Folic acid-polydopamine nanofibers show enhanced ordered-stacking via π-π interactions.

Recent research has indicated that polydopamine and synthetic eumelanins are optoelectronic biomaterials in which one-dimensional aggregates composed of ordered-stacking oligomers have been proposed as unique organic semiconductors. However, improving the ordered-stacking of oligomers in polydopamine nanostructures is a big challenge. Herein, we first demonstrate how folic acid molecules influence the morphology and nanostructure of polydopamine via tuning the π-π interactions of oligomers. MALDI-TOF mass spectrometry reveals that porphyrin-like tetramers are characteristic of folic acid-polydopamine (FA-PDA) nanofibers. X-ray diffraction combined with simulation studies indicate that these oligomers favour aggregation into graphite-like ordered nanostructures via strong π-π interactions. High-resolution TEM characterization of carbonized FA-PDA hybrids show that in FA-PDA nanofibers the size of the graphite-like domains is over 100 nm. The addition of folic acid in polydopamine enhances the ordered stacking of oligomers in its nanostructure. Our study steps forward to discover the mystery of the structure-property relationship of FA-PDA hybrids. It paves a way to optimize the properties of PDA through the design and selection of oligomer structures.

Characterization of carbonized polydopamine nanoparticles suggests ordered supramolecular structure of polydopamine.

Polydopamine is not only a multifunctional biopolymer with promising optoelectronic properties but it is also a versatile coating platform for different surfaces. The structure and formation of polydopamine is an active area of research. Some studies have supposed that polydopamine is composed of covalently bonded dihydroxyindole, indoledione, and dopamine units, but others proposed that noncovalent self-assembly contributes to polydopamine formation as well. However, it is difficult to directly find the details of supramolecular structure of polydopamine via self-assembly. In this study, we first report the graphite-like nanostructure observed in the carbonized polydopamine nanoparticles in nitrogen (or argon) environment at 800 °C. Raman characterization, which presents the typical D band and G band, confirmed the existence of graphite-like nanostructures. Our observation provides clear evidence for a layered-stacking supramolecular structure of polydopamine. Particularly, the size of graphite-like domains is similar to that of disk-shaped aggregates hypothesized in previous study about the polymerization of 5,6-dihydroxyindole [ Biomacromolecules 2012 , 13 , 2379 ]. Analysis of the hierarchical structure of polydopamine helps us understand its formation.

Freezing polystyrene-b-poly(2-vinylpyridine) micelle nanoparticles with different nanostructures and sizes.

Herein we report how to control the nanostructures and sizes of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) nanoparticles via manipulating freezing in solvent-exchange. By characterizing and analyzing the distinct structural features of the obtained nanoparticles, we recognized that micelle self-assembly happens in the precipitation of PS-b-P2VP when water is added into the block copolymer (BCP) solution. Solvent properties significantly influence micelle types that are vesicles in acetone/H2O and spherical micelles in tetrahydrofuran/H2O, respectively, thus further inducing different frozen nanostructures of the obtained nanoparticles, onion-like in acetone/H2O and large compound micelles in tetrahydrofuran/H2O. By changing the concentration of the block copolymers and the Vsolvent/VH2O ratio to modify the freezing stage at which block copolymer micelles are frozen, we can further control the size of the nanoparticles. Moreover, small molecules (phosphotungstic acid, pyrene, 1-pyrenebutyric acid) can be trapped into the block copolymer nanoparticles via the freezing process. Their distribution in the nanoparticles relies not only on the solvent property, but also on their interactions with block copolymers. The hybrid nanoparticles with ordered distribution of small molecules can be further changed to partially-void nanoparticles. Our study demonstrated that manipulating the freezing of block copolymers in the solvent exchange process is a simple and controllable fabrication method to generate BCP nanoparticles with different architectures.

Formation of polydopamine nanofibers with the aid of folic acid.

