To Close or to Collapse: The Role of Charges on Membrane Stability upon Pore Formation.

Resealing of membrane pores is crucial for cell survival. Membrane surface charge and medium composition are studied as defining regulators of membrane stability. Pores are generated by electric field or detergents. Giant vesicles composed of zwitterionic and negatively charged lipids mixed at varying ratios are subjected to a strong electric pulse. Interestingly, charged vesicles appear prone to catastrophic collapse transforming them into tubular structures. The spectrum of destabilization responses includes the generation of long-living submicroscopic pores and partial vesicle bursting. The origin of these phenomena is related to the membrane edge tension, which governs pore closure. This edge tension significantly decreases as a function of the fraction of charged lipids. Destabilization of charged vesicles upon pore formation is universal-it is also observed with other poration stimuli. Disruption propensity is enhanced for membranes made of lipids with higher degree of unsaturation. It can be reversed by screening membrane charge in the presence of calcium ions. The observed findings in light of theories of stability and curvature generation are interpreted and mechanisms acting in cells to prevent total membrane collapse upon poration are discussed. Enhanced membrane stability is crucial for the success of electroporation-based technologies for cancer treatment and gene transfer.

Molecular Interpretation of the Compaction Performance and Mechanical Properties of Caffeine Cocrystals: A Polymorphic Study.

The 1:1 caffeine (CAF) and 3-nitrobenzoic acid (NBA) cocrystal (CAF:NBA) displays polymorphism. Each polymorph shares the same docking synthon that connects individual CAF and NBA molecules within the asymmetric unit; however, the extended intermolecular interactions are significantly different between the two polymorphic modifications. These alternative interaction topologies translate to distinct structural motifs, mechanical properties, and compaction performance. To assist our molecular interpretation of the structure-mechanics-performance relationships for these cocrystal polymorphs, we combine powder Brillouin light scattering (p-BLS) to determine the mechanical properties with energy frameworks calculations to identify potentially available slip systems that may facilitate plastic deformation. The previously reported Form 1 for CAF:NBA adopts a 2D-layered crystal structure with a conventional 3.4 Å layer-to-layer separation distance. For Form 2, a columnar structure of 1D-tapes is displayed with CAF:NBA dimers running parallel to the (110) crystallographic direction. Consistent with the layered crystal structure, the shear modulus for Form 1 is significantly reduced relative to Form 2, and moreover, our p-BLS spectra for Form 1 clearly display the presence of low-velocity shear modes, which support the expectation of a low-energy slip system available for facile plastic deformation. Our energy frameworks calculations confirm that Form 1 displays a favorable slip system for plastic deformation. Combining our experimental and computational data indicates that the structural organization in Form 1 of CAF:NBA improves the compressibility and plasticity of the material, and from our tabletability studies, each of these contributions confers superior tableting performance to that of Form 1. Overall, mechanical and energy framework data permit a clear interpretation of the functional performance of polymorphic solids. This could serve as a robust screening approach for early pharmaceutical solid form selection and development.

Velocity dispersion and backscatter in marrow-filled and water-filled trabecular bone samples in vitro.

The phase velocity and the backscatter coefficient were measured in 28 bovine femoral trabecular bone samples filled with marrow and water in vitro from 0.2 to 0.6 MHz. The phase velocities decreased approximately linearly with increasing frequency and the average dispersion rate of -34 ms-1 MHz-1 in the marrow-filled samples was higher than that of -42 ms-1 MHz-1 in the water-filled samples. The backscatter coefficients exhibited nonlinear, monotonically increasing dependences on the frequency and the average value of the exponent n = 2.92 (frequency dependence) in the marrow-filled samples was higher than the value of n = 2.79 in the water-filled samples.

Nanoscale Control over the Mixing Behavior of Surface-Confined Bicomponent Supramolecular Networks Using an Oriented External Electric Field.

Strong electric fields are known to influence the properties of molecules as well as materials. Here we show that by changing the orientation of an externally applied electric field, one can locally control the mixing behavior of two molecules physisorbed on a solid surface. Whether the starting two-component network evolves into an ordered two-dimensional (2D) cocrystal, yields an amorphous network where the two components phase separate, or shows preferential adsorption of only one component depends on the solution stoichiometry. The experiments are carried out by changing the orientation of the strong electric field that exists between the tip of a scanning tunneling microscope and a solid substrate. The structure of the two-component network typically changes from open porous at negative substrate bias to relatively compact when the polarity of the applied bias is reversed. The electric-field-induced mixing behavior is reversible, and the supramolecular system exhibits excellent stability and good response efficiency. When molecular guests are adsorbed in the porous networks, the field-induced switching behavior was found to be completely different. Plausible reasons behind the field-induced mixing behavior are discussed.

