Static secondary ion mass spectrometry for nanoscale analysis: surface characterisation of electrospun nanofibres

The viability of static secondary ion mass spectrometry (S-SIMS) for selected applications of nanoscale analysis has been investigated, focusing on nanofibres produced by electrospinning (ES) as a test case. The samples consist of non-woven nanowebs of which the individual fibres have diameters in the range of 100 nm. Use of solutions with functionalised polymers or polar additives potentially allows the surface composition to be tailored as a function of the application. So far nanowebs are primarily characterised by morphological examination. This paper describes the first detailed characterisation of molecular composition at the surface of nanofibres electrospun from poly(epsilon-caprolactone) (PCL) solutions in acetone containing 0-15 mol% (relative to PCL) of cetyltrimethylammonium bromide (CTAB). Application of S-SIMS to nanowebs has allowed mass spectra to be recorded containing the major diagnostic ions of both components. Their relative intensities point to surface enrichment and depletion of the polar CTAB additive relative to the PCL matrix for samples electrospun from solution containing low and high CTAB concentrations, respectively.     

Static secondary ion mass spectrometry for the surface characterisation of individual nanofibres of polycaprolactone functionalised with an antibacterial additive

Electrospinning (ES) of polymer solutions generates non-woven webs of nanofibres. The fibre diameter ranges between 10 nm and 1 μm depending on the operating conditions. Surface functionalisation can be performed by the use of suitable additives. Detailed characterisation of the molecular composition at the fibre surface is a key issue. Biodegradable nanowebs with potential antibacterial activity have been prepared by ES of solutions containing polycaprolactone (PCL) and a functionalising additive with PCL segments and hexyldimethylammonium groups (PCLhexaq). Static secondary ion mass spectrometry with Bi₃⁺ projectiles has been applied to individual nanofibres. The positive ion mass spectra contain several signals with high structural specificity allowing the presence of PCLhexaq to be traced back in spite of its low concentration (0.16–1.4% w/w relative to PCL) and its structural similarity to the PCL fibre matrix. Imaging of structural ions visualises the homogeneous distribution of PCLhexaq over the fibre surface. Quantifying the surface concentration of PCLhexaq relative to that of PCL reveals electric field-driven surface enrichment of the additive during ES. Finally, nanofibres subjected to leaching in water for up to 72 h have been analysed. The PCLhexaq surface concentration decreases almost linearly with time at a rate of 0.6% h⁻¹.     

Electrospinning of cyclodextrin functionalized polyethylene oxide (PEO) nanofibers

By means of the electrospinning technique we have successfully synthesized cyclodextrin (CD) functionalized polyethylene oxide (PEO) nanofibers (PEO/CD) with the ultimate goal to develop functional nanowebs. Three different types of CDs; α-CD, β-CD and γ-CD are incorporated individually in electrospun PEO nanofibers. The aqueous solutions containing different amount of PEO (3%, 3.5% and 4% (w/v), with respect to solvent) and CDs (25% and 50% (w/w), with respect to PEO) are electrospun and bead-free nanofibers are obtained. The presence of the CDs in the PEO solutions is found to facilitate the electrospinning of bead-free nanofibers from the lower polymer concentrations and this behavior is attributed to the high conductivity and viscosity of the PEO/CD solutions. The presence of CDs in the electrospun PEO nanofibers is confirmed by Fourier transform infrared (FTIR) spectroscopy studies. The 2-D X-ray diffraction (XRD) spectra of PEO/CD nanowebs did not show any significant diffraction peaks for CDs indicating that the CD molecules are distributed within the polymer matrix without any phase separated crystalline aggregates.     

Effect of the surface topography of electrospun poly(ε-caprolactone)/poly(3-hydroxybuterate-co-3-hydroxyvalerate) fibrous substrates on cultured bone cell behavior

The use of electrospun fibrous matrices as substrates for cell/tissue culture has usually been confined to those consisting of smooth fibers. Here, we demonstrated that in vitro responses of mouse-calvaria-derived preosteoblastic cells (MC3T3-E1) that had been cultured on electrospun fibrous substrates made from blend solutions of 50/50 w/w poly(ε-caprolactone) (PCL) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) of varying concentrations, ranging from 4 to 14 wt %, depended strongly on the topography of the individual fibers. As the concentration of the blend solutions increased from 4 to 14 wt %, the topography of the individual fibers changed from discrete beads/smooth fibers to beaded fibers/smooth fibers and finally to smooth fibers, and the average diameter of the individual, smooth fibers increased from ～0.4 to ～1.8 μm. The results clearly showed that MC3T3-E1 preferred the smooth hydrophilic surface of the fibrous substrate from 10 wt % PCL/PHBV solution because the cells appeared to attach, proliferate, and differentiate on the surface of this substrate particularly well.     

