Biodegradable nanoparticles made from polylactide-grafted dextran copolymers

Polysaccharide-covered polyester nanoparticles were prepared using the emulsion/solvent evaporation process. The core of the nanoparticles was made either of PLA or of a blend of polylactide and polylactide-grafted dextran copolymer in various proportions. The surface of the nanoparticles was covered by dextran chains via the use of water-soluble polylactide-grafted dextrans as polymeric stabilizers during the emulsification step. The characteristics of the nanoparticles (size, surface coverage, thickness of superficial layer, colloidal stability) were correlated to the structural parameters (length and number of polylactide grafts) of the copolymers as well as to their surface active properties. The complete biodegradability of the nanoparticles was evaluated by considering the rate of hydrolysis of polylactide grafts in phosphate buffer and the rate of enzymatic degradation of dextran backbone by dextranase.     

Configuration of bovine serum albumin adsorbed on polymer particles with grafted dextran corona

The configuration of BSA macromolecules adsorbed on the surfaces of poly(alkylcyanoacrylate) nanoparticles has been determined using small angle neutron scattering (SANS). The nanoparticles were made by anionic emulsion polymerization (AEP) and self-assembly of dextran–poly(isobutylcyanoacrylate) (PICBA) copolymers. They have a hydrophobic PICBA core and a hydrophilic dextran corona. In vivo, they are recognized by the macrophages of the mononuclear phagocyte system. The amount of BSA bound to the particles, at adsorption equilibrium, has been determined through immunodiffusion, immunoelectrophoresis, and SANS. For particles with a radius of 25.3 nm, the adsorption was found to saturate at 64 adsorbed BSA molecules per particle. The configuration of the adsorbed BSA molecules was determined from the SANS scattering curves, first at full contrast, and then at contrast match. Both experiments indicate that the BSA molecules are adsorbed on the PICBA core, in a flat configuration. This result may be important for understanding the in vivo opsonization mechanisms of nanoparticles and their resulting biodistribution.     

Facile fabrication of pH-sensitive core-shell nanoparticles based on HEC and PMAA via template polymerization

Taking advantage of the specific hydrogen bonding interactions between the components, core-shell nanoparticles based on poly(methacrylic acid) (PMAA) and hydroxyethyl cellulose (HEC) can be efficiently prepared via facile one-step polymerization of MAA on HEC template in water. Various techniques were used to characterize in detail the sizes, morphology, and structures of the nanoparticles, as well as the interactions between the components. The core-shell structures of the nanoparticles were confirmed by TEM observation. Dynamic light scattering and fluorescence spectrometry were used to monitor the polymerization process, which indicates a size decrease and a hydrophobicity increase of the nanoparticles. A mechanism was proposed to explain the formation of core-shell nanoparticles during the template polymerization. The obtained nanoparticles are stable against urea, salt, temperature and in the storage; meanwhile, they exhibit pH-response: the volume of the nanoparticles increased more than six times as pH value of the medium increased from 2.8 to 3.7.     

Development and characterization of new insulin containing polysaccharide nanoparticles

A nanoparticle insulin delivery system was prepared by complexation of dextran sulfate and chitosan in aqueous solution. Parameters of the formulation such as the final mass of polysaccharides, the mass ratio of the two polysaccharides, pH of polysaccharides solution, and insulin theorical loading were identified as the modulating factors of nanoparticle physical properties. Particles with a mean diameter of 500 nm and a zeta potential of approximately −15 mV were produced under optimal conditions of DS:chitosan mass ratio of 1.5:1 at pH 4.8. Nanoparticles showed spherical shape, uniform size and good shelf-life stability. Polysaccharides complexation was confirmed by differential scanning calorimetry and Fourier transformed infra-red spectroscopy. An association efficiency of 85% was obtained. Insulin release at pH below 5.2 was almost prevented up to 24 h and at pH 6.8 the release was characterized by a controlled profile. This suggests that release of insulin is ruled by a dissociation mechanism and DS/chitosan nanoparticles are pH-sensitive delivery systems. Furthermore, the released insulin entirely maintained its immunogenic bioactivity evaluated by ELISA, confirming that this new formulation shows promising properties towards the development of an oral delivery system for insulin.     

