叶酸和聚乙二醇接枝作基因载体用壳聚糖的合成与表征

本研究将叶酸和聚乙二醇接枝到四种不同分子量的壳聚糖氨基侧链上,以改善壳聚糖的靶向性和水溶性作基因载体。用FTIE、1HNMR、UV-Vis、DSC和TEM对产物进行了表征,结果表明,叶酸和聚乙二醇被成功地接枝到壳聚糖上,所制得的载体有望作为潜在的肿瘤细胞靶向基因载体。     

An analysis of the complexation between poly(aspartic acid) and poly(ethylene glycol)

The compatibility between poly(aspartic acid) and poly(ethylene glycol) for the formation of an interpolymer complex (IPC) was investigated by dynamic rheology and evaluation of zeta potential values. The homogeneity of the realized IPC was observed by near infrared chemical imagistic (NIR-CI) technique. The data were sustained and underlined by the assessment of the compatibility between the polymeric compounds.     

Preparation, characterization and application of pyrene-loaded methoxy poly(ethylene glycol)–poly(lactic acid) copolymer nanoparticles

Pyrene-loaded biodegradable polymer nanoparticles were prepared by incorporating pyrene into the polymer nanoparticles formulated from amphiphilic diblock copolymer, methoxy poly(ethylene glycol)–poly(lactic acid) (MePEG–PLA). Their morphological structure and physical properties were characterized by nuclear magnetic resonance (NMR), dynamic light scattering, fluorescence spectroscopy, transmission electronic microscopy and zeta potential measurements. Further, MePEG–PLA nanoparticles containing pyrene as fluorescent marker were administered intranasally to rats, and the distribution of nanoparticles in the nasal mucosa and the olfactory bulb were visualized by fluorescence microscopy. NMR results confirmed that MePEG–PLA copolymer can form nanoparticles in water, and hydrophilic PEG chains were located on the surface of the nanoparticles. The particle size, zeta potential and pyrene loading efficiency of MePEG–PLA nanoparticles were dependent on the PLA block content in the copolymer. Following nasal administration, the absorption of nanoparticles across the epithelium was rapid, with fluorescence observed in the olfactory bulb at 5 min, and a higher level of fluorescence persisted in the olfactory mucosa than that in the respiratory mucosa. These results show that pyrene could serve as a useful fluorescence probe for incorporation into polymer nanoparticles to study tissue distribution and MePEG–PLA nanoparticles might have a great potential as carriers of hydrophobic drugs.     

Electrospun fibers of poly(ethylene terephthalate) blended with poly(lactic acid)

Fibrous blends of polyethylene terephthalate (PET) and polylactic acid (PLA) were fabricated by electrospinning (ES) from a common solvent, at concentrations of PET/PLA = 100/0, 70/30, 50/50, 30/70, and 0/100. Oriented fiber mats were studied either as-spun, or after a cold-crystallization treatment. Scanning electron microscopy of as-spun amorphous fibers showed that addition of PLA into the ES solution prevents occurrence of beads. In some compositions, two glass transitions were observed by temperature-modulated differential scanning calorimetry indicating that the two components in the ES fibers were phase separated. Thermogravimetric analysis was used to study thermal degradation at high temperatures. PLA degrades at a temperature about 100 °C lower than that of PET, and holding or cycling the blends to high temperature can result in the degradation of PLA. Degree of crystallinity was determined using DSC for as-spun and cold-crystallized ES blend fibers. The degree of crystallinity of each blend component is reduced by the presence of the other blend component, and the overall crystallinity of the blend fibers is less than that of the homopolymer fibers. Wide-angle X-ray scattering results show that oriented crystals were formed in the blended electrospun fibers collected on a rotating collector. The cold-crystallization process leads to both PET and PLA crystallizations. Oriented crystallites form even when the fiber is crystallized with its ends free to shrink.     

Synthesis and pyrolysis of ABC type miktoarm star copolymers with polystyrene,poly(lactic acid) and poly(ethylene glycol) arms

