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PubMed1991

Surface properties and platelet reactivity of segmented poly(etherurethanes) and poly(etherurethaneureas).

Segmented poly(etherurethanes) (SPUs) and segmented poly(etherurethaneureas) (SPUUs) with various hard and soft segment components were prepared. The surface characterization of SPUs and SPUUs in the air-equilibrated state and in the hydrated-state was carried out by means of X-ray photoelectron spectroscopic (XPS) and dynamic contact angle measurements. XPS revealed that in the air-equilibrated state, lower surface free energy components were enriched at the air-solid interface, whereas in the hydrated-state higher surface free energy components were enriched at the water-solid interface. The change in environment from air to water induced the surface reorganization in order to minimize interfacial free energy. The large contact angle hysteresis was observed for SPUs and SPUUs. This hysteresis can be mainly ascribed to the surface reorganization process. Platelet adhesion tests on SPU and SPUU surfaces indicated that the existence of surface microphase separated structure played an important role in the attainment of blood compatibility.

Adsorption↗
PubMed2000

Body distribution of poly-DL-lactide-poly(ethylene glycol) microspheres with entrapped leptospira interrogans antigens following intravenous and oral administration to guinea-pigs.

Poly-DL-lactide-poly(ethylene glycol) (PELA) microspheres with entrapped antigens were administered intravenously and orally into guinea-pigs to quantitatively determine the in-vivo distribution and release profiles. PELA microspheres containing 125I-labelled outer-membrane protein Leptospira interrogans antigens (125I-OMP) were prepared by double-emulsion solvent extraction procedure, and characterized with respect to size, morphology and in-vitro release profiles. The fractured sections of liver and spleen were inspected by scanning electron microscopy, which indicated that microspheres had successfully been entrapped within the above tissues after intravenous injection and oral administration. At predetermined intervals, the blood and such tissues as the liver, spleen, kidney, thyroid, small intestine and mesentery were collected, and the radioactivity was measured by gamma scintillation counting. Following intravenous administration, 56.7% of administered microspheres were accumulated in immunization-related tissues, and 40.1% of microspheres were located in the liver and spleen. However, there was limited uptake efficiency (8.33%) following oral administration, and 49.5% of the absorbed microspheres were located in the intestinal mucosa. Compared with in-vitro release, the in-vivo release profiles of 125I-OMP from PELA microspheres, determined from the decreasing radioactivity in the above tissues, were much faster and the burst effect was higher. Antigen-loaded PELA microspheres were efficiently entrapped within immunization-related tissues after intravenous administration, but orally administered PELA microspheres showed limited uptake efficiency. Further investigation is needed to improve intestinal absorption.

Administration, Oral↗
PubMed2005

Explaining the phase behaviour of the pharmaceutically relevant polymers poly(ethylene glycol) and poly(vinyl pyrrolidone) in semi-fluorinated liquids.

Phase behaviour studies of low molecular weight poly(ethylene glycol) (denoted PEG 600 and PEG 1000, corresponding to molecular weights of 600 and 1000 g mol(-1), respectively) have been carried out in 2H,3H-perfluoropentane (HPFP) with and without added poly(vinyl pyrrolidone). The concentration and temperature dependencies of their phase behaviour and the effect of moisture on these systems have been established. Furthermore, the solubility of PEG 600 in binary mixtures of HPFP and perfluoropentane (PFP), as well as HPFP and perfluorodecalin (PFD) have been considered at high HPFP contents. A phase separation phenomenon in fluorinated non-aqueous media is reported for the first time: PEG 600 and PEG 1000 both show a lower critical solution temperature type phase separation boundary. The size of the PEGs was obtained from small-angle neutron scattering (radius of gyration) and pulsed-gradient spin-echo NMR (hydrodynamic radius) measurements. It is shown that polymer conformation follows a regular trend with solution concentration; the size increases from <10 A at 3 wt% in HPFP to 45 +/- 2 A at 20 wt% PEG. On changing the solvent composition by substitution of HPFP by PFP or PFD, the size decreases, consistent with a decrease in the hydrogen-bonding capacity of the solvent mixture. Computer modelling indicates an interaction between the PEG oxygen and the hydrogen of HPFP, an interaction that is absent for the fully fluorinated solvents. This indicates that hydrogen bonding is the driving force for polymer solubility in these solvents.

