Electrospinning Bombyx mori silk with poly(ethylene oxide)

Electrospinning for the formation of nanoscale diameter fibers has been explored for high-performance filters and biomaterial scaffolds for vascular grafts or wound dressings. Fibers with nanoscale diameters provide benefits due to high surface area. In the present study we explore electrospinning for protein-based biomaterials to fabricate scaffolds and membranes from regenerated silkworm silk, Bombyx mori, solutions. To improve processability of the protein solution, poly(ethylene oxide) (PEO) with molecular weight of 900,000 was blended with the silk fibroin. A variety of compositions of the silk/PEO aqueous blends were successfully electrospun. The morphology of the fibers was characterized using high-resolution scanning electron microscopy. Fiber diameters were uniform and less than 800 nm. The composition was estimated by X-ray photoelectron spectroscopy to characterize silk/PEO surface content. Aqueous-based electrospining of silk and silk/PEO blends provides potentially useful options for the fabrication of biomaterial scaffolds based on this unique fibrous protein.     

Adsorption properties of proteins at and near the air/water interface from IRRAS spectra of protein solutions

A detailed study is performed using infrared reflection absorption spectroscopy (IRRAS) to characterize the molecular behaviour of proteins at and near the air/water interface of protein solutions. IRRAS spectra of beta-casein solutions in H2O and D2O show spectral shifts and derivative-like features not commonly observed in monomolecular layer systems. They can be fully understood using optical theory. Fair agreement between experimental and simulated IRRAS spectra over a broad spectral range (4000-1000 cm(-1)) is obtained using a stratified layer model. An attenuated total reflection and transmission spectrum is used to represent the protein extinction coefficient in H2O and D2O, respectively. It is shown that the derivative-like features observed result from the reflective properties of the proteins themselves. Furthermore, both concentration and film thickness could be fitted. At high protein concentrations (100 mg/mL) the spectrum is that of a single homogeneous protein solution. At 0.1 mg/mL, beta-casein is accumulated at the surface in a thin layer of approximately 10 nm thickness, with a concentration about 2500 times higher than in the sub-phase. At an initial concentration of 10 mg/mL, the concentration in the surface layer is about 15 times higher than in the subphase, while the thickness is about 30 nm.     

Adhesion of Azospirillum brasilense to polystyrene: Influence of ionic strength through protein adsorption

The influence of ionic strength on the adhesion of Azospirillum brasilense to polystyrene has been examined by comparing water and phosphate buffer saline (PBS) as suspending media. Polystyrene supports analysed by X‐ray photoelectron spectroscopy (XPS) after adhesion in PBS for 2 h or 24 h and detachment of adhering cells showed a higher protein surface concentration, reflected by the N/C atomic concentration ratio, compared to supports analysed after adhesion in water. It was shown that PBS both favours protein release by the cells into the solution and enhances the tendency of proteins to adsorb at the support surface.

After 2 h contact time, the increase in the concentration of adsorbed proteins in PBS was related to an increase in adhesion density. However, the observation that the adhesion density after 24 h was lower in PBS than in water indicated that the amount of proteins adsorbed at the support surface controls cell adhesion in a complex way. In PBS, a thick layer of proteinaceous material retaining the bacterial cells is formed; this leads to underestimation of the density of adhering cells as well as to a heterogeneous adhesion pattern and to a relatively low adhesion density due to detachment of pellicles upon rinsing.

The ionic strength thus influences bacterial adhesion in a more subtle way than simply through double layer interactions between the cells and the support.     

Correlation of chitosan's rheological properties and its ability to electrospin

Chitosan-based, defect-free nanofibers with average diameters ranging from 62 +/- 9 nm to 129 +/- 16 nm were fabricated via electrospinning blended solutions of chitosan and polyethylene oxide (PEO). Several solution parameters such as acetic acid concentration, polymer concentration, and polymer molecular weight were investigated to optimize fiber consistency and diameter. These parameters were evaluated using the rheological properties of the solutions as well as images produced by scanning electron microscopy (SEM) of the electrospun nanofibers. Generally, SEM imaging demonstrated that as total polymer concentration (chitosan + PEO) increased, the number of beads decreased, and as chitosan concentration increased, fiber diameter decreased. Chitosan-PEO solutions phase separate over time; as a result, blended solutions were able to be electrospun with the weakest electric field and the least amount of complications when solutions were electrospun within 24 h of initially being blended. The addition of NaCl stabilized these solutions and increased the time the blended solutions could be stored before electrospinning. Pure chitosan nanofibers with high degrees of deacetylation (about 80%) were unable to be produced. When attempting to electrospin highly deacetylated chitosan from aqueous acetic acid at concentrations above the entanglement concentration, the electric field was insufficient to overcome the combined effect of the surface tension and viscosity of the solution. Therefore, the degree of deacetylation is an extremely important parameter to consider when attempting to electrospin chitosan.     

