The Relationship Between the Rigidity of the Liposomal Membrane and the Absorption of Insulin After Nasal Administration of Liposomes Modified with an Enhancer Containing Insulin in Rabbits

The relationship between the rigidity of the liposomal membrane and the absorption of insulin after nasal administration of liposomes modified with an enhancer containing insulin was investigated for the nasal delivery of peptide drugs in rabbits. The rigid liposomal membrane makes liposomes stable, protecting insulin from enzymatic degradation. Soybean-derived sterol (SS) or its sterylglucoside (SG) was used as an enhancer. Dipalmitoylphosphatidylcholine (DPPC) liposomes modified with SG had increased fluidity of the hydrophobic group of the liposome bilayer compared with the liposomes modified with cholesterol (Ch) or SS, as shown by measurements of the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5,-hexatriene (DPH); however, the fluidity of the polar group of the liposome bilayer was decreased according to measurements of steady-state fluorescence anisotropy of dansylhexadecylamine (DSHA) at 37°C. These findings suggest that the fluidity of the hydrophobic group of the liposome bilayer is responsible for the increase of liposomal leakage and instability of the liposomes. When insulin was administered nasally to rabbits as a solution, no hypoglycemic effect was observed. The administration of insulin contained in DPPC/SG (7/4, mole) liposomes with high fluidity caused a high glucose reduction of long duration (8 hr). DPPC/SS and DPPC/Ch (7/4) liposomes with low fluidity caused low glucose reductions. These results demonstrated that liposomes modified with SG can be useful as carriers of insulin administered nasally.     

Biomimetic interfaces based on S-layer proteins,lipid membranes and functional biomolecules

Designing and utilization of biomimetic membrane systems generated by bottom-up processes is a rapidly growing scientific and engineering field. Elucidation of the supramolecular construction principle of archaeal cell envelopes composed of S-layer stabilized lipid membranes led to new strategies for generating highly stable functional lipid membranes at meso- and macroscopic scale. In this review, we provide a state-of-the-art survey of how S-layer proteins, lipids and polymers may be used as basic building blocks for the assembly of S-layer-supported lipid membranes. These biomimetic membrane systems are distinguished by a nanopatterned fluidity, enhanced stability and longevity and, thus, provide a dedicated reconstitution matrix for membrane-active peptides and transmembrane proteins. Exciting areas in the (lab-on-a-) biochip technology are combining composite S-layer membrane systems involving specific membrane functions with the silicon world. Thus, it might become possible to create artificial noses or tongues, where many receptor proteins have to be exposed and read out simultaneously. Moreover, S-layer-coated liposomes and emulsomes copying virus envelopes constitute promising nanoformulations for the production of novel targeting, delivery, encapsulation and imaging systems.     

Silica ceramic nanofiber membrane with ultra-softness and high temperature insulation

Silica ceramic nanofiber (SCNF) membranes with ultra-softness were fabricated by electrospinning and precursor derived ceramic technology. Firstly, the precursor fiber membrane was obtained by electrospinning from spinnable precursor sol, which was prepared by using silica sol as raw material and polyvinyl alcohol (PVA) as spinning aid, and after heat treatment, it was converted into the SCNF membrane composed of pure inorganic components, which had the ultra-softness to restore the original shape after arbitrary folding. Then the effects of different PVA dosages and heat treatment temperatures on the fiber morphology, thermal stability, mechanical properties, and thermal conductivity of SCNF membranes were investigated. Among all the membranes, the SCNF membrane that was made with a precursor sol of 5% PVA and sintered at 900 °C (Ss?+?PVA 5%-900 °C) showed the smoothest as well as the most uniform fiber morphology, with an average fiber diameter of 285.19 nm, a density of 0.106 g cm^?3, the best mechanical properties (tensile strength of 4.145 MPa), and it also had the lowest thermal conductivity of 0.05285 Wm^?1 K^?1. The Ss?+?PVA 5%-900 °C SCNF membrane still maintained intact fiber morphology after being treated at 1200 °C. These excellent properties make the SCNF membrane have a potential application prospect as an insulation material in ultra-high temperature environments.

