Hybrid analogs for the production of porous calcium phosphate scaffolds

A polymer–inorganic sol mixture has been used to develop interconnected and highly porous calcium phosphate networks. The inorganic sol was developed by reacting triethyl phosphite and calcium nitrate. The sol was directly added to an aqueous solution of PVA with molecular weights between 40,500 and 155,000 g/mol. This mixture was electrospun at a voltage of 20 kV to produce fibers, whose diameter was less than 1 μm. This electrospun structure was calcined at 600 °C obtain to a highly interconnected sub-micron fibrous network (fiber size ∼ 200 nm) of calcium phosphate. The crystal size is on the order of 30 nm. Micropores could be introduced in each of the fibers by controlling the polymer molecular weight and the sol volume fraction. Such structures can have many potential uses in the repair and treatment of bone defects and in drug delivery.     

Effect of molecular weight on fibrous PVA produced by electrospinning

The effects of polymer weight average molecular weight (M_W) on the fiber structure of electrospun polyvinylalcohol (PVA) have been studied. PVA with a degree of hydrolysis of 98–99% and with molecular weights ranging from 9000 to 186,000 g/mol was dissolved in water. The concentration (C) of the polymer in the solution was varied depending on the molecular weight. The solution was electrospun at 30 kV and the sample obtained on the collector was examined by scanning electron microscopy. It was observed that for each molecular weight, a fibrous structure was stabilized above a minimum concentration, generally corresponding to [η]C>5. The average fiber diameter was between 250 nm and 2 μm. The fiber diameter increases with M_W and concentration. At low M_W and/or concentrations ([η]C<9), the fibers exhibit a circular cross-section. Flat fibers were observed at high M_W and concentrations ([η]C>9).     

A novel electrospun silk fibroin/hydroxyapatite hybrid nanofibers

A novel electrospinning of silk fibroin/hydroxyapatite hybrid nanofibers with different composition ratios was performed with methanoic acid as a spinning solvent. The silk fibroin/hydroxyapatite hybrids containing up to 30% hydroxyapatite nanoparticles could be electrospun into the continuous fibrous structure. The electrospun silk fibroin/hydroxyapatite hybrid nanofibers showed bigger diameter and wider diameter distribution than pure silk fibroin nanofibers, and the average diameter gradually increased from 95 to 582 nm. At the same time, the secondary structure of silk fibroin/hydroxyapatite nanofibers was characterized by X-ray diffraction, Fourier transform infrared analysis, and DSC measurement. Comparing with the pure silk fibroin nanofibers, the crystal structure of silk fibroin was mainly amorphous structure in the hybrid nanofibers. X-ray diffraction results demonstrated the hydroxyapatite crystalline nature remained as evidenced from the diffraction planes (002), (211), (300), and (202) of the hydroxyapatite crystallites, which was also confirmed by Fourier transform infrared analysis. The thermal behavior of hybrid nanofibers exhibited the endothermic peak of moisture evaporation ranging from 86 to 113 °C, and the degradation peak at 286 °C appeared. The SF/HAp nanofibers mats containing 30% HAp nanoparticles showed higher breaking tenacity and extension at break for 1.1688 ± 0.0398 MPa and 6.55 ± 1.95%, respectively. Therefore, the electrospun silk fibroin/hydroxyapatite hybrid nanofibers should be provided potentially useful options for the fabrication of biomaterial scaffolds for bone tissue engineering.     

Molecular weight dependent structural regimes during the electrospinning of PVA

The cumulative effects of molecular weight and concentration on the structural transitions in the electrospun polymer have been studied. Experiments have been conducted with water as the solvent for molecular weights of polyvinylalcohol (PVA) ranging from 9500 g/mol to 155,000 g/mol. The structural regimes for beads, beaded fibers, complete fibers and flat ribbons have been mapped. The development of a stable fiber structure generally corresponds to the onset of significant molecular entanglements.     