Physico-chemical and structural properties of the surfaces of Peptostreptococcus micros and Streptococcus mitis as compared to those of mutans streptococci, Streptococcus sanguis and Streptococcus salivarius.

The surface properties of nine Streptococcus mitis and four Peptostreptococcus micros strains from the oral cavity were examined and compared with a large group of oral streptococci. Zeta potential and contact angle measurements were employed to determine physico-chemical cell surface properties. In addition, elemental surface concentration ratios were obtained via X-ray photoelectron spectroscopy, and surface structures were examined with transmission electron microscopy. The S. mitis and P. micros strains were found to have higher isoelectric points, higher hydrophobicities and higher N/C surface concentration ratios than some other oral streptococci. The combined data suggest that both species possess large amounts of surface protein. All the S. mitis strains displayed abundant surface fibrils in negative staining, but the P. micros strains were devoid of surface appendages indicating that surface protein is present in different forms in the two species. The surfaces of S. mitis and P. micros type strains differed significantly from the other strains examined.     

Preparation and Evaluation of Electrospun Zein/HA Fibers Based on Two Methods of Adding HA Nanoparticles

Zein/HA fibrous membranes were successfully prepared by electrospinning the zein/HA solution mixed by magnetic stirrer （Method I） or ultrasonic power （Method Ⅱ）. The morphology of zeirdHA nanocomposite fibers and the distribution of HA within the fibers electrospun by two methods were researched by Scanning Electron Microscopy （SEM） and Energy-dispersive X-ray spectroscopy （EDX）. In Method I, the distribution of HA nanoparticles is not homogeneous and HA particles tend to agglom- erate. The relatively homogeneous HA distribution can be observed in the membranes electrospun by Method Ⅱ. Using mag- netic stirrer to prepare the electrospinning solution improves the wettability of zein/HA membranes. From the viewpoint of application, electrospun zein/HA membranes fabricated by the solution mixed via Methods I and II both possessed reasonable tensile strength and elongation at break for both handling and sterilization. Considering two aspects of strength and elongation, electrospun zein/HA membranes fabricated by Method I are more balanced than those fabricated by Method Ⅱ. Biological performances of the control zein and zein/HA membranes were assessed by in vitro culture of hMSCs. Results show that both types of the membranes can support cell proliferation. The cells cultured on the zein/HA membranes electrospun by Method I with 5 wt% HA （on weight ofzein） show significantly higher proliferation than those cultured on the control zein membranes on the seventh day. The electrospun zein/HA fibrous membranes show promises for bone tissue engineering applications.     

Nano-patterned layers of a grafted coumarinic chromophore.

We report on the grafting of coumarin chromophores on flat silicon surfaces and in regions of nanometric dimensions drawn on silicon surfaces. The coumarin derivative was grafted by using the quaternization of a tertiary amine group of the chromophore with a ((chloromethyl)phenylethyl)-dimethylchlorosilane (CMPDCS) grafted on silicon. Complete characterization of the grafted layer was performed as a function of reaction time by X-ray photoelectron spectroscopy, X-ray reflectometry, atomic force microscopy, fluorescence spectroscopy and laser-scanning confocal microscopy. The results indicate that about one chromophore molecule is grafted every second CMPDCS molecule, resulting in a surface density of coumarin of slightly more than one coumarin per nm2. A broadening of the distribution of the fluorescence lifetimes was observed, suggesting that the grafted molecules experience a larger distribution of environments in the grafted layer than in solution. Since this reaction is fully compatible with silicon processing technology, the grafting could also be performed in nano-regions of size as small as 250 nm defined by combining electron-beam lithography with silanization. In such nano-sized regions the distribution of fluorescence lifetimes was narrower, suggesting a possible influence of the confinement on the organization of the molecules.     