Model for Porosity Changes Occurring during Ultrasound-Enhanced Transcorneal Drug Delivery.

Ultrasound-enhanced drug delivery through the cornea has considerable therapeutic potential. However, our understanding of how ultrasound enhances drug transport is poor, as is our ability to predict the increased level of transport for given ultrasound parameters. Described here is a computational model for quantifying changes in corneal porosity during ultrasound exposure. The model is calibrated through experiments involving sodium fluorescein transport through rabbit cornea. Validation was performed using nylon filters, for which the properties are known. It was found that exposure to 800-kHz ultrasound at an intensity 2 W/cm2 for 5 min increased the porosity of the epithelium by a factor of 5. The model can be useful for determining the extent to which ultrasound enhances the amount of drug transported through biological barriers, and the time at which a therapeutic dose is achieved at a given location, for different drugs and exposure strategies.

Imaging the dynamics of individual electropores.

Electroporation is a widely used technique to permeabilize cell membranes. Despite its prevalence, our understanding of the mechanism of voltage-mediated pore formation is incomplete; methods capable of visualizing the time-dependent behavior of individual electropores would help improve our understanding of this process. Here, using optical single-channel recording, we track multiple isolated electropores in real time in planar droplet interface bilayers. We observe individual, mobile defects that fluctuate in size, exhibiting a range of dynamic behaviors. We observe fast (25 s(-1)) and slow (2 s(-1)) components in the gating of small electropores, with no apparent dependence on the applied potential. Furthermore, we find that electropores form preferentially in the liquid disordered phase. Our observations are in general supportive of the hydrophilic toroidal pore model of electroporation, but also reveal additional complexity in the interactions, dynamics, and energetics of electropores.

Characterisation of potato crisp effective porosity using micro-CT.

BACKGROUND: The effective porosity is an important quantitative parameter for food products that has a significant effect on taste and quality. It is challenging to quantify the apparent porosity of fried potato crisps as they have a thin irregularly shaped cross section containing oil and water. This study uses a novel micro-CT technique to determine the solid volume fraction and hence the effective porosity of three types of potato crisps: standard continuously fried crisps, microwaved crisps, and continuously fried 'kettle' crisps. RESULTS: It was found that continuously fried kettle crisps had the lowest effective porosity at 0.54, providing the desired crunchy taste and lower oil contents. Crisps produced using a microwave process designed to mimic the dehydration process of standard continuous fried crisps had an effective porosity of 0.65, which was very similar to the effective porosity of 0.63 for standard continuously fried crisps. The results were supported by the findings of a forced preference consumer test. CONCLUSION: The effective porosity affects the product taste and is therefore a critical parameter. This study shows that micro-CT analysis can be used to characterise the change in effective porosity of a thin irregularly shaped food product, caused by a change of cooking procedure. © 2016 Society of Chemical Industry.

The Role of Pulse Repetition Rate in nsPEF-Induced Electroporation: A Biological and Numerical Investigation.

The impact of pulse repetition rate (PRR) in modulating electroporation (EP) induced by nanosecond pulsed electric fields (nsPEFs) in mammalian cells was approached here by performing both biological and numerical analysis. Plasma membrane permeabilization and viability of Jurkat cells were analyzed after exposure to 500, 1.3 MV/m, 40 ns PEFs with variable PRR (2-30 Hz). A finite-element model was used to investigate EP dynamics in a single cell under the same pulsing conditions, by looking at the time course of transmembrane voltage and pore density on the ns time scale. The biological observations showed an increased EP and reduced viability of the exposed cells at lower PRR in the considered range. The numerical analysis resulted in different dynamics of plasma membrane response when ns pulses were delivered with different PRR, consistently with a phenomenon of electrodesensitization recently hypothesized by another research group.

Femtosecond laser high-efficiency drilling of high-aspect-ratio microholes based on free-electron-density adjustments.

We studied the micromachining of high-aspect-ratio holes in poly(methylmethacrylate) using a visible double-pulse femtosecond laser based on free-electron-density adjustments. Hole depth and aspect ratio increased simultaneously upon decreasing the wavelength in the visible-light zone. When the pulse energy reached a high level, the free-electron density was adjusted by using a double-pulse laser, which induced fewer free electrons, a lower reflectivity plasma plume, and more pulse energy deposition in the solid bottom. Thus, the aspect ratio of the hole was improved considerably. At a moderate pulse energy level, a 1.3-1.4 times enhancement of both the ablation depth and the aspect ratio was observed when the double-pulse delay was set between 100 and 300 fs, probably due to an enhanced photon-electron coupling effect through adjusting the free-electron density. At a lower pulse energy level, this effect also induced the generation of a submicrometer string. In addition, the ablation rate was improved significantly by using visible double pulses.

