Biye Ren

Facile fabrication of well-defined hydrogel beads with magnetic nanocomposite shells.

Well-defined magnetic nanocomposite beads with alginate gel cores and shells of iron oxide (gamma-Fe(2)O(3)) nanoparticles were prepared by self-assembly of colloidal particles at liquid-liquid interfaces and subsequent in situ gelation. Fe(2)O(3) nanoparticles could spontaneously adsorb onto the water droplet surfaces to stabilize water-in-hexane emulsions. Water droplets containing sodium alginate were in situ gelled by calcium cations, which were released from calcium-ethylenediamine tetraacetic acid (Ca-EDTA) chelate by decreasing pH value through slow hydrolysis of d-glucono-delta-lactone (GDL). The resulting hybrid beads with a core-shell structure were easily collected by removing hexane. This facile and high efficient fabrication had a 100% yield and could be carried out at room temperature. Insulin microcrystal was encapsulated into the hybrid beads by dispersing them in the aqueous solution of alginate sodium in the fabrication process. The sustained release could be obtained due to the dual barriers of the hydrogel core and the close-packed inorganic shell. The release curves were nicely fitted by the Weibull equation and the release followed Fickian diffusion. The hybrid beads may find applications as delivery vehicles for biomolecules, drugs, cosmetics, food supplements and living cells.

Novel ferrocenyl-terminated linear-dendritic amphiphilic block copolymers: synthesis, redox-controlled reversible self-assembly, and oxidation-controlled release.

Novel linear-dendritic amphiphilic block copolymers with hydrophilic poly(ethylene glycol) (PEG) block and hydrophobic Percec-type dendrons containing ferrocenyl terminals were synthesized by the esterification reaction of poly(ethylene glycol) methyl ether with ferrocenyl-terminated alkyl-substituted benzoic acid dendrons. On the basis of the results that the critical aggregation concentration (CACox) of the oxidation state polymer is much higher than CACred of the corresponding reduction state, these polymers can reversibly self-assemble into various aggregates, such as spherical, wormlike micelles, and vesicles, and also disassemble into irregular fragments in aqueous solution by redox reaction when changing the polymer concentrations. Copolymer PEG45-b-Fc3 (3) with 3,4,5-tris(11-ferrocenylundecyloxy) benzoic acid (2) can self-assemble into nanoscale wormlike micelles when the polymer concentration in aqueous solution is above its CACox. These wormlike micelles can be transformed into nanosized vesicles by Fe2(SO4)3 and regained by vitamin C. Interestingly, copolymer PEG45-b-Fc2 (5) with 3,5-bis(11-ferrocenylundecyloxy) benzoic acid (4) can reversibly self-assemble into spherical micelles with two different sizes by redox reaction above the CACox, indicating that the terminal hydrophobic tail number of dendrons plays a key role in determining the self-assembled structures. Furthermore, rhodamine 6G (R6G)-loaded polymer aggregates have been successfully used for the oxidation-controlled release of loaded molecules, and the release rate can be mediated by the concentrations of oxidant and copolymers. The results provide an effective approach to the reversible self-assembly of linear-dendritic amphiphilic block copolymers and also promise the potential of these novel redox-responsive amphiphilic block copolymers in drug delivery systems, catalyst supports, and other research fields.

A novel photoreversible poly(ferrocenylsilane) with coumarin side group: synthesis, characterization, and electrochemical activities

A novel poly(ferrocenylsilane) with a coumarin side group was synthesized. This photoreversible polymer exhibits interesting electrochemical activities, which change with photodimerization and photoscission reactions of the coumarin moieties.

Surfactant structure effects on binding with oppositely charged polyelectrolytes observed by fluorescence of a pyrene probe and label

Poly(2-(acrylamido)-2-methylpropanesulfonic acid) (PAMPS) and three copolymers containing about 40 mol% of AMPS and N,N-dimethylacrylamide with a single label of naphthalene or pyrene and with both labels were synthesized. The binding of cationic surfactants cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium chloride (DTAC), and nonionic surfactant octaethylene glycol monododecyl ether (C12E8) on these anionic polyelectrolytes was observed in dilute aqueous solutions with the relative emission intensity of excimer to monomer, I E/I m, of cationic probe 1-pyrenemethylamine hydrochloride (PyMeA·HCl), the nonradiative energy transfer (NRET), I Py/I Np, between the labels, the emission intensity ratio, I 1/I 3, of the first peak to the third peak and the fluorescence anisotropy, r, of the pyrene label. The binding with cationic surfactants made the polyelectrolyte chains much curlier, leading to an increase in I E/I M and I Py/I Np. The intermolecular NRET occurred at higher CTAB concentrations owing to the hydrophobic aggregation between CTAB tails bound on different polyelectrolyte chains, which induced an increase in r of the pyrene label. No intermolecular aggregation was observed from the intermolecular NRET and r of the pyrene label for DTAC-bound polyelectrolytes owing to its weaker hydrophobicity of 12 carbon atoms in the tail, shorter than that of CTAB. As shown with constant values of the previously mentioned photophysical parameters of the labels with increasing C12E8 concentration, there was no obvious binding for C12E8 on the anionic polyelectrolytes. However, the presence of PAMPS promoted the micelle formation for C12E8 below its critical micelle concentration as detected by the excimer emission of PyMeA·HCl probe.