An ABC type miktoarm star copolymer possessing polystyrene (PS), poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) arms was synthesized by combining Atom Transfer Radical Polymerization (ATRP) and Ring Opening Polymerization (ROP) with two click chemistries, namely thiol–ene and copper catalyzed azide–alkyne cycloaddition (CuAAC). For this purpose, a core 1-(allyloxy)-3-azidopropan-2-ol with allyl and azide functionalities was synthesized in two steps. Then, clickable polymers, polystyrene with thiol functionality (PS–SH) and poly(ethylene glycol) with alkyne functionality (PEG–acetylene) were independently prepared. As the first step of the grafting onto process, PS–SH was thiol–ene clicked onto the core to yield PS–N₃–OH. The second arm was then incorporated onto the core by the Ring Opening Polymerization (ROP) of l-(?)-Lactide (LA) using as PS–N₃–OH initiator and tin(II) 2-ethylhexanoate as catalyst. Finally, alkyne–PEG–acetylene was bonded to the resulting PLA–PS–N₃ using CuAAC click reaction. All intermediates, related polymers at different stages and final PS–PLA–PEG miktoarm star copolymer were characterized by ¹H NMR, FT-IR, SEC and DP-MS analyses. Direct pyrolysis mass spectrometry, (DP-MS) analyses of PS–PLA–PEG and all intermediate polymers indicated that the decomposition of PS and PEG chains occurred almost independently, following the degradation mechanisms of the corresponding homopolymers. On the other hand, during the pyrolysis of PS–PLA–PEG, elimination of H₂O during the decomposition of PEG chains at the early stages of pyrolysis caused hydrolysis of PLA chains and increased the yields of CO₂, CO and units involving unsaturation and/or crosslinked structure.     

Thermal behaviors and mechanical properties of halloysite nanotube-reinforced poly(lactic acid) nanocomposites

Poly(lactic acid)/halloysite nanotubes (PLA/HNTs) nanocomposites were prepared using melt compounding followed by compression molding. N,N′-ethylenebis(stearamide) (EBS) was used to improve the dispersion of HNTs and toughen the PLA nanocomposites. The thermal properties of PLA/HNTs nanocomposites were assessed by using differential scanning calorimeter and thermogravimetric analyzer (TG). The TG measurements were performed at both nitrogen and oxygen atmosphere. The mechanical properties of PLA/HNTs were characterized through tensile and impact tests. The morphological properties of the PLA/HNTs nanocomposites were investigated by using transmission electron microscopy and field emission scanning electron microscopy. The degree of crystallinity of PLA nanocomposites was increased slightly by the addition of EBS. The decomposition process of PLA/HNTs depends on the atmosphere reaction during TG test as well as the amount of EBS. The best mechanical properties of PLA/HNTs nanocomposites expressed by the impact strength and elongation at break were achieved by the addition of 5 mass% of EBS.     

Improved heat resistance in poly (lactic acid)/ethylene butyl methacrylate glycidyl methacrylate terpolymer blends by controlling highly filled talc particles

Journal of Thermal Analysis and Calorimetry - Heat resistance poly(lactic acid) PLA/ethylene butyl methacrylate glycidyl methacrylate terpolymer (GEBMA)/talc composites were fabricated by melt...     

Vibrational analysis of molten poly(ethylene glycol)

The infrared absorption of poly(ethylene glycol) was measured in the molten state. Characteristic bands of the molten state were identified. Normal vibrations and frequency distributions were treated for various conformation models with CH₂CH₂O repeat units. The infrared absorption peaks of the molten state closely correspond to the frequency distribution peaks of the TGT conformation with gauche O? CH₂? CH₂? O groups, although infrared bands due to trans O? CH₂? CH₂? O groups are also observed. Vibrational assignments of the infrared bands and Raman lines were made on the basis of potential energy distributions.     

Molecular structure and dynamics of poly(methacrylic acid) and poly(acrylic acid) complexes with dodecyl-substituted poly(ethylene glycol)

The molecular dynamics and the structure of molecular complexes formed by micelles of dodecyl-substituted poly(ethylene glycol) with poly(methacrylic acid) and poly(acrylic acid) in aqueous solutions were studied by viscosimetry, pH measurement, and electron spin resonance spin-probe techniques. At low surfactant concentrations, the conformation of the complex is a compact globule. The local mobility of surfactant molecules in such a complex is much slower than that in the free micelle. At high surfactant concentration, the nonionic micelles and polyacids form hydrophilic associates. The associates have the conformation of extended coils. In an associate, a major part of the micellar poly(ethylene glycol) groups is free. The local mobility of the micellar phase depends on the number of micelles involved in an associate. The mobility of surfactant molecules is slower in the complexes of poly(methacrylic acid) than in the complexes of poly(acrylic acid).     