Chemistry, Pharmaceutical↗
PubMed2005

Towards an understanding of adsorption behaviour in non-aqueous systems: adsorption of poly(vinyl pyrrolidone) and poly(ethylene glycol) onto silica from 2H, 3H-perfluoropentane.

The adsorption behaviour of low molecular weight poly(ethylene glycol) (PEG 600) and poly(vinyl pyrrolidone) (PVP K25) to silica particles has been investigated at room temperature (21 degrees C) in the partially fluorinated solvent 2H,3H-perfluoropentane (HPFP). PVP (absorbed amount, Gamma = 12 mg g(-1)) was found to adsorb more strongly than PEG (Gamma = 4 mg g(-1)). Both of these values were higher than observed in water. In a further distinction to the aqueous case, where PVP displaces PEG from the interface, no competitive adsorption effects were observed between these two polymers in HPFP, with the adsorbed amounts of each polymer being unchanged by the presence of the other. The stability of silica suspensions in HPFP was primarily dependent on the presence of PVP; PEG/silica systems were unstable, but PVP/silica and PEG/PVP/silica systems formed stable suspensions. All suspensions were destabilized by the addition of small (0.15 wt%) amounts of water. The observations made in this work would point to a flocculation phenomenon due to the addition of water, and not Ostwald ripening. The mechanism of this destabilization is likely to be water acting as a flocculation bridge between particles.

Adsorption↗
PubMed1987

Biopharmaceutical characteristics of a suppository base containing poly (oxyethylene)-poly (oxypropylene) copolymer, Unilube. I. Effects of a suppository base containing Unilube 70DP-950B on release and rectal absorption of aminopyrine in rabbit.

The rectal absorption of aminopyrine (AP) from a three-component-system suppository base (TCS), which is a mixture of oleaginous base, water-soluble base and the poly-(oxyethylene) poly-(oxypropylene) block copolymer, Unilube, was investigated. Albino rabbits were used as the animal model. The bioavailability of oleaginous base and water-soluble base (polyethylene glycol 4000) were 44.3% and 82.6%, respectively. The time to reach maximum plasma concentration (Tmax) of the oleaginous and the water-soluble bases were 21.0 +/- 8.2 min and 33.0 +/- 16.4 min, respectively. When TCS was used, its Tmax was 30 min and increasing the amount of Unilube in the base from 5% (w/w) to 20% (w/w) decreased the bioavailability from 100.4% to 47.2%. The softening temperature of TCS was 55-57 degrees C. Collectively, TCS containing 5% of Unilube gave significantly higher bioavailability than the other bases without softening until 57 degrees C. Also, the results of the two different release tests were compared with the results of an animal experiment in this paper.

Animals↗
PubMed1995

Physical-chemistry characteristics and biodistribution of poly(ethylene glycol)-coated liposomes using poly(oxyethylene) cholesteryl ether.

Poly(ethylene glycol)-coated liposomes were prepared with poly(oxyethylene) cholesteryl ethers (mPEG-Chol). PEG unit numbers tested were 50, 100 and 200, of which the average molecular weights (m) of PEG were 2200, 4400 and 8800, respectively. Properties of both PEG-coated liposomes and PEG-Chol molecules were investigated. These liposomes exhibited a long circulation time in the blood after i.v. injection in rats, estimated by both the lipid membrane marker, L-alpha-dipalmitoylphosphatidylcholine [2-palmitoyl-9,10-3H](3H-DPPC), and an internal aqueous marker, 3H-inulin. Accumulation in the liver and spleen at 8h-post-injection was significantly reduced compared with conventional liposomes. The percentage of PEG-Chol incorporation in liposomal membranes was also investigated. Liposomes composed of egg yolk phosphatidylcholine (EPC)/PEG-Chol at various molar ratios were separated from free PEG-Chol molecules, which are not incorporated in liposomal membranes by chromatography over Sepharose CL-4B columns, PEG-Chol incorporation reached approx. 14 and 18 mol% of the total lipids with 25% PEG-Chol unit numbers of 200 and 50, respectively. The occupied area per molecule of PEG-Chol was larger than that of Chol, and the fluorescence anisotropy (r) of the initial 25 mol% (8800)PEG-Chol liposomes was smaller than that observed for 12.5 mol% Chol liposomes. PEG-coated liposomes containing calcein were incubated at 37 degrees C in heat-inactivated fetal bovine serum (FBS). In the presence of FBS, calcein leakage was increased with PEG-Chol percentage incorporation and an increase in FBS concentration. The amount released from PEG-coated liposomes represented 60% at maximum and was larger than that of the control liposomes. PEG-Chol molecules are interesting compounds since they can be easily synthesized in a large amount on an industrial scale. The basic physical-chemistry characteristics investigated in this article are critical to assess the pharmacological application of PEG-Chol liposomes as drug delivery systems.

