Patterned supported lipid bilayers and monolayers on poly(dimethylsiloxane)

A simple and practical method for patterning supported lipid bilayers on poly(dimethylsiloxane) is presented. By using electron microscopy grids to laterally control the extent of plasma oxidation, the substrate is partitioned into regions of different hydrophilicities. Addition of vesicles then results in the spontaneous formation of lipid bilayers and monolayers side-by-side on the surface, separated by regions that contain no lipid and/or a region with adhering vesicles. By using millimeter-sized plastic masks we are able to control the formation of these lipid structures on macroscopic patches by simply varying the plasma-cleaning time. For the first time, we are able to influence, in a controlled fashion, the chemical composition of a substrate in such a way that it supports fluid lipid monolayers, rejects lipid adhesion, adsorbs intact lipid vesicles, or supports fluid bilayers.     

Preparation and characterization of tetra(4-pyridyl)porphyrinatomanganese(III) cation supported covalently on poly(siloxane)

Tetra(4-pyridyl)porphyrinatomanganese(III), [Mn^III(TPyP)]⁺, has been covalently bonded to the surface of a chlorinated crosslinked poly(siloxane) which contains the immobilized chloropropyl group, -CH₂CH₂CH₂Cl. The metalloporphyrin complex was found to react with the immobilized ligand via a quaternization reaction of the 4-pyridine N-atom. The porphyrin binding involves a chemical process rather than physical adsorption. There is evidence that two porphyrins species coexist, both bonded to the surface, one being [Mn^III(TPyP)]⁺ and the other (H₂TPyP), both in the quaternary salt forms, when the quaternization reaction is carried out at higher temperature (150 °C). At moderate reaction temperatures (70–80 °C) the quaternization reaction resulted in only one species, supported [Mn^III(TPyP)]⁺, as evident from electronic spectra of the solid. Also, visible absorption spectra taken of the solution remaining after the quaternization reaction showed no demetallated porphyrm. Solid state electronic absorption, dispersive IR and FT-IR spectra have been used for confirmation.     

Preparation and characterization of novel physically cross-linked hydrogels composed of poly(vinyl alcohol) and amine-terminated polyamidoamine dendrimer

Poly(vinyl alcohol) (PVA) and polyamidoamine (PAMAM) dendrimers are water-soluble, biocompatible and biodegradable polymers, which have been widely applied in biomedical fields. In this paper, novel physically cross-linked hydrogels composed of PVA and amine-terminated PAMAM dendrimer G6-NH(2) were prepared by cyclic freezing/thawing treatment of aqueous solutions containing PVA and G6-NH(2). The FT-IR analysis and elemental analysis indicated that PAMAM dendrimer G6-NH(2) was successfully introduced into the formed hydrogels, possibly via hydrogen bonds among hydroxyl groups, amide groups and amino groups in PVA and PAMAM dendrimer in the process of freezing-thawing cycle. Compared with physically cross-linked PVA hydrogel, PVA/G6-NH(2) hydrogels show higher swelling ratios and faster re-swelling rate due to the higher hydrophilicity of PAMAM dendrimer G6-NH(2). Higher contents of G6-NH(2) in PVA/G6-NH(2) hydrogels resulted in higher swelling ratios and faster re-swelling rates. With increasing freezing/thawing cyclic times, the swelling ratios and re-swelling rates of PVA/G6-NH(2) hydrogels decreased, which is similar to that of physically cross-linked PVA hydrogel. Combining the special host property of polyamidoamine dendrimer, these novel physically cross-linked hydrogels are expected to have potential use in drug delivery, including improving drug-loading amounts in hydrogels and prolonging drug release time. Swelling ratios of physically cross-linked PVA/G6-NH(2)-50 hydrogels prepared by three, six, nine freezing/thawing cycles. The swelling equilibrium experiments were carried out in distilled water at 25 degrees C.     

Preparation and characterization of asymmetric polyethersulfone (PES) membranes

Flat‐sheet asymmetric polyethersulfone (PES) membranes were prepared from polyethersulfone (PES)/ polyethylene glycol (PEG)/ N‐methyl‐2‐pyrrolidone (NMP) system via phase inversion induced by immersion precipitation in water coagulation bath. Effects of propionic acid (PA) as a non‐solvent additive (NSA) on morphology and performance of the membranes prepared from PES/PEG 6000/NMP system in water coagulation bath were investigated. The cross section morphology of the membranes was studied by scanning electron microscopy (SEM). In addition, performance of the membranes was studied by water content measurements and separation experiments using pure water and human serum albumin (HSA) protein solution as feeds. According to SEM analysis, it was found out that the NSA has a significant influence on the structure of the skin layer and the sublayer. The obtained results indicated that addition of PA to the casting solution decreases permeation flux of the prepared membranes. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and characterization of cyclic poly(oxypropylene)

