Yunwei Wang

Supramolecular polymer assembly in aqueous solution arising from cyclodextrin host–guest complexation

Summary The employment of cyclodextrin host–guest complexation to construct supramolecular assemblies with an emphasis on polymer networks is reviewed. The main driving force for this supramolecular assembly is host–guest complexation between cyclodextrin hosts and guest groups either of which may be discrete molecular species or substituents on a polymer backbone. The effects of such complexation on properties at the molecular and macroscopic levels are discussed. It is shown that cyclodextrin complexation may be used to design functional polymer materials with tailorable properties, especially for photo-, pH-, thermo- and redox-responsiveness and self-healing.

Protein Immobilization onto Cationic Spherical Polyelectrolyte Brushes Studied by Small Angle X-ray Scattering

The immobilization of bovine serum albumins (BSA) onto cationic spherical polyelectrolyte brushes (SPB) consisting of a solid polystyrene (PS) core and a densely grafted poly(2-aminoethyl methacrylate hydrochloride) (PAEMH) shell was studied by small-angle X-ray scattering (SAXS). The observed dynamics of adsorption of BSA onto SPB by time-resolved SAXS can be divided into two stages. In the first stage (tens of milliseconds), the added proteins as in-between bridge instantaneously caused the aggregation of SPB. Then BSA penetrated into the brush layer driven by electrostatic attractions, and reached equilibrium in the second stage (tens of seconds). The amount of BSA immobilized onto brush layer reached the maximum when pH was increased to about 6.1 and BSA concentration to 10 g/L. The cationic SPB were confirmed to provide stronger adsorption capacity for BSA compared to anionic ones.

Modification of Spherical Polyelectrolyte Brushes by Layer-by-Layer Self-Assembly as Observed by Small Angle X-ray Scattering

Multilayer modified spherical polyelectrolyte brushes were prepared through alternate deposition of positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly-l-aspartic acid (PAsp) onto negatively charged spherical poly(acrylic acid) (PAA) brushes (SPBs) on a poly(styrene) core. The charge reversal determined by the zeta potential indicated the success of layer-by-layer (LBL) deposition. The change of the structure during the construction of multilayer modified SPBs was observed by small-angle X-ray scattering (SAXS). SAXS results indicated that some PAH chains were able to penetrate into the PAA brush for the PAA-PAH double-layer modified SPBs whereas part of the PAH moved towards the outer layer when the PAsp layer was loaded to form a PAA-PAH-PAsp triple-layer system. The multilayer modified SPBs were stable upon changing the pH (5 to 9) and ionic strength (1 to 100 mM). The triple-layer modified SPBs were more tolerated to high pH (even at 11) compared to the double-layer ones. SAXS is proved to be a powerful tool for studying the inner structure of multilayer modified SPBs, which can establish guidelines for the a range of potential applications of multilayer modified SPBs.

Core–Shell–Corona Silica Hybrid Nanoparticles Templated by Spherical Polyelectrolyte Brushes: A Study by Small Angle X-ray Scattering

Core-shell-corona silica/polymer hybrid nanoparticles with narrow size distribution were prepared in the template of spherical polyelectrolyte brushes (SPB) which consist of a solid polystyrene (PS) core densely grafted with linear poly(acrylic acid) (PAA) chains. The microstructure of obtained hybrid nanoparticles was studied by small-angle X-ray scattering (SAXS) and in combination with dynamic light scattering (DLS) and transmission electron microscopy (TEM). The generation of silica shell within the brush is confirmed by the significant increase of the electron density in the shell, and the silica shell showed a unique inner-loose-outer-dense structure, whose thickness is pH sensitive but is insensitive to ionic strength as revealed by fitting SAXS data. After dissolving the PS core, hollow silica nanoparticles were obtained and determined by SAXS, which should be ideal carriers for pH-triggered drug delivery. SAXS is confirmed to be a powerful method to characterize the core-shell-corona silica/polymer hybrid and hollow silica nanoparticles.

Characterization of hollow silica-polyelectrolyte composite nanoparticles by small-angle X-ray scattering

Hollow silica–polyelectrolyte composite nanoparticles were prepared using templates of spherical polyelectrolyte brushes which consist of a polystyrene (PS) core and a densely grafted linear poly(acrylic acid) shell. The obtained hollow particles were systematically studied by small-angle X-ray scattering (SAXS) in combination with other characterization methods such as transmission electron microscopy and dynamic light scattering. The hollow structure formed by dissolving the PS core was confirmed by the reduction of electron density to zero in the cavity through fitting SAXS data. SAXS revealed both the inward and outward expansions of the hollow silica–polyelectrolyte composite particles upon increasing pH from 3 to 9, while further increasing pH led to the partial dissolution of silica layer and even destruction of the hollow structure. SAXS was confirmed to be a unique and powerful characterization method to observe hollow silica nanoparticles, which should be ideal candidates for controlled drug delivery.