Effect of ultrasonication on physical properties of mineral trioxide aggregate.

AIM: To evaluate the effect on physical properties of Mineral Trioxide Aggregate (MTA) of using direct hand compaction during placement and when using hand compaction with indirect ultrasonic activation with different application times. METHODS: One hundred acrylic canals were obturated in 3 increments with MTA in sample sizes of 10. One group was obturated by hand with an endodontic plugger and the remainder obturated with indirect ultrasonic application, with times ranging from 2 seconds to 18 seconds per increment. Microhardness values, dye penetration depths, and radiographs of the samples were evaluated. RESULTS: As ultrasonic application time per increment increased, microhardness values fell significantly (P < 0.001) while dye penetration values increased (P < 0.001). Microhardness of MTA ultrasonicated for 2 seconds was significantly higher than hand compaction (P = 0.03). Most radiographic voids were visible in the hand-compacted group (P < 0.001), which also had higher dye penetration depths than the 2-second ultrasonicated samples. Ultrasonication of MTA for 10-18 seconds resulted in significantly more voids than 2-8 seconds of ultrasonication (P = 0.02). CONCLUSION: The use of ultrasonics with MTA improved the compaction and flow of MTA, but excessive ultrasonication adversely affected MTA properties. A time of 2 seconds of ultrasonication per increment presented the best compromise between microhardness values, dye penetration depths, and lack of radiographic voids.

Evidence that pulsed electric field treatment enhances the cell wall porosity of yeast cells.

The application of rectangular electric pulses, with 0.1-2 ms duration and field intensity of 2.5-4.5 kV/cm, to yeast suspension mediates liberation of cytoplasmic proteins without cell lysis. The aim of this study was to evaluate the effect of pulsed electric field with similar parameters on cell wall porosity of different yeast species. We found that electrically treated cells become more susceptible to lyticase digestion. In dependence on the strain and the electrical conditions, cell lysis was obtained at 2-8 times lower enzyme concentration in comparison with control untreated cells. The increase of the maximal lysis rate was between two and nine times. Furthermore, when applied at low concentration (1 U/ml), the lyticase enhanced the rate of protein liberation from electropermeabilized cells without provoking cell lysis. Significant differences in the cell surface of control and electrically treated cells were revealed by scanning electron microscopy. Data presented in this study allow us to conclude that electric field pulses provoke not only plasma membrane permeabilization, but also changes in the cell wall structure, leading to increased wall porosity.

Near-infrared femtosecond laser-triggered nanoperforation of hollow microcapsules.

Fabrication of a nanopore in a hollow microcapsule was demonstrated using near-infrared femtosecond laser irradiation. The shape of the irradiated microcapsules was kept spherical except for a pore in the shell owing to the nonthermal processing by a femtosecond laser. The simulation results for the near-field and far-field scattering around a microcapsule revealed that highly-enhanced optical intensity can be generated at a spot on the shell of a microcapsule, which would in turn contribute to localized ablation. To the best of our knowledge, this is the first demonstration of the nanoperforation of transparent hollow microcapsules by a near-infrared laser without any doping with absorbing metals or dyes that may cause cell toxicity. The presented method is a promising approach for safer drug delivery and the controlled release of therapeutic drugs.

Electrically pumped random lasing from FTO/porous insulator/n-ZnO/p(+)-Si devices.

Electrically pumped random lasing (RL) has been realized in FTO/porous insulator/n-ZnO/p(+)-Si devices. It is demonstrated that RL originates from the confining and recurrent scattering of light in the random cavities within the insulating layer, which are formed due to the glow discharge. The glow discharge also induces the observed negative differential resistance (NDR) effect following the normal I-V characteristics. The results present a new strategy to realize electrically pumped RL in ZnO-based metal-insulator-semiconductor device by simply modifying the morphology of the insulating layer.

Hierarchically porous materials from layer-by-layer photopolymerization of high internal phase emulsions.