The investigation of electrospun polymer nanofibers as a solid-phase extraction sorbent for the determination of trazodone in human plasma

A novel micro-extraction procedure was developed through the use of an electrospun polymer nanofiber as a solid-phase extraction (SPE) sorbent to directly extract trazodone from human plasma. The target compound was then monitored by a high performance liquid chromatography with ultraviolet detector (HPLC-UV) system. Parameters of influencing the extraction efficiency, such as fiber diameter, fiber packing amount, eluted solvent, pH and ionic strength were investigated. Under the optimized conditions, a linear response for trazodone over the range of 20-2000 ng mL⁻¹ was achieved with a γ² value of 0.9996. The precision of the method was examined with relative standard deviations of 5.7, 2.7, 2.2% corresponding to 50, 200, and 500 ng mL⁻¹, respectively, of trazodone spiked into 0.1 mL of plasma samples. The extraction recoveries of 58.3-75.2% and the relative recoveries of 94.6-105.5% were obtained. The limit of detection (LOD) was determined to be 8 ng mL⁻¹. A 15 min of HPLC gradient was successfully applied to determine trazodone from human plasma. Due to its simplicity, selectivity and sensitivity, the method may be applied to pharmacokinetic and pharmacodynamic studies of drugs.     

Study on morphology of electrospun poly(vinyl alcohol) mats

Submicron poly(vinyl alcohol) (PVA) fiber mats were prepared by electrospinning of aqueous PVA solutions in 6-8% concentration. Fiber morphology was observed under a scanning electron microscope and effects of instrument parameters including electric voltage, tip-target distance, flow rate and solution parameters such as concentration on the morphology of electrospun PVA fibers were evaluated. Results showed that, when PVA with higher degree of hydrolysis (DH) of 98% was used, tip-target distance exhibited no significant effect on the fiber morphology, however the morphological structure can be slightly changed by changing the solution flow rate. At high voltages above 10 kV, electrospun PVA fibers exhibited a broad diameter distribution. With increasing solution concentration, the morphology was changed from beaded fiber to uniform fiber and the average fiber diameter could be increased from 87 ± 14 nm to 246 ± 50 nm. It was also found that additions of sodium chloride and ethanol had significant effects on the fiber diameter and the morphology of electrospun PVA fibers because of the different solution conductivity, surface tension and viscosity. When the DH value of PVA was increased from 80% to 99%, the morphology electrospun PVA fibers was changed from ribbon-like fibers to uniform fibers and then to beaded fibers. The addition of aspirin and bovine serum albumin also resulted in the appearance of beads.     

Humidity sensing properties of ZnO-based fibers by electrospinning

Zinc oxide (ZnO) based fibers with a diameter of 80-100 nm were prepared by electrospinning. Polyvinyl alcohol (PVA) and zinc acetate dihydrate were dissolved in water and the polymer/salt solution was electrospun at 2.5 kV cm⁻¹. The resulting electrospun fibers were subjected to calcination at 500 °C for 2 h to obtain ZnO-based fibers. Humidity sensing properties of the fiber mats were investigated by quartz crystal microbalance (QCM) method and electrical measurements. The adsorption kinetics under constant relative humidity (RH) between 10% and 90% were explained using Langmuir adsorption model. Results of the measurements showed that ZnO-based fibers were found to be promising candidate for humidity sensing applications at room temperature.     

Biomedical applications of electrospun polycaprolactone fiber mats

Polycaprolactone (PCL) is a biodegradable polyester emerging into biomedical applications because of its biodegradability, biocompatibility, chemical stability, thermal stability and good mechanical properties. Electrospinning is a versatile method using electrostatic forces for fabricating continuous ultrafine fibers that offer various advantages such as high surface area and high porosity. Thus, this method has gained interest for use in many fields, especially biomedical fields. This review focuses on researches and studies in electrospinning, PCL, electrospinning of PCL and also biomedical applications of the electrospun PCL fiber mats. Copyright © 2016 John Wiley & Sons, Ltd.     