Novel cationic 6-lauroxyhexyl lysinate modified poly(lactic acid)-poly(ethylene glycol) nanoparticles enhance gene transfection

The leading principle of non-viral delivery systems for gene therapy is to mediate high levels of gene expression with low cytotoxicity. Nowadays, biodegradable nanoparticles formulated with poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) were wildly developed. However, the relative lower gene transfection efficiency and higher cytotoxicity still remained critical problems. To address these limitations, PLA-PEG nanoparticles have been composited with other components in their formulation. Here, a novel cationic lipid, 6-lauroxyhexyl lysinate (LHLN), was fabricated onto PLA-PEG nanoparticles as a charge modifier to improve the transfection efficiency and cytotoxicity. The obtained cationic LHLN modified PLA-PEG nanoparticles (LHLN-PLA-PEG NPs) could condense pDNA thoroughly via electrostatic force, leading to the formation of the LHLN-PLA-PEG NPs/pDNA complexes (NPs/DNA complexes). The nanoparticles obtained have been characterized in relation to their physicochemical and biological properties, and the results are extremely promising in terms of low cell toxicity and high transfection efficiency. These results indicated that the novel cationic LHLN modified PLA-PEG nanoparticles could enhance gene transfection in vitro and hold the potential to be a promising non-viral nanodevice.     

Well-defined Poly(lactic acid)s Containing Poly(ethylene glycol) Side-chains

Poly(ethylene glycol) (PEG) side-chain functionalized lactide analogues have been synthesized in four steps from commercially available L-lactide. The key step in the synthesis is the 1,3-dipolar cycloaddition between PEG-azides and a highly strained spirolactide-heptene monomer, which proceeds in high conversions. The PEG-grafted lactides analogues were polymerized via ring-opening polymerization using triazacyclodecene as organocatalyst to give well-defined tri- and hepta-(ethylene glycol)-poly(lactide)s (PLA) with molecular weights above 10 kDa and polydispersity indices between 1.6 and 2.1. PEG-poly(lactide) (PLA) with PEG chain M(n) 2000 was also prepared but GPC analysis showed a bimodal profile indicating the presence of starting macromonomer. Cell adhesion assays were performed using MC3T3 E-1 osteoblast-like cells demonstrating that PEG-containing PLA reduces cell adhesion significantly when compared to unfunctionalized PLA.     

Multiple melting behavior of poly(lactic acid) filled with modified carbon black

Two melting peaks are generally observed in a heating scan for isothermally crystallized poly(lactic acid) (PLA)/carbon black (CB) and PLA/modified carbon black (MCB) composites. To investigate the origin of the above double melting behavior, the melting behavior after isothermal crystallization was analyzed with differential scanning calorimetry, wide‐angle X‐ray diffraction, and small angel X‐ray scattering techniques. The double melting of the crystallized samples can be explained by the model of two populations of lamellae, the double peaks of low and high temperatures are contributed to the melting of the small lamellae produced by secondary crystallization and that of the major crystals formed in the primary crystallization process, respectively. Spherulitic growth rates of the neat PLA and PLA/MCB composite were analyzed and the occurrence of a regime transition was demonstrated. For the PLA, a clear regime transition was observed at around 125 °C. For the PLA/MCB, it occurred at 130 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1971–1980, 2009     

Segmented block copolymers of poly(ethylene glycol) and poly(ethylene terephthalate)

A new series of segmented copolymers were synthesized from poly(ethylene terephthalate) (PET) oligomers and poly(ethylene glycol) (PEG) by a two‐step solution polymerization reaction. PET oligomers were obtained by glycolysis depolymerization. Structural features were defined by infrared and nuclear magnetic resonance (NMR) spectroscopy. The copolymer composition was calculated via ¹H NMR spectroscopy. The content of soft PEG segments was higher than that of hard PET segments. A single glass‐transition temperature was detected for all the synthesized segmented copolymers. This observation was found to be independent of the initial PET‐to‐PEG molar ratio. The molar masses of the copolymers were determined by gel permeation chromatography (GPC). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4448–4457, 2004     

Gas‐forming poly(ethylene glycol)‐b‐poly(L‐lactic acid) micelles

In this study, a novel drug‐carrying micelle composed of methoxy poly(ethylene glycol) (mPEG)‐b‐poly(L‐lactic acid) (PLLA) with gas‐forming carbonate linkage was fabricated. Here, the gas‐forming carbonate linkage was formed by the chemical coupling of the terminal hydroxyl group of the PLLA block and benzyl chloroformate (BC). mPEG‐b‐PLLA‐BC was self‐organized in aqueous solution: the PEG block on the hydrophilic outer shell and the PLLA‐BC block in the hydrophoboic innor core. The cleavage of carbonate linkage by hydrolysis and formation of carbon dioxide nanobubbles in the micellar core enabled an accelerated release of the encapsulated anticancer drug (doxorubicin: DOX) from the mPEG‐b‐PLLA‐BC micelles. The amount of drug (DOX) released from the mPEG‐b‐PLLA‐BC micelle was higher than that from the conventional mPEG‐b‐PLLA micelle, which allowed for increased in vitro toxicity against KB tumor cells. Copyright © 2013 John Wiley & Sons, Ltd.     