Controlled Self-Assembly of Multiple-Responsive Superamphiphilc Polymers Based on Host-Guest Inclusions of a Modified PEG with β-Cyclodextrin

Superamphiphilic polymers (SAPs) constructed by host-guest inclusion can self-assemble into various nanostructures in solution, which can find applications in many fields such as nanodevices, drug delivery, and template synthesis. Herein, we report the controlled self-assembly of multiple-responsive SAP based on a selective host-guest inclusion of β-cyclodextrin (β-CD) with a modified poly(ethylene glycol) (PEG) (FcC11AzoPEG) consisting of a ferrocene (Fc) end group, a C11 alkyl chain, an azobenzene (Azo) block, and a poly(ethylene glycol)methyl ether (PEG) chain. These SAPs can self-assemble into interesting nanostructures in water upon exposure to different stimuli because β-CD can be selectively included with different guests, such as Fc, Azo, and C11 alkyl chain, under different stimuli. The inclusion complex of Fc with β-CD (Fc@β-CD SAP) can form nanowire micelles in aqueous solution. The nanowire micelles can be transformed into spindle micelles with the addition of oxidant because the majority of β-CDs dissociated from the complex Fc@β-CD SAP due to a conversion of Fc to Fc+ and will preferentially include with Azo group to form another dominant inclusion complex (Azo@β-CD SAP). After UV irradiation, the spindle micelles can be further transformed into spherical micelles because most of β-CDs are excluded from the complex Azo@β-CD SAP due to a trans- to cis-Azo conversion and then form a dominant inclusion complex with C11 alkyl chains (C11@β-CD SAP). This work not only demonstrates the selective host-guest inclusion of stimuli-responsive groups modified PEG with β-CD but also provides a useful approach for construction of diverse morphologies.

A dual stimuli-responsive amphiphilic polymer: reversible self-assembly and rate-controlled drug release

AbstractWe report the dual stimuli-responsive self-assembly and rate-controlled drug release of a novel functionalized PEG amphiphilic polymer (FcC11AzoPEG) in aqueous solution. The novel FcC11AzoPEG amphiphilic polymer was synthesized by the esterification reaction of poly (ethylene glycol) methyl ether (PEG) and 4-(4′-(11-ferrocenyl-undecanoxy)) azobenzoic acid. The azobenzene (Azo) and ferrocene (Fc) moieties respectively afford the polymer a slow photo-response and a fast redox-response. Upon exposure to different stimuli (light irradiation, redox reaction, and a combination of light irradiation and redox reaction), FcC11AzoPEG in aqueous solution can reversibly self-assemble into various nanostructures and also disassemble either slowly by light irradiation or fast by redox reaction in an appropriate concentration range. Moreover, the drug release from the drug-loaded micelles can be precisely controlled by different stimuli: a slow release rate and a small amount of release for UV irradiation, a fast rate and a medium amount of release for oxidation by Fe2(SO4)3, and a large amount of release for the combined stimulation of UV irradiation and oxidation by Fe2(SO4)3. This work not only demonstrates the effect of stimuli-induced amphiphilicity change of functional groups on the solution aggregation behavior of functionalized PEG amphiphilic polymers but also provides a useful smart system with great potential application in drug delivery. Graphical abstractᅟ

Multiple stimuli-responsive rheological behavior of a functionalized telechelic associative model polymer in aqueous solution

Hydrophobically modified telechelic associative polymers (TAPs) composed of hydrophilic backbone and two hydrophobic end groups can form dynamic transient networks in water and have been widely used as thickeners for improving solution rheological properties in many industrial fields. In this work, we designed and prepared a novel telechelic associative model polymer (FcC11AzoTAP) end-functionalized by photo-responsive azobenzene (Azo) unit along with the redox-responsive ferrocene extremity, which was used to investigate the effects of stimuli responsive behaviors such as redox reaction or/and photo isomerization of end groups on its solution aggregation and rheological properties. It has been demonstrated that the network structures and rheological properties of FcC11AzoTAP aqueous solutions can be readily tuned by the magnitude of stimuli-responsive hydrophobicity change of end groups to a certain degree. Moreover, a rearrangement of network through bridge to inactive loop and/or pending arm transitions is proposed to describe the dense to sparse network conversion. This work will not only provide new insights into the effects of end groups on the network structure and rheological properties of solution but it also opens a new perspective for some special applications of TAPs in industrial fields.Hydrophobically modified telechelic associative polymers (TAPs) composed of hydrophilic backbone and two hydrophobic end groups can form dynamic transient networks in water and have been widely used as thickeners for improving solution rheological properties in many industrial fields. In this work, we designed and prepared a novel telechelic associative model polymer (FcC11AzoTAP) end-functionalized by photo-responsive azobenzene (Azo) unit along with the redox-responsive ferrocene extremity, which was used to investigate the effects of stimuli responsive behaviors such as redox reaction or/and photo isomerization of end groups on its solution aggregation and rheological properties. It has been demonstrated that the network structures and rheological properties of FcC11AzoTAP aqueous solutions can be readily tuned by the magnitude of stimuli-responsive hydrophobicity change of end groups to a certain degree. Moreover, a rearrangement of network through bridge to inactive loop and/or pending arm transition...

Rheology of a spiropyran functionalized hydrophobically modified ethoxylated urethane in aqueous solution

Hydrophobically modified ethoxylated urethanes (HEURs) have been widely used as effective thickeners for improving the solution rheological properties in a variety of applications for over 40 years. We designed and prepared a novel photosensitive spiropyran-functionalized HEUR polymer (SP-HEUR), which was used to investigate the influence of hydrophobicity change of hydrophobes induced by photoisomerization of spiropyran (SP) group on the solution aggregation and rheological properties. The concentrated SP-HEUR solutions show an interesting photoresponsive rheological behavior upon alternative exposure to ultraviolet and visible light due to a reversible SP- to merocyanine-form conversion and back. A reversible rearrangement of micellar junctions through loop-bridge or bridge-loop transitions is proposed to interpret the influence of photoisomerozation of spiropyran groups on the associative structure and rheological properties of the polymer solution. This work will not only provide new insights into the...