Stably Grafting Polymer Brushes on Both Active and Inert Surfaces Using Tadpole-Like Single-Chain Particles with an Interactive "Head".

We report a "grafting to" method for stably grafting high-molecular-weight polymer brushes on both active and inert surfaces using tadpole-like single-chain particles (TSCPs) with an interactive "head" as grafting units. The TSCPs can be efficiently synthesized through intrachain cross-linking one block of a diblock copolymer; the "head" is the intrachain cross-linked single-chain particle, and the "tail" is a linear polymer chain that has a contour length up to micrometers. When grafted to a surface, the "head", integrating numerous interacting groups, can synergize multiple weak interactions with the surface, thereby enabling stable grafting of the "tail" on both active and traditionally challenging inert surfaces. Because the structural parameters and composition of the "heads" and "tails" can be separately adjusted over a wide range, the interactivity of the "heads" with the surface and properties of the brushes can be controlled orthogonally, accomplishing surface brushes that cannot be achieved by existing methods.

Boosting Organic Afterglow Performance via a Two-Component Design Strategy Extracted from Macromolecular Self-Assembly.

Because intersystem crossing and phosphorescence decay are spin-forbidden in organic systems, it is challenging to obtain high-performance organic afterglow materials. Inspired by two-component design strategy from macromolecular self-assembly, here we report the utilization of synthetic polymers to control the excited state properties of difluoroboron ß-diketonate (BF2bdk) and deuterated BF2bdk compounds for the fabrication of room-temperature organic afterglow materials. The polymer component can interact with BF2bdk excited states by dipole-dipole interactions, lower BF2bdk S1 levels with insignificant effect on T1 levels, reduce ΔEST, and thus enhance intersystem crossing of BF2bdk excited states. The polymer component can also suppress intramolecular motion of BF2bdk triplets and protect BF2bdk triplets from oxygen quenching. The obtained BF2bdk-polymer afterglow materials exhibit emission lifetimes up to 2.2 s and high photoluminescence quantum yields under ambient conditions, display excellent processability and flexibility, and can function as efficient donors for excited state energy transfer to construct red afterglow materials.

Noncovalent Postmodification Guided Reversible Compartmentalization of Polymeric Micelles.

Compartmentalized micelles (CMs) are promising tailor-made soft matters that mimic natural designed structures and functions. Despite the structure of complex CMs, manipulating CM structures accessibly and reversibly remains elusive. Here, we report the fabrication of CMs via a generally valid noncovalent postmodification process. Starting from precursor micelles (PMs) based on one diblock copolymer, aromatic modification leads to the compartmentalization of PMs into well-defined spherical CMs. Control over compartment number, size and distribution in CMs, and segment distribution in their linear hierarchical assemblies is attained by simply tuning the postmodification degree and solvent composition. We also demonstrate the reversible transformation between PM and CMs during several heating-cooling cycles, which endows the micelles with potential in reversible functional transitions in situ close to nature's capability. Moreover, both hierarchically assembled or ill-structured micelles can rearrange into homogeneous CMs after one heating-cooling cycle, featuring the postmodification guided compartmentalization strategy with unprecedented micelle reproducibility.

Effectiveness of varicella vaccine as post-exposure prophylaxis: a meta-analysis.

BACKGROUND: To evaluate the effectiveness of varicella vaccine (VarV) as post-exposure prophylaxis (PEP) among children during varicella outbreaks. MATERIAL AND METHODS: A comprehensive literature search was performed in PubMed, Embase, Web of Science, SinoMed, Wanfang and CNKI. Relevant outcomes included the incidence of varicella. Pooled estimates were calculated using a fixed-effects or random-effects model according to the heterogeneity among studies. RESULTS: A total of 15 studies with 7,474 children that received one or two dosages of VarV as PEP and 183,827 children who received no VarV were included in the meta-analysis. In total, one-dose and two-dose VarV as PEP had 43% (95% confidence interval (CI):27%, 55%) and 60% (95%CI: 35%, 75%) efficacy, respectively. When PEP was applied within 3 days, the pooled VarV as PEP for prevention of varicella was 80% (95%CI: 68%, 88%); when PEP was administered beyond 3 days, the pooled VarV as PEP for the prevention of varicella was 50% (95%CI: 11%, 72%). If the PEP was implemented with a coverage of more than 80%, the VarV could prevent 82% of varicella cases from occurring (95%CI: 15%, 96%); if the PEP covered a maximum of 80% of the susceptible cases, the VarV could prevent 65% of varicella cases from occurring (95%CI: 50%, 76%). CONCLUSION: The two-dose VarV had better efficacy than one-dose VarV in the control of varicella outbreaks, especially if PEP was applied within 3 days of an outbreak and in conjunction with a high coverage rate ≥80%.

