Xanthate‐mediated polymerization of styrene on hyperbranched polyethylenimine: Synthesis,characterization, and guest‐encapsulating property

Hyperbranched polyethylenimine (HPEI) is a highly polar, multifunctional polymer bearing active amines throughout its globular structure. In this article, the amino protons, which were incompatible with living radical polymerization techniques, were alkylated with propylene oxide, leading to tertiary amines and hydroxyls, and part of the hydroxyl groups were further transformed into xanthate groups. The HPEI‐xanthate could mediate the polymerization of styrene, leading to a star‐like, multiarm amphiphilic polymer. It was found that the polymerization was a hybrid of living and conventional radical processes. The resulting amphiphilic, core‐shell‐structured polymer existed as a unimolecular micelle (UIM) in apolar solvent and could irreversibly encapsulate water‐soluble anionic dyes. At high pH, the encapsulated dyes could be partly released. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

季铵化聚乙烯亚胺/SiO_2微粒的制备及其抗菌性能

通过4-溴丁酰氯的媒介,将水溶性聚乙烯亚胺(PEI)接枝在纳米SiO2表面,分别用1-溴己烷和碘甲烷对接枝的PEI进行N-烷基化修饰,使PEI中的部分氨基转变成季铵盐,得到水不溶性季铵化聚乙烯亚胺(QPEI)/SiO2微粒,其中PEI接枝量质量分数为14.8%,季铵化的氨基质量分数22.8%。红外光谱分析证实PEI接枝在纳米SiO2表面,随后成功地被卤代烷N-烷基化修饰。透射电镜观察发现QPEI/SiO2的形态不规则,大多数颗粒团聚成200—300 nm的微粒。抗菌检测结果表明,QPEI/SiO2微粒对金黄色葡萄球菌(S.aureu)和大肠杆菌(E.coli)的最小抑菌质量浓度(MIC)分别为80μg/mL和1 200μg/mL。QPEI/SiO2微粒破坏了细胞的完整性,最终将整个细胞分解成碎片。     

Innovative Strategy for MicroRNA Delivery in Human Mesenchymal Stem Cells via Magnetic Nanoparticles

Bone marrow derived human mesenchymal stem cells (hMSCs) show promising potential in regeneration of defective tissue. Recently, gene silencing strategies using microRNAs (miR) emerged with the aim to expand the therapeutic potential of hMSCs. However, researchers are still searching for effective miR delivery methods for clinical applications. Therefore, we aimed to develop a technique to efficiently deliver miR into hMSCs with the help of a magnetic non-viral vector based on cationic polymer polyethylenimine (PEI) bound to iron oxide magnetic nanoparticles (MNP). We tested different magnetic complex compositions and determined uptake efficiency and cytotoxicity by flow cytometry. Additionally, we monitored the release, processing and functionality of delivered miR-335 with confocal laser scanning microscopy, real-time PCR and live cell imaging, respectively. On this basis, we established parameters for construction of magnetic non-viral vectors with optimized uptake efficiency (~75%) and moderate cytotoxicity in hMSCs. Furthermore, we observed a better transfection performance of magnetic complexes compared to PEI complexes 72 h after transfection. We conclude that MNP-mediated transfection provides a long term effect beneficial for successful genetic modification of stem cells. Hence, our findings may become of great importance for future in vivo applications.     

Immobilization of invertase onto crosslinked poly(p‐chloromethylstyrene) beads

Invertase was immobilized onto poly(p‐chloromethylstyrene) (PCMS) beads that were produced by a suspension polymerization with an average size of 186 μm. The beads had a nonporous but reasonably rough surface. Because of this, a reasonably large external surface area (i.e., 14.1 m²/g) could be achieved with the proposed carrier. A two‐step functionalization protocol was followed for the covalent attachment of invertase onto the bead surface. For this purpose, a polymeric ligand that carried amine groups, polyethylenimine (PEI), was covalently attached onto the bead surface by a direct chemical reaction. Next, the free amine groups of PEI were activated by glutaraldehyde. Invertase was covalently attached onto the bead surface via the direct chemical reaction between aldehyde and amine groups. The appropriate enzyme binding conditions and the batch‐reactor performance of the immobilized enzyme system were investigated. Under optimum immobilization conditions, 19 mg of invertase was immobilized onto each gram of beads with 80% retained activity after immobilization. The effects of pH and temperature on the immobilized invertase activity were determined and compared with the free enzyme. The kinetic parameters K_M and V_M were determined with the Michealis–Menten model. K_M of immobilized invertase was 1.75 folds higher than that of the free invertase. The immobilization caused a significant improvement in the thermal stability of invertase, especially in the range of 55–65°C. No significant internal diffusion limitation was detected in the immobilized enzyme system, probably due to the surface morphology of the selected carrier. This result was confirmed by the determination of the activation energies of both free and immobilized invertases. The activity half‐life of the immobilized invertase was approximately 5 times longer than that of the free enzyme. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1268–1279, 2002     