An ultrasensitive post chemiluminescence reaction of ammonium in NBS-dichlorofluorescein system and its application

A strong post chemiluminescence (PCL) phenomenon was observed when ammonium was injected into the reaction mixture after the finish of CL reaction of N-bromosuccinimide (NBS) and dichlorofluorescein. Based on this, a sensitive flow injection PCL method was established for the determination of ammonium. The possible CL mechanism of the reaction was proposed based on a series of experiments. The PCL intensity responded linearly to the concentration of ammonium in the range 3.0 × 10⁻¹¹-1.0 × 10⁻⁷ g mL⁻¹ with a detection limit of 1 × 10⁻¹¹ g mL⁻¹. The relative standard deviation (R.S.D.) was 1.4% for 1.0 × 10⁻⁹ g mL⁻¹ ammonium (n = 11). This method had been applied to the determination of ammonium in samples of mineral water, tap water and river water.     

In situ fabrication of nanostructured titania coating on the surface of titanium wire: A new approach for preparation of solid-phase microextraction fiber

Nanostructured titania-based solid-phase microextraction (SPME) fibers were fabricated through the in situ oxidation of titanium wires with H₂O₂ (30%, w/w) at 80 °C for 24 h. The obtained SPME fibers possess a ∼1.2 μm thick nanostructured coating consisting of ∼100 nm titania walls and 100-200 nm pores. The use of these fibers for headspace SPME coupled with gas chromatography with electron capture detection (GC-ECD) resulted in improved analysis of dichlorodiphenyltrichloroethane (DDT) and its degradation products. The presented method to detect DDT and its degradation products has high sensitivity (0.20-0.98 ng L⁻¹), high precision (relative standard deviation R.S.D. = 9.4-16%, n = 5), a wide linear range (5-5000 ng L⁻¹), and good linearity (coefficient of estimation R² = 0.991-0.998). As the nanostructured titania was in situ formed on the surface of a titanium wire, the coating was uniformly and strongly adhered on the titanium wire. Because of the inherent chemical stability of the titania coating and the mechanical durability of the titanium wire substrate, this new SPME fiber exhibited long life span (over 150 times).     

Preparation and self-assembly of copper nanoparticles via discharge of copper rod electrodes in a surfactant solution: a combination of physical and chemical processes

Cu nanoparticles with a mean diameter of 10-15 nm were prepared and self-assembled via discharge of bulk copper rods in a cetyltrimethylammonium bromide (CTAB)/ascorbic acid solution. Ascorbic acid was used as a protective agent to prevent the nascent Cu nanoparticles from oxidation in the solution; otherwise spindle-like Cu₂O/CuO structures, with a lateral dimension of 30-50 nm and length of up to 100 nm, were formed in pure deionized water. The surfactant CTAB had a critical influence on self-assembly of spherical Cu nanostructures (with diameter of 700 nm-1 μm). Such a low-temperature and non-vacuum method, exhibiting the characters of both physical and chemical processes, provides a versatile choice for economical preparation and assembly of various metal nanostructures.     

Novel evaluation method of biodegradabilities for oil-based polycaprolactone by naturally occurring radiocarbon-14 concentration using accelerator mass spectrometry based on ISO 14855-2 in controlled compost

The biodegradabilities of poly(?-caprolactone) (PCL) powders (av. size = 180.7 μm) in controlled compost at 58 °C have been studied using the microbial oxidative degradation analyzer (MODA) based on ISO 14855-2 entitled “Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions - Method by analysis of evolved carbon dioxide - Part 2: Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test”. The biodegradability of the PCL powders was 101.4% in a 56-day test period by the ISO method. The biodegradabilities of PCL powders have been studied using percent modern carbon (pMC) measured by accelerated mass spectrometry (AMS). Trapped CO₂ was analyzed by AMS to determine the pMC (sample) using ¹⁴C radiocarbon concentration. By using the theory that the pMC (sample) was the sum of pMC (compost) (104.88%) and pMC (PCL) (0%) as the respective ratios in the determined period, CO₂ (respiration) was calculated only from one reaction vessel. The biodegradability of PCL powders was 79.9% in a 56-day test period by the AMS method. It was found that respiration activities in the sample vessel including PCL, compost and sea sand were the same as that in the blank vessel including compost and sea sand without PCL during the active biodegradation period (0-33 day) at 58 °C. It was confirmed that respiration activities in the sample vessel were slightly higher than that in the blank vessel after active biodegradation due to the propagation of microorganisms using energy and metabolites by PCL biodegradation during those periods.     