Animals↗
PubMed2001

Preparation of a novel aggregate like sugar-ball micelle composed of poly(methylglutamate) and poly(ethyleneglycol) modified by lactose and its molecular recognition by lectin.

We report the preparation and characteristics of a novel micellar aggregate of an amphiphilic diblock copolymer, poly(methylglutamate) (PMG)-poly(ethyleneglycol) (PEG), whose terminus was modified by lactose lactone (LA). Due to the terminal LA moiety, this aggregate could be specifically recognized by RCA120 lectin. PMG-PEG-LA was synthesized by polymerizing the N-carboxy anhydride of L-glutamic acid gamma-methyl ester with H2N-PEG-LA as a polymerization initiator. By applying a fluorescence method using pyrene as a probe molecule, we found that PMG-PEG-LA could form the aggregate in aqueous solution. Fluorescence measurements showed that the critical aggregation concentration (C.A.C.) was 1.1 x 10(-5) M. The average diameter of the aggregate was 220 nm at 25 degrees C, as determined by the dynamic light scattering method. Circular dichroism measurements for the aggregate solution showed that the PMG residue took an alpha-helical structure, and that they associated to constitute the hydrophobic core of the aggregate. By adding RCA120 lectin to the aggregate solution, the turbidity of the solution increased rapidly, due to association of the aggregates. This implies that the aggregate could be recognized by lectin, and also suggests that sugar residues locate at the surface of the aggregates. From these findings, we concluded that the PMG-PEG-LA molecules form an aggregate like a "sugar ball" micelle, whose surface is covered by the sugar moieties. Application of the present aggregate system as a drug carrier is briefly discussed.

Lactose↗
PubMed2006

In vitro and in vivo characterization of huperzine a loaded microspheres made from end-group uncapped poly(d,l-lactide acid) and poly(d,l-lactide-co-glycolide acid).

The purpose of this work was to develop biodegradable microspheres for long term delivery of a potent acetyl cholinesterase inhibitor, huperzine A (Hup-A), which is of interest in the palliative treatment of Alzheimer's disease. Microspheres were successfully prepared with specifically end-group uncapped poly(d,l-lactide acid) and poly(d,l-lactide-co-glycolide acid) using a simple o/w solvent evaporation method. The morphology, particle size and size distribution, drug loading capacity, drug entrapment efficiency (EE) and in vitro drug release were studied in detail. It was found that the terminal group and the inherent viscosity (IV) of the polymers played key role in the drug encapsulation: higher EE was achieved with end-group uncapped and low IV polymers. In vitro drug release from microspheres made from the selected three kinds of polymers revealed sustained release of Hup-A without significant burst release. Preliminary pharmacokinetic study following subcutaneous injection of Hup-A loaded microspheres illustrated the sustained release of the drug over 6-8 weeks at clinically relevant doses in vivo. The studies demonstrated the feasibility of long term delivery of Hup-A using biodegradable microspheres.

Alkaloids↗
PubMedDate not supplied

Preparation of multi-phase microspheres of poly(D,L-lactic acid) and poly(D,L-lactic-co-glycolic acid) containing a W/O emulsion by a multiple emulsion solvent evaporation technique.

