Study on the Flame Retardancy of Rigid Polyurethane Foam with Phytic Acid-Functionalized Graphene Oxide.

A rigid polyurethane foam (RPUF) composite was prepared by compounding phytic acid (PA)-functionalized Graphite oxide (PA-GO) with flame-retardant poly (Ammonium phosphate) (APP) and expandable graphite (EG). The effects of PA-GO on the thermal, flame-retardant, and mechanical properties of RPUF were studied using a thermogravimetric analyzer, a limiting oxygen index (LOI) tester, a UL-94 vertical combustion tester, a cone calorimeter, scanning electron microscopy, and a universal tensile testing machine. The results indicated that there was a significant synergistic flame-retardant effect between PA-GO and the intumescent flame retardants (IFR) in the RPUF matrix. Compared with RPUF-1, the addition of 0.3 wt% PA-GO could increase LOI from 25.7% to 26.5%, increase UL-94 rating from V-2 to V-0, and reduce the peak heat release rate (PHRR) and total heat release rate (THR) by 28.5% and 22.2%, respectively. Moreover, the amount of residual char increased from 22.2 wt% to 24.6 wt%, and the char layer was continuous and dense, with almost no holes. Meanwhile, the loss of mechanical properties was apparently lightened.

Vaginal Drug Delivery Systems to Control Microbe-Associated Infections.

The vagina has been regarded as a crucial route for drug delivery. Despite the wide range of available vaginal dosage forms for vaginal infection control, poor drug absorptivity remains a significant challenge due to various biological barriers in the vagina, such as mucus, epithelium, immune systems, and others. To overcome these barriers, different types of vaginal drug delivery systems (VDDSs), with outstanding mucoadhesive, mucus-penetrating properties, have been designed to enhance the absorptivity of vagina-administered agents in the past decades. In this Review, we introduce a general understanding of vaginal administration, its biological barriers, the commonly used VDDSs, such as nanoparticles and hydrogels, and their applications in controlling microbe-associated vaginal infections. Additionally, further challenges and concerns regarding the design of VDDSs will be discussed.

Synergistic Flame Retardant Effect between Ionic Liquid Functionalized Imogolite Nanotubes and Ammonium Polyphosphate in Epoxy Resin.

Ionic liquid functionalized imogolite nanotubes (INTs-PF6-ILs) were introduced into the epoxy resin (EP)/ammonium polyphosphate (APP) system to investigate the flame retardant performance and thermal properties using the limiting oxygen index (LOI) test, the UL-94 test, and the cone calorimeter test (CCT). The results suggested that a synergistic effect exists between INTs-PF6-ILs and APP on the char formation and anti-dripping behavior of EP composites. For the EP/APP, an UL-94 V-1 rating was obtained for the loading of 4 wt% APP. However, the composites containing 3.7 wt% APP and 0.3 wt% INTs-PF6-ILs could pass the UL-94 V-0 rating without dripping behavior. In addition, compared with the EP/APP composite, the fire performance index (FPI) value and fire spread index (FSI) value of EP/APP/INTs-PF6-ILs composites were remarkably reduced by 11.4% and 21.1%, respectively. Moreover, the char formed by EP/APP composites was intumescent, but of poor quality. In contrast, the char for EP/APP/INTs-PF6-ILs was strong and compact. Therefore, it can resist the erosion due to heat and gas formation and protect the inside of the matrix. This was the main reason for the good flame retardant property of EP/APP/INTs-PF6-ILs composites.

A Solvent Co-cross-linked Organogel with Fast Self-Healing Capability and Reversible Adhesiveness at Extreme Temperatures.

Antifreezing gels are promising in diverse engineering applications such as structural soft matters, sensors, and wearable devices. However, the capability of fast self-healing and reversible adhesiveness still remain a huge challenge for gels at extreme temperatures. Here, we proposed a solvent-involved cross-linking system composed of polyacrylic acid, polyvinyl alcohol, borax, ethylene glycol, and water, capable of antifreezing below -90 °C. It was not only antifreezing, anticrystalline, and abundant in dynamic bonds but also highly transparent, stretchable (over 800%), and conductive over the scope of temperature from -60 to 60 °C. Moreover, this gel could self-heal within 1 min and repeatedly adhere to multiple substrates including glass, metal, and rubber with an adhesive strength greater than 18 kPa. These key functions of the gel could be mostly preserved after 5 days of storage at 70% relative humidity. It is anticipated that our research opens a new scope for high-performance extreme environment-tolerant adhesives or wearable devices.

