Conventional electrospinning is an effective and versatile method employed for fabricating nanofi... more Conventional electrospinning is an effective and versatile method employed for fabricating nanofibers. However, the relatively low production rate is the major challenge of electrospinning as an economic and scalable method. Recently, several approaches have been developed to ensure the high production rate of nanofibers. This paper has reviewed the latest developed electrospinning methods, such as multi-jet, needleless, bubble, centrifuge and electro-centrifuge systems. Furthermore, the jet formation in centrifugal spinning, as well as electro-centrifuge systems, was investigated through experimental and numerical analysis.
The phase structure and dynamic mechanical properties of poly(acrylonitrile-co-methyl acrylate) (... more The phase structure and dynamic mechanical properties of poly(acrylonitrile-co-methyl acrylate) (P(AN-co-MA)) nanofibers collected in the form of twisted yarn via the two-nozzle conjugated electrospinning method were investigated to study the effects of solution concentration and take-up velocity on the relaxation behavior of nanofibers yarn. The wide-angle X-ray diffraction analyses of P(AN-co-MA) nanofibers show a two-phase structure of nanofibers consisting of crystalline and amorphous phases and polymorphic transition from hexagonal to orthorhombic. Heating P(AN-co-MA) nanofibers at over the glass transition temperature led to an increased degree of both crystallinity and crystallite size with no polymorphic change. Three transitions (tan δ peaks) were observed in nanofibrous yarn prepared at different spinning dope concentrations and take-up speeds, except for the specimen prepared at a concentration of 14 wt% and collecting speed of 8 cm/min, wherein no α transition was observed due to improved molecular orientation. The temperature dependence of the dynamic Young’s modulus of nanofibrous yarn at different spinning dope concentrations was mainly affected by the diameter of the nanofiber as the morphological property and molecular orientation. Take-up speed was found to affect the γ and α transitions more than the β transition. Moreover, the maximum storage modulus was obtained at a take-up speed of 8 cm/min at all over recorded temperatures.
AB.S_IXA.CE A new type of braided fiber seal has been developed for high temperature engine appli... more AB.S_IXA.CE A new type of braided fiber seal has been developed for high temperature engine applications. Development work performed in this study includes seal design, fabrication, leakage flow testing, and flow resistance modeling. This new type of seal utilizes the high flow resistance of tightly packed fibers and the conformability of textile structures. The seal contains a core part with aligned fibers, and a sheath with braided fiber layers. Seal samples are made by using the conventional braiding process. Leakage flow measurements are then performed. Mass flow rate versus the simulated engine pressure and preload pressure is recorded. The flow resistance of the seal is analyzed using the Ergun equation for flow through porous media, including both laminar and turbulent effects. The two constants in the Ergun equation are evaluated for the seal structures. Leakage flow of the seal under the test condition is found to be in the transition flow region. The analysis is used to predict the leakage flow performance of the seal with the determined design parameters.
This work presents a continuous roll-to-roll electrochemical coating system for producing silver/... more This work presents a continuous roll-to-roll electrochemical coating system for producing silver/silver chloride (Ag/AgCl)-coated yarns, and their application in e-textile electrodes for biosignal monitoring. Ag/AgCl is one of the most preferred electrode materials as an interface between the conductive backbone of an electrode and skin. E-textile Ag/AgCl-coated multi-filament nylon yarns offer stable, flexible, and breathable alternatives to standard rigid or flexible film-based Ag/AgCl electrodes. The developed system allows for highly controlled process parameters to achieve stable and uniform AgCl film deposition on Ag-coated nylon yarns. The electrical, electrochemical properties, and morphology of the coated yarns were characterized. Dry electrodes were fabricated and could measure electrocardiogram (ECG) signals with comparable performance to standard gel electrodes. Ag/AgCl e-textile electrodes demonstrated high stability, with low average polarization potential (1.22 mV/ min) compared with Ag-coated electrodes (3.79 mV/min), low impedance (below 2 MΩ, 0.1-150 Hz), and are excellent candidates for heart rate detection and monitoring. Biosignals can be detected and monitored from various locations of the body, by employing electrode sensors. Electrodes used for biosignal monitoring function by transducing ionic current (i.e., sodium, potassium, calcium, chloride ions) from the skin surface, into electron current, through