Self-Assembling Nonconjugated Poly(amide-imide) into Thermoresponsive Nanovesicles with Unexpected Red Fluorescence for Bioimaging.

Nonconjugated red fluorescent polymers have been increasingly studied to improve the biocompatibility and penetration depth over conventional fluorescent materials. However, the accessibility of such polymers remains challenging due to the scarcity of nonconjugated fluorophores and lacking relevant mechanism of red-shifted fluorescence. Herein, we discovered that the combination of hydrogen bonding and π-π stacking interactions provides nonconjugated poly(amide-imide) with a large bathochromic shift (>100 nm) from blue-green fluorescence to red emission. The amphiphilic PEGylated poly(amide-imide) derived from in situ PEGylation self-assembled into nanovesicles in water, which isolated the aminosuccinimide fluorophore from the solvents and suppressed the hydrogen bonds formation between aminosuccinimide fluorophores and water. Therefore, the fluorescence of PEGylated poly(amide-imide) in water was soundly retained. Furthermore, the strong hydrogen bonding and hydrophobic interactions with water provided PEGylated poly(amide-imide) with a reversible thermoresponsiveness and presented a concentration-dependent behavior. Finally, accompanied by the excellent biostability and photostability, PEGylated poly(amide-imide) exhibited as a good candidate for cell imaging.

Bioreducible nanocapsules prepared from the self-assembly of branched polymer in nanodroplet.

Though great attention has been paid in constructing well-defined nano-structures via the self-assembly of amphiphilic macromolecules, the self-assembly of non-amphiphilic macromolecules in nanodroplet has drawn less attention up to now. Recently, we prepared a temperature-responsive PEG-based branched polymer with disulfide bonds in its backbone via reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-(2-methoxyethoxy) ethyl methacrylate, oligo(ethylene glycol) methacrylate, and N,N'-cystamine bisacrylamide. Subsequently, we loaded the branched polymer into nanodroplets, and have found that the self-assembly behaviors of this branched poly-mer in the nanodroplet are different from those in common solution. Bioreducible nanocapsules with tunable size can easily formed in nanodroplet even at high concentration.

Stimuli-triggered growth and removal of a bioreducible nanoshell on nanoparticles.

A new and easy method of stimuli-triggered growth and removal of a bioreducible nanoshell on nanoparticles is reported. The results show that pH or temperature could induce the aggregation of disulfide-contained branched polymers at the surface of nanoparticles; subsequently, the aggregated polymers could undergo intermolecular disulfide exchange to cross-link the aggregated polymers, forming a bioreducible polymer shell around nanoparticles. When these nanoparticles with a polymer shell are treated with glutathione (GSH) or d,l-dithiothreitol (DTT), the polymer shell could be easily removed from the nanoparticles. The potential application of this method is demonstrated by easily growing and removing a bioreducible shell from liposomes, and improvement of in vivo gene transfection activity of liposomes with a bioreducible PEG shell.

Synthesis of thermo-responsive polymers with both tunable UCST and LCST.

New water-soluble block copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO(2) MA), oligo(ethylene glycol) methacrylate (OEGMA), and N-(3-(dimethylamino) propyl) methacrylamide (DMAPMA) (poly(OEGMA-co-MEO(2) MA)-b-poly(DMAPMA)) were prepared via sequential reversible addition-fragmentation chain transfer (RAFT) polymerization. Selective quaternization of poly(DMAPMA) block gives poly(OEGMA-co-MEO(2) MA)-b-poly((3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]ammoniopropane sulfonate)-co-N-(3-(dimethylamino) propyl) methacrylamide), such block copolymer exhibits double thermo-responsive behavior in water, poly(MEO(2) MA-co-OEGMA) block shows a lower critical solution temperature (LCST), and poly((3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]ammoniopropane sulfonate)-co-N-(3-(dimethylamino) propyl) methacrylamide) block shows a upper critical solution temperature (UCST). Both of LCST and UCST can be controlled: LCST could be tuned by the fraction of OEGMA units in poly(OEGMA-co-MEO(2) MA), and UCST was found to be dependent on the degree of quaternization (DQ).

Synthesis of Bioreducible Polycations with Controlled Topologies.

Bioreducible polycations, which possess disulfide linkages in the backbone, have emerged as promising nucleic acid delivery carriers due to their high stability in extracellular physiological condition and bioreduction-triggered release of the genetic material. Further benefits of bioreducible polycations include decreased cytotoxicity due to intracellular reducing environment in the cytoplasm that contains high levels of reducing molecules such as glutathione. Here, we describe the synthesis of bioreducible polycations with emphasis on methods to control their topology.

[Application of research-based learning for bachelor intern students of stomatology].

PURPOSE: To apply research-based learning in education of bachelor intern students of stomatology and evaluate its role in promoting the comprehensive quality of the students. METHODS: Sixty students from grade 2007 and 2008 in school of stomatology, Wenzhou Medical University were enrolled in this study. Thirty of them were randomly selected into a group for research-based learning, while the others were taught with traditional teaching mode. Survey and assessment of the teaching effect was performed after the course. Independent t test was employed to evaluate the differences with SPSS16.0 software package. RESULTS: No significant difference of exam results was revealed between the two groups. Questionnaire survey showed a good evaluation for the teaching mode and the teachers in the group research-based learning, but the evaluation of mastering research capability was lower. CONCLUSIONS: Research-based learning mode promotes the study interest and comprehensive quality of the students. No evidence of interference with mastering clinical skills is disclosed.

A versatile method for encapsulating large-sized DNA into small-sized bioreducible nanocapsules.

Encapsulation of negatively charged plasmid DNA into a small-sized nanocapsule without using any condensing agent is very challenging up to now. Here we report a versatile method for encapsulating large-sized plasmid DNAs into small-sized bioreducible nanocapsules in which shearing force and surfactant can fold large-sized plasmid DNAs into small-sized emulsion droplets containing bioreducible branched polymers. Subsequently, temperature triggers the bioreducible branched polymers to aggregate and cross-link at the water/oil interface of the emulsion nanodroplet, forming a bioreducible shell around the nanodroplet. Thus, a small-sized nanocapsule (∼110 nm) containing large-sized plasmid DNA (∼1900 nm long) forms by removal of the surfactant.

Synthesis of bioreducible polycations with controlled topologies.

Bioreducible polycations, which possess disulfide linkages in the backbone, have appeared as promising gene delivery carriers due to their high stability in extracellular physiological condition and bioreduction-triggered release of genetic materials, as well as reduced cytotoxicity because intracellular cytosol is a reducing environment containing high level of reducing molecules such as glutathione. Here, we describe the syntheses of bioreducible polycations, and the methods for control over their topology are also presented.

Synthesis of sequence-ordered polymers via sequential addition of monomers in one pot.

Sequence-ordered polymers can be simply prepared in one pot via sequential monomer addition.