Jun Nie

Electrodeposition of alginate/chitosan layer-by-layer composite coatings on titanium substrates

In this study, alginate/chitosan layer-by-layer composite coatings were prepared on titanium substrates via electrodeposition. The mechanism of anodic deposition of anionic alginate based on the pH decrease at the anode surface, while the pH increase at the cathode surface enabled the deposition of cationic chitosan coatings. The surface of coatings was characterized by using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The properties of coatings were characterized by X-ray diffraction (XRD) and differential thermal analysis (DTA). Indirect in vitro cytotoxicity test showed that the extracts of coating had no significant effects on cell viability. Moreover, in vitro cytocompatibility test exhibited cell population and spreading tendency, suggesting that the coatings were non-toxic to L929 cells. However, the results revealed that alginate coating was more benefit for cells growing than chitosan coating. The results indicated that the proposed method could be used to fabricate alginate/chitosan layer-by-layer composite coatings on the titanium surface at room temperature and such composite coatings might have potential applications in tissue engineering scaffolds field.

Facile Method for the Fabrication of Robust Polyelectrolyte Multilayers by Post-Photo-Cross-Linking of Azido Groups

In this letter, we have developed a facile method to enhance the stability of polyelectrolyte multilayers. We fabricate conventional polyelectrolyte multilayers of PAH/PAA through electrostatic layer-by-layer (LbL) assembly and then postinfiltrate photosensitive cross-linking agent 4,4-diazostilbene-2,2-disulfonic acid disodium salt into the LbL films. After cross-linking by UV irradiation, the stability of the photo-cross-linked multilayer is highly improved as evidenced by the lack of dissolution under ultrasonication in saturated SDS aqueous solutions for 10 min. Moreover, by taking advantage of the different stability of the LbL film before and after UV irradiation, a patterned surface can be achieved.

Design of genipin-crosslinked microgels from concanavalin A and glucosyloxyethyl acrylated chitosan for glucose-responsive insulin delivery

Glucose-responsive systems are significant for self-regulated insulin delivery. The aim of this study was to assess the potential of genipin-crosslinked concanavalin A/GEA-chitosan microgels as a glucose-responsive insulin delivery system. A chitosan derivative (GEA-chitosan) was designed in this study as the polymer ligand of concanavalin A (Con A), which not only exhibits a strong affinity to Con A, but also could be directly crosslinked with Con A by genipin, thus avoiding the modification of Con A during an immobilization process. Glucose responsive microgels were fabricated by the reversed-phase emulsion crosslinking method. The in vitro release of insulin indicated that the insulin release was influenced by glucose concentrations, and a desired pulsatile release behavior was detected in response to stepwise glucose challenges for more than eight cycles. The release data were fitted well to an exponential model, without any significant influence of the surface effect. The released insulin was proved to remain active without destruction of the tertiary structure. The analysis of L929 cells viability suggested that these microgels possessed no in vitro cytotoxicity. The obtained genipin crosslinked Con A/GEA-chitosan microgels might be a potential candidate for self-regulated insulin delivery.

Direct, Rapid, Facile Photochemical Method for Preparing Copper Nanoparticles and Copper Patterns

We develop a facile method for preparing copper nanoparticles and patterned surfaces with copper stripes by ultraviolet (UV) irradiation of a mixture solution containing a photoinitiator and a copper-amine coordination compound. The copper-amine compound is formed by adding diethanol amine to an ethanol solution of copper chloride. Under UV irradiation, free radicals are generated by photoinitiator decomposition. Meanwhile, the copper-amine coordination compound is rapidly reduced to copper particles because the formation of the copper-amine coordination compound prevents the production of insoluble cuprous chloride. Poly(vinylpyrrolidone) is used as a capping agent to prevent the aggregation of the as-prepared copper nanoparticles. The capping agent increases the dispersion of copper nanoparticles in the ethanol solution and affects their size and morphology. Increasing the concentration of the copper-amine coordination compound to 0.1 M directly forms a patterned surface with copper stripes on the transparent substrate. This patterned surface is formed through the combination of the heterogeneous nucleation of copper nanoparticles and photolithography. We also investigate the mechanism of photoreduction by UV-vis spectroscopy and gas chromatography-mass spectrometry.

