Yen Bach Truong

Recent advances in nanofibre fabrication techniques

Over the past decade, there has been a tremendous increase in the demand for polymeric nanofibres which are promising candidates for various applications including tissue engineering, protective clothing, filtration and sensors. To address thisdemand, researchers have turned to the development of various techniques such as electrospinning, meltblowing, bicomponent spinning, forcespinning and flash-spinning for the fabrication of polymeric nanofibres. However, electrospinning is the widely used technique for the fabrication of continuous nanofibres. The ability to fabricate nanofibrous assemblies of various materials (such as polymers, ceramics and metals) with possible control of the fibre fineness, surface morphology, orientation and cross-sectional configuration, gives electrospinning an edge over other processes. Although several researches have been done in electrospinning, understanding some of the other processes is still in infancy. In this perspective article, we summarize the fundamentals of various techniques for the fabrication of nanofibres. This paper also highlights a gamut of recent advances in the techniques for nanofibre fabrication.

Collagen-based layer-by-layer coating on electrospun polymer scaffolds

Preparation of microfibre constructs of collagen by electrospinning has been problematic due to the instability of collagen in volatile solvents, such as 1,1,1,3,3,3-hexafluoro-2-propanol, so that electrospinning leads to a substantial amount of gelatin fibres. In the present study we have demonstrated the production of collagen-based microfibre constructs by use of a layer-by-layer coating process onto a preformed synthetic polymer microfibre base. Soluble native collagen, which has a basic isoelectric point, has been used with modified triple-helical collagens that have acidic isoelectric points. These modified collagens have been prepared as deamidated, succinylated, maleylated and citraconylated derivatives. Together, the acidic and basic collagens have successfully coated polyacrylonitrile and poly(DL-lactide-co-glycolide) fibres, as shown by spectroscopy and microscopy. These coatings allow good cell attachment and spreading on the fibres. The native, triple helical form of the collagen has been confirmed through use of a conformation dependent monoclonal antibody.

Bioremediation of pesticide contaminated water using an organophosphate degrading enzyme immobilized on nonwoven polyester textiles

Bioremediation using enzymes has become an attractive approach for removing hazardous chemicals such as organophosphate pesticides from the environment. Enzymes immobilized on solid carriers are particularly suited for such applications. In this study, the organophosphate degrading enzyme A (OpdA) was covalently immobilized on highly porous nonwoven polyester fabrics for organophosphate pesticide degradation. The fabrics were first activated with ethylenediamine to introduce free amine groups, and the enzyme was then attached using the bifunctional crosslinker glutaraldehyde. The immobilization only slightly increased the Km (for methyl parathion, MP), broadened the pH profile such that the enzyme had significant activity at acidic pH, and enhanced the stability of the enzyme. The OpdA-functionalized fabrics could be stored in a phosphate buffer or in the dry state at 4°C for at least 4 weeks without a large loss of activity. When used in batch mode, the functionalized textiles could degrade 20 μM MP in un-buffered water at liquor to fabric ratios as high as 5000:1 within 2h, and could be used repeatedly. The fabrics could also be made into columns for continuous pesticide degradation. The columns were able to degrade 50 μM MP at high flow rates, and could be used repeatedly over 2 months. These results demonstrate that OpdA immobilized on nonwoven polyester fabrics is useful in environmental remediation of organophosphate compounds.

Effect of viscosity and electrical conductivity on the morphology and fiber diameter in melt electrospinning of polypropylene

The feasibility of fabricating polypropylene (PP) nanofibers has been explored by using different additives, such as sodium oleate (SO), poly(ethylene glycol) (PEG) and poly(dimethyl siloxane) (PDMS), during melt electrospinning. PP of high melt flow index (1000) was used with PEG and PDMS for the reduction of the melt viscosity; and it was used with SO for improving the electrical conductivity during melt electrospinning. It was observed that all the additives used in this study helped to reduce the fiber diameter. The most promising additive, SO, was effective in reducing the fiber diameter to the nanometer scale due to the increase in the electrical conductivity. The fiber diameter was decreased by the addition of PEG and PDMS due to the decrease in the melt viscosity. The effect of die shape on the fiber cross-sectional shape was analyzed and an interesting finding is that the die shapes did not have an effect on the cross-sectional shape of the fibers. That is, irrespective of the die shapes (i.e. trilobal, tetralobal, multilobal and circular) used in this study, the cross-sectional shapes of melt electrospun fibers were circular. The distribution of the additives in the fiber was analyzed by energy-dispersive X-ray analysis and was found to be uniform. Tensile tests were performed on single nanofibers with limited success, due to the problems in preparing fiber samples and successfully holding them in the jaws of the testing machine without slippage.

High surface area mesoporous titanium–zirconium oxide nanofibrous web: a heavy metal ion adsorbent

A mixed titanium–zirconium (Ti :  Zr = 2 : 1 atomic ratio) oxide non-woven nanofibrous web was prepared by using an electrospinning technique followed by thermal treatment. A hydrocarbon surfactant was incorporated into the electrospinning solution and was pyrolysed during heating. The surfactant acted as a structure-directing agent to create intra-fibre pores, and significantly increased the surface area of the fibres, thereby maximising the number of sites for further surface modification as well as heavy metal ion adsorption. The high surface area (248 m2 g−1) titanium–zirconium oxide nanofibre surface was functionalised via a phosphonic acid coupling reaction to give different functional groups for attracting metal ions (i.e., phosphonate and amine groups). The cadmium adsorption capacity of the phosphonate-functionalised nanofibres was up to 10 times higher than that of the non-modified or amine-functionalised nanofibres. In addition, the cadmium adsorption on the phosphonate-functionalised nanofibres was less dependent on the pH of analyte solutions than the metal oxide nanofibres where the surface charge changed in varied pH environments. The size of the nanofibrous web can be easily scaled for making a large web convenient for handling and recovery after use, compared with high surface area heavy metal ion adsorbents that are nanometre or micrometre in size.