A novel worm-like micelles@MOFs precursor for constructing hierarchically porous CoP/N-doped carbon networks towards efficient hydrogen evolution reaction.

Constructing electrocatalysts with plentiful active sites, great mass transfer ability, and high electrical conductivity is critical to realize efficient hydrogen evolution reaction (HER). Hierarchically porous cobalt phosphide/N-doped nanotubular carbon networks (CoP/NCNs) that have all the features were fabricated in this work. For the fabrication, the polymeric worm-like micelles (PWs) with a large aspect ratio were coated by a uniform nanolayer of Zn-Co zeolitic imidazolate frameworks (Zn-Co-ZIFs) on their surface, resulting in the hybrid nanofibers PWs@Zn-Co-ZIFs (HPWs). Inheriting the randomly curved and entanglement properity of PWs, the rigid HPWs formed hybrid networks with the packing voids sized tens to 200 nm. Then, the hybrid networks were treated by pyrolysis-oxidation-phosphidation and ZnO-removal processes, leading to the hierarchically porous CoP/NCNs. In the CoP/NCNs, there are plentiful CoP nanoparticles embedded on the surface of conductive carbon network and fully exposed. When used for HER electrocatalyst, the CoP/NCNs only need small overpotentials (98 and 118 mV in acid and alkaline electrolyte) at 10 mA cm-2. This novel strategy is instructive for tailoring hierarchically porous transition metal phosphide/carbon nanocomposites as promising electrocatalysts.

Fabrication of the Polymersomes with Unique and Even Nonequilibrium Morphologies.

Herein, efficient fabrication of polymersomes that have unique and nonequilibrium morphologies is reported. Starting from preparing big polymeric vesicles sized around 2 µm with a flexible but crosslinkable structure, a controllable morphological transformation process from the vesicles via prolate vesicles and the pearl-chain-like structure, which are the two intermediate structures, to vesicle-end-capped tubes is conducted. Significantly, each of the intermediates is a regular polymersome and occupies a distinct phase space in the transformation process and thus can be separately processed and prepared. By crosslinking the structures, respectively, regular polymersomes with unique but stable morphologies are fabricated. Furthermore, the 1D polymersomes contain narrow necks. These narrow necks are sensitive to ultrasound vibration and broken by gentle ultrasound treatment to form regular open-ended tubes and open-ended vesicles, which are nonequilibrium but stable morphologies and difficult to prepare by existing methods.

Strictly sparse surface modification and its application for endowing nanoparticles with an exact "valency".

Sparsely modified surfaces can be used as a general platform for precisely modifying small nanoparticles. However, strictly, rather than statistically, sparse surface modification remains a big challenge. Herein, we report a new and general method for strictly sparse modification of the surface of relatively large nanoparticles. The method is analogous to planting big trees and then removing the big crowns, leaving the stumps on the ground; due to the large exclusive size of the crowns, the stumps are strictly sparsely distributed. As a proof of concept, strictly sparse modification of surfaces was demonstrated by the successful preparation of "monovalent" and "divalent" golden nanoparticles (AuNPs) with different sizes. Starting from the "monovalent" and "divalent" AuNPs, AuNP dimers and chain-like AuNP assemblies were prepared, respectively.

In situ synthesis of polyaniline/carbon nanotube composites in a carbonized wood scaffold for high performance supercapacitors.

Carbonized and activated wood scraps are appealing scaffolds upon which to host active materials for supercapacitors, realizing the transformation of waste into a valuable device. However, the active material when loaded on the inner walls of the wood tracheids can be easily peeled off, resulting in poor cycling stability of the capacitor and low energy density. Here, we designed a novel composite electrode material for high-performance supercapacitors based on a polyaniline/carbon nanotube composite material with a core-shell structure synthesized in situ in a carbonized wood scaffold. Carbon nanotubes with excellent conductivity were first synthesized in situ on the inner walls of the tracheids via chemical vapor deposition, which were stably embedded in the wood tracheids to increase the specific surface area and active material loading active sites. Then, a layer of polyaniline was deposited on the outer surface of each carbon nanotube via electrochemical deposition to form a core-shell nanostructure. The composite material as a single electrode has high specific capacitances of 240.0 F cm-3 and 1019.5 F g-1 at 10 mA cm-2. Finally, the asymmetric supercapacitor based on the carbon nanotubes/carbonized wood scaffold as the anode and polyaniline/carbon nanotubes/carbonized wood scaffold as the cathode exhibited a high energy density of 40.5 W h kg-1 at 162.5 W kg-1 and a high capacity retention rate of 93.74% after 10 000 charge and discharge cycles at a current density of 20 mA cm-2.