Poly(propylene glycol) [α-hydro-ω-hydroxypoly(oxypropylene)] of number-average molar mass M̄_n ≈ 2000 g · mol⁻¹ (PPG2000) was cyclised with high conversion (ca. 75%) by reaction with dichloromethane in the presence of powdered KOH. The cyclic product was separated from chain extended polymer by preparative GPC, giving an overall yield of polymer (M̄_n ≈ 2000 g · mol⁻¹, narrow molar mass distribution) in excess of 50%. Characterisation by analytical GPC and ¹³C NMR spectroscopy confirmed cyclisation. DEPT and ¹H-coupled NMR spectra were used to show that the links in cyclic poly(oxypropylene) were 77% single acetal, 12% double acetal and 11% triple acetal (or higher). This complexity probably results from competitive reaction with water introduced with KOH.     

Lipid diffusion compared in outer and inner leaflets of planar supported bilayers

The translational diffusion coefficient (D) of lipids located in the outer and inner leaflets of planar supported DLPC (1,2-dilauroyl-sn-glycero-3-phosphocholine) bilayers in the fluid phase was measured using fluorescence correlation spectroscopy of dye-labeled lipids at the low concentration of 0.001% and using iodide quenching of dyes in the outer leaflet to distinguish diffusion in the inner leaflet from that in the outer leaflet. To confirm the generality of these findings, the bilayers were prepared not only by vesicle fusion but also by Langmuir-Blodgett deposition. We conclude that regardless of whether the bilayers were supported on quartz or on a polymer cushion, D in the inner and outer leaflets was the same within an experimental uncertainty of +/-10% but with a small systematic tendency to be slower (by <5%) within the inner leaflet.     

Preparation and characterization of poly(copper 2,3,9,10,16,17,23,24-octacyanophthalocyanine)

Dark blue poly(copper 2,3,9,10,16,17,23,24-octacyanophthalocyanine) has been prepared by reacting 1,2,4,5-tetracyanobenzene with cuprous chloride in 1-methyl-2-pyrrolidone at ca. 150°C. The product has been characterized by elemental analysis, thermal analysis, infrared and UV-VIS spectroscopies. The polymer has high purity and exhibits good thermal stability in an inert atmosphere.     

紫外光交联可降解聚对二氧环己酮/聚乙二醇薄膜制备与表征

以2,2-二甲氧基-2-苯基苯乙酮(DMPA)为引发剂,将四臂端丙烯酸酯聚对二氧环己酮(PPDO-4AC)和聚乙二醇双丙烯酸酯(PEG-DA)经紫外光照射制得PPDO/PEG交联薄膜.研究了光照时间和DMPA用量对PPDO/PEG交联薄膜凝胶含量的影响.DSC研究表明共聚物中两组分的相容性较好,Tg随着共聚物中PEG链...     

In situ formation and characterization of poly(ethylene glycol)-supported lipid bilayers on gold surfaces

Inclusion of a polymer cushion between a lipid bilayer membrane and a solid surface has been suggested as a means to provide a soft, deformable layer that will allow for transmembrane protein insertion and mobility. In this study, mobile, tethered lipid bilayers were formed on a poly(ethylene glycol) (PEG) support via a two-step adsorption process. The PEG films were prepared by coadsorbing a heterofunctional, telechelic PEG lipopolymer (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-(pyridyldithio)propionate]) (DSPE-PEG-PDP) and a nonlipid functionalized PEG-PDP from an ethanol/water mixture, as described in a previous paper (Munro, J. C.; Frank, C. W. Langmuir 2004, 20, 3339-3349). Then a two-step lipid adsorption strategy was used. First, lipids were adsorbed onto the PEG support from a hexane solution. Second, vesicles were adsorbed and fused on the surface to create a bilayer in an aqueous environment. Fluorescence recovery after photobleaching experiments show that this process results in mobile bilayers with diffusion coefficients on the order of 2 microm2/s. The mobility of the bilayers is decreased slightly by increasing the density of tethered lipids. The formation of bilayers, and not multilayer structures, is also confirmed by surface plasmon resonance, which was used to determine in situ film thickness, and by fluorimetry, which was used to determine quantitatively the fluorescence intensity for each 18 by 18 mm sample. Unfortunately, fluorescence microscopy also shows that there are large defects on the samples, which limits the utility of this system.     