Multi-phase microspheres of poly(D,L-lactic acid) (PLA) or poly(D,L-lactic-co-glycolic acid) (PLGA) containing a water-in-oil (W/O) emulsion were prepared by a multiple emulsion solvent evaporation technique. Acetonitrile was used as the solvent for the polymers and light mineral oil as the dispersion medium for the encapsulation procedure. Process and formulation parameters to optimize the microencapsulation of a W/O emulsion containing water-soluble drugs were investigated. Drug loading efficiencies of 80-100 per cent were obtained under specific preparative conditions. The drug loading efficiency in the microspheres was dependent upon the ratio of the W/O emulsion to polymer and the concentration of surfactant in the mineral oil. Compared to conventional microspheres, in which fine drug particles are homogeneously dispersed in the polymer beads, the multi-phase microspheres permit the higher encapsulation efficiency of water-soluble drugs and eliminate partitioning into the polymer-acetonitrile phase which results in low encapsulation efficiency with conventional solvent evaporation techniques.

Acetonitriles↗
PubMedDate not supplied

Microencapsulation of lobster carotenoids within poly(vinyl alcohol) and poly(D,L-lactic acid) membranes.

The use of natural pigments such as lobster carotenoids in fish feed formulations offers advantages over the use of the synthetic alternatives. Microencapsulation of the pigments, with or without the addition of antioxidants to the formulation, may be of benefit in terms of stabilizing pigment colour. In the present study, lobster carotenoids were extracted from lobster shell into petroleum ether and microencapsulated by phase separation and salt coacervation within (poly vinyl alcohol) and poly(vinyl alcohol)/poly(D,L-lactic acid) membranes. Spherical microcapsules, with smooth, thin and resilient membranes were obtained with mean diameters ranging from 50 to 150 microns, depending on the membrane material, and source of pigment. The microcapsules were pink-orange in colour, and colour stability was followed spectrophotometrically. Enhanced stability was observed in both membrane materials, in comparison to the non-encapsulated control. Rates of discoloration were determined under a variety of storage conditions, including the absence of light, reduced temperatures and under nitrogen atmosphere. The best stability of lobster carotenoids was observed under a nitrogen atmosphere within PVA/PLA membranes, representing an 11-fold enhancement of pigment stability in comparison to the controls. Under ambient conditions, the enhancement in pigment stability was approximately 6-fold. The optimum concentration of PVA during microencapsulation was 3-4%, and the microencapsulated pigments appeared most stable under acidic conditions. The rate of discoloration appeared independent of pigment concentration.

Animals↗
PubMedDate not supplied

Properties of multiphase microspheres of poly(dl-lactic acid) or poly(dl-lactic-co-glycolic acid) produced by mechanical agitation, sonication, or potentiometric dispersion.

The effect of processing techniques on the molecular weight of the polymer in biodegradable microspheres of poly(dl-lactic acid) (PLA) and poly(dl-lactic-co-glycolic acid) (PLGA) was investigated. Multiphase microspheres were produced by conventional agitation, potentiometric dispersion, or sonication. Gel permeation chromatography was used to determine the molecular weight of the polymer before and after processing. Polymer in microspheres of PLA produced by sonication experienced a 21% decrease in molecular weight of the polymer after 90 s of sonication, while microspheres made by potentiometric dispersion or mechanical agitation exhibited insignificant changes in molecular weight. Microspheres produced by potentiometric dispersion were found to have a more narrow particle size distribution compared to the other methods. A decrease in the internal diameter of the infusion tube used to produce multiphase microspheres by the potentiometric dispersion method was found to decrease the mean particle size of the resultant microspheres. Two surfactants were investigated at varied levels for utilization in the continuous phase, and particle size analysis revealed that increased surfactant levels caused an increase in the mean particle size of microspheres containing BSA produced by potentiometric dispersion. This phenomenon was attributed to an increase in conductivity of the continuous phase as the surfactant level was increased.

Chemistry, Pharmaceutical↗
PubMed1999

High-resolution A-DNA crystal structures of d(AGGGGCCCCT). An A-DNA model of poly(dG) x poly(dC).

