Yiguang Wu

Multiaction antibacterial nanofibrous membranes fabricated by electrospinning: an excellent system for antibacterial applications

In this paper, novel multiaction antibacterial nanofibrous membranes containing apatite, Ag, AgBr and TiO2 as four active components were fabricated by an electrospinning technique. In this antibacterial membrane, each component serves a different function: the hydroxyapatite acts as the adsorption material for capturing bacteria, the Ag nanoparticles act as the release-active antibacterial agent, the AgBr nanoparticles act as the visible sensitive and release-active antibacterial agent, and the TiO2 acts as the UV sensitive antibacterial material and substrate for other functional components. Using E. coli as the typical testing organism, such multicomponent membranes exhibit excellent antimicrobial activity under UV light, visible light or in a dark environment. The significant antibacterial properties may be due to the synergetic action of the four major functional components, and the unique porous structure and high surface area of the nanofibrous membrane. It takes only 20 min for the bacteria to be completely (99.9%) destroyed under visible light. Even in a dark environment, about 50 min is enough to kill all of the bacteria. Compared to the four component system in powder form reported previously, the addition of the electrospun membrane could significantly improve the antibacterial inactivation of E. coli under the same evaluation conditions. Besides the superior antimicrobial capability, the permanence of the antibacterial activity of the prepared free-standing membranes was also demonstrated in repeated applications.

Poly(ionic liquid) brush coated electrospun membrane: a useful platform for the development of functionalized membrane systems

In this work, poly(ionic liquid) brushes were successfully grafted to the electrospun SiO2 nanofiber surface with atom transfer radical polymerization (ATRP) technology. By adjusting the density of initiator sites on the nanofiber surface, the core–shell structure was fabricated, which could clearly be “seen” with transmission electron microscopy (TEM). Combining the unique properties of an ionic liquid and electrospun nanofibrous mat, this hierarchically structured membrane provides a useful platform for developing functionalized membrane systems. With counteranion exchange of the attached poly(ionic liquid) brushes, the properties and functionality of the prepared membrane can be easily adjusted or integrated on need. As a demonstration, such a membrane served as an nion-directed molecular gating system. With counteranion exchange, the surface properties of the membrane were reversibly altered between hydrophilic to hydrophobic, which makes pores withdraw or expel solvent molecules (H2O), thus controlling the transport of probe molecules through the membrane. As a further example, electroactive polyoxometalate (POM) units were incorporated into the membrane through simple counteranion exchange, and a functionalized membrane with electroactivity was also achieved. In this work, various characterization techniques including infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electrochemical measurements were used to characterize the related membrane systems.

Surface molecularly imprinted electrospun affinity membranes with multimodal pore structures for efficient separation of proteins

Molecular imprinting is an important tool for generating synthetic receptors with specific recognition sites. The resulting artificial receptor has been extensively used in areas that require molecular recognition. Nevertheless, various imprinted materials synthesized using conventional imprinting protocols have low binding capacities and slow binding kinetics because of difficulty in extracting the original templates and high resistance to mass transfer. The combination of molecular imprinting and nanostructured materials is expected to overcome such difficulties. In this work, template molecules were attached onto the electrospun fibers and by using electrospun nanofibers and attached molecules as sacrificial templates, surface molecularly imprinted membranes with bi-, tri- or tetramodal pore structures were fabricated in the absence or presence of SiO2 nanoparticles in the molecular imprinting precursor. As a demonstration, bovine serum albumin (BSA) and hemoglobin from bovine blood (bHb) were chosen as template molecules and imprinted electrospun affinity membranes with multimodal pore structures were successfully fabricated for protein separation. Compared with the membrane with a bi- or trimodal pore structure, the tetramodal membrane, which consisted of tubule channels, imprinted nanocavities on the inner surface of tube wall, gaps between tubes and pores in the tube wall left by SiO2 nanoparticles, exhibited a very favorable recognition property and efficient separation toward the template protein molecules in aqueous medium. In a two-protein system, the tetramodal membrane has also shown a very high specific recognition for the template proteins over the non-template proteins. Dynamic binding tests and reusability tests further revealed that tetramodal porous membranes had excellent selectivity, faster binding kinetics and good regenerability. These results indicate that in conjugation with the surface molecular imprinting technique the use of electrospun fibers as sacrificial templates could be used as an efficient strategy for development of high performance affinity membrane materials.