Electrospinning nanosuspensions loaded with passivated Au nanoparticles

Aqueous polyethylene oxide (PEO) solutions (2 MDa, 2-5 wt %) with or without citrate passivated Au nanoparticles (5.7×10⁻⁷ wt %) have been electrospun, producing fibres with diameters from 290 μm to 55 nm. The incorporation of nanoparticles suppresses the diameter of the fibres and increases the degree of crystallinity. Such nanocomposite fibres are of interest as self-assembled templates for bottom-up fabrication methodologies.     

Bioactive Electrospun Fibers of Poly(ε-Caprolactone) Incorporating α-Tocopherol for Food Packaging Applications

Antioxidant activity is an important feature for food contact materials such as packaging, aiming to preserve freshness and retard food spoilage. Common bioactive agents are highly susceptible to various forms of degradation; therefore, protection is required to maintain functionality and bioavailability. Poly(ε-caprolactone) (PCL), a biodegradable GRAS labeled polymer, was used in this study for encapsulation of α-tocopherol antioxidant, a major component of vitamin E, in the form of electrospun fibers. Rheological properties of the fiber forming solutions, which determine the electrospinning behavior, were correlated with the properties of electrospun fibers, e.g., morphology and surface properties. Interactions through hydrogen bonds were evidenced between the two components. These have strong effect on structuration of macromolecular chains, especially at low α-tocopherol amounts, decreasing viscosity and elastic modulus. Intra-molecular interactions in PCL strengthen at high α-tocopherol amounts due to decreased solvation, allowing good structural recovery after cease of mechanical stress. Morphologically homogeneous electrospun fibers were obtained, with ~6 μm average diameter. The obtained fibers were highly hydrophobic, with fast release in 95% ethanol as alternative simulant for fatty foods. This induced good in vitro antioxidant activity and significant in vivo reduction of microbial growth on cheese, as determined by respirometry. Therefore, the electrospun fibers from PCL entrapping α-tocopherol as bioactive agent showed potential use in food packaging materials.     

Electrospun Poly(ε‐caprolactone)/Polyhedral Oligomeric Silsesquioxane‐Based Copolymer Blends: Evolution of Fiber Internal Structures

This study reports the structural transition of electrospun poly(ε‐caprolactone) (PCL)/poly[(propylmethacryl‐heptaisobutyl‐polyhedral oligomeric silsesquioxane)‐co‐(methyl meth­acrylate)] (POSS‐MMA) blends, from PCL‐rich fibers, to bicontinuous PCL core/POSS‐MMA shell fibers, to POSS‐MMA‐rich fibers with a discontinuous PCL inner phase. A ternary phase diagram depicting the electrospinnability of PCL/POSS‐MMA solutions is constructed by evaluating the morphological features of fibers electrospun from solutions with various concentrations and PCL/POSS‐MMA blend ratios. X‐ray diffraction, Raman spectroscopy, and differential scanning calorimetry are further used to characterize the electrospun PCL/POSS‐MMA hybrid fibers. These physicochemical characterization results are thoroughly discussed to understand the internal structures of the hybrid fibers, which are directly correlated to the phase separation behavior of the electrospun solutions. The current study provides further insight into the complex phase behavior of POSS‐copolymer‐based systems, which hold great potential for a broad spectrum of biomedical applications.

     

Functionalized mesoporous materials for adsorption and release of different drug molecules: A comparative study

The adsorption capacity and release properties of mesoporous materials for drug molecules can be improved by functionalizing their surfaces with judiciously chosen organic groups. Functionalized ordered mesoporous materials containing various types of organic groups via a co-condensation synthetic method from 15% organosilane and by post-grafting organosilanes onto a pre-made mesoporous silica were synthesized. Comparative studies of their adsorption and release properties for various model drug molecules were then conducted. Functional groups including 3-aminopropyl, 3-mercaptopropyl, vinyl, and secondary amine groups were used to functionalize the mesoporous materials while rhodamine 6G and ibuprofen were utilized to investigate the materials’ relative adsorption and release properties. The self-assembly of the mesoporous materials was carried out in the presence of cetyltrimethylammonium bromide (CTAB) surfactant, which produced MCM-41 type materials with pore diameters of ∼2.7-3.3 nm and moderate to high surface areas up to ∼1000 m²/g. The different functional groups introduced into the materials dictated their adsorption capacity and release properties. While mercaptopropyl and vinyl functionalized samples showed high adsorption capacity for rhodamine 6G, amine functionalized samples exhibited higher adsorption capacity for ibuprofen. While the diffusional release of ibuprofen was fitted on the Fickian diffusion model, the release of rhodamine 6G followed Super Case-II transport model.     