     

Interaction of Soybean Oil with Phosphatidylcholine and Their Formation of Small Dispersed Particles

Stable aqueous dispersions of soybean oil (SO) were obtained by cosonication with dipalmitoylphosphatidylcholine (DPPC) in the SO mole fraction range 0.1–0.8. To clarify the dispersal mechanism, the dispersed particles were characterized, and the interaction between SO and DPPC was investigated using several physicochemical techniques. Dynamic light scattering (DLS) measurements showed that the diameter of the dispersed particles was 40–60 nm. The trapped aqueous volume inside the particles was determined fluorometrically using the aqueous space marker calcein. The trapped volume in the SO/DPPC particles decreased remarkably with the addition of SO into small unilamellar vesicles of DPPC. The decline in fraction of vesicular particles was also confirmed by fluorescence quenching of N-dansylhexadecylamine in the DPPC membrane by the addition of the quencher CuSO₄. These results indicate that the excess SO separated from the DPPC bilayers is stabilized as emulsion particles by the DPPC surface monolayer. Monolayer-bilayer equilibrium of SO/DPPC mixtures was estimated by measurement of spreading and collapse pressures. The results showed that the coexistence of emulsion particles (surface monolayer of DPPC + core of SO) with vesicular particles (bilayer) was critically important for the formation of stably dispersed particles of the lipid mixture.     

Interaction of ubiquinone-10 with dipalmitoylphosphatidylcholine and their formation of small dispersed particles

Stable aqueous dispersions of ubiquinone-10 (UQ) were obtained by cosonication with dipalmitoylphosphatidylcholine (DPPC) in the UQ mole fraction range 0.1-0.7. To clarify the dispersal mechanism, the dispersed particles were characterized, and the interaction between UQ and DPPC was investigated using several physicochemical techniques. Dynamic light scattering (DLS) measurements showed that the diameter of the dispersed particles was 50-70 nm. A limited amount of UQ was incorporated into DPPC bilayer membranes (approximately 5 mol%). The trapped aqueous volume inside the particles was determined fluorometrically using the aqueous space marker calcein, and the volume in the UQ/DPPC particles decreased remarkably with the addition of UQ into small unilamellar vesicles of DPPC. The decline in the fraction of vesicular particles was also confirmed by fluorescence quenching of N-dansylhexadecylamine in the DPPC membrane by the addition of the quencher CuSO₄. These results indicate that the excess UQ separated from the DPPC bilayers is stabilized as emulsion particles by the DPPC surface monolayer.     

In Vitro Interaction of Sized and Unsized Liposome Vesicles with High Density Lipo Proteins

An in vitro method of interaction of liposome vesicles with high density lipoproteins (HDL) was studied. A formulation of lipids was hydrated, and homogenized with a high shear mixer and designed as “unsized” liposomes. A portion of this preparation was further processed by passing through a polycarbonate membrane and it is labelled as “sized”. Both these preparations were incubated with HDL. Destabilization rate of liposome preparations in presence of HDL was determined. Time course of drug release from sized and unsized liposomes was followed upon HDL addition to liposomes. These in vitro studies clearly showed that HDL destabilized the small sized liposomes (0.25 ± 0.09 Hm). The destabilization effect of HDL on unsized is not significant.     

Polymeric amine membrane materials for carbon dioxide (CO2)/methane (CH4) separation

Carbon dioxide separation from methane using membrane technology is getting attraction, and polymeric membranes are the most prominent polymer membrane materials. However, the existing polymeric membranes performance is inadequate due to trade-off limitation open new windows to explore. Therefore, in this study, amine polymeric membrane (APM) has been fabricated by the addition of different concentration (5 wt.% and 15 wt.%) of diethanolamine (DEA). The developed amine polymeric membranes have been characterized in term of morphology and thermal analysis using field emission scanning electron microscope and thermogravimetric analyzer, respectively. The permeance and selectivity have been determined by using pure carbon dioxide (CO₂) and methane (CH₄). Also, the effect of amine concentration on permeance and selectivity has been studied. The results confirmed the symmetric and homogenous structure and thermal stability of membranes up to 490 °C. The maximum percent increase by the 15 wt.% addition of diethanolamine is 102.08 % at 10 bar pressure.     