Multistage Polymerization Design for g-C3N4 Nanosheets with Enhanced Photocatalytic Activity by Modifying the Polymerization Process of Melamine.

Graphene-like g-C3N4 nanosheets (NSs) have been successfully synthesized with a modified polymerization process of melamine by cocondensation with volatile salts. Volatile ammonium salts such as urea-NH4Cl/(NH4)2SO4/(NH4)3PO4 were added with melamine to modulate the thermodynamic process during polymerization and optimize the structure formation in situ. The surface area, surface structure, and surface charge state of the obtained g-C3N4 NSs could be controlled by simply adjusting the mass ratio of the melamine/volatile ammonium salt. As a consequence, the g-C3N4 NSs exhibited much higher activity than bulk g-C3N4 for the photocatalytic degradation of target pollutants (rhodamine B, methylene blue, and methyl orange), and it also exhibited greater hydrogen evolution under visible light irradiation with an optimal melamine/volatile ammonium salt ratio. The as-prepared g-C3N4 NSs with melamine-urea-NH4Cl showed the highest visible light photocatalytic H2 production activity of 1853.8 µmol·h-1·g-1, which is 9.4 times higher than that of bulk g-C3N4 from melamine. The present study reveals that the synergistic effect of the enhanced surface area, surface structure, and surface charge state is the key for the enhancement of photocatalytic degradation and hydrogen evolution, which could be controlled by the proposed strategy. The result is a good explanation for the hypothesis that adding properly selected monomers can truly regulate the polymerization process of melamine, which is beneficial for obtaining g-C3N4 NSs without molecular self-assembly. Considering the inexpensive feedstocks used, a simple synthetic controlling method provides an opportunity for the rational design and synthesis, making it decidedly appealing for large-scale production of highly photocatalytic, visible-sensitizable, metal-free g-C3N4 photocatalysts.

Endowing Polymeric Assemblies with Unique Properties and Behaviors by Incorporating Versatile Nanogels in the Shell.

Herein, we report an example of self-driven morphological transition and the unique dissociation behavior of polymeric assemblies. Polymeric nanogels were introduced into the shell of polymeric assemblies and used as a powerful platform to endow the assemblies with unique properties and behaviors. It is exhibited that the nanogel can host an intrananogel cross-linking reaction and thus contracts automatically to change the geometrical packing parameters of the building blocks, driving morphological transitions of the assemblies; the transitions are self-driven without any external stimuli. Additionally, when the nanogels in the shell expand, the assemblies dissociate into small fragments even when the core is in a frozen state; in existing studies, polymeric assemblies with a frozen core cannot dissociate, except the core becomes dynamic under the stimuli. Both the self-driven morphological transition and the dissociation behavior are unique and have never been reported before.

From Tunable DNA/Polymer Self-Assembly to Tailorable and Morphologically Pure Core-Shell Nanofibers.

In reported experimental studies, DNA/polymer self-assemblies are usually kinetically trapped, leading to the encapsulation and irregular collapse of DNA chains within the resultant assemblies. In striking contrast, eukaryotic cells use tetrasome-to-nucleosome pathways to escape possible kinetic trapping for the formation of well-defined 10 nm chromatin fibers. Here, we report a novel pathway for DNA and amphiphilic diblock copolymer self-assembly inspired by the tetrasome pathway with highly controllable kinetics. The polymer is an A- b-B diblock copolymer with a hydrophilic and noninteractive block A and a hydrophobic and interactive block B. Below the critical water content for the micellization, B blocks wrap the backbone of a DNA chain by weak electrostatic interactions to form a linear DNA/polymer complex. With a gradual increase in the water content, the diblock copolymer unimers in the bulk solution tend to aggregate on the linear DNA/polymer complex, which induces the originally wrapped DNA chain, to change its conformation to wrap around the polymer aggregate, guiding and tailoring the self-assembly. Highly controllable kinetics is achieved via the reduced DNA/polymer electrostatic interactions and the high dynamics of the polymer chains in the system. DNA/polymer self-assembly leads to tailorable and morphologically pure core-shell nanofibers. Compared to the DNA/micelle self-assembly pathway described in our previous study, the present self-assembly pathway exhibits advantages for the fabrication of flexible nanofibers with lengths in micrometers and the potential for unique applications in preparing not only 2D networks at extremely low percolation thresholds but also chemiresistors with large on/off current ratios.