A-DNA conformation is favored by guanine-rich sequences, such as (dG)n x (dC)n, or under low-humidity conditions. Earlier A-DNA crystal structures revealed some conformational variations which may be the result of sequence-dependent effects and/or crystal packing forces. Here we report the high-resolution crystal structure of d(AGGGGCCCCT) in two crystal forms (either in the P212121 or the P6122 space group) to gain insights into the conformation and dynamics of the (dG)n x (dC)n sequence. The P212121 form has been analyzed using data to 1.1 A resolution by the anisotropic temperature factor refinement procedure of the SHELX97 program. Such analysis affords us with the detailed geometric, conformational and motional property of an A-DNA structure. The backbone torsional angles fall in a narrow range, except for the alpha/gamma angles which have two distinct combinations (gauche-/gauche+ or trans/trans). An A-DNA model of poly(dG) x poly(dC) has been constructed using the conformational parameters derived from the crystal structure of the P212121 form. In the crystal structure of the P6122 space group, the central eight base pairs of the decamer adopt A-DNA conformation with the two terminal nucleotides flipped out to form base pairs with the neighboring nucleotides. Comparison of the A-DNA structure of the same sequence from two different crystal forms, reinforced the conclusion that molecules crystallized in the same space group have a more similar conformation, whereas the same molecule crystallized in different space groups has different (local) conformations.

DNA↗
PubMed2001

Biodegradation of poly(tetramethylene succinate-co-tetramethylene adipate) and poly(tetramethylene succinate) through water-soluble products.

Poly(tetramethylene succinate-co-tetramethylene adipate) (PBSA) and poly(tetramethylenesuccinate) (PBS) were hydrolyzed experimentally into water-soluble oligomers and monomers by Chromobacterium extracellular lipase. The oligomers were identified by high-performance liquid chromatography-mass spectrometry and 1H-nuclear magnetic resonance, which indicated that a total of 28 oligomer species were liberated from PBSA, and that 13 of them were identical to the hydrolysates from PBS. Moreover, 20 of the species were polyester-based compounds of monomer units, and the other 8 species were small amounts of diurethane compounds. Bis(hydroxybutyl) succinate (BSB) and bis(hydroxybutyl) hexamethylene dicarbamate (BHB) were the typical oligomers and were chemically synthesized. Biodegradability of BSB and BHB was examined for 28 d in the activated sludge, and analysis of the results of this study indicated that the final conversion rate of constituent carbon to carbon dioxide was estimated at 80 mol% for BSB and 10 mol% for BHB. The remaining amount of carbon in the undegraded BHB was 20 mol%. In the presence of BSB, the biodegradability of BHB was increased by about 1.5 times. The suggestion was made that BSB induced a growth of microorganisms and helped BHB degradation. This is consistent with the observation that the biodegradation of BHB in native soil for 60 d reached > 60%.

Adipates↗
PubMed2003

(211)At-labeled and biotinylated effector molecules for pretargeted radioimmunotherapy using poly-L- and poly-D-Lysine as multicarriers.

Poly-L- and poly-D-lysine were evaluated as carriers of astatine and biotin for prospective use as effector molecules in pretargeted radioimmunotherapy of micrometastases. The precursor polylysine was derivatized in a three-step, single-pot procedure, including biotinylation with biotin amidocaproic N-hydroxysuccinimide, astatination via the intermediate reagent N-succinimidyl 3-(trimethylstannyl)benzoate, and, finally, charge modification using succinic anhydride. The chemistry was shown to be very facile, with a biotinylation efficiency of 75 +/- 5%, and overall radiochemical yields in the range of 50-70%. After charge modification, no amines could be detected in the final product. The biotin function was unaffected by the chemistry and the radiation, as confirmed by almost complete binding of the effector molecule to avidin beads using a convenient filter tube assay. The effector molecules were evaluated in tumor-free female nude mice with regard to whole-body retention and tissue distribution after i.p. administration. The distribution of the L-isomer effector molecule showed rapid whole-body clearance with low uptake in all tissues, whereas the D-isoform showed whole-body clearance related to uptake in the kidneys. Both D-isomer and L-isomer showed faster blood clearance and generally lower tissue uptakes than labeled antibodies. The normal tissue distribution after the peritoneal administration implies that pretargeting using L-structure polylysine as the effector molecule may give a higher therapeutic index than that achieved in conventional radioimmunotherapy.