A combination of high internal phase emulsion (HIPE) templating and additive manufacturing technology (AMT) is applied for creating hierarchical porosity within an acrylate and acrylate/thiol-based polymer network. The photopolymerizable formulation is optimized to produce emulsions with a volume fraction of droplet phase greater than 80 vol%. Kinetic stability of the emulsions is sufficient enough to withstand in-mold curing or computer-controlled layer-by-layer stereolithography without phase separation. By including macroscale cellular cavities within the build file, a level of controlled porosity is created simultaneous to the formation of the porous microstructure of the polyHIPE. The hybrid HIPE-AMT technique thus provides hierarchically porous materials with mechanical properties tailored by the addition of thiol chain transfer agent.

A stimuli-responsive nanopore based on a photoresponsive host-guest system.

The open-close states of the ion channels in a living system are regulated by multiple stimuli such as ligand, pH, potential and light. Functionalizing natural channels by using synthetic chemistry would provide biological nanopores with novel properties and applications. Here we use para-sulfonato-calix[4]arene-based host-guest supramolecular system to develop artificial gating mechanisms aiming at regulating wild-type α-HL commanded by both ligand and light stimuli. Using the gating property of α-hemolysin, we studied the host-guest interactions between para-sulfonato-calix[4]arene and 4, 4'-dipyridinium-azobenzene at the single-molecule level. Subsequently, we have extended the application of this gating system to the real-time study of light-induced molecular shuttle based on para-sulfonato-calix[4]arene and 4, 4'-dipyridinium-azobenzene at the single-molecule level. These experiments provide a more efficient method to develop a general tool to analyze the individual motions of supramolecular systems by using commercially available α-HL nanopores.

Self-sacrificial templating synthesis of porous quaternary Cu-Fe-Sn-S semiconductor nanotubes via microwave irradiation.

Uniform quaternary Cu(2)FeSnS(4) (CITS) nanotubes of outer diameter 400-800 nm and thickness 100-200 nm have been synthesized for the first time by a simple, rapid and easily scaled-up microwave nonaqueous route using benzyl alcohol as the microwave absorbing solvent. An interesting in situ generated one-dimensional Cu(Tu)Cl nanorod acting as a self-sacrificial template was crucial for the formation of the well-defined CITS nanotubes. Based on the designed time-dependent experiments, a formation mechanism for the CITS nanotubes was also proposed. The resulting CITS nanotubes had a strong absorption in the visible region with a bandgap of 1.71 eV that was optimal for photovoltaic applications. Our study provided a microwave nonaqueous route generally applicable for the synthesis of quaternary chalcogenide semiconductor nanotubes.

Cascaded photoinduced drug delivery to cells from multifunctional core-shell mesoporous silica.

Different bioactive molecules are released into living cells from lipid-covered mesoporous silica nanoparticles. The release is triggered by light, as the particles feature covalently attached photosensitizers as membrane-opening agents. It is demonstrated that the particles achieve endosomal escape and that they release their cargo into the cytosol.

Thirty-minute total synthesis of microfluidic systems and functionalized porous elements via "living" radical photo-polymerization.

A "living" radical photo-polymerization (LRPP) technique is used to rapidly fabricate microfluidic channels and micro-patterned porous polymer monoliths. Surface-initiated LRPP is then used to functionalize porous elements in a robust one-step surface modification process. Assay-ready platforms can be fully realized in less than 30 minutes. An application relevant to clinical diagnostics is presented.

Porous carbon spheres from energetic carbon precursors using ultrasonic spray pyrolysis.

Porous carbon spheres with unique structures and morphologies are prepared from energetic carbon precursors, alkali propiolates, via ultrasonic spray pyrolysis. Aerosolized liquid droplets containing alkali propiolates act as microreactors that confine the thermal decomposition of energetic precursors and lead to the formation of several unprecedented carbon morphologies.

Tailoring galvanic replacement reaction for the preparation of Pt/Ag bimetallic hollow nanostructures with controlled number of voids.

Here we report the synthesis of Pt/Ag bimetallic nanostructures with controlled number of void spaces via a tailored galvanic replacement reaction (GRR). Ag nanocubes (NCs) were employed as the template to react with Pt ions in the presence of HCl. The use of HCl in the GRR caused rapid precipitation of AgCl, which grew on the surface of Ag NCs and acted as a removable secondary template for the deposition of Pt. The number of nucleation sites for AgCl was tailored by controlling the amount of HCl added to the Ag NCs or by introducing PVP to the reaction. This strategy led to the formation of Pt/Ag hollow nanoboxes, dimers, multimers, or popcorn-shaped nanostructures consisting of one, two, or multiple hollow domains. Due to the presence of large void space and porous walls, these nanostructures exhibited high surface area and improved catalytic activity for methanol oxidation reaction.