Jinying Yuan

Voltage-Responsive Vesicles Based on Orthogonal Assembly of Two Homopolymers

Two end-decorated homopolymers, poly(styrene)-beta-cyclodextrin (PS-beta-CD) and poly(ethylene oxide)-ferrocene (PEO-Fc), can orthogonally self-assemble into a supramolecular diblock copolymer (PS-beta-CD/PEO-Fc) in aqueous solutions based on the terminal host-guest interactions. These assemblies can further form supramolecular vesicles, and their assembly and disassembly behaviors can be reversibly switched by voltage through the reversible association and disassociation of the middle supramolecular connection. The vesicles possess an unprecedented property that their assembly or disassembly speed can be controlled by the applied voltage strength. Luminescence spectroscopy demonstrates that the vesicles act as nanocapsules carrying molecules within their hollow cavities and that the external voltage strength accurately regulates the drug release time.

Redox-responsive polymers for drug delivery: from molecular design to applications

Glutathione has been regarded as a significant signal for distinguishing between tumor and normal tissue. Recently, reactive oxygen species have attracted much attention for their close connection with many diseases. Taking advantage of the physiological signals, redox-responsive polymeric drug carriers constitute a significant research area in the various stimuli-responsive polymers for biomedical applications. During the rapid development of redox-responsive polymers, molecular design and related synthetic methodology plays a crucial role. In this review, we discuss the reduction- and oxidation-responsive polymeric drug carriers from the view of functional groups, as well as their applications in controlled release.

Synthesis of cellulose-graft-poly(N,N-dimethylamino-2-ethyl methacrylate) copolymers via homogeneous ATRP and their aggregates in aqueous media.

Cellulose-graft-poly(N,N-dimethylamino-2-ethyl methacrylate) (cellulose-g-PDMAEMA) copolymers were prepared by homogeneous atom transfer radical polymerization (ATRP) under mild conditions. Cellulose macroinitiator was successfully synthesized by direct acylation of cellulose with 2-bromopropionyl bromide in a room temperature ionic liquid (RTIL), 1-allyl-3-methylimidazolium chloride. Copolymers were obtained via ATRP of N,N-dimethylamino-2-ethyl methacrylate (DMAEMA) with CuBr/pentamethyldiethylenetriamine (PMDETA) as catalyst and N,N-dimethylformamide (DMF) as solvent without homopolymer byproduct. The grafting copolymers were characterized by (1)H NMR, FT-IR, and TGA measurements. The results confirmed that PDMAEMA had been covalently bonded to cellulose backbone. Furthermore, the assemblies or aggregates formed by cellulose-g-PDMAEMA copolymers in water were studied at various concentrations, temperatures, and pH values by means of UV, DLS, TEM, and AFM. The results indicate that the copolymers had the pH- and temperature-responsive properties similar to the expected stimuli-responses by PDMAEMA. The synthetic strategy presented here could be employed in the preparation of other novel biomaterials from a variety of polysaccharides.

Schiff's base as a stimuli-responsive linker in polymer chemistry

Schiff-base reactions are widely used in the field of chemistry. With many advantages, such as mild reaction conditions and high reaction rates, they were employed for protecting various functional groups and synthesizing a series of organic ligands. In polymer chemistry, they can serve as potential pH-responsive linkers in polymer chains because of their sensitive responses to changes in the pH value. With certain particular designs, the Schiff-base structure can cooperate with other reversible covalent bonds or supra-molecular interactions to form assemblies or gels, providing various functions and applications. This article aims to give a critical review of the recent literature on the Schiff-base reactions used in polymer chemistry and how they serve as a way of linking structures together. We will also cover some of the important developments on the functions and applications of these polymers.

Breathing Polymersomes: CO2‐Tuning Membrane Permeability for Size‐Selective Release, Separation, and Reaction

Selective substance channels and confined reaction spaces that span scales ranging from the macroscopic world down to nanometer-sized structures are abundant in biological systems. A basic entity is a cell, the membrane of which offers a confining boundary to control substance exchange and to compartmentalize complex biochemical processes. To comprehend the selective permeation mechanism of lipid membranes and to imitate their working principles, biomimetic cellular models have been explored. Several artificial liposome systems with membrane selectivity have been successfully developed. Within the last few years, a polymer-based equivalent, the polymersome, has come to be regarded as a promising candidate for such a system. By tailoring the polymer structure and altering the polymer composition, one can endow these polymersomes with tunable permeability. For example, Meier et al. studied the use of channel proteins and block copolymer bioconjugated membranes to selectively filter guest molecules. Recently, an effective method based on the self-assembly of stimuli-responsive block copolymers was used to build intelligent vesicles. This approach allows the bilayer gates to turn on and off when an external stimulus is given. Herein, to enrich the scope of responsive polymersomes and improve polymeric membrane selectivity, we propose a new method to tune the permeability of polymersome membranes by means of carbon-dioxide-responsive copolymers. Utilizing CO2 levels to control the size of nanopores in the membrane, these nanocontainers can attain the goal of releasing and separating globular nanoparticles of different sizes. Furthermore, they have the potential to act as nanoreactors that can insulate different catalytic reactions with the aid of CO2-regulated transmembrane traffic. We have synthesized a series of amphiphilic block copolymers, consisting of biocompatible and nonimmunogenic poly(ethylene glycol) (PEG) for the hydrophilic portion, and CO2-sensitive poly(N-amidino)dodecyl acrylamide (PAD) as the hydrophobic portion. The target diblock copolymers, PEG-b-PAD, were prepared by atom transfer radical polymerization (Scheme 1a). Owing to their amphiphilicity, the copolymers can self-assemble into vesicular nanostructures in aqueous solution, and, most importantly, the polymersomes can continuously self-expand in a CO2 atmosphere. Once vesicular shape changes, the membrane structure and permeability must alter. On the basis of this concept, we wondered if we could make use of CO2 as a stimulus to tune polymersome membrane permeability over a broad range. We first tested the self-assembly behavior of the PEG-bPAD in aqueous solution. The critical aggregation concentration (CAC) is ca. 0.12 mgmL 1 (Supporting Information, Figure S3). Transmission electron microscopy (TEM) showed that the average size of the initial vesicles was (112 6.0) nm, which is consistent with the hydrodynamic radius (Rh) of 59.8 nm determined by dynamic light scattering (DLS; Figure 1a and d) analysis. As expected, these vesicles started to expand when CO2 passed through the solution at a rate of 1.0 mLmin . As shown in Figure 1b, much larger intact vesicles with diameters of (151 28) nm were found after 10 min of CO2 treatment. Under these conditions, the Rh of these aggregates increased to 83.5 nm, which corresponds to the TEM results. When the CO2 aeration time was prolonged to 30 min, the polymersomes finally extended to a maximum diameter of (238 26) nm (Figure 1c), which is close to the value of 137.2 nm determined by DLS analysis. The change in vesicle size is proportional to the gas stimulation time, and their radii grow at a constant rate of ca. 2.5 nmmin 1 Scheme 1. a) Gas-switchable chemical structural change of the PEG-bPAD block copolymer. b) The self-assembly of the copolymer into polymersomes and reversible gas-controlled breathing behavior in aqueous media.