Oleyl group-functionalized insulating gate transistors for measuring extracellular pH of floating cells

The extracellular ionic microenvironment has a close relationship to biological activities such as by cellular respiration, cancer development, and immune response. A system composed of ion-sensitive field-effect transistors (ISFET), cells, and program-controlled fluidics has enabled the acquisition of real-time information about the integrity of the cell membrane via pH measurement. Here we aimed to extend this system toward floating cells such as T lymphocytes for investigating complement activation and pharmacokinetics through alternations in the plasma membrane integrity. We functionalized the surface of tantalum oxide gate insulator of ISFET with oleyl-tethered phosphonic acid for interacting with the plasma membranes of floating cells without affecting the cell signaling. The surface modification was characterized by X-ray photoelectron spectroscopy and water contact angle measurements. The Nernst response of ?37.8 mV/pH was obtained for the surface-modified ISFET at 37 °C. The oleyl group-functionalized gate insulator successfully captured Jurkat T cells in a fluidic condition without acute cytotoxicity. The system was able to record the time course of pH changes at the cells/ISFET interface during the process of instant addition and withdrawal of ammonium chloride. Further, the plasma membrane injury of floating cells after exposure by detergent Triton? X-100 was successfully determined using the modified ISFET with enhanced sensitivity as compared with conventional hemolysis assays.     

Interaction of soybean oil with phosphatidylcholine and their formation of small dispersed particles

Stable aqueous dispersions of soybean oil (SO) were obtained by cosonication with dipalmitoylphosphatidylcholine (DPPC) in the SO mole fraction range 0.1-0.8. To clarify the dispersal mechanism, the dispersed particles were characterized, and the interaction between SO and DPPC was investigated using several physicochemical techniques. Dynamic light scattering (DLS) measurements showed that the diameter of the dispersed particles was 40-60 nm. The trapped aqueous volume inside the particles was determined fluorometrically using the aqueous space marker calcein. The trapped volume in the SO/DPPC particles decreased remarkably with the addition of SO into small unilamellar vesicles of DPPC. The decline in fraction of vesicular particles was also confirmed by fluorescence quenching of N-dansylhexadecylamine in the DPPC membrane by the addition of the quencher CuSO₄. These results indicate that the excess SO separated from the DPPC bilayers is stabilized as emulsion particles by the DPPC surface monolayer. Monolayer-bilayer equilibrium of SO/DPPC mixtures was estimated by measurement of spreading and collapse pressures. The results showed that the coexistence of emulsion particles (surface monolayer of DPPC + core of SO) with vesicular particles (bilayer) was critically important for the formation of stably dispersed particles of the lipid mixture.     

Chitosan effect on the mesophase behavior of phosphatidylcholine supramolecular systems

Two distinct supramolecular self assemblies of phosphatidylcholine and chitosan, namely liposomes and their precursory organogel, have been investigated by means of SAXS, Light Scattering and Polarized Optical Microscopy. The main goal was the evaluation of the chitosan effect on the self assemblies phase transition behavior upon heating. A distinct smectic organization was observed for the organogel prepared in the presence of chitosan, if compared to that prepared only with phosphatidylcholine. In addition, the phosphatidylcholine–chitosan organogel showed unchanged optical properties upon heating and after 24 h, indicating increased stability when compared to the organogel prepared without chitosan. For the liposomes containing chitosan, the thermotropic behavior features a lamellar pattern that is preserved under heating, until at least 81 °C. A phase transition temperature has been determined around 64 °C, which was clearly higher than that observed for liposomes prepared without chitosan. The bilayer repeat distance typical of the liposomes increases slowly by increasing the temperature and stacking fluctuations of the bilayers are delayed due to enhancement of the membrane rigidity.     