Hydrogen storage properties of highly cross-linked polymers derived from chlorinated polypropylene and polyethylenimine

Highly cross-linked polymer derived from chlorinated polypropylene (CPP) grafted with polyethylenimine (PEI) was synthesized by hydrothermal amination reaction. The influence of different reaction conditions on the structure and properties of highly cross-linked polymer was investigated. The structures of the polymers named CPP-g-PEI were characterized by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis (EA), ¹³C solid-state NMR (¹³C NMR), thermogravimetric analysis (TG), scanning electron microscopy (SEM), transmission electron microscope (TEM), powder X-ray diffraction (PXRD) and nitrogen sorption technique. CPP-g-PEI had honeycomb-like pores with an average size of between 5.37 and 13.54 nm and was thermally stable up to 250 °C. CPP-g-PEI was amorphous porous polymer with some spherulites. The N content of CPP-g-PEI increased and the Cl content of CPP-g-PEI decreased after hydrothermal amination reaction. The hydrogen storage properties of different CPP-g-PEI samples were determined by a hydrogen storage analyzer. Among all samples, hydrogen storage capacity of CPP-g-PEI at 100 °C and triethylamine solvent (CPP-g-PEI-2) achieved the highest hydrogen uptake 11.26 wt% at 77 K, 5 MPa. In addition, OH⁻ type CPP-g-PEI (CPP-g-PEI_OH−) exhibited a hydrogen uptake of 2.47 wt% at 300 K, 5 MPa. BET specific surface area of the sample was not directly associated with hydrogen storage capacity. Hydrogen adsorption enthalpy of CPP-g-PEI-2 was calculated by the Arrhenius equation to be 38.79 kJ/mol and the adsorption process of CPP-g-PEI was investigated to be reversible physical adsorption.     

Photothermally Controlled Gene Delivery by Reduced Graphene Oxide–Polyethylenimine Nanocomposite

Externally stimuli‐triggered spatially and temporally controlled gene delivery can play a pivotal role in achieving targeted gene delivery with maximized therapeutic efficacy. In this study, a photothermally controlled gene delivery carrier is developed by conjugating low molecular‐weight branched polyethylenimine (BPEI) and reduced graphene oxide (rGO) via a hydrophilic polyethylene glycol (PEG) spacer. This PEG–BPEI–rGO nanocomposite forms a stable nano‐sized complex with plasmid DNA (pDNA), as confirmed by physicochemical studies. For the in vitro gene transfection study, PEG–BPEI–rGO shows a higher gene transfection efficiency without observable cytotoxicity compared to unmodified controls in PC‐3 and NIH/3T3 cells. Moreover, the PEG–BPEI–rGO nanocomposite demonstrates an enhanced gene transfection efficiency upon NIR irradiation, which is attributed to accelerated endosomal escape of polyplexes augmented by locally induced heat. The endosomal escaping effect of the nanocomposite is investigated using Bafilomycin A1, a proton sponge effect inhibitor. The developed photothermally controlled gene carrier has the potential for spatial and temporal site‐specific gene delivery.     

Biodegradable synthetic polymers: Preparation, functionalization and biomedical application

Biodegradable polymers have been widely used and have greatly promoted the development of biomedical fields because of their biocompatibility and biodegradability. The development of biotechnology and medical technology has set higher requirements for biomedical materials. Novel biodegradable polymers with specific properties are in great demand. Biodegradable polymers can be classified as natural or synthetic polymers according to the source. Synthetic biodegradable polymers have found more versatile and diverse biomedical applications owing to their tailorable designs or modifications. This review presents a comprehensive introduction to various types of synthetic biodegradable polymers with reactive groups and bioactive groups, and further describes their structure, preparation procedures and properties. The focus is on advances in the past decade in functionalization and responsive strategies of biodegradable polymers and their biomedical applications. The possible future developments of the materials are also discussed.     

Proton-resistant quantum dots: Stability in gastrointestinal fluids and implications for oral delivery of nanoparticle agents

Semiconductor quantum dots (QDs) have shown great promise as fluorescent probes for molecular, cellular and in vivo imaging. However, the fluorescence of traditional polymer-encapsulated QDs is often quenched by proton-induced etching in acidic environments. This is a major problem for applications of QDs in the gastrointestinal tract because the gastric (stomach) environment is strongly acidic (pH 1–2). Here we report the use of proton-resistant surface coatings to stabilize QD fluorescence under acidic conditions. Using both hyperbranched polyethylenimine (PEI) and its polyethylene glycol derivative (PEG-grafted PEI), we show that the fluorescence of core shell CdSe /CdS/ ZnS QDs is effectively protected from quenching in simulated gastric fluids. In comparison, amphiphilic lipid or polymer coatings provide no protection under similarly acidic conditions. The proton-resistant QDs are found to cause moderate membrane damage to cultured epithelial cells, but PEGylation (PEG grafting) can be used to reduce cellular toxicity and to improve nanoparticle stability.