Precise surface structure of nanofibres with nearly atomic-level precision.

We report the first example of endowing the surface structure of a polymeric assembly with nearly atomic-level precision. The solenoidal wrapping of a DNA chain around the surface of a nanofibre transcribes the precise sequence structure of the DNA onto the nanofibre surface, resulting in a precise surface structure.

Effectiveness of post-exposure prophylaxis during varicella outbreaks among primary and middle school students in Shanghai: An analysis of three-year surveillance data.

OBJECTIVES: To evaluate the effectiveness of post-exposure prophylaxis conducted during varicella outbreaks among students in Shanghai. METHODS: Surveillance data were collected from September 1, 2013 to December 31, 2016 involving 3524 susceptible students in 109 primary and middle school classes where emergency vaccinations (EVs) had been administered. Students were divided into two groups according to their prior vaccination (PV) varicella vaccine status. A secondary attack rate was used to compare EV and non-EV groups using a chi-squared test. Stratification analyses were performed, adjusting for the EV administration date, the vaccination coverage rate, and the number of cases prior to the EV. RESULTS: The effectiveness rate was 92.2% (95% confidence interval (CI): 37.1-99.0%) when EV was applied within 3 days following the outbreak onset date, and 95.2% (95% CI: 79.9-98.8%) when vaccination coverage was ≥80% among students with PV. When students with PV received an EV for varicella within 3 days, the effectiveness rate was 100%. CONCLUSIONS: EV showed high protective effectiveness for varicella during outbreaks, especially if administered within 3 days of an outbreak and in conjunction with a high coverage rate.

Efficient Fabrication of Pure, Single-Chain Janus Particles through Their Exclusive Self-Assembly in Mixtures with Their Analogues.

We report the first example of the fabrication of pure, single-chain Janus particles (SCJPs). The SCJPs were prepared by double-cross-linking an A-b-B diblock copolymer in a common solvent. Inevitably, the double-cross-linking led to a mixture containing not only SCJPs but also multichain particles and irregular single-chain particles. Under well-controlled conditions, the SCJPs in the mixture self-assemble with high exclusivity to form regularly structured macroscopic assemblies (MAs) with a crystal-like appearance that precipitate from the suspension. Pure SCJPs that are uniform in size, shape and Janus structure were efficiently prepared by collection and dissociation of the MAs. Block copolymers with different structural parameters were successfully used for the exclusive self-assembly (ESA), and pure SCJPs with varied structural parameters were produced, confirming the reliability of the ESA method.

Multiheteroatom-Doped Porous Carbon Catalyst for Oxygen Reduction Reaction Prepared using 3D Network of ZIF-8/Polymeric Nanofiber as a Facile-Doping Template.

We report a facile and versatile method for fabrication of multiheteroatom-doped hierarchically porous carbon with a large specific surface area, using the 3D network constructed by ZIF-8 coated wormlike micelles as template. The uniform and highly pure wormlike micelles developed in our laboratory is essential, because they not only are responsible for the formation of hierarchical porosity, but also play as a versatile platform for multiheteroatoms doping. In a primary experiment, S, N, B, and P heteroatoms were doped conveniently and the resultant porous carbons have the excellent oxygen reduction reaction performance comparable to the commercial 20% Pt/C.

Solution-Based Thermodynamically Controlled Conversion from Diblock Copolymers to Janus Nanoparticles.

Nanosized polymeric Janus particles (NPJPs) have important applications in a variety of theoretical and practical research fields. However, the methods that are versatile and can prepare NPJPs highly efficiently are very limited. Herein, we reported a two-step thermodynamically controlled preparation of NPJPs with a high yield using a diblock copolymer as the precursor. At the first step, A-b-B coassembled in the solution with a partner diblock copolymer C-b-B to form the mixed shell micelles (MSMs) with B core and A/C mixed shell. Then, intramicellarly covalently cross-linking the A block chains resulted in the complete phase separation of A and C chains in the mixed shell, leading to the direct conversion of the MSMs into NPJPs. The first step, diblock copolymer micellization, is known as a thermodynamically controlled process, and we also made the second step, conversion from MSMs to NPJPs, be thermodynamically controlled due to the application of covalent cross-linking. As the result, the conversion efficiency is close to 100%. Besides, it was further confirmed that the method can be applied to different systems and used to tune the Janus balance. Therefore, this conversion should be very significant for the fabrication and application of the NPJPs.