Animals↗
PubMedDate not supplied

[Parallel DNA helices. Conformational analysis of regular poly(dG).poly(dC) helices with different variants of base binding].

We have performed a conformational analysis of DNA double helices with parallel directed backbone strands. The calculations were made for homopolymers poly(dG).poly(dC). All possible models of base binding were checked. By the potential energy optimization the dihedral angles and helices parameters of stable conformations of parallel double polynucleotides were calculated. The dependences of conformational energy on the base pair structure were studied. Possible structure of parallel helices with various nucleotide composition are discussed.

DNA↗
PubMed1992

Micelles of poly(oxyethylene)-poly(oxypropylene) block copolymer (pluronic) as a tool for low-molecular compound delivery into a cell: phosphorylation of intracellular proteins with micelle incorporated [gamma-32P]ATP.

Pluronic P85 (poly(oxyethylene)-poly(oxypropylene) block copolymer) was used for in vitro delivery of [gamma-32P]ATP into intact Jurkat cells. Negatively charged ATP molecules are not able to penetrate cell plasma membrane. Hence, exogenous [gamma-32P]ATP added to a cell culture does not participate in phosphorylation of intracellular proteins. The addition to cells of [gamma-32P]ATP solubilized in positively charged (containing dodecylamine) pluronic micelles results in considerable increase of protein phosphorylation. In this case the treatment of intact cells with alkaline phosphatase (resulting in dephosphorylation of external proteins) causes no essential decrease of [32P]-incorporation in cell proteins. That gives an evidence of delivery of solubilized ATP into a cell. Under the experimental conditions used, pluronic micelles neither influence the viability of cells nor permeabilize cell plasma membrane.

Adenosine Triphosphate↗
PubMed2000

Utilization of oxidative pressure for enhanced production of poly-beta-hydroxybutyrate and poly(3-hydroxybutyrate-3-hydroxyvalerate) in Ralstonia eutropha.

Ralstonia eutropha was cultivated under oxidative conditions in the presence of hydrogen peroxide and methyl viologen to stimulate the flux of NADPH to the PHA biosynthesis pathway. The effects of oxidants on the biosynthesis of poly-beta-hydroxybutyrate(PHB) and poly(3-hydroxybutyrate-3-hydroxyvalerate)[P(3HB-3HV)] were investigated. The biosynthesis rate and concentrations of PHB and its copolymer P(3HB-3HV) increased significantly under the oxidative pressure of methyl viologen, meanwhile, the molar fraction of 3HV in P(3HB-3HV) remained constant. The effect of methyl viologen on the flux of the intermediate compounds was investigated by measuring the activity of enzymes related to PHB biosynthesis, glucose 6-phosphate dehydrogenase (G6PD), and NADPH level. The oxidant significantly activated the G6PD of R. eutropha, increasing the NADPH level used for the reduction reaction of acetoacetyl-CoA to beta-hydroxybutyryl-CoA, thereby enhancing the biosynthesis of PHB and P(3HB-3HV).

Journal Article↗
PubMed2006

[Study of poly (3,4-ethylene dioxythiophene) : poly (styrene sulfonate) by in-situ resonance Raman spectroscopy].

Poly (3,4-ethylene dioxythiophene) (PEDOT): Poly (styrene sulfonate) (PSS) has attracted a lot of interest for application in organic electronics due to good stability and high electronic conductivity in its doped state. Indeed, thin layers of PEDOT:PSS was regularly used in light emitting diodes (PLEDs) as hole injection and transportation layer. Here, Doping and dedoping states of PEDOT:PSS were studied by absorbance spectra and Raman spectra. A new absorption band centered at 620 nm was observed on dedoped PEDOT:PSS. Consistently, Raman signals of dedoped PEDOT:PSS are resonantly intensified since the Raman excitation wavelength (633 nm) is set in the enhanced absorption band. So it gives a sensitive way to study the doping and dedoping states of PEDOT:PSS. Furthermore, for the encapsulated polymer light-emitting diodes, Raman spectroscopy is a powerful way to study the polymer layers inside the devices.

English Abstract↗