DNA deposition on carbon electrodes under controlled dc potentials

The native calf-thymus DNA molecule fully dispersed in solution was deposited onto highly oriented pyrolytic graphite, carbon fiber column and disk electrodes under controlled dc potentials. X-ray photoelectron spectroscopy, atomic force microscopy and electrochemical investigations indicated that network structures of DNA could be formed on various carbon electrode surfaces resulting in significant surface enlargement. The conformation, conductivity and stability of the deposited DNA layer largely depended on the concentration of the DNA deposition solution, the applied dc potential and the mode of electric field. The optimal condition for deposition of the DNA on carbon fiber disk electrode was determined as a deposition potential of 1.8 +/- 0.3 V versus 50 mM NaCl-Ag/AgCl and a deposition DNA solution of 0.1 mg ml(-1). Under this condition, the DNA was covalently bonded on the electrode surface forming a three-dimensional modified layer, generating a 500-fold enlarged effective electrode surface area and similarly enlarged current sensitivity for redox species, such as Co(phen)3(3+). A possible mechanism for the formation of DNA networks is proposed.     

Morphology and structure of electrospun mats from regenerated silk fibroin aqueous solutions with adjusting pH

In this paper, regenerated silk fibroin (SF) aqueous solutions were adjusted to a pH of 6.9 by mimicing the condition in the posterior division of silkworm's gland and rheological behavior of solutions was investigated. The electrospinning technique was used to prepare fibers, and non-woven mats of regenerated B. mori silk fibroin were successfully obtained. The effects of electrospinning parameters on the morphology and diameter of regenerated silk fibers were investigated by orthogonal design. Statistical analysis showed that voltage, the concentration of regenerated SF solutions and the distance between tip and collection plate were the most dominant parameters to fiber morphology, diameter and diameter distribution, respectively. An optimal electrospinning condition was obtained in producing uniform cylindrical fibers with an average diameter of 1300nm. It was as follows: the concentration 30%, voltage 40kV, distance 20cm. The structure of electrospun mats was characterized by Raman spectroscopy (RS), wide-angle X-ray diffraction (WAXD) and modulated differential scanning calorimetry (MDSC). It was found that electrospun mats were predominantly random coil/silk I structure, and the transition to silk II (beta-sheet) rich structure should be further explored.     

Structural and Surface Compatibility Study of Modified Electrospun Poly(ε-caprolactone) (PCL) Composites for Skin Tissue Engineering

In this study, biodegradable poly(ε-caprolactone) (PCL) nanofibers (PCL-NF), collagen-coated PCL nanofibers (Col-c-PCL), and titanium dioxide-incorporated PCL (TiO₂-i-PCL) nanofibers were prepared by electrospinning technique to study the surface and structural compatibility of these scaffolds for skin tisuue engineering. Collagen coating over the PCL nanofibers was done by electrospinning process. Morphology of PCL nanofibers in electrospinning was investigated at different voltages and at different concentrations of PCL. The morphology, interaction between different materials, surface property, and presence of TiO₂ were studied by scanning electron microscopy (SEM), Fourier transform IR spectroscopy (FTIR), contact angle measurement, energy dispersion X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). MTT assay and cell adhesion study were done to check biocompatibilty of these scaffolds. SEM study confirmed the formation of nanofibers without beads. FTIR proved presence of collagen on PCL scaffold, and contact angle study showed increment of hydrophilicity of Col-c-PCL and TiO₂-i-PCL due to collagen coating and incorporation of TiO₂, respectively. EDX and XPS studies revealed distribution of entrapped TiO₂ at molecular level. MTT assay and cell adhesion study using L929 fibroblast cell line proved viability of cells with attachment of fibroblasts over the scaffold. Thus, in a nutshell, we can conclude from the outcomes of our investigational works that such composite can be considered as a tissue engineered construct for skin wound healing.     

Electrospun core-shell nanofibers from homogeneous solution of poly(vinyl alcohol)/bovine serum albumin

We report on the preparation and characterization of core-shell structure of bovine serum albumin (BSA) blended poly(vinyl alcohol) (PVA) composite nanofibers by using electrospinning process. The core-shell structure nanofibers have been electrospun from the homogeneous solution of BSA (as shell) and PVA (as core). The morphology, chemical compositions, structure and thermal properties of the resultant products were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDX), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) techniques. The blending ratio of PVA and BSA, molecular weight of BSA and the applied voltage of electrospinning process were observed to be the key influence factors on the formation of core-shell nanofibers structure. Based on the experimental findings, we proposed a possible physical mechanism for the formation of core-shell nanofibers structure of PVA blended BSA composite.     

