross-linked with genipin has been widely used as biomaterials, with the addition of partially oxidized Bletilla striata polysaccharide, the newly developed material in this study (coded as CSGB) showed less gelling time, more uniform aperture distribution, higher water retention, demanded mechanical strength and more L929 cell proliferation compared to the chitosan cross-linked only with genipin. Owning to partial blocking of free amino groups of chitosan, CSGB revealed almost no antibacterial activities, thus the bilayer composite of chitosan-silver nanoparticles (CS-AgG) on CSGB was designed to inhibit microbial invasion. The in vivo studies indicated that both CSGB and bilayer wound dressing significantly accelerated the healing rate of cutaneous wounds in mice, and the bilayer exhibited better mature epidermization with less inflammatory cells on Day 7. Therefore, this novel bilayer composite has great potential in wound dressing applications.

Formulation and in vitro evaluation of a fast-disintegrating/sustained dual release bucoadhesive bilayer tablet of captopril for treatment of hypertension crises

Hypertension crisis is one of the main health problems and its effective treatment is of high importance. For this purpose, fast-disintegrating and sustained release formulations of captopril, as a drug of choice, were prepared using conventional mucoadhesive polymers hydroxypropyl methylcellulose (HPMC), sodium carboxymethyl cellulose (Na-CMC), hydroxypropyl cellulose (HPC), Carbopol 934 (CP934) and sodium alginate (Na-alg). The optimum sustained release formulations were selected based on mean dissolution time (MDT). The swellability and mucoadhesive properties of selected formulations were assessed and compared. A direct relationship between swelling and release rates/adhesiveness of sustained release formulations was observed. The results showed that formulations containing combination of CP934 and cellulose-based polymers had the highest swellability, sustainability and adhesion strength. These formulations prolonged drug release up to 8 h showing good fitness to Korsemeyer-Peppas model. Moreover, the adopted fast-disintegrating tablet could release up to 100% of drug within 3 min in oral pH. Finally, a dual fast-disintegrating/sustained release bucoadhesive bilayer tablet consisting of optimized formulations was prepared releasing 30% of the drug initially within 15 min and the remaining up to 8 h which could be considered as an appropriate formulation for the treatment of hypertension crises.

Continuum descriptions of membranes and their interaction with proteins: Towards chemically accurate models

Biological membranes deform in response to resident proteins leading to a coupling between membrane shape and protein localization. Additionally, the membrane influences the function of membrane proteins. Here we review contributions to this field from continuum elastic membrane models focusing on the class of models that couple the protein to the membrane. While it has been argued that continuum models cannot reproduce the distortions observed in fully-atomistic molecular dynamics simulations, we suggest that this failure can be overcome by using chemically accurate representations of the protein. We outline our recent advances along these lines with our hybrid continuum-atomistic model, and we show the model is in excellent agreement with fully-atomistic simulations of the nhTMEM16 lipid scramblase. We believe that the speed and accuracy of continuum-atomistic methodologies will make it possible to simulate large scale, slow biological processes, such as membrane morphological changes, that are currently beyond the scope of other computational approaches. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.

Structural perturbation of a dipalmitoylphosphatidylcholine (DPPC) bilayer by warfarin and its bolaamphiphilic analogue: A molecular dynamics study

Compounds with nominally similar biological activity may exhibit differential toxicity due to differences in their interactions with cell membranes. Many pharmaceutical compounds are amphiphilic and can be taken up by phospholipid bilayers, interacting strongly with the lipid-aqueous interface whether or not subsequent permeation through the bilayer is possible. Bolaamphiphilic compounds, which possess two hydrophilic ends and a hydrophobic linker, can likewise undergo spontaneous uptake by bilayers. While membrane-spanning bolaamphiphiles can stabilize membranes, small molecules with this characteristic have the potential to create membrane defects via disruption of bilayer structure and dynamics. When compared to the amphiphilic therapeutic anticoagulant, warfarin, the bolaamphiphilic analogue, brodifacoum, exhibits heightened toxicity that goes beyond superior inhibition of the pharmacological target enzyme. We explore, herein, the consequences of anticoagulant accumulation in a dipalmitoylphosphatidylcholine (DPPC) bilayer. Coarse-grained molecular dynamics simulations reveal that permeation of phospholipid bilayers by brodifacoum causes a disruption of membrane barrier function that is driven by the bolaamphiphilic nature and size of this molecule. We find that brodifacoum partitioning into bilayers causes membrane thinning and permeabilization and promotes lipid flip-flop - phenomena that are suspected to play a role in triggering cell death. These phenomena are either absent or less pronounced in the case of the less toxic, amphiphilic compound, warfarin.