Preparation of dextran immunological magnetic nanoparticles and their application to combined targeting carrier

Superparamagnetic dextran nanoparticles were prepared by coprecipitation. Effects of concentration of dextran, amount of ironic salts, stirring speed, concentration of ammonium hydroxide and mole ratio of Fe3+/Fe2+ on the effective diameter of dextran magnetic nanopartides (DMNP) were studied. Dextran immunological magnetic nanoparticles (DIMNP) were formed by the reaction of the monoclonal anti-human mammary cancer antibody with DMNP oxidized by sodium periodate, and the properties of magnetic susceptibility, shape and retention of antibody activity were investigated. The in vitro cancer antigen binding ability of DIMNP was demonstrated by radioimmunoassay, and the in vivo magnetic localization and antibody targeting ability of radiolabeled DIMNP were studied.     

Influence of stabilizers on particle size and polydispersity of polybutyl- and polyisobutil-cyanoacrylate nanoparticles

The effect of dextran 40 and Poloxamer 188 as stabilizers in nanoparticle systems produced by dispersion polymerization is studied. Two different polymeric nanoparticle compositions are selected: polybutyl and polyisobutyl-2-cyanoacrylate. The parameters analyzed are the particle size and the polydispersity index which are determined by photon correlation spectroscopy. Results point out that the two polymers exhibit a nearly identical behavior. The action of both stabilizers is different and the addition of the two stabilizers together does not improve the particle size distribution of a nanoparticle system. The possible explanation of the different behavior is discussed.     

Synthesis of Ni-poor NiO nanoparticles for p-DSSC applications

To improve the performances of p-Dye Sensitized Solar Cell (p-DSSC) for the future, the synthesis of modified p-type nickel oxide semiconductor, commonly used as photocathode in such devices, was initiated with Ni₃O₂(OH)₄ as precursor. This specific nickel oxyhydroxide was first characterized by X-ray photo-electron spectroscopy and magnetic susceptibility measurements. Then its thermal decomposition was thoroughly studied in order to control the particles size of the as-prepared NiO nanopowders. Low temperature decomposition in air of this precursor allows the formation of Ni_1−xO nanoparticles with a large amount of Ni vacancies and specific surface areas up to 250 m² g⁻¹. Its ammonolysis at 250 °C leads to nanostructured N-doped NiO (NiO:N) materials.     

Thermoresponsive polymeric nanoparticles stabilized by surfactants

Solutions of poly(N-isopropylacrylamide) (PNIPA) with ionic and nonionic surfactants were investigated by light scattering methods at temperatures 15–45 °C. In contrast to previous studies, where surfactants were used in excess, lower concentrations of surfactants were used. The formation of well-defined nanoparticles of PNIPA was observed on heating above the lower critical solution temperature. The effect of PNIPA and surfactant concentrations, and molecular weight of PNIPA on nanoparticle parameters and on the phase transition temperature of PNIPA solutions were investigated. An interpretation based on stabilization of PNIPA nuclei by surfactants was suggested.     

Colloidal surfactant-free syntheses of precious metal nanoparticles for electrocatalysis

The successful study, understanding, optimization, and ultimately scaling up of electroactive and stable electrodes strongly rely on the careful design and preparation of electrocatalytic materials. In particular, precious metal nanoparticles are key electrocatalysts for a wide range of reactions. Colloidal syntheses offer several advantages to develop precious metal nanoparticles but unfortunately often require capping agents to stabilize the nanoparticles. These ligands or surfactants often block the surface active sites and need to be removed by time and/or energy demanding steps. These extra steps potentially (unnecessarily) complicate studies, might impair reproducibility and limit a direct transfer of fundamental breakthroughs to real-life applications. Fortunately, a range of surfactant-free syntheses have been reported and are well-suited to develop electrocatalysts with improved activity. Surfactant-free syntheses also bear promising features towards high-throughput screening of multi-metallic nanomaterials to explore new concepts in electrode design.     