Self-assembly of polymeric micelles into complex but regular superstructures based on highly controllable core-core fusion between the micelles.

Herein, we report a facile but highly controllable method to induce core-core fusion for not only spherical but also worm-like polymeric micelles, leading to various complex but regular superstructures including "random worm-like co-micelles", "block worm-like co-micelles" and octopus-like superparticles.

Solution-Based Fabrication of Narrow-Disperse ABC Three-Segment and Θ-Shaped Nanoparticles.

Nanoparticles sized tens of nm with not only a highly complex but also a highly regular nanostructure, although ubiquitous in nature, are very difficult to prepare artificially. Herein, we report efficient solution-based preparation of narrow-disperse ABC three-segment hierarchical nanoparticles (HNPs) with a size of tens of nm through a three-level hierarchical self-assembly of A-b-B-b-C triblock copolymers in solution. An ABC HNP is composed of three nanoparticles, A, B, and C that are linearly connected; in the ABC HNP, the B nanoparticle is sandwiched between the A and C nanoparticles. The method for the preparation is highly efficient, because all of the A-b-B-b-C chains in the solution are converted into the ABC HNPs. Furthermore, the ABC HNPs self-assembled into Θ-shaped HNPs tens nm in size. Both the ABC and Θ-shaped HNPs, are highly complex but highly regular, and are novel HNPs, and they should be very promising for addressing various theoretical and practical problems.

Recovering 3D images of polymeric nanofibers in solution through theoretical analysis and Monte-Carlo simulations of their 2D TEM images.

Nanofibers are well-known nanomaterials that are promising for many important applications. Since sample preparation for the applications usually starts from a nanofiber solution, characterization of the original conformation of nanofibers in the solution is significant because the conformation affects remarkably the behavior of nanofibers in the samples. However, the characterization is very difficult by existing methods: light scattering can only roughly evaluate the conformation in solution; cryo-TEM is laborious, time-consuming, and challenging technically, and thus difficult to study a system statistically. Herein we report a novel and reliable method to recover the 3D original image of nanofibers in solution through theoretical analysis and Monte-Carlo simulations of TEM images of the nanofibers. Firstly, six kinds of monodisperse nanofibers with the same composition and inner structure but different contour lengths were prepared by the method developed in our laboratory. Then, each kind of nanofiber deposited on the substrate of the TEM sample was measured by TEM and meanwhile simulated by the Monte Carlo method. By matching the simulation results with the TEM results, we determined information about the nanofibers including their rigidity and the interaction between the nanofibers and the substrate. Furthermore, for each kind of nanofiber, based on the information, 3D images of the nanofibers in solution can be re-constructed, and then the average gyration radius and hydrodynamic radius can be calculated, which were compared with the corresponding values measured experimentally to demonstrate the reliability of this method.

pH-activated size reduction of large compound nanoparticles for in vivo nucleus-targeted drug delivery.

Nucleus-targeted drug delivery is a promising strategy for anticancer therapy, but in vivo nucleus-targeted drug delivery has been challenging. Limited by the channel size of the nucleopore, vehicles that enter the nucleus via the nucleopore actively should be small and decorated with nuclear localization signal (NLS). However, the small vehicle size may promote leakage of vehicles into normal tissues, and the positively-charged NLS can lead to strong non-specific interactions in vivo. In the present study, we demonstrate an in vivo nucleus-targeted drug delivery using large compound nanoparticles with detachable PEG shell. The nanoparticles are composed of PEG-benzoic imine-oligo-l-lysine/iridium(III) metallodrug complex and formed in a kinetically-controlled fashion. Under physiological conditions (pH 7.4), the nanoparticles are large (ca. 150 nm) and protected by an inert PEG shell. When internalized into intracellular acidic endo/lysosomes of cancer cells, the nanoparticles dissociate into smaller ones (ca. 40 nm) and the PEG chains detach due to the cleavage of the benzoic imine bond at low pH. The small nanoparticles, with exposure of the oligo-l-lysine after the detachment of the PEG shield, then translocate into the nucleus via the nucleopore due to the small size and nuclear localization ability of the oligo-l-lysine. Importantly, the small particles could significantly release the contained drug into the nucleus, leading to ca. 20-fold higher cytotoxicity compared to the native drug in vitro. Further in vivo application of the nucleus-targeting nano-system in a nude-mice model showed significant tumor inhibition and remarkable life-span elongation.