Crystallization behavior and mechanical properties of poly(lactic acid)/poly(ethylene oxide) blends nucleated by a self-assembly nucleator

Poly(lactic acid) (PLA)/poly(ethylene oxide) (PEO) blends nucleated by a self-assembly nucleating agent, N,N′,N″-tricyclohexyl-1,3,5-benzenetricarboxylamide (BTCA), were prepared by melt blending. The crystallization behavior and mechanical properties of the materials were investigated by differential scanning calorimetry, polarized optical microscopy, wide-angle X-ray diffraction, dynamic mechanical analyzer and tensile testing. It was found that PEO had a synergistic effect together with BTCA on promoting PLA crystallization, besides its toughening effect on the material. Moreover, BTCA revealed prominent reinforcement effect on both neat PLA and PLA/PEO blends in the glass transition region and above, indicating the improvement on the heat resistance of the materials.

     

Micropallet arrays with poly(ethylene glycol) walls

Arrays of releasable micropallets with surrounding walls of poly(ethylene glycol) (PEG) were fabricated for the patterning and sorting of adherent cells. PEG walls were fabricated between the SU-8 pallets using a simple, mask-free strategy. By utilizing the difference in UV-transmittance of glass and SU-8, PEG monomer was selectively photopolymerized in the space surrounding the pallets. Since the PEG walls are composed of a cross-linked structure, the stability of the walls is independent of the pallet array geometry and the properties of the overlying solution. Even though surrounded with PEG walls, the individual pallets were detached from the array by the mechanical force generated by a focused laser pulse, with a release threshold of 6 microJ. Since the PEG hydrogels are repellent to protein adsorption and cell attachment, the walls localized cell growth to the pallet top surface. Cells grown in the microwells formed by the PEG walls were released by detaching the underlying pallet. The released cells/pallets were collected, cultured and clonally expanded. The micropallet arrays with PEG walls provide a platform for performing single cell analysis and sorting on chip.     

In‐situ thermal reduction and effective reinforcement of graphene nanosheet/poly (ethylene glycol)/poly (lactic acid) nanocomposites

This study aims to achieve a molecule‐level dispersion of graphene nanosheets (GNSs) and a maximum interfacial interaction between GNSs and a polymer matrix. GNS‐reinforced poly (ethylene glycol) (PEG)/poly (lactic acid) (PLA) nanocomposites are obtained by a facile and environment‐friendly preparation method. Graphite oxide and GNSs are characterized by atomic force microscopy, Raman spectroscopy, and X‐ray diffraction. Scanning electron microscopy shows that the state of dispersion of the GNS in the PEG/PLA matrix is distribution. The tensile strength and Young's modulus increases by 45% and 188%, respectively, with the addition of 4.0 wt% GNSs. The thermal stability of the GNS‐based nanocomposites also improves. Differential scanning calorimetry indicates that GNSs have no remarkable effect on the crystallinity of the nanocomposites. The effective reinforcement of the nanocomposites is mainly attributed to the highly strong molecular‐level dispersion of the GNSs in the polymer matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Complex formation of daunomycin with poly(vinylpyrrolidone) and poly(ethylene glycol)

Russian Journal of General Chemistry - Complexes of the anthracycline antitumor antibiotic daunomycin with biocompatible polymer carriers, poly(vinylpyrrolidone) and poly(ethylene glycol), have...     

Competitive complex forming reactions between monosubstituted and nonsubstituted poly(ethylene glycol)s with poly(methacrylic) acid

A competitive complex forming reaction between a number of monosubstituted poly(ethylene glycol)s (PEG*) containing a hydrophobic group of differing chemical nature and nonsubstituted PEG of various molecular weights with poly(methacrylic acid) (PMAA) was studied. A UV spectroscopy method was used. During the transfer of the hydrophobic chromophoric group from the aqueous medium into the hydrophobic domains of the polycomplex (PMAA.PEG*), a bathochromic effect was observed. The introduction of a hydrophobic group into the PEG chain leads to stabilization of the polycomplex (PMAA.PEG) that is formally the same as growing the chain length of PEG. The polymerization degree of PEG having the same competitive power as PEG* can be used as the peculiar scale of the complex forming ability of PEG* in the complexation with PMAA. © 1996 John Wiley & Sons, Inc.