Polydopamine (PDA) generated by the oxidative self-polymerization of dopamine shows great potential for surface modification. Observed PDA nanostructures are nanoparticles and thin films. The formation mechanism of PDA is still unclear; thus, the manipulation of PDA nanostructures is a big challenge. In this study, we first demonstrated that folic acid shows a dramatic effect on the PDA nanostructure: New aggregated nanostructures of PDA, nanobelts and nanofibers, were generated in a dopamine/folic acid system. We hypothesized that folic acid may be involved in the stacking of protomolecules of PDA by π-π interactions and hydrogen bonding. Herein we describe the first experimental strategy to manipulate the aggregation of PDA by using small molecules. This study not only provides a new method for generating PDA nanofibers, which are proposed bioorganic electronic materials, but also a possible way to understand the formation mechanism of PDA and its analogues in nature, melanins.

Cooperation of Zr(IV)-N and Zr(IV)-O coordinate bonds of Zr(IV)-amide ensures the transparent and tough polyacrylamide hydrogels.

Developing advanced soft machines and tissue engineering for load-bearing cartilage or tendons requires tough hydrogels. However, the construction of double or triple crosslinked networks for these tough hydrogels, i.e., a strong network crosslinked by covalent bonds and one or two sacrificial networks built by hydrogen bonds or coordinate bonds, generally asks for multiple steps. It remains a challenge to develop hydrogels with a combination of excellent toughness and a high content of water through the time-saving one-pot process. This study demonstrates that this puzzle could be solved through engineering zirconium(IV)-amide coordinate bonds. To be specific, the combination of strong Zr(IV)-O and moderate Zr(IV)-N coordinate bonds in Zr-polyacrylamide (Zr-PAAm) hydrogels has the advantage that they are usually generated through multiple cross-linked networks. Compared to chemical crosslinked PAAm hydrogels, the highly transparent Zr-PAAm hydrogels crosslinked by Zr(NO3)4 displayed a 26-times increase in fracture stress, 4-times in fracture strain, 6-times in elastic modulus, and over 250-times in toughness. Besides, the mechanical properties of Zr-PAAm hydrogels could be altered over a wide range via changing the anion species, showing a dependence on the Hofmeister effect. The co-existence of Zr(IV)-N and Zr(IV)-O has been confirmed through XPS and FTIR characterizations. In particular, the effect of Zr(IV)-N in Zr-PAAm hydrogels has been verified by comparing the property changes of Zr-PAAm hydrogels before and after swelling in water, in which the Zr(IV)-N in the as-prepared hydrogels was replaced by Zr(IV)-O in the swollen gels. With ultra-stretchability and high transparency, the colorless Zr-PAAm hydrogels displayed rich interference colors under stretching, which brought great potential in anti-counterfeiting materials.

Wettability transition induced transformation and entrapment of polymer nanostructures in cylindrical nanopores.

We apply the concept of wettability transition to manipulate the morphology and entrapment of polymer nanostructures inside cylindrical nanopores of anodic aluminum oxide (AAO) membranes. When AAO/polystyrene (PS) hybrids, i.e., AAO/PS nanorods or AAO/PS nanotubes, are immersed into a polyethylene glycol (PEG) reservoir above the glass transition temperature of PS, a wettability transition from wetting to nonwetting of PS can be triggered due to the invasion of the more wettable PEG melt. The wettability transition enables us to develop a nondestructive method to entrap hemispherically capped nanorods inside nanopores. Moreover, we can obtain single nanorods with the desired aspect ratio by further dissolving the AAO template, in contrast to the drawbacks of nonuniformity or destructiveness from the conventional ultrasonication method. In the case of AAO/PS nanotubes, the wettability transition induced dewetting of PS nanotube walls results in the disconnection and entrapment of nonwetting PS domains (i.e., nanospheres, nanocapsules, or capped nanorods). Moreover, PEG is then washed to recover the pristine wettability of PS on the alumina surface; further annealing of the PS nanospheres inside AAO nanopores under vacuum can generate some unique nanostructures, particularly semicylindrical nanorods.

Formation of superhydrophobic microspheres of poly(vinylidene fluoride- hexafluoropropylene)/graphene composite via gelation.