Surface modification of poly(l-lactide) electrospun fibers with nanocrystal hydroxyapatite for engineered scaffold applications

The hydrophobicity of the poly(l-lactide) (PLLA) surface was modified by incorporating hydroxyapatite (HAp) nanocrystalline particles during the electrospinning process for the engineered scaffold applications. The HAp nanocrystals were synthesized with 30 nm in diameter and 100–120 nm in length, which subsequently formed micrometer-sized agglomerates in the range of 2.5 μm. The synthesized HAp agglomerates were electrospun in the PLLA solution, and the HAp nanocrystals were desirably exposed on the surface of the electrospun PLLA fibers to give higher surface energy and lower contact angles with water. The surface-exposed hydrophilic HAp nanocrystals substantially increased the precipitation of various salts on the HAp/PLLA fiber surfaces in a buffer solution due to the hydrophilic nature and ionic affinity of HAp. Finally, the developed HAp/PLLA fibers desirably sustained the fibrous structural integrity during the accelerated-aging test in water, which was not the case with the pristine PLLA fibers.     

Electrospinning of porphyrin/polyvinyl alcohol (PVA) nanofibers and their acid vapor sensing capability

Fluorescing 5,10,15,20-terakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP)-embedded and -coated polyvinyl alcohol (PVA) nanofibers were fabricated by using the electrospinning technique. To improve nonpolar solvent solubility of TMPyP/PVA nanofibers, tetraethyl orthosilicate (TEOS) was used as a cross-linking agent. UV-vis spectroscopy showed a strong Q band and two relatively weak Soret bands from the TMPyP/PVA nanofibers, and revealed that the TMPyP molecules were homogeneously loaded to the fibers. Scanning electron microscopy revealed that the electrospun nanofibers had ultrafine structures with an average diameter of ca. 250 nm. X-ray photoelectron spectroscopy confirmed the compositional structure of TMPyP/PVA/TEOS nanofibers and revealed the relative coverage of TMPyP molecules on the surface of TMPyP-embedded and TMPyP-coated PVA/TEOS fibers. For the comparison of the acid vapor sensitivity, TMPyP-embedded PVA/TEOS films, and TMPyP-embedded PVA/TEOS fibers, TMPyP-coated PVA/TEOS fibers were exposed to 1N nitric-acid vapor for 20-60 seconds. Fluorescence microscopy revealed that TMPyP-coated PVA/TEOS nanofibers exhibited better acid-sensing capability than TMPyP-embedded PVA/TEOS nanofibers and films.     

Ultrafine porous fibers electrospun from cellulose triacetate

Ultrafine porous cellulose triacetate (CTA) fibers were prepared by electrospinning with methylene chloride (MC) and a mixed solvent of MC/ethanol (EtOH) and their intra- and inter-fiber pore structures was investigated. Ultrafine porous CTA fibers electrospun with MC had isolated circular shape pores with a narrow size distribution in the range of 50–100 nm. In the case of ultrafine CTA fibers electrospun with MC/EtOH (90 / 10 v/v), they had interconnected larger pores in the range of 200–500 nm. These porous structures were induced by phase separation resulting from the rapid evaporation of solvent during the electrospinning process. However, non-porous corrugated fibers were obtained from MC/EtOH (85 / 15 v/v) and MC/EtOH (80 / 20 v/v) due to their lower vapor pressure. The pore sizes in ultrafine CTA fibers electrospun with MC showed a bimodal distribution centered at ∼17 and ∼64 nm. CTA fibers electrospun with MC/EtOH (90 / 10 v/v) showed the greatest porosity due to their larger intra-fiber pores and fiber diameter.     

Structural and luminescent properties of Er3+ and Tb3+-doped sol–gel-based bioactive glass powders and electrospun nanofibers

In this study, sol–gel-based erbium (Er³⁺), terbium (Tb³⁺) and Er³⁺: Tb³ co-doped 1393 bioactive glass powders and electrospun nanofibers were prepared. Structural and morphological properties of the bioactive glasses as well as the photoluminescence characteristics were investigated in detail. The median particle size and average diameter of the prepared glass powders and fibers were in the range of ~ 1.5–3.5 μm and 280–660 nm, respectively. The steady-state photoluminescence and decay kinetics of the samples were investigated under excitation (374 nm) where only Er³⁺ and Tb³⁺ ions close to Si nanoclusters can be excited. All the samples prepared in the study exhibited bright green emission upon excitation at 374 nm. Results showed that the dopant concentration and the sample morphology have significant influence on the photoluminescence and decay properties of the glasses. Sol–gel-derived bioactive glass particles exhibited stronger emission intensity, whereas electrospun nanofibers showed extended decay times. In vitro bioactivity experiments revealed that Er³⁺ and Tb³⁺ doping did not inhibit the conversion of the glass samples to hydroxyapatite treated in simulated body fluid for 30 days. It was concluded that Er³⁺ and Tb³⁺-containing 1393 bioactive glasses have a potential to be used in tissue engineering applications as well as bioimaging studies.