Pyrrole containing ionic liquid as tecton for construction of ordered mesoporous silica with aligned polypyrrole nanowires in channels

Two types of ionic liquid (IL) based surfactants bearing a terminal pyrrole moiety were synthesized, and used as both structure-directing agents and monomers to prepare mesostructured silica with densely packed pyrrole units within channels via a hydrothermal synthesis procedure. A systematic study was carried out to address the influence of the relative concentration of the IL and the type of head group and counter ions on the mesostructure. As a main result, it was found that both the prepared imidazolium- and pyridium-based surfactants displayed a significantly strong tendency towards formation of a highly ordered two-dimensional (2D) hexagonal mesostructure in a broad range of conditions with excellent reproducibility. In situpolymerization of the pyrrole groups closely packed in the central region of the formed silica pore channels led to the desired mesostructured silica with well-distinct aligned polypyrrole (PPy) molecular wires in channels, which are clearly visible under TEM after the removal of silica framework. It is found that, due to the spatial confinement of the silica framework, the encapsulated PPys are elongated and straight, leading to longer conjugation length.

Confined Self-Assembly Approach to Produce Ultrathin Carbon Nanofibers

A surfactant containing a terminal carbon source moiety was synthesized and used simultaneously as both template molecule and carbon source. On the basis of this special structure-directing agent, an efficient strategy for producing uniform carbon nanowires with diameter below 1 nm was developed using a confined self-assembly approach. Besides the capability of producing ultralong and thin carbon wires inaccessible by the previously reported approaches, the method described here presents many advantages such as the direct use of residue iron complex as catalyst for carbonization and no requirement of conventional tedious infiltration process of carbon source into small channels. Different methods including SEM, TEM, XRD, Raman spectroscopy, and conductivity measurement were employed to characterize the formed ultrathin carbon nanofibers. Additionally, the described strategy is extendable. By designing an appropriate surfactant, it is also possible for the fabrication of the finely structured carbon network and ultrathin graphitic sheets through the construction of the corresponding cubic and lamellar mesostructured templates.

Highly potent silver-organoalkoxysilane antimicrobial porous nanomembrane

We used a simple electrospinning technique to fabricate a highly potent silver-organoalkoxysilane antimicrobial composite from AgNO3-polyvinylpyrrolidone (PVP)/3-aminopropyltrimethoxysilane (APTMS)/tetraethoxysilane (TEOS) solution. Spectroscopic and microscopic analyses of the composite showed that the fibers contain an organoalkoxysilane ‘skeleton,’ 0.18 molecules/nm2 surface amino groups, and highly dispersed and uniformly distributed silver nanoparticles (5 nm in size). Incorporation of organoalkoxysilanes is highly beneficial to the antimicrobial mat as (1) amino groups of APTMS are adhesive and biocidal to microorganisms, (2) polycondensation of APTMS and TEOS increases the membrane’s surface area by forming silicon bonds that stabilize fibers and form a composite mat with membranous structure and high porosity, and (3) the organoalkoxysilanes are also instrumental to the synthesis of the very small-sized and highly dispersed silver metal particles in the fiber mat. Antimicrobial property of the composite was evaluated by disk diffusion, minimum inhibition concentration (MIC), kinetic, and extended use assays on bacteria (Escherichia coli, Bacillus anthracis, Staphylococcus aureus, and Brucella suis), a fungus (Aspergillus niger), and the Newcastle disease virus. The membrane shows quick and sustained broad-spectrum antimicrobial activity. Only 0.3 mg of fibers is required to achieve MIC against all the test organisms. Bacteria are inhibited within 30 min of contact, and the fibers can be used repeatedly. The composite is silver efficient and environment friendly, and its membranous structure is suitable for many practical applications as in air filters, antimicrobial linen, coatings, bioadhesives, and biofilms.