Development of glucose oxidase-immobilized alginate nanoparticles for enhanced glucose-triggered insulin delivery in diabetic mice.

In this work, we successfully developed poly(acrylamido phenylboronic acid)/sodium alginate nanoparticles (NPs) via formation of cycloborates (glucose- and H2O2-responsive functional groups), as an improved glucose-mediated insulin delivery system loaded with glucose oxidase (GOx). Dynamic light scattering revealed that the GOx-loaded NPs showed better glucose-sensitivity than the GOx-unloaded NPs. In addition, compared to insulin-loaded NPs, the insulin/GOx-loaded NPs displayed faster glucose-responsive insulin release. Importantly, there was a significant hypoglycemic effect on diabetic mice following the subcutaneous injection of insulin/GOx-loaded NPs. Furthermore, the NPs exhibited favorable biocompatibility as demonstrated by cytotoxicity assay, hemolysis study, and histopathological examination. The NPs have the advantages of easy preparation, enhanced glucose-responsiveness, and good biocompatibility, making them as potential candidates for subcutaneous insulin delivery.

Glycopolypeptide Nanocarriers Based on Dynamic Covalent Bonds for Glucose Dual-Responsiveness and Self-Regulated Release of Insulin in Diabetic Rats.

An intelligent carrier system is based on fast glucose response mechanism to regulate the insulin release. Here, glucose dual-responsive nanoparticles were quickly and efficiently obtained, by dynamic covalent bonds between phenylboronic acid-containing homopolymer poly(3-acrylamidophenylboronic acid) (PAAPBA) and glycopolypeptide poly(ethylene glycol)-b-poly(aspartic acid-co-aspart-glucosamine) (PEG-b-P(Asp-co-AGA)) through the formation of cycloborates. Meanwhile, insulin and glucose oxidase (GOx) were loaded during the formation of nanoparticles. The cycloborates in the nanoparticles could be destroyed by the replacement of glycosyl moieties by glucose and oxidized by H2O2 generated from the glucose-GOx system, resulting in the rapid insulin release. After subcutaneous delivery of the insulin/GOx-loaded nanoparticles to diabetic mice, a significant hypoglycemic effect was observed over time. Cytotoxicity study, hemolysis assay, and histological analyses suggested that the nanoparticles showed excellent biocompatibility and safety. This work lays the important theoretical and technical foundations for expanding the scope of applications of nanocarriers in diabetes treatment.

Fabrication of Hybrid Polymeric Micelles Containing AuNPs and Metalloporphyrin in the Core.

Multi-structure assemblies consisting of gold nanoparticles and porphyrin were fabricated by using diblock copolymer, poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP). The copolymer of PEG-b-P4VP was used in the formation of core-shell micelles in water, in which the P4VP block serves as the core, while the PEG block forms the shell. In the micellar core, gold nanoparticle and metalloporphyrin were dispersed through the axial coordination. Structural and morphological characterizations of the complex micelle were carried out by transmission electron microscopy, laser light scatting, and UV-visible spectroscopy. Metalloporphyrin in the complex micelle exhibited excellent photostability by reducing the generation of the singlet oxygen. This strategy may provide a novel approach to design photocatalysts that have target applications in photocatalysis and solar cells.

Development of a novel nanoprobe from alginate functionlized gold nanoparticles and 3-(dansylamino)phenylboronic acid for glucose detection and enhanced 4-nitrophenol reduction.

Gold nanoparticles (AuNPs) were prepared by a solvothermal method using sodium alginate (SA) as both, the reductant and stabilizer. The formation of SA-AuNPs was confirmed by UV-Vis spectroscopy, transmission electron microscopy, X-ray diffractometry, and X-ray photoelectron spectroscopy. SA-AuNPs were functionalized with fluorescent 3-(dansylamino)phenylboronic acid (DAPB) moieties, through interactions between boronic acids and diol groups. The fluorescence resonance energy transfer from DAPB to AuNPs quenched the fluorescence of DAPB. In the presence of glucose, the competitive binding of DAPB with glucose resulted in the release of assembled DAPB from the surface of SA-AuNPs, resulting in the increase in fluorescence intensity. Furthermore, catalytic reduction of 4-nitrophenol was monitored via spectrophotometry using DAPB functionalized SA-AuNPs probes as catalyst. Compared to SA-AuNPs, the nanoprobes exhibited higher catalytic rates.