Surface Properties and Corrosion Behavior of Co–Cr Alloy Fabricated with Selective Laser Melting Technique

We sought to study the corrosion behavior and surface properties of a commercial cobalt–chromium (Co–Cr) alloy which was fabricated with selective laser melting (SLM) technique. For this purpose, specimens were fabricated using different techniques, such as SLM system and casting methods. Surface hardness testing, microstructure observation, surface analysis using X-ray photoelectron spectroscopy (XPS) and electrochemical corrosion test were carried out to evaluate the corrosion properties and surface properties of the specimens. We found that microstructure of SLM specimens was more homogeneous than that of cast specimens. The mean surface hardness values of SLM and cast specimens were 458.3 and 384.8, respectively; SLM specimens showed higher values than cast ones in hardness. Both specimens exhibited no differences in their electrochemical corrosion properties in the artificial saliva through potentiodynamic curves and EIS, and no significant difference via XPS. Therefore, we concluded that within the scope of this study, SLM-fabricated restorations revealed good surface properties, such as proper hardness, homogeneous microstructure, and also showed sufficient corrosion resistance which could meet the needs of dental clinics.     

Effect of materials for micro-electro-mechanical systems on PCR yield

In this study we analyzed the surface properties of different silicon-based materials used for micro-electro-mechanical systems (MEMS) production, such as thermally grown silicon oxide, plasma-enhanced chemical vapor deposition (PECVD)-treated silicon oxide, reactive-ion etch (RIE)-treated silicon oxide, and Pyrex. Substrates were characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) to define the surface chemical and morphological properties, and by fluorescence microscopy to directly assess the absorption of the different polymerase chain reaction (PCR) components. By using microchips fabricated with the same materials we investigated their compatibility with PCR reactions, exploiting the use of different enzymes and reagents or proper surface treatments. We established the best conditions for DNA amplification in silicon/Pyrex microdevices depending on the type of device and fabrication method used and the quality of reagents, rather than on the passivation treatment or increment in standard Taq polymerase concentration.     

Osteoblast adhesion on poly(L-lactic acid)/polystyrene demixed thin film blends: effect of nanotopography, surface chemistry, and wettability

Biomaterial surface characteristics are critical cues that regulate cell function. We produced a novel series of poly(l-lactic acid) (PLLA) and polystyrene demixed nanotopographic films to provide nonbiological cell-stimulating cues. The increase in PLLA weight fraction (phi) in blend solutions resulted in topography changes in spin-cast films from pit-dominant to island-dominant morphologies having nanoscale depth or height (3-29 nm). Lower molecular weight PLLA segregated to the top surface of demixed films, as observed by X-ray photoelectron spectroscopy and secondary ion mass spectroscopy (SIMS). For phi > or = 0.5, the topmost film layer was predominantly filled with PLLA (>96% by SIMS at 20-A depth). Nanotextured substrata stimulated osteoblastic cell adhesion to a greater degree than did flat PLLA (phi = 1), and this effect was more pronounced for nanoisland (phi = 0.7 and 0.9) relative to nanopit topographies (phi = 0.5). Demixed films having relatively lower water contact angles generally enhanced cell adhesion and spreading. Our results reveal that cell adhesion is affected by surface chemistry, topography, and wettability simultaneously and that nanotextured surfaces may be utilized in regulating cell adhesion.     

Synergic Effect between Adsorption and Photocatalysis of Metal-Free g-C3N4 Derived from Different Precursors

Graphitic carbon nitride (g-C₃N₄) used in this work was obtained by heating dicyandiamide and melamine, respectively, at different temperatures. The differences of g-C₃N₄ derived from different precursors in phase composition, functional group, surface morphology, microstructure, surface property, band gap and specific surface area were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-visible diffuse reflection spectroscopy and BET surface area analyzer, respectively. The photocatalytic discoloration of an active cationic dye, Methylene Blue (MB) under visible-light irradiation indicated that g-C₃N₄ derived from melamine at 500°C (CN-M500) had higher adsorption capacity and better photocatalytic activity than that from dicyandiamide at 500°C (CN-D500), which was attributed to the larger surface area of CN-M500. MB discoloration ratio over CN-M500 was affected by initial MB concentration and photocatalyst dosage. After 120 min reaction time, the blue color of MB solution disappeared completely. Subsequently, based on the measurement of the surface Zeta potentials of CN-M500 at different pHs, an active anionic dye, Methyl Orange (MO) was selected as the contrastive target pollutant with MB to reveal the synergic effect between adsorption and photocatalysis. Finally, the photocatalytic mechanism was discussed.     