Directed Nanoscale Self-Assembly of Low Molecular Weight Hydrogelators Using Catalytic Nanoparticles

The work presented here shows that the growth of supramolecular hydrogel fibers can be spatially directed at the nanoscale by catalytic negatively charged nanoparticles (NCNPs). The NCNPs with surfaces grafted with negatively charged polymer chains create a local proton gradient that facilitates an acid-catalyzed formation of hydrogelators in the vicinity of NCNPs, ultimately leading to the selective formation of gel fibers around NCNPs. The presence of NCNPs has a dominant effect on the properties of the resulting gels, including gelation time, mechanical properties, and network morphology. Interestingly, local fiber formation can selectively entrap and precipitate out NCNPs from a mixture of different nanoparticles. These findings show a new possibility to use directed molecular self-assembly to selectively trap target nano-objects, which may find applications in therapy, such as virus infection prevention, or engineering applications, like water treatment and nanoparticle separation.

Spherical polyelectrolyte nanogels as templates to prepare hollow silica nanocarriers: observation by small angle X-ray scattering and TEM

Hollow silica nanoparticles were prepared through generating a silica layer in spherical polyelectrolyte nanogels (SPN), which consisted of a solid core of polystyrene (PS) and a shell of crosslinked poly(acrylic acid) (PAA), followed by removing the PS core via solvent dissolution. Small angle X-ray scattering (SAXS) in combination with TEM were employed to observe SPN, silica–polymer composite, and hollow silica nanoparticles. It was confirmed that SAXS is a powerful method to monitor the generation of silica layer in SPN. The density and thickness of generated silica layer in SPN were found to be tunable by controlling the crosslinking density of the templates. The porous structure and pH sensitivity of silica layer allowed the obtained hollow silica to be ideal carriers for controlled drug delivery.

Hollow silica–polyelectrolyte composite nanoparticles for controlled drug delivery

The stimulus-responsive drug delivery system has attracted increasing attention due to its ability to enhance therapeutic efficacy and reduce side effects. Herein, a pH and glutathione (GSH) dually responsive drug carrier, hollow silica–-polyelectrolyte composite nanoparticle, was successfully prepared by using a template of spherical polyelectrolyte brush (SPB) which consists of a polystyrene (PS) core and a densely grafted linear poly(acrylic acid) (PAA) shell. The existence of PAA chains and introduction of disulfide bonds in silica framework endow the composite nanoparticles with pH and GSH dually responsive properties which were confirmed by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). With doxorubicin hydrochloride (DOX) as the model drug, the loading content and encapsulation efficiency could reach up to 43% and 96%, respectively. The drug release behavior was investigated under various environments, showing that the drug release rate increased with the decrease in pH value and the increase in GSH concentration. The prepared hollow SiO2–PAA composite nanoparticles possess a great potential as carriers for controlled drug delivery.

Facile Fluorescence “Turn on” Sensing of Lead Ions in Water via Carbon Nanodots Immobilized in Spherical Polyelectrolyte Brushes

Heavy metal detection has become very important for the protection of water resource. In this work, a novel controllable probe is presented for the sensitive detection of Pb2+ in aqueous solutions. The probe was synthesized via the immobilization of surface functionalized carbon dots (named as CAEA-Hs) into the shell of the spherical polyelectrolyte brushes (SPB). The fluorescence of CAEA-H was firstly “turned off” via electrostatic interaction induced quenching. Based on the aggregation induced emission enhancement (AIEE), the fluorescence of the immobilized CAEA-H could be specifically turned on via the aggregation of the SPB particles. This fluorescence “turn on” sensor could selectively detect Pb2+ among five different metal ions with a relatively wide detecting range (0–1.67 mM) and good linear relationship (R2 = 0.9958). Moreover, the aggregating behavior and nano-structure of CAEA-H loaded SPB have been systematically analyzed via small angle X-ray scattering, turbidity titration, and Zeta-potential measurement. Based on a series of control experiments, we finally gain an insight into the sensing mechanism of this novel sensing probe. This contributed a proof of concept demonstration that sensitive and selective chemical detection can be achieved via a C-dot/SPB synergistic platform.