Design, Preparation, and Application of a Novel, Microencapsulated, Intumescent, Flame-Retardant-Based Mimicking Mussel.

A novel microencapsulated intumescent flame retardant (TMAPP) was prepared, in which ammonium polyphosphate (APP) is the core and functions as an acid source, melamine-urea formaldehyde (MUF) resin is in the intermediate layer and functions as a blowing agent, and ferric tannin (mimicking mussel) is in the outermost shell layer and functions as a carbonization agent and also as a smoke inhibitor and surface modifier. TMAPP was prepared by treating MUF-microencapsulated APP with tannin acid and FeCl3. Its structure is characterized by Fourier transform infrared, elemental analysis, and thermogravimetry (TG). TMAPP in epoxy was evaluated for its effect on flame retardancy and mechanical properties. The flame-retardant and smoke suppression performances of EP/TMAPP were studied using cone calorimetry (CONE) and limit oxygen index, and the flame-retardant mechanism was investigated by scanning electron microscopy and TG. The resultant data indicate that EP/TMAPP has very good mechanical properties, flame retardancy, and smoke suppression, whose char residue and thermal stability are increased, and the initial decomposition temperatures are decreased. Meanwhile, the char residue structures were very intumescent and compact. The char residue effectively prevents the underlying materials of EP/TMAPP from further combustion.

Development of shell cross-linked nanoparticles based on boronic acid-related reactions for self-regulated insulin delivery.

Shell cross-linked nanoparticles were fabricated by the complexation of poly(3-methacrylamido phenylboronic acid) (PMAPBA) and thiolated chitosan (chitosan-SH) via boronic acid-related reactions. The formation of PMAPBA/chitosan-SH nanoparticles was confirmed by transmission electron microscopy, dynamic light scattering, and UV spectroscopy. The nanoparticles had a narrow size distribution with a relatively high positive charge density, and the size and zeta potential of the nanoparticles correlated with the chitosan-SH concentration. Furthermore, owing to the cross-linking of the nanoparticle shell, insulin was encapsulated in the nanoparticles with a loading capacity of up to 18%. The release of insulin from the nanoparticles slowed down because of the presence of disulfide bonds and increased with increasing glucose level in the medium. The structure of the released insulin was not distorted. More importantly, the nanoparticles had good cytocompatibility, as demonstrated by in vitro experiments. The simplicity of this strategy along with a high loading capacity, glucose sensitivity, and cytocompatibility of the produced nanoparticles should significantly boost their application in self-regulated insulin delivery.

Phenylboronic acid as a glucose-responsive trigger to tune the insulin release of glycopolymer nanoparticles.

An amphiphilic glycopolymer, poly(D-gluconamidoethyl methacrylate -r-3-methacrylamido phenylboronic acid), which could self-assemble to form nanoparticles with a narrow size distribution, was synthesized. Transmission electron microscopy showed that the nanoparticles were spherical in shape with diameters of about 120 nm. The phenylboronic acid rendered the glycopolymer nanoparticles glucose sensitive, which was evident from swelling behavior of the nanoparticles at different glucose concentrations and was found to be dependent on the glucose level. Insulin was efficiently encapsulated within the nanoparticles (up to 15%), and the release of insulin increased with an increase in the level of glucose in the medium. Cell viability tests proved that the glycopolymer nanoparticles had good cytocompatibility, due to which the glycopolymers have the potential to be used in biomedical fields.

Preparation and responsive behaviors of chitosan-functionalized nanoparticles via a boronic acid-related reaction.

We presented here a facile strategy for constructing chitosan-functionalized nanoparticles through the coordinating interaction between phenylboronic acids in poly(3-methacrylamido phenylboronic acid) and amine groups in chitosan. The formation of nanoparticles was confirmed by Fourier transform infrared spectrometer, thermal analysis, dynamic light scattering, and transmission electron micrographs, and the nanoparticles were stable over three days in aqueous solution. The pH-sensitivity of the nanoparticles was revealed by the light scattering intensity ratio (I/I0) at different pH values. I/I0 kept constant at pH 7.0 and 8.0. When the pH value was further increased in the range of 8.0-10, I/I0 reduced. As the pH value increased above 10, I/I0 kept constant. The nanoparticles were also sensitive to glucose, and the glucose-responsive behavior was dependent on the pH values, nanoparticle concentrations, and nanoparticle compositions.