Dissolvable microneedle fabrication using piezoelectric dispensing technology

Dissolvable microneedle (DMN) patches are novel dosage forms for the percutaneous delivery of vaccines. DMN are routinely fabricated by dispensing liquid formulations into microneedle-shaped moulds. The liquid formulation within the mould is then dried to create dissolvable vaccine-loaded microneedles. The precision of the dispensing process is critical to the control of formulation volume loaded into each dissolvable microneedle structure. The dispensing process employed must maintain vaccine integrity. Wetting of mould surfaces by the dispensed formulation is also an important consideration for the fabrication of sharp-tipped DMN. Sharp-tipped DMN are essential for ease of percutaneous administration. In this paper, we demonstrate the ability of a piezoelectric dispensing system to dispense picolitre formulation volumes into PDMS moulds enabling the fabrication of bilayer DMN. The influence of formulation components (trehalose and polyvinyl alcohol (PVA) content) and piezoelectric actuation parameters (voltage, frequency and back pressure) on drop formation is described. The biological integrity of a seasonal influenza vaccine following dispensing was investigated and maintained voltage settings of 30 V but undermined at higher settings, 50 and 80 V. The results demonstrate the capability of piezoelectric dispensing technology to precisely fabricate bilayer DMN. They also highlight the importance of identifying formulation and actuation parameters to ensure controlled droplet formulation and vaccine stabilisation.

Mechanical transduction by ion channels: A cautionary tale

Mechanical transduction by ion channels occurs in all cells. The physiological functions of these channels have just begun to be elaborated, but if we focus on the upper animal kingdom, these channels serve the common sensory services such as hearing and touch, provide the central nervous system with information on the force and position of muscles and joints, and they provide the autonomic system with information about the filling of hollow organs such as blood vessels. However, all cells of the body have mechanosensitive channels (MSCs), including red cells. Most of these channels are cation selective and are activated by bilayer tension. There are also K⁺ selective MSCs found commonly in neurons where they may be responsible for both general anesthesia and knockout punches in the boxing ring by hyperpolarizing neurons to reduce excitability. The cationic MSCs are typically inactive under normal mechanical stress, but open under pathologic stress. The channels are normally inactive because they are shielded from stress by the cytoskeleton. The cationic MSCs are specifically blocked by the externally applied peptide GsMtx4 (aka, AT-300). This is the first drug of its class and provides a new approach to many pathologies since it is nontoxic, non-immunogenic, stable in a biological environment and has a long pharmacokinetic lifetime. Pathologies involving excessive stress are common. They produce cardiac arrhythmias, contraction in stretched dystrophic muscle, xerocytotic and sickled red cells, etc. The channels seem to function primarily as “fire alarms”, providing feedback to the cytoskeleton that a region of the bilayer is under excessive tension and needs reinforcing. The eukaryotic forms of MSCs have only been cloned in recent years and few people have experience working with them. “Newbies” need to become aware of the technology, potential artifacts, and the fundamentals of mechanics. The most difficult problem in studying MSCs is that the actual stimulus, the force applied to the channel, is not known. We don’t have direct access to the channels themselves but only to larger regions of the membrane as seen in patches. Cortical forces are shared by the bilayer, the cytoskeleton and the extracellular matrix. How much of an applied stimulus reaches the channel is unknown. Furthermore, many of these channels exist in spatial domains where the forces within a domain are different from forces outside the domain, although we often hope they are proportional. This review is intended to be a guide for new investigators who want to study mechanosensitive ion channels.

Free Volume in Membranes: Viscosity or Tension?

Many papers have used fluorescent probe diffusion to infer membrane viscosity but the measurement is actually an assay of the free volume of the membrane. The free volume is also related to the membrane tension. Thus, changes in probe mobility refer equally well to changes in membrane tension. In complicated structures like cell membranes, it appears more intuitive to consider variations in free volume as referring to the effect of domains structures and interactions with the cytoskeleton than changes in viscosity since tension is a state variable and viscosity is not.