     

LaOCl nanofibers derived from electrospun PVA/Lanthanum chloride composite fibers

Electrospun nanofibers of poly (vinyl alcohol) (PVA)/Lanthanum (Ш) chloride (LaCl₃) composite were employed to prepare the LaOCl nanofibers by calcination. TG-DSC was used to investigate the thermal property of precursor, while FT-IR, XRD, FESEM and TPD were employed to characterize the derived LaOCl nanofibers. Results indicate that the addition of LaCl₃ leads to the formation of fork segments in the structure of electrospun PVA/LaCl₃ composite nanofibers, therefore, changing the decomposition behavior of the fibers. Pure LaOCl fibers with a diameter range of 90-220 nm can be obtained by calcination of electrospun PVA/LaCl₃ composite nanofibers at 700 °C for 7 h. The resultant LaOCl nanofibers show a good sensing behavior for CO₂ gas.     

Nanocrystalline hydroxyapatite doped with magnesium and zinc: Synthesis and characterization

During recent years, there have been efforts in developing nanocrystalline bioceramics, to enhance their mechanical and biological properties for use in tissue engineering applications. In this research, we made an attempt to synthesize nanocrystalline bioactive hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) ceramic powder in the lower-end of nano-range (2–10 nm), using a simple low-temperature sol–gel technique and studied its densification behavior. We further studied the effects of metal ion dopants during synthesis on powder morphology, and the properties of the sintered structures. Calcium nitrate and triethyl phosphite were used as precursors for calcium and phosphorous, respectively, for sol–gel synthesis. Calculated quantities of magnesium oxide and zinc oxide were incorporated as dopants into amorphous dried powder, prior to calcination at 250–550 °C. The synthesized powders were analyzed for their phases using X-ray diffraction technique and characterized for powder morphology and particle size using transmission electron microscopy (TEM). TEM analysis showed that the average particle size of the synthesized powders were in the range of 2–10 nm. The synthesized nano-powders were uniaxially compacted and then sintered at 1250 °C and 1300 °C for 6 h, separately, in air. A maximum average sintered density of 3.29 g/cm³ was achieved in structures sintered at 1300 °C, developed from nano-powder doped with magnesium. Vickers hardness testing was performed to determine the hardness of the sintered structures. Uniaxial compression tests were performed to evaluate the mechanical properties. Bioactivity and biodegradation behavior of the sintered structures were assessed in simulated body fluid (SBF) and maintained in a dynamic state.     

Dual-source dual-power electrospinning and characteristics of multifunctional scaffolds for bone tissue engineering

Electrospun tissue engineering scaffolds are attractive due to their distinctive advantages over other types of scaffolds. As both osteoinductivity and osteoconductivity play crucial roles in bone tissue engineering, scaffolds possessing both properties are desirable. In this investigation, novel bicomponent scaffolds were constructed via dual-source dual-power electrospinning (DSDPES). One scaffold component was emulsion electrospun poly(d,l-lactic acid) (PDLLA) nanofibers containing recombinant human bone morphogenetic protein (rhBMP-2), and the other scaffold component was electrospun calcium phosphate (Ca–P) particle/poly(lactic-co-glycolic acid) (PLGA) nanocomposite fibers. The mass ratio of rhBMP-2/PDLLA fibers to Ca–P/PLGA fibers in bicomponent scaffolds could be controlled in the DSDPES process by adjusting the number of syringes used to supply solutions for electrospinning. Through process optimization, both types of fibers could be evenly distributed in bicomponent scaffolds. The structure and properties of each type of fibers in the scaffolds were studied. The morphological and structural properties and wettability of scaffolds were assessed. The effects of emulsion composition for rhBMP-2/PDLLA fibers and mass ratio of fibrous components in bicomponent scaffolds on in vitro release of rhBMP-2 from scaffolds were investigated. In vitro degradation of scaffolds was also studied by monitoring their morphological changes, weight losses and decreases in average molecular weight of fiber matrix polymers.     

静电纺丝法制备尼龙-6/SiO2-TiO2杂化纳米纤维

采用静电纺丝法结合溶胶凝胶技术,制备了尼龙-6/SiO2-TiO2杂化纳米纤维。采用红外光谱（FT-IR）、X射线衍射（XRD）、UV-vis、热重分析（TG）和扫描电镜（SEM）等对杂化纳米纤维进行分析表征。结果表明,随着SiO2-TiO2溶胶的引入,电纺纤维的结晶度下降,耐热性能提升。尼龙-6电纺纤维的平均直径约为...     