Effect of human plasma on the stability of large multilamellar liposomes with digitoxin

Abstract

The stability of multilamellar liposomes with digitoxin in human plasma at 37° C is studied “in vitro”. It is noted that as plasma/liposomal suspension ratio is increased, the porcentage of drug retained in the liposomes decreases. Just so, independently from the dosage form, the efflux rate is maximum during the first hour and then falls gradually and in a non linear way. The physical state of the bilayer is a conditioning factor in the release of the encapsulated drug. The dosage forms of egg yolk phosphatidylcholine (EYPC) and of dimiristoylphosphatidylcholine (DMPC) quickly release digitoxin; while dipalmitoylphosphatidylcholine (DPPC) retains 54% of the entrapped drug after 24 hours incubation with 80% of plasma at 37°C. The inclusion of cholesterol (CHOL) and dicetylphosphate (DCP) in the liposomal matrix neither aids in the incorporation of digitoxin to the liposomes, nor augments the stability of the system in the human plasma.     

Microstructural studies of self-supported (1.5–10 μm) Pd/23 wt%Ag hydrogen separation membranes subjected to different heat treatments

The microstructure of self-supported 1.5–10-μm thick Pd/23 wt%Ag membranes grown by magnetron sputtering have been studied after heat treatment and hydrogen permeation tests using electron microscopy and synchrotron X-ray diffraction. After hydrogen flux stabilization and permeance measurements at 300 °C, the membranes were annealed in air at 300 °C or in N₂/Ar at 300/400/450 °C for 4 days and then tested for hydrogen permeation. The permeation results show that changes in permeability depend on the treatment atmosphere and temperature, as well as membrane thickness. Air treatment at ~300 °C generally induced a positive effect on permeation in the thickness range of 1.5–10 μm. Significant microstructural changes, including grain growth, strain relief, void formation, and growth of nodules occurred in the membranes. The changes in microstructure are more severe for the thinner membranes, and may be attributed mainly to the oxidation processes at or near the surface. For samples annealed in N₂/Ar, enhanced permeation was only obtained with treatment at ~450 °C for 5 and 10 μm. The changes in the microstructure generally increased with heat-treatment temperature, and decreased with membrane's thickness. The membrane with enhanced permeation was accompanied by significant grain growth, strain relief, and surface roughening. For all the membranes, the relative changes in the microstructure were substantially more prominent on the permeate surface than on the feed surface. Details of the analysis are presented and discussed.     

Determination of Vanadyl Ions by a New PVC Membrane Sensor Based on N, N'-bis-(Salicylidene)-2,2-Dimethylpropane-1,3-Diamine

N, N'-bis-(salicylidene)-2,2-dimethylpropane-1,3-diamine (NNPD) was found to be a suitable neutral ion carrier for the construction of a highly selective and sensitive vanadyl membrane sensor. Poly(vinyl chloride) (PVC) based membranes of NNPD with potassium tetrakis (p-chlorophenyl) borate (KTpCIPB) as an anionic excluder and diethyl sebacate (DES), dibutyl phthalate (DBP), banzyl acetate (BA) and o-nitrophenyloctyl ether (NPOE) as plasticizing solvent mediators were investigated in vanadyl membrane sensors. A membrane, composed of NNPD-PVC-KTpCIPB-DES with the ratio 4.0:30.0:1.0:65.0, works well over a wide concentration range (7.0 times 10^-6 to 1.0 times 10 ^-2 M) with a Nernstian slope of 28.8plusmn0.3 mV per decade of activity between pH values of 4.0 and 5.10. The detection limit of the sensor was calculated to be 5.0 times 10^-6 M. It displays satisfactorily good discrimination toward vanadyl ions with regard to most common transitional metal ions. The proposed sensor demonstrates a short response time (-10 s). It was successfully applied for the determination of vanadyl ions in water samples     

Immobilization of liposomes in nanostructured layer-by-layer films containing dendrimers

Artificial vesicles or liposomes composed of lipid bilayers have been widely exploited as building blocks for artificial membranes, in attempts to mimic membrane interaction with drugs and proteins and to investigate drug delivery processes. In this study we report on the immobilization of liposomes of 1,2-dipalmitoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (Sodium Salt) (DPPG) in layer-by-layer (LbL) films, alternated with poly(amidoamine) G4 (PAMAM) dendrimer layers. The average size of the liposomes in solution was 120 nm as determined by dynamic light scattering, with their spherical shape being inferred from scanning electron microscopy (SEM) in cast films. LbL films containing up to 20 PAMAM/DPPG bilayers were assembled onto glass and/or silicon wafer substrates. The growth of the multilayers was achieved by alternately immersing the substrates into the PAMAM and DPPG solutions for 5 and 10 min, respectively. The formation of PAMAM/DPPG liposome multilayers and its ability to interact with BSA were confirmed by Fourier transform infrared spectroscopy (FTIR). The structural features and film thickness were obtained using X-ray diffraction and surface plasmon resonance (SPR).     