Synthesis and characterization of gallium oxide nanoparticles

This review is based on the literature describing several methods for the synthesis of gallium oxide nanoparticles. Several techniques have been used for the synthesis of gallium oxide Ga₂O₃ nanoparticles. Gallium oxide Ga₂O₃ nanoparticles have been synthesized from different precursors. Different synthetic methods and different precursors produce nanoparticles which vary in size and shape. Over a dozen of synthetic methods for preparation of gallium oxide Ga₂O₃ nanoparticles together with the characterization techniques used have been discussed.     

Synthetic antigens based on polymeric coumarin derivatives

The paper gives the results of the synthesis and a study of the structure of copolymers of 14 coumarin derivatives with N-vinylpyrrolidone. Using physicochemical methods, their characteristic viscosities, molecular masses, and chemical compositions have been determined. As the result of the immunological investigation performed, it has been shown that some of them possess antigenic properties. Thus, a new type of synthetic antigen has been created.Institute of Toxicology, Ministry of Health of the USSR, Leningrad. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 38–43, January–February, 1984.     

Preparation, characterization and enzyme inhibition of methylmethacrylate copolymer nanoparticles with different hydrophilic polymeric chains

Methylmethacrylate copolymer nanoparticles with different hydrophilic chains were prepared by the free radical polymerization of methylmethacrylate with N-isopropylacrylamide (NIPAAm), N-methacrylic acid (MAA), N-trimethylaminoethylmethacrylate chloride (TMAEMC) or N-dimethylaminoethylmethacrylate hydrochloride (DMAEMC). These particles were characterized by particle size and zeta potential. The polymerization conditions were shown to influence the particle size and surface charge. Particle sizes of MMA-NIPAAm nanoparticles after 3 h of reaction reached constant level at 180 nm. An increasing amount of total monomer (0.5-5%) would result in the nanoparticles of particle size of 115-204 nm for 30% NIPAAm of the total monomer. In the same range of 5-40% NIPAAm of the total monomer, the particle size decreased from 280 to 170 nm. The concentration of the initiator APS up to a concentration of 0.2% for MMA-TMAEMC and 0.1% for MMA-NIPAAm showed no effect on the particle size of the final nanoparticle suspensions, while higher concentration would lead to aggregation in the polymerization process. MMA-NIPAAm nanoparticles were pH-dependent in zeta potential at pH 1-12 values reducing from 12.2 mV to −16.8 mV, respectively. Nanoparticles were incubated with pepsin and trypsin at 37 °C for 20 min and their enzyme inhibition was determined. The activity of pepsin decreased to 27% in the presence of MMA-NIPAAm nanoparticles, and MMA-MAA nanoparticles reduced the activity of trypsin to 39%, respectively.     

Preparation and study of photoswitchable fluorescence nanoparticles based on spirobenzopyran

The preparation and performance characterization of〈50 nm spirobenzopyran-based photochromic nanocomposites with photoswitchable fluorescence are presented.The nanocomposites were fabricated by means of a modifed miniemulsion polymerization process,in which the hydrophobic spirobenzopyran was covalently attached to the polymer chains and the matched fluorescent dyes were noncovalently embedded in the nanoscale cross-linked polymeric matrix,respectively.The obtained nanocomposites with a high relative fluorescence quantum yield（Q）exhibited superior fluorescent photoswitchable performance due to the effective photo-induced intermolecular energy transfer.The stability of photomerocyanine was also improved.     

Preparation of reactive polymeric nanoparticles (RPNPs)

A series of reactive polymeric nanoparticles (RPNPs) was prepared by free radical nonlinear copolymerization of mono (M ₁) and trivinyl acrylic (M ₂) monomers in miniemulsion. The crosslinking density was determined by the mole ratio of the trivinyl component. It was found that the unswelled latex nanoparticles showed a narrower dispersity than in the organic solution of macromolecules. In latex, the size increased with the ratio of M ₂ monomer due to its higher polarity in the aqueous medium. However, the swollen nanoparticles, dissolved or dispersed in organic solvent, showed a higher dispersity as a function of composition and the crosslinking density. The residual vinyl groups adjacent to the nanoparticles were subjected to further crosslinking reactions. The reactive vinyl groups were detected by nuclear magnetic resonance spectroscopy (NMR). The size of particles in swollen state was determined by dynamic laser light scattering (DLS) method and the dried form by scanning electron microscopy (SEM). It was found that size of RPNPs is in the range of 50 to 500 nm. These particles possess properties that may allow their application in areas as disparate as dental filling material and as a component in industrial powder-based coatings.     