Silica ceramic nanofiber membrane with ultra-softness and high temperature insulation

Silica ceramic nanofiber (SCNF) membranes with ultra-softness were fabricated by electrospinning and precursor derived ceramic technology. Firstly, the precursor fiber membrane was obtained by electrospinning from spinnable precursor sol, which was prepared by using silica sol as raw material and polyvinyl alcohol (PVA) as spinning aid, and after heat treatment, it was converted into the SCNF membrane composed of pure inorganic components, which had the ultra-softness to restore the original shape after arbitrary folding. Then the effects of different PVA dosages and heat treatment temperatures on the fiber morphology, thermal stability, mechanical properties, and thermal conductivity of SCNF membranes were investigated. Among all the membranes, the SCNF membrane that was made with a precursor sol of 5% PVA and sintered at 900 °C (Ss?+?PVA 5%-900 °C) showed the smoothest as well as the most uniform fiber morphology, with an average fiber diameter of 285.19 nm, a density of 0.106 g cm^?3, the best mechanical properties (tensile strength of 4.145 MPa), and it also had the lowest thermal conductivity of 0.05285 Wm^?1 K^?1. The Ss?+?PVA 5%-900 °C SCNF membrane still maintained intact fiber morphology after being treated at 1200 °C. These excellent properties make the SCNF membrane have a potential application prospect as an insulation material in ultra-high temperature environments.

     

Activated carbon nanofibers derived from coconut shell charcoal for dye removal application

Activated carbon nanofibers (ACNF) have been successfully prepared using an electrospinning method with coconut shell charcoal (CSC) as a carbon source and poly(vinyl alcohol) (PVA) as a spinning polymer agent. The high voltage of 10 kV was applied for the electrospinning system. The positive electrode of the high voltage power supply was connected to the needle tip, and the grounded electrode was connected to the metallic collector wrapped with an aluminum foil. The dry fibers in the form of a fibrous mat were collected in the aluminum foil. The average pore diameters of the generated fibers for all variables ranging from 2.23 to 3.73 nm corresponding to mesoporous carbon nanofibers. The total pore volumes were ranging from 0.50 to 0.92 cm³/g. IACNF-60 had the largest surface area of 1,277 m²/g obtained from the use of PVA 12 w/v %, 60 wt% CSC, and the use of iodine treatment before thermal stabilization, carbonization, and activation stages. Methylene blue solution was used as a model for the dye adsorption capacity that followed the Langmuir adsorption model. IACNF-60 also indicated the highest theoretical maximum monolayer adsorption capacity in the amount of 166.7 mg/g. Furthermore, the methylene blue removal ability of IACNF-60 for the third cycle was maintained relatively constant at 96%.     

Fabrication and characterization of hybrid nanofibers from poly(vinyl alcohol), milk protein and metal carbonates

Porous three dimensional nanofibrous membranes were fabricated from poly(vinyl alcohol) (PVA), milk protein and inorganic salts such as calcium carbonate (CaCO3) or magnesium carbonate (MgCO3). Microscopic investigations showed that the fibers have smooth morphology with an average diameter of 300-500 nm and a surface area of 5.29 m2g(-1). Thermal analysis of the composite nanofibers showed a decrease in glass transition temperature as compared to PVA nanofiber. Incorporation of CaCO3 and MgCO3 into the nanofiber matrix was confirmed by energy dispersive spectroscopy and X-ray diffraction analysis. The cytocompatibility of electrospun composite nanofiber sheets was evaluated using human lung fibroblasts (IMR-90). There was an increase in cell attachment and cell density on milk protein incorporated to PVA-CaCO3 and PVA-MgCO3 fibers within a week of cell seeding. The cytocompatibility and increase in cell adhesion property of the hybrid nanofiber may provide significant advantages for such materials in biomedical applications.     