Core–shell structural iron oxide hybrid nanoparticles: from controlled synthesis to biomedical applications

Superparamagnetic iron oxide nanoparticles have received great research attention due to their wide spectrum of potential applications. Core–shell structures with iron oxide nanoparticles as the core and with covalently grafted organic polymers as the shell, which has specific functions, such as biocompatibility, fluorescence, and biological activity have been synthesised. These nanostructured compounds could find numerous biomedical applications. This feature article provides a review on the synthetic methodologies for building such magnetic core–shell structures, and on their applications in targeted drug delivery, enhanced magnetic resonance imaging (MRI), enzyme immobilization, hyperthermia and biosensors. Promising future directions of this active research field are also discussed.

CO2‐Responsive Nanofibrous Membranes with Switchable Oil/Water Wettability

Responsive polymer interfacial materials are ideal candidates for controlling surface wetting behavior. Here we developed smart nanostructured electrospun polymer membranes which are capable of switching oil/water wettability using CO2 as the trigger. In particular, the combination of CO2 -responsiveness and porous nanostructure enables the as-prepared membranes to be used as a novel oil/water on-off switch. We anticipate that the promising versatility and simplicity of this system would not only open up a new way of surface wettability change regulation by gas, but also have obvious advantages in terms of highly controlled oil/water separation and CO2 applications.

Cellulose-Based Dual Graft Molecular Brushes as Potential Drug Nanocarriers: Stimulus-Responsive Micelles, Self-Assembled Phase Transition Behavior, and Tunable Crystalline Morphologies

Well-defined cellulose-based dual graft molecular brushes, composed of ethyl cellulose-graft-poly(N,N-dimethylaminoethyl methacrylate)-graft-poly(epsilon-caprolactone) (EC-g-PDMAEMA-g-PCL), have been prepared by ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Unlike other brush copolymers, the new molecular brushes show some unique physicochemical properties and multifunction due to their unique topological structures. These biocompatible copolymers self-assembled to micelles in aqueous solution. Upon pH change, the single micelles further assembled into micellar aggregates. As a result, the micelles in aqueous media could act as excellent drug nanocarriers for controlled drug release. The crystallinity and crystal morphology of the copolymers can be controlled to a certain extent by varying the length of the side chains, which may exert strong spacial restriction and, hence, affect the crystal structures.

β-Cyclodextrin-modified hybrid magnetic nanoparticles for catalysis and adsorption

β-Cyclodextrin-modified hybrid magnetic nanoparticles (Fe3O4@SiO2-PGMACD) were synthesized via the combination of atom transfer radical polymerization on the surfaces of silica coated iron oxide particles (Fe3O4@SiO2) and ring-opening reaction of epoxy groups. The feasibility of using Fe3O4@SiO2-PGMACD as separable immobilized catalyst and adsorbent was demonstrated. It was found: (1) the prepared Fe3O4@SiO2-PGMACD could be used as catalyst in substrate-selective oxidation of alcohols system and the catalytic efficiency was close to pure β-Cyclodextrin of equal quantity; (2) the resulting particles appeared remarkably dominant adsorption capacity compared with poly(glycidyl methacrylate) grafted magnetic nanoparticles (Fe3O4@SiO2-PGMA) in the removal of bisphenol A from aqueous solutions. The results suggest that the novel fabricated nanoparticles could serve as bifunctional materials in catalysis or adsorption and subsequently become potential multifunctional materials.

Redox-switchable supramolecular polymers for responsive self-healing nanofibers in water

Self-healing nanomaterials that respond to new stimuli sources are attractive. In particular, redox potential is one of the most universal and convenient stimuli in nature. Here we report utilization of ferrocene- and cyclodextrin-terminated monomers to form water-soluble AA-BB-type supramolecular polymers on the basis of host–guest interactions of ferrocene (Fc) and cyclodextrin (CD). These noncovalent polymers can further hierarchically assemble into one-dimensional supramolecular nanofiber architectures. The electrochemical-responsive Fc–CD host–guest connections endow these nanofibers with unique self-degradable and -healable features under redox potential control. Moreover, different redox conditions can exactly regulate the self-repairable rates of these nanostructures. It is anticipated that this supramolecular polymer model would open up a way for redox-tunable one-dimensional nanomaterials.