Morphology evolution of ZrB2 nanoparticles synthesized by sol-gel method

Zirconium diboride (ZrB₂) nanoparticles were synthesized by sol-gel method using zirconium n-propoxide (Zr(OPr)₄), boric acid (H₃BO₃), sucrose (C₁₂H₂₂O₁₁), and acetic acid (AcOH). Clearly, it was a non-aqueous solution system at the very beginning of the reactions. Here, AcOH was used as both chemical modifier and solvent to control Zr(OPr)₄ hydrolysis. Actually, AcOH could dominate the hydrolysis by self-produced water of the chemical propulsion, rather than the help of outer water. C₁₂H₂₂O₁₁ was selected, since it can be completely decomposed to carbon. Thus, carbon might be accounted precisely for the carbothermal reduction reaction. Furthermore, we investigated the influence of the gelation temperature on the morphology of ZrB₂ particles. Increasing the gelation temperature, the particle shapes changed from sphere-like particles at 65 °C to a particle chain at 75 °C, and then form rod-like particles at 85 °C. An in-depth HRTEM observation revealed that the nanoparticles of ZrB₂ were gradually fused together to evolve into a particle chain, finally into a rod-like shape. These crystalline nature of ZrB₂ related to the gelation temperature obeyed the “oriented attachment mechanism” of crystallography.     

The synthesis of polyacrylamide nanoparticles in supercritical carbon dioxide

Polyacrylamide nanoparticles, 50 to 200 nm, were created by inverse emulsion polymerization of acrylamide in supercritical carbon dioxide. The cross-linked polyacrylamide was produced by intermolecular imidization.     

Immobilization of the enzymeL-asparaginase fromE. coli on polysaccharides. VI. Preparation and properties of polymeric derivatives based on dextran carbonates

Methods have been developed for obtaining soluble and insoluble dextran carbonates. The addition of the latter to E. coli L-asparaginase has given water-soluble, gel-like, and insoluble forms of the immobilized enzyme. The influence of the bound polymer on some physicochemical properties of L-asparaginase has been determined. The antileukemic action of soluble dextran derivatives of L-asparaginase has shown that their efficiency is greater than that of the native enzyme. A. Kirkhenshtein Institute of Microbiology, Latvian Academy of Sciences, Riga. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 432–436, May–June, 1993.     

Effect of dextran molecular weight on resonance light-scattering of quantum dots modified with dextran and concanavalin A

The reversible aggregation between dextran-conjugated CdSe quantum dots(Dex-CdSe-QDs) and concanavalin A(Con A) was explored based on the specific affinity of polysaccharide for Con A by resonance light-scattering technique.In this study,the aggregation of Dex-CdSe-QDs induced by Con A and sequential dissociation by glucose was determined over a wide range of dextran molecular mass(10-500 kDa).The results demonstrate that the sensitivity of lectin-dextran-modified-QDs interactions increase with dextran molecular mass,and an optimum dextran molecular mass is 500 kDa.     

葡聚糖及其衍生物对大麦细胞电融合的影响

葡聚糖及其衍生物对大麦细胞电融合的影响①王伟江志裕＊（复旦大学化学系上海２００４３３）细胞融合是指用人工方法使两个细胞融合成一个细胞的过程［１,２］．体细胞融合可在不同种,不同属,甚至更远的生物间进行,所得到的细胞可具有新的特性．对于植物细胞,有望通...     

Effect of dextran polymer on glycocalyx structure and cell electrophoretic mobility

We determined the electrophoretic mobility of human red blood cells suspended in physiological dextran solution for polymer samples with different polydispersity indexes. The electrophoretic mobility of cells is shown to depend mainly on the physical and hydrodynamical characteristics of the porous glycocalyx coating the membrane bilayer. We then propose a new model for the observed increases in effective mobility when cells are exposed to neutral polymers. The extension of glycoproteins under the action of weakly adsorbed chains is shown to reduce the frictional interaction of the surface coat on the flowing liquid. Such a structural rearrangement of the outer membrane improves the penetration of the electro-osmotic flow within the glycocalyx and increases the effective cell mobility.