Template assisted synthesis of porous nanofibrous cellulose membranes for tissue engineering

Porous, nanofibrous bacterial cellulose (BC) membranes were produced by the bacterium Acetobacter xylinum. The bacterium was cultivated in an appropriate culture medium under static conditions. In situ pore formation was attained through the use of pin templates with diameters varying from 60 to 300 μm composed of polyestirene (ϕ = 300 μm) or optical fibers (ϕ = 60 μm), which were placed on culture medium with the pins immersed in the liquid. Cellulose biosynthesis occurred around the pins leaving tiny pores on the cellulose membrane. After removal of the template the biofilm was dried at 50 °C/24 h. Physico-chemical properties of BC membranes, like degree of crystallinity, swelling and tensile strength were not significantly altered after pore formation. Microstructure evaluation revealed that the film matrix is composed of long nanofibers isotropically distributed on its surface. Round-shaped pores with diameters varying between 60 and 300 μm, depending on the pin template used, were formed in the cellulose membranes. These pores exhibited no border failures that could start crack propagation along the film surface. Microporous membranes could be useful for applications in repairing tissues, which require high oxygenation rates or wound contracture delay.     

Thermodynamic and structural studies of mixed monolayers: Mutual mixing of DPPC and DPPG with DoTAP at the air–water interface

Phospholipid monomolecular films at the air–water interface are useful model membranes to understand miscibility among various components. Surface pressure (π)–area (A) isotherms of pure and mixed monolayers of dioleoyltrimethylammonium propane (DoTAP)–dipalmitoylphosphatidylcholine (DPPC) and DoTAP–dipalmitoyphosphatidylglycerol (DPPG) were constructed using a surface balance. DPPC and DPPG produced isotherms as expected and reported earlier. DoTAP, an unsaturated lipid, demonstrated a continuous π–A isotherm. Associative interactions were identified in DPPC–DoTAP mixtures compared to the pure components, while DPPG–DoTAP mixtures showed repulsive interaction up to an equimolar ratio. Compression moduli of the monolayers revealed that DPPC–DoTAP mixtures had increasing stability with increasing surface pressure, but addition of DoTAP to DPPG showed instability at low and intermediate concentrations. In both cases increased stability was returned at higher X_DoTAP values and surface pressures. Lipid monolayer film thickness values, determined on a gold coated glass substrate by surface plasmon resonance spectroscopy (SPR), indicated a systematic change in height profile for DPPC–DoTAP mixtures with increasing X_DoTAP. However, DPPG–DoTAP mixed monolayer systems demonstrated a biphasic response. The SPR data were in excellent agreement with our interpretation of the structure of solid supported lipid monolayers.     

Optical trapping of unilamellar phospholipid vesicles: investigation of the effect of optical forces on the lipid membrane shape by confocal-Raman microscopy

Optical trapping of liposomes is a useful tool for manipulating these lipid vesicles for sampling, mechanical testing, spectroscopic observation, and chemical analysis. Through the use of confocal Raman microscopy, this study addresses the effects of optical forces on the structure of unilamellar, dipalmitoylphosphatidylcholine (DPPC) vesicles, both optically trapped in solution and adhered to a coverslip. The energy and forces involved in optical trapping of lipid vesicles were derived in terms of the dielectric contrast between the phospholipid membrane and the surrounding solution; reflection forces at the membrane/water interface were found to be negligible. At optical powers of 9 mW and greater, unilamellar liposomes trapped in bulk solution experience a gradient force sufficiently strong to bend the vesicle membrane, so that a second bilayer from the same vesicle is drawn into the optical trap, with an energy of approximately 6 x 10(-13) erg. For vesicles adhered to a coverslip, the confocal probe can be scanned through the attached vesicle. Optical forces are insufficient to detach the bilayer that is adhered to the glass; however, the upper DPPC bilayer can be manipulated by the optical trap and the shape of the vesicle distorted from a spherical geometry. The effect of calcium ion on the flexibility of membrane bilayers was also tested; with 5 mM calcium ion in solution, the lipid bilayer of a surface-attached liposome is sufficiently rigid so that it cannot be distorted at moderate laser powers.     