Electrospinning of aligned biodegradable polymer fibers and composite fibers for tissue engineering applications

Fibrous membranes of aligned poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) fibers have been made through electrospinning. A high-speed rotating drum was used as the fiber collector while the electric field was manipulated by using five knife-edged auxiliary electrodes. It was found that a high drum rotating speed of 3000 rpm could lead to a nearly perfect alignment of PHBV fibers during electrospinning. Multilayered fibrous structures with each layer having a different direction of fiber alignment could also be constructed through electrospinning. The electrospun PHBV fibers were further modified by incorporating carbonated hydroxyapatite (HA) nanospheres (up to 20% of HA) in the fibers. The fibrous membranes made of aligned PHBV fibers and made of HA/PHBV composite fibers should be very useful for the tissue engineering of different human body tissues.     

Syndiotactic 1,2-polybutadiene fibers produced by electrospinning

Syndiotactic 1,2-polybutadiene (s-PB) is a typical thermoplastic elastomer with various applications because of its high reactivity. In the past, it is difficult to form s-PB fibers with a diameter below 10 μm because of the limitation of the conventional method such as melt spinning. Here, we report for the first time on the production of s-PB nanofibers by using a simple electrospinning method. Ultrafine s-PB fibers without beads were electrospun from s-PB solutions in dichloromethane and characterized by environmental scanning electron microscope (ESEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). At 4 wt.% concentration of s-PB, the average diameter of s-PB was about 130 nm. We found that dichloromethane was a unique suitable solvent for the electrospinning of s-PB fibers, and the structure of syndiotactic was changed through the electrospinning process.     

Structure and properties of novel electrospun tussah silk fibroin/poly(lactic acid) composite nanofibers

The tussah silk fibroin (TSF)/poly(lactic acid) (PLA) composite nanofibers with different composition ratios were prepared by electrospinning with 1,1,1,3,3,3-Hexafluoro-2-propanol as the solvent. The morphology and secondary structure of the fibers were characterized by Scanning electronic microscope, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The thermal and mechanical tests were also performed. The spinnability of TSF solution was improved significantly through adding 10% PLA, and the average diameter of the fibers decreased from 583 nm to 178 nm with an obvious improvement in fiber diameter uniformity. In addition, the mechanical properties of electrospun nanofibers increased evidently after blending 10% PLA, whereas the thermal properties kept stable. FTIR and XRD analysis indicated the addition of 5% PLA could induce a conformation transformation of TSF from random coil and α-helix to β-sheet, however, when PLA content was more than 10%, the β-sheet structure of TSF in composite nanofibers decreased, and the phase separation of two compositions occurred. Therefore, when PLA content exceeded 15%, the average diameters of TSF/PLA composite nanofibers increased and appeared to be polarized, moreover, the mechanical properties of the fibers decreased with the increase of PLA content, and the fibers displayed the mechanical behavior of PLA component more.     

Preparation of poly(vinyl alcohol)/tin glycolate composite fibers by combined sol–gel/electrospinning techniques and their conversion to ultrafine tin oxide fibers

Ultrafine composite fibers made from poly(vinyl alcohol) (PVA)/tin glycolate — a moisture-stable tin oxide containing compound — were prepared by a combined sol–gel processing and electrospinning technique. These fibers were subsequently converted to ultrafine tin oxide fibers by calcination treatment, with the aim of producing tin oxide fiber with a high surface area-to-mass ratio and a high specific conductivity value. The acidity of spinning solution plays an important role to the morphology and size of the obtained fibers. The average diameters of the obtained composite fibers were in the range of 87–166 nm. It was found that the ultrafine tin oxide fiber showed the high conductivity value of 1.59 × 10³ S cm^?1 at calcinations temperature of 600 °C, and the BET surface area was in a range of 71 and 275 m² g^?1. Moreover, the effect of calcinations temperature on the phase and the size of the tin oxide fibers were investigated in this study.     

Synthesis of ultrafine lanthanum ferrite (LaFeO3) fibers via electrospinning

Ultrafine one-dimensional LaFeO₃ nanofibers were synthesized by electrospinning utilizing sol-gel precursors. The surface morphology, microstructure and crystal structure were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The nanofibers with smaller diameter were continuous and uniformly distributed. Typical fiber diameter was between 180 nm and 220 nm and the average diameter was 200 nm. The fibers consisted of many single-crystal LaFeO₃ grains and the grain size was about 20-50 nm. The relationship between the diameter of as-synthesized fibers and the PVP concentration of the precursor was investigated. The experimental results indicated that the PVP concentration had a great impact on the fiber size and 5.89 wt.% PVP concentration in sol-gel precursors was advantageous to the formation of more uniform electrospun composite fibers with smaller diameter.