Surface analysis and depth profiles of calcium in hepatoma cells during pyruvate-induced DNA synthesis

Induction of DNA synthesis is associated with increased uptake of calcium in cultured cells. Calcium distribution within the plasma membrane and adjacent cytoplasmic layers of hepatoma cells was investigated with X-ray photoelectron spectroscopy and oxygen plasma etching. Cells in minimal growth medium initiate active DNA synthesis 16 h after addition of sodium pyruvate. Cells stimulated with pyruvate and pyruvate-free controls were analysed by X-ray photoelectron spectroscopy--oxygen plasma etching at 0--40 A (layer I), 0--450 A (layer II) and 0--4000 A (layer III from the outer cell surface. Calcium concentrations were elevated in induced cells compared with controls: +20% in layer I, +60% in layer II, and +300% in layer III. As the plasma membrane is 90--120 A thick, these results indicate that pyruvate-induced DNA synthesis is preceded by an increase in calcium, most marked in the cytoplasm subjacent to the plasma membrane, moderate at its inner surface, and minimal at its outer surface.     

Effects of chain conformation and entanglement on the electrospinning of pure alginate

As a natural biopolymer, sodium alginate (SA) has been widely used in the biomedical field in the form of powder, liquid, gel, and compact solid, but not in the form of nanofiber. Electrospinning is an effective method to fabricate nanofibers. However, electrospinning of SA from its aqueous solution is still a challenge. In this study, an effort has been made to solve this problem and find the key reasons that hinder the electrospinning of alginate aqueous solution. Through this research, it was found that pure SA nanofibers could be fabricated successfully by introducing a strong polar cosolvent, glycerol, into the SA aqueous solutions. The study on the properties of the modified SA solution showed that increasing glycerol content increased the viscosity of the SA solution greatly and, meanwhile, decreased the surface tension and the conductivity of the SA solution. The rheological results indicated that the increase in glycerol content could result in the enhanced entanglements of SA chains. Two schematic molecular models were proposed to depict the change of SA chain conformation in aqueous solution with and without glycerol. The main contribution of glycerol to the electrospinning process is to improve the flexibility and entanglement of SA chains by disrupting the strong inter- and intramolecular hydrogen bondings among SA chains, then forming new hydrogen bondings with SA chains.     

Electro-optical behaviour of CuFe2O4@rGO nanocomposite for nonenzymatic detection of uric acid via the electrochemical method

Uric acid (UA) is a blood and urine component obtained as a metabolic by-product of purine nucleotides. Abnormalities in UA metabolism cause crystal deposition as monosodium urate and lead to various diseases such as gout, hyperuricemia, Lesch–Nyhan syndrome, etc. Monitoring these diseases requires a rapid, sensitive, selective, and portable detection approach. Therefore, this study demonstrates the hydrothermal synthesis of CuFe₂O₄/reduced graphene oxide (rGO) nanocomposite for selective detection of UA. After the nanocomposite synthesis, characterization was performed by X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, UV–visible spectrometry, atomic force spectroscopy, scanning electron microscopy, and electrochemical analysis. Furthermore, from the electrochemical analysis using cyclic voltammetry (CV), kinetic studies were carried out by varying the scan rate to obtain the diffusion coefficient, surface concentration, and rate of charge transfer to achieve a calibration curve that indicates the quasi reversible nature of the fabricated electrode with a linear regression coefficient of oxidation (R²: 0.9992) and reduction (R²: 0.9971) peaks. Moreover, the fabricated nonenzymatic amperometric sensor to detect UA with a linearity (R²: 0.9989) of 1–400 μM was highly sensitive (2.75 × 10⁻⁴ mAμM⁻¹ cm⁻²) and had a lower limit of detection (0.01231 μM) at pH 7.5 in phosphate-buffered saline solution. Therefore, the CuFe₂O₄/rGO/ITO-based nonenzymatic sensor could detect interfering agents and spiked real bovine serum samples with higher sensitivity and selectivity for UA detection.     

Fabrication of self-assembled protein A monolayer and its application as an immunosensor

The self-assembled layer of modified protein A was fabricated. In order to modify protein A, the surface group of protein A was substituted with thiol (-SH) functionality by using N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP) and dithiothreitol (DTT). The formation of a self-assembled protein A layer on a Au substrate and its increased binding capacity to antibody were confirmed by surface plasmon resonance (SPR) spectroscopy. The surface structure of self-assembled protein A layer, and the binding status of anti-bovine serum albumin (anti-BSA) and BSA were determined by atomic force microscopy (AFM). Treatment on the self-assembled protein A layer with a detergent, such as Tween 20, increased the binding capacity of anti-BSA, because protein A aggregation was reduced significantly by the detergent; this was confirmed by SPR spectroscopy. The self-assembled layer of chemically modified protein A with enhanced binding capacity can be used for immunosensor fabrication.