Preparation of lysozyme imprinted magnetic nanoparticles via surface graft copolymerization.

Molecular imprinting as a facile and promising separation technique has received considerable attention because of their high selectivity for target molecules. In this study, we imprinted lysozyme (Lys) on the surface of core-shell magnetic nanoparticles via surface imprinting. The magnetic supports were functionalized with maleic acid and then coated with imprinted polymer layers. The structure and morphology of the resulting magnetic imprinted nanoparticles were characterized by transmission electron microscopy, scanning electron microscope, dynamic light scatting, vibrating sample magnetometer, and thermogravimetric analysis. Binding experiments were carried out to evaluate the properties of magnetic molecularly imprinted polymers (magnetic MIPs) and magnetic non-molecularly imprinted polymers (magnetic NIPs). The protein adsorption results showed that the magnetic MIPs had significant specific recognition toward the template protein and could be easily separated from solution by an external magnetic field. Moreover, the MIPs exhibited fast kinetics for the rebinding of the target protein due to the thin-imprinted layer and showed good reusability by four adsorption-desorption cycles. Therefore, the surface imprinting approach combined with magnetic nanoparticles provided an easy and fast method for the specific recognition of Lys.

Hemin-block copolymer micelle as an artificial peroxidase and its applications in chromogenic detection and biocatalysis.

Following an inspiration from the fine structure of natural peroxidases, such as horseradish peroxidase (HRP), an artificial peroxidase was constructed through the self-assembly of diblock copolymers and hemin, which formed a functional micelle with peroxidase-like activity. The pyridine moiety in block copolymer poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP) can coordinate with hemin, and thus hemin is present in a five-coordinate complex with an open site for binding substrates, which mimics the microenvironment of heme in natural peroxidases. The amphiphilic core-shell structure of the micelle and the coordination interaction of the polymer to the hemin inhibit the formation of hemin µ-oxo dimers, and thereby enhance the stability of hemin in the water phase. Hemin-micelles exhibited excellent catalytic performance in the oxidation of phenolic and azo compounds by H2O2. In comparison with natural peroxidases, hemin-micelles have higher catalytic activity and better stability over wide temperature and pH ranges. Hemin-micelles can be used as a detection system for H2O2 with chromogenic substrates, and they anticipate the possibility of constructing new biocatalysts tailored to specific functions.

Facile and green synthesis of core-shell structured magnetic chitosan submicrospheres and their surface functionalization.

Submicrometer-sized magnetite colloid nanocrystal clusters (MCNCs) provide a new avenue for constructing uniformly sized and highly magnetic composite submicrospheres. Herein, a facile and eco-friendly method is described for the synthesis of Fe3O4@poly(acrylic acid) (PAA)/chitosan (CS) core-shell submicrospheres using MCNCs bearing carboxyl groups as the magnetic cores. It is based on the self-assembly of positively charged CS chains on the surface of the oppositely charged MCNCs dispersed in the aqueous solution containing acrylic acid (AA) and a cross-linker N,N'-methylenebis(acrylamide) (MBA), followed by radical induced cross-linking copolymerization of AA and MBA along the CS chains. The resulting polymer shell comprises a medium shell of cross-linked PAA/CS polyelectrolyte complexes and an outer shell of protonated CS chains. It was found that the shell thickness could be tuned by varying either the concentration of radical initiator or the molar ratio of AA to aminoglucoside units of CS. To the surface of thus obtained Fe3O4@PAA/CS particles, Au nanoparticles, a variety of functional groups such as fluorescein, carboxyl, quaternary ammonium, and aliphatic bromide, and even functional polymer chains were successfully introduced. Therefore, such Fe3O4@PAA/CS submicrospheres may be used as versatile magnetic functional scaffolds in biorelated areas like bioseparation and medical assay, considering the unique features of CS like nontoxicity and biocompatibility.

Silica nanoparticle supported molecularly imprinted polymer layers with varied degrees of crosslinking for lysozyme recognition.