Carbon nanofibers produced from modified electrospun PAN/hydroxyapatite precursors as scaffolds for bone tissue engineering

In the current study we have proposed a method to obtain a carbon/HAp bioactive nanofibrous scaffold. The modified carbon nanofibrous nonwoven' fabrics were obtained by the use of electrospinning and subsequent stabilization and carbonization processes. The modified with HAp powder nanofibrous PAN nonwovens were thermally stabilized using a multi-stage process in the temperature ranging from 100 °C to 300 °C in an oxidative environment and then carbonized at 1000 °C in argon atmosphere. The changes of properties of composite precursor membranes taking place during stabilization and carbonization processes were investigated using the methods of: DSC, TGA, FTIR, SEM, EDX, WAXD and mechanical tests. Bioactivity was determined by assessing the formation of crystalline apatite on the surface of membranes upon immersion in Simulated Body Fluid (SBF). The FTIR, SEM and WAXD investigation clearly prove that hydroxyapatite added to the electrospinning solution was present also in composites nanofibrous nonwovens after stabilization and carbonization process. It was found that due to HAp addition: the significant decrease of fibers average diameter occurs and that the average pore size for modified membranes is smaller than for the unmodified one. On the other hand it was shown that the ceramic additive protects fibers from mass reduction during the stabilization treatment. Finally a drastic increase of mineralization activity of nCF/HAp scaffolds as compared to their nCF counterparts has been proved.     

The effect of high temperature heat treatment on the structure and properties of anodic aluminum oxide

Nanoporous anodic aluminum oxide (AAO) membranes can be fabricated with highly controllable thickness and porosity, making them ideal for filtration applications. Use of these membranes is currently limited largely due to their size and overall fragility. The objective of this research was to improve mechanical properties of AAO membranes through use of high temperature heat treatment to induce phase transformations in the material. A repeatable two-step anodization process was developed for consistent sample fabrication and heat treatments were performed at 900 °C and 1200 °C in air. The pore morphology and phase composition of the as-anodized and heat-treated membranes were then observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microhardness testing was utilized to evaluate the mechanical behavior of the membranes before and after heat treatment. As-anodized AAO membranes were determined to be amorphous, and membranes heat-treated to 900 °C and 1200 °C were transformed to crystalline phases while retaining their original porous structure. Heat treatment to 900 °C resulted in formation of the γ-alumina transition phase in the skeleton regions of the membrane and nanocrystalline regions of α-alumina throughout the structure, while heat treatment to 1200 °C completely transformed the material to the stable α-alumina structure. The microhardness testing showed an increase in hardness from 2.5 ± 0.4 GPa to 4.7 ± 1.0 GPa in the transformation from amorphous to α-alumina.     

Liposomal Encapsulation and Stability of Dideoxyinosine Triphosphate

Dideoxyinosine triphosphate (ddITP) was encapsulated in multilamellar liposomes prepared with various lipid composition. The stability of liposomes in terms of retention of ddITP was measured at 4°, 25° and 37°C. The encapsulation of ddITP was 7.5 times greater in liposomes prepared with dipalmitoylphosphatidylcholine (DPPC) compared to dimyristoylphosphatidyl-choline (DMPC). When equimolar cholesterol (CHOL) was added to DM PC liposomes the encapsulation of ddITP was increased by 4.5 times. The leakage of ddITP was 60% from DMPC liposomes stored at 4° and 25° C after a month and 100% leakage after 16 days when stored at 37° C. The leakage of ddITP from DMPC:CHOL liposomes was only 20% after a month at 4° C, 50% at 25° and 90% at 37° C. These results suggest that the encapsulation of hydrophilic compound such as ddITP can be increased either by increasing the fatty acid chain length (DPPC) or by inclusion of CHOL. However, the optimum encapsulation and retention of ddITP was achieved using DMPC:CHOL liposomes. Retention of ddITP in these liposomes was maximum when stored at 4°c.