We report on the spontaneous formation of superhydrophobic poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)/graphene composite microspheres with uniform size via gelation. When the suspension of PVDF-HFP/graphene (0.25 wt. % with respect to PVDF-HFP) in DMF adsorbs water vapor, it changes to a hybrid gel. A dried porous gel is obtained after solvent exchange and freeze drying. Morphology characterization shows that this hybrid gel is composed of PVDF-HFP/graphene microspheres with a diameter of 8-10 µm. In contrast, PVDF-HFP solution gives rise to a cellular microstructure following the same experimental procedures. We further elucidate the formation mechanism on the basis of the characterization by freeze fracture transmission electron microscopy, X-ray diffraction, and differential scanning calorimetry characterizations. Furthermore, contact angle measurements of water on PVDF-HFP/graphene indicates that the hydrophobic nature of PVDF-HFP combined with the micro/nanoscale hierarchical texture creates a superhydrophobic surface. Such superhydrophobic microspheres may have potential applications as water-repellent catalyst-supporting materials.

Reduced Graphene Oxide-Polypyrrole Aerogel-Based Coaxial Heterogeneous Microfiber Enables Ultrasensitive Pressure Monitoring of Living Organisms.

Pressure sensors for living organisms can monitor both the movement behavior of the organism and pressure changes of the organ, and they have vast perspectives for the health management information platform and disease diagnostics/treatment through the micropressure changes of organs. Although pressure sensors have been widely integrated with e-skin or other wearable systems for health monitoring, they have not been approved for comprehensive surveillance and monitoring of living organisms due to their unsatisfied sensing performance. To solve the problem, here, we introduce a novel structural design strategy to manufacture reduced graphene oxide-polypyrrole aerogel-based microfibers with a typical coaxial heterogeneous structure, which significantly enhances the sensitivity, resolution, and stability of the derived pressure microsensors. The as-fabricated pressure microsensors exhibit ultrahigh sensitivities of 12.84, 18.27, and 4.46 kPa-1 in the pressure ranges of 0-20, 20-40, and 40-65 Pa, respectively, high resolution (0.2 Pa), and good stability in 450 cycles. Furthermore, the microsensor is applied to detect the movement behavior and organic micropressure changes for mice and serves as a platform for monitoring micropressure for the integrative diagnosis both in vivo and in vitro of organisms.

Fabrication, mechanical properties, and biocompatibility of graphene-reinforced chitosan composites.

Few-layered graphene sheets, synthesized by direct current arc-discharge method using NH(3) as one of the buffer gases, were dispersed in chitosan/acetic acid solutions. FTIR and X-ray photoelectron spectroscopy showed the presence of oxygen-containing functional groups on the surface of graphene sheets that may assist the good dispersion of graphene in chitosan solution. Graphene/chitosan films were produced by solution casting method. The mechanical properties of composite films were tested by nanoindentation method. With the addition of a small amount of graphene in chitosan (0.1-0.3 wt %), the elastic modulus of chitosan increased over ∼ 200%. The biocompatibility of graphene/chitosan composite films was checked by tetrazolium-based colorimetric assays in vitro. The cell adhesion result showed that the L929 cell can adhere to and develop on the graphene/chitosan composite films as well as on pure chitosan film, indicating that graphene/chitosan composites have good biocompatibility. Because there is no metallic impurity in graphene raw materials, the time-consuming purification process for removing metal nanoparticles entrapped in carbon nanotubes is thus avoided when graphene is used to prepare biomedical materials. Graphene/chitosan composites are potential candidates as scaffold materials in tissue engineering.

A biocompatible chitosan composite containing phosphotungstic acid modified single-walled carbon nanotubes.