Surface imprinting over nanosized support materials is particularly suitable for protein templates, considering the problems with mass transfer limitation and low binding capacity. Previously we have demonstrated a strategy for surface protein imprinting over vinyl-modified silica nanopartiles with lysozyme as a model template by polymerization in high-dilution monomer solution to prevent macrogelation. Herein, the synthesis process was further studied toward enhancement of the imprinting performance by examining the effect of several synthesis conditions. Interestingly, the feed crosslinking degree was found to have a great impact on the thickness of the formed imprinting polymer layers and the recognition properties of the resulting imprinted materials. The imprinted particles with a crosslinking degree up to 50% showed the best imprinting effect. The imprinting factor achieved 2.89 and the specific binding reached 23.3 mg g(-1), which are greatly increased compared to those of the lowly crosslinked imprinted materials reported previously. Moreover, the relatively high crosslinking degree led to no significant retarding of the binding kinetics to the imprinted particles, and the saturated adsorption was reached within 10 min. Therefore, this may be a promising method for protein imprinting.

Synthesis of Fe3O4@poly(methacrylic acid) core-shell submicrospheres via RAFT precipitation polymerization.

Submicron-sized superparamagnetic magnetite colloid nanocrystal clusters (MCNCs) composed of many interconnected tiny Fe(3)O(4) nanoparticles provide a new avenue for constructing highly magnetic polymer submicrospheres for biotechnological and medical applications. Herein, a facile and efficient method is described for the synthesis of Fe(3)O(4)@poly(methacrylic acid) (PMAA) core-shell submicrospheres using the MCNCs modified with polymerizable vinyl groups as the submicronic cores. The controlled encapsulation of the MCNCs with PMAA shells was achieved via precipitation polymerization mediated by a reversible addition-fragmentation chain transfer (RAFT) agent. A variety of factors influencing the formation of PMAA layers were examined, such as the loading amounts of the magnetic seeds and monomers, polymerization time, and the MCNCs' surface chemistry. Compared with previous approaches, much higher seed dosage could be employed in the polymerization system without leading to significant particle conglutination. The shell thickness was readily tailored via varying two synthesis parameters, that is, monomer dosage and reaction time. The resulting hybrid particles showed high saturation magnetization and pH responsiveness. Also, this method was successfully extended to coating other hydrophilic polymer shells over the MCNCs and hence may be a general way for the synthesis of magnetic polymer submicrospheres.

Enhancement of the photostability and photoactivity of metallo-meso-5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrins by polymeric micelles.

Metallo-meso-5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrins (metallo-TPPSs), such as ZnTPPS, have been widely used as photosensitizers. However, their vulnerability to photodegradation significantly limits their applications. In this contribution, we demonstrate a method to enhance the photostability of metallo-TPPSs while retaining photoactivity via encapsulation inside cores of complex micelles. Poly(ethylene glycol)-b-poly(4-vinylpyridine) (PEG-b-P4VP) and metallo-TPPSs can form complex micelles in acidic solution through electrostatic interactions and then undergo axial coordination with the pyridine moieties of PEG-b-P4VP when the pH is adjusted to 7.4. In this way, metallo-TPPSs are entrapped in the hydrophobic, compact micellar cores, which effectively prevents photodegradation of the metallo-TPPSs that would otherwise occur in aqueous solution. In addition, the photodebromination of 2,3-dibromo-3-phenylpropionic acid (DPP) sensitized with ZnTPPS has been used as a model reaction to study the photosensitive activity of ZnTPPS entrapped in complex micelles. The entrapped ZnTPPSs exhibit pronounced activity and have much higher efficiency and faster photosensitive reaction rates than free ZnTPPS.

Enhanced lysozyme imprinting over nanoparticles functionalized with carboxyl groups for noncovalent template sorption.

Surface molecular imprinting, in particular over nanosized support materials, is very suitable for a template of bulky structure like protein. Inspired by the surface template immobilization method reported previously, we herein demonstrate an alternative strategy for enhancing specific recognition of core-shell protein-imprinted nanoparticles through prefunctionalizing the cores with noncovalent template sorption groups. For proof of this concept, silica nanoparticles chosen as the core materials were modified consecutively with 3-aminopropyltrimethoxysilane and maleic anhydride to introduce polymerizable double bonds and terminal carboxyl groups, hence capable of physically adsorbing the print protein. With lysozyme as a template, thin protein-imprinted shells were fabricated according to our newly developed approach for surface protein imprinting over nanoparticles. The rebinding experiments confirmed that the introduction of the carboxyl groups could remarkably improve the imprinting effect in relation to a significantly increased imprinting factor and specific rebinding capacity. Moreover, in contrast to the harsh template removal conditions required for the covalent template coupling approach, the template removal during the imprinted particle synthesis as well as desorption after rebinding could be mildly achieved via washing with salt solution.