A polymer/metal core–shell nanofiber membrane by electrospinning with an electric field, and its application for catalyst support

In the present study, PVP/Ag nanofibers with a core–shell structure have been successfully prepared by using the electrospinning technique under the action of electric field induction. PVP (polyvinyl pyrrolidone), as the functional template during electrospinning, plays an important role both as the reducing agent and as the capping agent. The structure and properties of the thus-obtained nanofibers have been investigated thoroughly through scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have also been employed to analyze the coordination interactions and chemical states of the core–shell nanofiber surface. Moreover, a static simulation of an electric-field-induced experiment has been carried out and energy-dispersive X-ray analysis (EDS) has been performed to demonstrate the field-induced mechanism. The results prove the fact that the electric field plays an important role on the induction of silver migration and formation of core–shell nanofibers. On the other hand, UV-Vis spectrophotometry has been used to test the catalytic properties of the samples for the reduction of methylene blue (MB) by NaBH4, it shows that PVP/Ag core–shell nanofibers hold great potential in the field of catalysis.

Smart Antibacterial Surface Made by Photopolymerization

On the basis of the use of photopolymerization technology, a facile and reliable method for in situ preparation of silver nanoparticles (AgNPs) within PNIPAAm functional surfaces is presented as a means to achieve nonfouling, antibacterial films. The surface properties were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), water contact angle, and thermogravimetric analysis (TGA). The antibacterial and release properties of the surfaces were tested against E. coli: at 37 °C (above the LCST of PNIPAAm), the functional films facilitated the attachment of bacteria, which were then killed by the AgNPs. Changing temperature to 4 °C (below the LCST), swollen PNIPAAm chains led the release of dead bacteria. The results showed that AgNPs/PNIPAAm hybrid surfaces offer a smart antibacterial capability in response to the change of environmental temperature.

Polymer–metal–organic framework core–shell framework nanofibers via electrospinning and their gas adsorption activities

In this study, we have fabricated of Polyacrylonitrile/Zeoliticimidazolate frameworks (PAN@ZIF-8) core–shell nanofibers by combining electrospinning techniques and the MOF synthesis method. In the first step, 2MI ligand was dispersed on PAN by using electrospinning, and then 2MI was made to coordinate Zn2+ ions derived from a zinc acetate solution. In the second step, the nanofiber mats were immersed in a ZIF-8 seed solution, and continuous and compact ZIF-8 was formed on the PAN surface by a second round of crystal growth. Analyses of XPS results and of SEM and TEM images revealed the core–shell structure of PAN@ZIF-8 nanofibers, and showed them to have a uniform nanoshell but a variety of crystal diameters. In addition, the core–shell PAN@ZIF-8 nanofibers were found to display unique properties such as a stable and flexible structure and an excellent gas adsorption capability. Our findings suggest that the core–shell PAN@ZIF-8 nanofiber mats may form a good filter material because of their gas absorption properties and because of the structural flexibility and stability of ZIF-8.

Crosslinked polyelectrolyte complex fiber membrane based on chitosan–sodium alginate by freeze-drying

Polyelectrolyte complex (PEC) membrane of cationic chitosan and anionic sodium alginate with fiber structure were prepared by freeze-drying method. Chitosan and sodium alginate were blended in different concentrations and frozen at different temperatures. Freeze-dried fiber membranes were extensively characterized for their inter-molecular interaction, the solution property, morphology and biocompatibility by using FTIR, XRD, zeta (ζ) potentials, SEM and cytotoxicity assay. The study of swelling property showed that PEC membrane with the fiber structure cross-linked with glutaraldehyde exhibited pH and ionic strength-dependent swelling in aqueous media, which might have a potential application in tissue engineering or drug controlled release. Furthermore, chitosan–sodium alginate samples showed better cell adhesion and proliferation than pure chitosan. The results indicated that two natural polyelectrolyte complex nanofibers were prepared by freeze-drying method and fitted for tissue engineering or as drug carriers.

Facile method for preparation of superfine copper nanoparticles with high concentration of copper chloride through photoreduction

Superfine copper nanoparticles were synthesized through direct photoreduction of a high concentration of copper ions in an ethanol solution with a photoinitiator at room temperature in the presence of polyethylene imine (PEI). This synthetic method was very effective in decreasing the effect of copper ion concentration on copper particle size. The reaction process was monitored using UV-vis spectroscopy, and the obtained copper nanoparticles were investigated using transmission electron microscopy. The results show that PEI acted not only as a coordinating agent to the copper ion, but also as a polymer cage that reduced the chance of copper nanoparticle aggregation.

A facile method to immobilize cucurbituril on surfaces through photocrosslinking with azido groups

We develop a facile method to immobilize cucurbituril on silicon substrates through photochemical reaction with azido groups. Combining photolithography and the competitive molecular recognition between CB[7] and acridine orange base or 1-adamantanecarboxylic acid, a patterned surface with reversible fluorescence emission can be obtained.