Thermogelling polymers composed of poly(cyclohexylenedimethylene adipate) and poly(ethylene glycol)

Block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic biodegradable polyesters have been reported as thermogelling polymers, because they feature temperature-dependent sol-to-gel or gel-to-sol transitions in aqueous solutions. In this study, a series of thermogelling poly(ethylene glycol methyl ether)-block–poly(cyclohexylenedimethylene adipate)-block–poly(ethylene glycol methyl ether) triblock copolymers and PEG-block–poly(cyclohexylenedimethylene adipate) multiblock copolymers was synthesized by reacting hydroxyl-terminated poly(cyclohexylenedimethylene adipate) (PCA) with poly(ethylene glycol methyl ether) and PEG, respectively, using 1,6-diisocyanatohexane as the coupling agent. Two hydroxyl-terminated PCAs, i.e., poly(1,4-cyclohexylenedimethylene adipate) and poly(1,3/1,4-cyclohexylenedimethylene adipate), were synthesized by the condensation reaction of adipic acid (AA) with 1,4-cyclohexanedimethanol (CHDM) and 1,3/1,4-CHDM, respectively, and used as the hydrophobic polyester blocks of these thermogelling copolymers to compare the effect of crystallinity on the sol-to-gel transition behavior.The polymers were characterized using proton nuclear magnetic resonance, Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, solubility testing, and rheological analysis. Experimental results revealed that the structure of the PCA block (crystalline vs. amorphous), the molecular weights of the hydrophobic PCA and hydrophilic PEG blocks, and the type of thermogelling polymer (triblock vs. multiblock) influenced the solubility, polymer micelle packing characteristics, maximum storage modulus, and sol-to-gel temperature of the polymers. Among all the samples at 40 wt.% aqueous solutions, triblock copolymer TB3 showed sol-to-gel temperature at 22 °C, and had the highest maximum storage modulus about 170 Pa.     

Preparation and characterization of carboxylic-containing poly(methyl methacrylate) nanolatexes

Poly(methyl methacrylate) (PMMA)-based latex particles bearing carboxylic groups at the surface were prepared via emulsion polymerization. The polymerization recipe and process were optimized in order to target monodisperse particles with diameters around 100 nm. The polymerizations were performed using 4,4-azobis(4-cyanopentanoic) acid (ACPA) as initiator and sodium dodecyl sulphate (SDS) as surfactant. The polymerization conversion was determined by both gas chromatography and gravimetry. The final latexes were characterized with respect to particle size, size distribution, surface charge density, electrokinetic properties (i.e. electrophoretic mobility vs pH and ionic strength) and colloidal stability (i.e. coagulation rate constants vs pH and stability factor vs ionic strength).     

Preparation and characterization of iodinated poly(vinyl alcohol) microfibril

Iodination of poly(vinyl alcohol) (PVA) microfibril, which was obtained from saponification of poly(vinyl pivalate), was conducted before and after zone drawing at various conditions. The resulting PVA microfibrils were characterized by differential scanning calorimeter and scanning electron microscopy. Surface morphologies of these PVA microfibrils showed some differences between PVA microfibril iodinated after and before drawing. Crude shapes of PVA microfibrils iodinated after drawing indicated that iodine decreased the structural regularity severely. On the other hand, PVA microfibrils iodinated before drawing showed relatively ordered surfaces. This was ascribed to the enhanced molecular ordering of PVA microfibrils due on zone drawing. Iodinated PVA microfibrils showed a decrease in crystal melting temperature of about 100°C compared to the untreated sample. PVA microfibrils drawn after iodination showed relatively higher crystal melting temperature than those of microfibrils iodinated after drawing. These results were considered as the proofs of the changes in crystalline lattice of the PVA microfibrils. Effects, of drawing temperature on sublimation of iodine were also evaluated.     

Preparation and characterization of cationic poly(n-isopropylacrylamide) copolymer latexes

Cationic poly(N-isopropylacrylamide) (NIPAM) copolymer latexes have been prepared at 70°C using methylene-bisacrylamide (MBA) as the crosslinking agent,2-2′-azobis-(2-amidinopropane hydrochloride) (V50) as the initiator and in the presence of 2-aminoethyl-methacrylate hydrochloride (AEM). It was found that the concentration of AEM plays a major role in the polymerization kinetics and particle nucleation. However, too high a concentration (2–5 mol%/NIPAM) caused the latex to be polydispersed together with the production of large amounts of polyelectrolytes. The presence of surface amino groups on the final particles under the protected form was revealed both by an ultraviolet spectrometry and nuclear magnetic resonance methods. It was indirectly evidenced through the electrophoretic mobility behavior of the latex particles (below and above the lower critical solubility temperature of the poly(NIPAM)) as well as by their stability against a monovalent electrolyte.     