Surface modification of carbon nanotubes is crucial for the dispersion and interfacial adhesion of carbon nanotubes in polymer composites. Here we present a novel method to construct single-walled carbon nanotube/chitosan composites using phosphotungstic acid as an anchor reagent to modify single-walled carbon nanotubes. The most direct benefit from this method is that this modification is mild but effective: the induced defects on single-walled carbon nanotubes are negligible based on Raman and transmission electron microscopy observations; and homogeneous dispersion of single-walled carbon nanotubes in chitosan matrices and strong binding between single-walled carbon nanotubes and chitosan are achieved. Moreover, according to the results of tetrazolium-based colorimetric assays in vitro, we demonstrate that the produced phosphotungstic-acid-modified single-walled carbon nanotube/chitosan composites have good biocompatibility. Thus, our study provides a feasible route to fabricate biocompatible composites containing single-walled carbon nanotubes for potential application in bone tissue engineering.

Carbon-nanotube-assisted high loading and controlled release of polyoxometalates in biodegradable multilayer thin films.

Carbon nanotubes loaded with peptides, proteins and drugs can translocate across the cell membrane. This big advantage has attracted increasing attention to design a novel delivery system using nanotubes. Polyoxometalate (POM) is a promising antitumor drug and it shows a very strong interaction with carbon nanotube surfaces. In this paper, a novel complex of POM-modified single-walled carbon nanotubes (SWNTs) and chitosan was fabricated through a layer-by-layer self-assembly process. With the addition of SWNTs, the loading of POM in this thin film was doubled in the high ionic strength. The initial burst release of POMs in the (POM/chitosan)(n) thin film was suppressed in the (POM-SWNT/chitosan)(n) thin film. Also the instability of POMs in a physiologically relevant pH environment was overcome. The strong interaction between POMs and SWNTs was believed to be the determinant factor in the higher loading and prolonged release of POMs in (POM-SWNT/chitosan)(n) thin films.

Effect of Tenax addition amount and desorption time on desorption behaviour for bioavailability prediction of polycyclic aromatic hydrocarbons.

In this work, Tenax consecutive extractions of polycyclic aromatic hydrocarbons (PAHs) were conducted in two spiked sediments to investigate the influence of different Tenax addition amounts and desorption times on the rapidly desorbing fraction of PAHs, and to determine a reliable method for estimating PAHs bioavailability. The results indicated that a large Tenax addition amount has a positive effect on the desorption of PAHs from sediments. The desorption amounts of target PAHs compounds (3-ring phenanthrene and 4-ring fluoranthene) increased as the Tenax: sediment ratios increased from 0.25 to 2 in two spiked sediments. The highest desorption percentages of phenanthrene and fluoranthene were 48.91% and 34.70% for Jialing industrial park sediment, and 43.36% and 33.24% for Huanghuayuan bridge sediment, respectively. The results of desorption kinetics were suitably fitted with first order three-compartment model to estimate the rapidly desorbing fraction, Moreover, the Tenax: sediment ratio of 1 and desorption time of 24 h were found to be suitable for the desorption of phenanthrene and fluoranthene from sediments. The PAHs in sediments were biodegraded well by the bacterial strain J1-q. Comparing the maximum biodegraded amount of target PAHs in 30 days and the desorbed fraction over 400 h, the results showed that Tenax had better correlation with the high molecular weight fluoranthene than with the low molecular weight phenanthrene.

Biodegradation potential of polycyclic aromatic hydrocarbons by immobilized Klebsiella sp. in soil washing effluent.

A strain KL (Klebsiella sp.), with a high polycyclic aromatic hydrocarbons (PAHs) degradation efficiency, was isolated and purified. Immobilization of strain KL using a boric acid-CaCl2 cross-linking method based on polyvinyl alcohol (PVA)-sodium alginate (SA)-nano alumina (ALNPs) composite was investigated for removal of phenanthrene (PHE), fluoranthene (FLA), and pyrene (PYR) in soil washing effluent. The concentration of PVA, SA, and ALNPs in immobilized beads had significant effects on the physicochemical properties and biodegradation performance. When beads had a PVA, SA, and ALNPs content of 10% (w/v), 0.8% (w/v), and 0.7% (w/v), and the initial biomass dosage was 10% (v/v), the biodegradation efficiency and mass transfer performance of the immobilized beads were optimal with the specific surface area of 13.3971 m2/g. Scanning electron microscopy (SEM) showed that the surface of immobilized beads was dense. The growth and adhesion of cells inside the beads were adequate, and pores of the beads were abundant and irregularly staggered. The immobilization method was successfully applied to the treatment of the three PAHs in soil washing effluent. Adsorption of beads contributed to PAHs removal in the initial stage of degradation. Higher residual concentrations of Tween 80 in the soil washing effluent have toxic effects on strain KL growth and reduce the PAHs degradation capacity. Tween 80 of 2500 mg/L was proper conditions for PAHs biodegradation efficiency. Compared to freely suspended KL cells, the removal rates of PHE, FLA, and PYR using the immobilization method on the 30th day were increased by 15.91%, 17.07%, and 19.08%, respectively.