Monitoring of dissolved reactive phosphorus in wastewaters by flow injection analysis. Part 1. Method development and validation

Abstract The optimisation and validation of a flow-injection (FI) procedure for dissolved reactive phosphorus (DRP) in wastewaters is described. The procedure is based on the formation of molybdophosphoric acid and subsequent reduction to molybdenum blue with tin(II) chloride. The limit of detection was 0.05 mg P l −1 and the linear range was 0–25 mg P l −1 . Particular emphasis is placed on the suitability of the procedure for application in an automated on-line FI analyser. This includes a comprehensive examination of potential interferences in the analytical procedure and comparison of the performance of the method with two other established procedures. Temperature effects and long-term reagent stability were also examined. The results from the proposed FI procedure for DRP in 11 wastewater samples showed very good correlation with those from the standard batch procedure.

Enhanced photocatalytic activity: Macroporous electrospun mats of mesoporous au/TiO2 nanofibers

An electrospinning technique coupled with sol–gel chemistry is applied for the one‐pot preparation of macroporous–mesoporous titanium dioxide nanofibrous mats embedded with Au nanoparticles. This facile approach produces nanofibers that are thermally treated to simultaneously 1) remove the organics, 2) reduce AuIII to Au0 to form Au nanoparticles, and 3) crystallize titania to the anatase phase. This methodology allows high‐temperature treatment (650 °C) for well‐crystallized titania without agglomeration of the nanoparticulate Au (13±3 nm), which thereby significantly advances the existing methods for the synthesis of Au/TiO2 materials for which multiple steps are required. Additionally, high Au yields (≈100 %) were achieved in the final structure, which demonstrates another merit of this technique. The X‐ray diffraction patterns of the nanofibers were monitored by using a synchrotron beamline as the sample was heated to determine the optimum calcination temperature required to maximize the anatase phase and minimize the formation of rutile. Both the material properties (which include morphology, pore size distribution, surface area, Au particle size, and TiO2 crystal phase and size) and photocatalytic activity can be readily tuned as a function of the calcination temperature and Au content. The material calcined at 550 °C with 2.0 wt % Au shows the highest photocatalytic activity. This material is anatase in phase (which maximizes the electron‐transfer activity) and has the highest loading of small Au nanoparticles (which act as electron sinks to decrease the recombination of photo‐excited electrons and holes). These Au/TiO2 nanofibrous mats have the advantage of easy recovery and, therefore, reuse after the photocatalytic reaction, which addresses the issue of photocatalyst separation when using nanoparticulate powders as photocatalysts.

A comparison of the effects of fibre alignment of smooth and textured fibres in electrospun membranes on fibroblast cell adhesion.

A polyester polycaprolactone-based polyurethane elastomer (PU) and poly-(l-lactide) (PLLA), two common biomaterials, were electrospun to produce membranes with fibres either randomly orientated or aligned. PU was used to produce membranes consisting of smooth fibres. PLLA was used to prepare fibres with a textured surface. Contact angle measurements of the PU and PLLA cast films reveal that they were both below 90 degrees and fully wetted in less than 60 s. These membranes were investigated for the effect of fibre topography and fibre alignment on cell adhesion, using mouse L929 fibroblasts. It was found that the alignment of electrospun fibres controls the directional spreading of fibroblast independent of fibre being smooth or textured.

Fabrication and Characterisation of Nanofibres by Meltblowing and Melt Electrospinning

Fabrication of nanofibres has become a growing area of research because of their unique properties (i.e. smaller fibre diameter and higher surface area) and potential applications in various fields such as filtration, composites and biomedical applications. Although several processes exist for fabrication of nanofibres, electrospinning is considered to be the simplest. Most of the research in electrospinning is based on solution rather than melt. The feasibility of fabricating nanofibres of polypropylene (PP) by meltblowing and melt electrospinning has been investigated in this paper. In meltblowing different fluids such as air and water were fed at different inlets along the extrusion barrel for the fabrication of nanofibres whereas in melt electrospinning it was achieved by using different additives. The results obtained by using water in meltblowing were better with respect to the morphology and fibre uniformity compared to air. In melt electrospinning although all the additives (i.e. sodium oleate (SO), polyethylene glycol (PEG) and polydimethyl siloxane (PDMS)) helped in reducing the fibre diameter, only SO was effective to reduce the diameter down to nanoscale. It was concluded that both the solvent-free processes have the potential to substantially increase the production of nanofibres compared to solution electrospinning.

Monitoring of dissolved reactive phosphorus in wastewaters by flow injection analysis. Part 2. On-line monitoring system

Abstract An automated-flow injection (FI) analyser for the determination of dissolved reactive phosphorus (DRP) in wastewaters is described. The analytical method is based on the formation of molybdenum blue. The limits of detection using a solid-state photometric detector (LED-photodiode) were 0.05 mg P l−1 and the linear range was 0–20 mg P l−1. Details of construction, field-testing (including sample filtration) and validation are given. The analyser proved very reliable during an unattended operational period of seven days. Operational costs were minimised, with low reagent consumption and minimal operator intervention. Data retrieval and analyser status were remotely interrogated by means of a cellular telephone-based communications link. The real-time results from the analyser showed good correlation with those generated by a validated laboratory method.