Flow-injection post chemiluminescence determination of atropine sulfate

A new post chemiluminescence (PCL) reaction was observed when atropine sulfate was injected into the reaction mixture after the finish of CL reaction of Ce(IV) and sodium sulfite. The possible mechanism for the PCL reaction was discussed via the investigation of the CL kinetic characteristics, the CL spectra, the UV absorption spectra and the fluorescence spectra of some related substances. The flow injection PCL method for the determination of atropine sulfate was established. The relative standard deviation (R.S.D.) was 2.8% (n = 11, c = 5.0 × 10⁻⁶ g mL⁻¹). The PCL intensity responded linearly to the concentration of atropine sulfate in the range 1.0 × 10⁻⁶ to 5.0 × 10⁻⁵ g mL⁻¹ with a linear correlation of 0.9947. The detection limit was 4 × 10⁻⁷ g mL⁻¹ atropine sulfate. The method had been applied to the determination of atropine sulfate in the tablets and the results were consistent with the method of Chinese pharmacopoeia.     

Voltammetric behavior of benzo[a]pyrene at boron-doped diamond electrode: a study of its determination by adsorptive transfer stripping voltammetry based on the enhancement effect of anionic surfactant, sodium dodecylsulfate

Benzo[a]pyrene (BaP), a member of the polycyclic aromatic hydrocarbon (PAH) class, is one of the most potent PAH carcinogens. The electrochemical oxidation of BaP was first studied by cyclic voltammetry at the boron-doped diamond electrode in non-aqueous solvent (dimethylsulphoxide with lithium perchlorate). The compound was irreversibly oxidized in a single step at high positive potential, resulting in the well-resolved formation of a couple with a reduction and re-oxidation wave at much lower potentials. Special attention was given to the use of adsorptive stripping voltammetry together with a medium exchange procedure in aqueous and aqueous/surfactant solutions over the pH range of 2.0-8.0. The technique in aqueous solutions had little value in practice because of too small oxidation peak current. This problem was solved when surfactants were added into the sample solution, by which the oxidation peak currents of BaP were found enhanced dramatically. The employed surfactants were sodium dodecylsulfate (anionic, SDS), cetyltrimethylammonium bromide (cationic, CTAB) and Tween 80 (non-ionic). Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in Britton-Robinson buffer, pH 2.0 containing 2.5 × 10⁻⁴ M SDS at +1.07 V (vs. Ag/AgCl) (after 120 s accumulation at +0.10 V). The process could be used to determine BaP in the concentration range of 16-200 nM (4.04-50.46 ng mL⁻¹), with a detection limit of 2.86 nM (0.72 ng mL⁻¹). This method was also applied to determine BaP in model water sample prepared by adding its different concentrations into tap water.     

High strength electrospun polymer nanofibers made from BPDA-PDA polyimide

A series of high molecular weight PI precursors, poly(p-phenylene biphenyltetracarboxamide acid), were synthesized from 3,4,3′,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) by using intense mechanical stirring at −15 to 0 °C for 48-72 h. The as-synthesized PI precursor solution was used to make BPDA/PDA polyimide thin films and electrospun nanofibers. IR, Ostward Viscometer, CMT-8102 Electromechanical Universal Testing Machine and scanning electron microscope (SEM) were used for the characterizations of the as-synthesized PI precursor, PI films and nanofiber sheets. The high molecular weight BPDA/PDA PI thin films and electrospun nanofiber sheets possess excellent mechanical properties of up to 900 MPa tensile strength with up to 18.0 GPa E-modulus and up to 210 MPa tensile strength with up to 2.5 GPa E-modulus, respectively.     

St-BA copolymer emulsions prepared by using novel cationic maleic dialkyl polymerizable emulsifier

A novel polymerizable cationic dialkyl maleic emulsifier with 12 carbon atomic hydrophobic chain lengths (R = C₁₂H₂₅) as well as a similar conventional cationic emulsifier, cetyltrimethyl ammonium bromide (CTAB) as comparison, were investigated in batch emulsion copolymerization of styrene and butyl acrylate. A series of emulsion samples have been prepared with two kinds of emulsifiers, and their properties have been characterized and compared. Compared with the emulsions prepared by using cationic CTAB emulsifier, the emulsions prepared by using maleic emulsifier have larger particle size, higher surface tension, generally more stable on certain electrolytes and less water absorption ratio as 34.87% after 30 days vs. 50.65% for the emulsion containing CTAB emulsifier. Whereas, the maleic emulsifier itself has lower CMC and surface tension compared with cationic CTAB emulsifier.