Starch-graft-polyacrylonitrile nanofibers by electrospinning.

Graft copolymer starch-graft-polyacrylonitrile (St-g-PAN) was synthesized by homo-grafting acrylonitrile (AN) from water soluble starch as Ce(IV) was used as an initiator. St-g-PAN nanofibers were prepared via electrospinning St-g-PAN solution in dimethyl sulfoxide (DMSO). The effects of the spinning parameters such as flow rate, spinning voltage, and collector distance on the St-g-PAN nanofiber diameter were investigated. Fourier transform infrared spectra (FT-IR), solid-state nuclear magnetic resonance (13C NMR) and scanning electron microscope (SEM) were used to characterize the structure and surface morphology of the nanofibers. The results showed that the nanofiber diameter depended strongly on the processing parameters. Moreover, the nanofiber had good water resistance, biocompatibility, and tensile intensity. As the cyano groups on St-g-PAN nanofibers were transformed to amidoxime groups, the obtained St-g-PAO nanofiber displayed an excellent adsorption ability, with the adsorption of Cr 533.4 mg·g-1 at pH = 2.0 as K2Cr2O7 solution 500 mg·L-1 in water was used as the adsorption target. Therefore, these St-g-PAN nanofibers may find potential applications in a wide variety of fields such as tissue engineering, pharmaceutics, energy, and environmental science and engineering.

Interactions of EPS with soil minerals: A combination study by ITC and CLSM.

The adsorption of extracellular polymeric substances (EPS) from Pseudomonas putida on montmorillonite, kaolinite and goethite was investigated as a function of pH using batch studies coupled with confocal laser scanning microscopy (CLSM) and isothermal titration calorimetry (ITC). Characterization by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy showed that the extracted EPS contained carboxyl, phosphoryl, amino, and hydroxyl on functional groups as well as polysaccharides, protein and nucleic acid on components. The mass fraction of EPS adsorption on minerals decreased with the final pH increased from 3.0 to 9.0. The mass fraction of EPS-N adsorption varied with pH values and was higher than that of EPS-C or EPS-P on montmorillonite and kaolinite, while the mass fraction of EPS-P adsorption was the highest on goethite. CLSM results further demonstrated that proteins were predominantly distributed on the montmorillonite and kaolinite surfaces, while nucleic acids were mainly on the goethite surface. ITC results revealed that the adsorption process in all mineral systems was exothermic, and pH altered the heat effect of EPS-mineral reactions. The data obtained in this study would facilitate a better understanding of the adsorption mechanisms of EPS on minerals.

Manufacture of degradable polymeric scaffolds for bone regeneration.

Many innovative technology platforms for promoting bone regeneration have been developed. A common theme among these is the use of scaffolds to provide mechanical support and osteoconduction. Scaffolds can be either ceramic or polymer-based, or composites of both classes of material. Both ceramics and polymers have their own merits and drawbacks, and a better solution may be to synergize the advantageous properties of both materials within composite scaffolds. In this current review, after a brief introduction of the anatomy and physiology of bone, different strategies of fabricating polymeric scaffolds for bone regeneration, including traditional and solid free-form fabrication, are critically discussed and compared, while focusing on the advantages and disadvantages of individual techniques.