Preparation and characterization of poly (N-isopropylacrylamide-co-dimethylaminoethyl methacrylate) microgel latexes

Monodisperse cationic thermosensitive latex microgels have been prepared by radical-initiated precipitation polymerization of N-isopropylacrylamide, methylene bisacrylamide using 2,2′-azobis(2-amidinopropane hydrochloride) as an initiator and dimethylaminoethyl methacrylate (DMAEMA) as a cationic monomer. The final microgel latexes were characterized with respect to water-soluble polymer formation, particle size and size distribution. Adding cationic monomer (DMAEMA) was found to drastically affect the particle size, but not the size distribution as observed both by transmission electron microscopy and quasielastic light scattering (QELS). However, too high a DMAEMA concentration in the feed composition led to enhanced formation of water-soluble polymer. The volume phase-transition temperature of cleaned microgels examined by QELS (particle size versus temperature) was found to be around 32 °C and was slightly dependent on the concentration of the cationic monomer. The volume phase-transition temperature range becomes broader with increasing cationic monomer concentration. In addition, the pH of the polymerization medium was found to affect the final particle size and amount of water-soluble polymer formed. Received: 29 March 2001 Accepted: 2 July 2001     

Preparation of poly(N-isopropylmethacrylamide) latexes kinetic studies and characterization

Thermosensitive crosslinked polymer latexes have been synthesized by precipitation polymerization of N-isopropylmethacrylamide (NIPMAM) as a main monomer, methylene bis-acrylamide (MBA) as a crosslinker, and potassium persulfate (KPS) as the initiator. Polymerizations kinetics were first investigated by studying both the influence of crosslinker (MBA) and initiator (KPS) concentrations and temperature effects on the polymerization conversion, the particle size, and water-soluble polymer (WSP) as a function of time. Particle size analysis by Scanning Electron Microscopy (SEM) showed that a short nucleation step afforded the synthesis of highly monodispersed latexes. In addition, a strong dependence of WSP formation on MBA and KPS concentration and polymerization temperature was found, as well. Comparison of particle size by SEM and quasielastic light scattering clearly evidenced the dramatic effect of temperature on particle size. Lower critical solubility temperatures (LCST) of latexes were determined and compared. Finally, based on these results, the mechanism of particle formation in this polymerization process is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1823–1837, 1999     

Electrochemical biosensor based on supported planar lipid bilayers for fast detection of pathogenic bacteria

This paper presents a new ion-channel biosensor based on supported bilayer lipid membrane for direct and fast detection of Campylobacter species. The sensing element of a biosensor is composed of a stainless-steel working electrode, which is covered by artificial bilayer lipid membrane (BLM). Antibodies to bacteria embedded into the BLM are used as channel forming proteins. The biosensor has a strong signal amplification effect, which is defined as the total number of ions transported across the BLM. The total number of (univalent) ions flowing through the channels is 10¹⁰ ions s⁻¹. The biosensor showed a very good sensitivity and selectivity to Campylobacter species.     

Preparation and characterization of poly(acrylic acid)-based nanoparticles

The present investigation describes the synthesis and characterization of nanoparticles based on poly(acrylic acid) (PAA) intramolecularly cross-linked with diamine, 2,2′-(ethylenedioxy)bis(ethylamine), using water-soluble carbodiimide. The aqueous colloid dispersions of nanoparticles were clear or mildly opalescent depending on the ratio of cross-linking, pH of the solution, and the molecular weight of PAA, finding consistent with values of transmittance between 3% and 99%. The structure was determined by nuclear magnetic resonance spectroscopy, and the particle size was identified by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that particle size depends on the pH, and at a given pH, it was caused by the ratio of cross-linking and the molecular weight of PAA. Particle size measured by TEM varied in the range of 20 and 80 nm. In the swollen state, the average size of the particles measured by DLS was in the range of 35–160 nm.     

Preparation and structural characterization of poly(4-vinylphenylacetate-co-maleic anhydride)

Poly(4-vinylphenylacetate-co-maleic anhydride) was synthesized by free-radical initiation to yield a 1:1 copolymer over a 0.2-0.8 mole fraction range of monomer feed in maleic anhydride. Evidence of 1:1 charge transfer complex between 4-vinylphenylacetate and maleic anhydride was obtained in the UV region at 355 nm. The ¹³C NMR chemical shifts and ¹H NMR integration data indicate that poly(4-vinylphenylacetate-co-maleic anhydride) has an alternating and stereoregular structure. The molecular weight of poly(4-vinylphenylacetate-co-maleic anhydride) was controlled by using specific solvents and initiator concentrations.