metallic wires of a given recording system/ instrument 1,2 . Electrodes made from conductive metals or polymer films are commonly being used, but tend to have high sensitivity to motion artifacts, produce fluctuations in potential, and cause signal distortion over time, owing to the absence of an electrolyte layer 3 . However, sweat and moisture that develops on the skin surface over time is thought to act as an electrolyte layer, thereby reducing skin impedance 4 . While these distortions in features can be corrected by signal processing methods, it is more ideal to develop materials with polarization potential stability, to reduce interference with the collected signal . Other considerations to be made when developing electrode materials for biosignal monitoring include low electrical resistance of the electrode compared with that for skin surface 7 , skin contact, conformability, and biocompatibility 8 . Silver/Silver chloride (Ag/AgCl) electrode material is the gold standard for biosignal acquisition (electrocardiogram, electroencephalography, endodermal activity etc.), owing to its low and stable half-cell potential 2 . The most commonly used electrode for biosignal monitoring includes a pellet of sintered high purity silver and silver chloride, with a thin layer of conductive gel electrolyte coating on its top surface. This configuration provides good electric contact with the skin, and a metallic salt coating acts as an intermediate bridge between electrode to and electrolyte, thereby reducing skin-electrode impedance, which translates to good signal quality. It is desirable for electrode-electrolyte materials to be electrochemically reversible and stable, with minimal fluctuations in potential over time . Efforts have been devoted to developing dry electrodes for biosignal monitoring, such as printed Ag/AgCl-based inks on flexible substrates or textiles . Work by Xu et al. 11 and Haddad et al. 12 have demonstrated the fabrication of Ag/AgCl based e-textiles comparable with Ag/AgCl solid gel electrodes for biosignal monitoring. Ag/AgCl coated yarn is the key element in developing e-textile electrodes. A wide range of Ag coated yarns made from a variety of core materials, fibre diameter, Ag film thickness, and quality are available on the market
International Journal of Biological Macromolecules, Mar 1, 2021
Pectin has been regarded as a drug carrier accelerating the healing process due to its bioactivit... more Pectin has been regarded as a drug carrier accelerating the healing process due to its bioactivities, abundance and lower cost of resources. However, a big challenge related to its practical application is its poor mechanical strength. In this study the modified Cu-based MOF containing Folic acid was synthesized and incorporated in the suitable pectin electrospun nanofibers which not only improved the copper ions release behavior but also made the fiber mat stronger, antibacterial and induce angiogenesis, fibroblast migration, and proliferation due to loaded copper ions and folic acid. The nanofibers composing of 75% pectin and 4000 kDa -PEO were chosen after morphological and mechanical characterization. Finally, the effect of MOF incorporation on the nanocomposite samples was characterized in terms of morphological, physiochemical and biological properties. The nanofibrous mats were evaluated by tensile testing, antibacterial and cytotoxicity. The release behavior of copper ions and folic acid was controlled and their burst release alleviated reducing cytotoxicity in vitro. It was found that the Young's moduli of the pectin nanofibers were improved to 19.13 MPa by the addition of Cu-based MOFs. Moreover, nanocomposite pectin nanofibers were found to be antibacterial and biocompatible. These results demonstrate that MOF-contained pectin nanofibers are promising for biomedical applications.
Knowing the basic properties of nanofibers (such as morphology, molecular structure and mechanica... more Knowing the basic properties of nanofibers (such as morphology, molecular structure and mechanical properties) is crucial for the scientific understanding of nanofibers and for the effective design and use of nanofibrous materials. In order to evaluate and develop the manufacturing process, the composition, structure and physical properties must be characterized to decide whether the produced fibers are suitable for their particular application. Evaluation of the various production parameters in processes such as electrospinning is a critical step towards production of nanofibers commercially. Many common techniques used to characterize conventional engineering materials, as well as some not so common techniques, have been employed in the characterization of nanofibers. Table 6.1 shows the scales of fibers and the corresponding characterization techniques. To provide an overall understanding, some of the general characterization techniques for structural, chemical, mechanical, thermal and other properties will be introduced in this chapter. Structural characterization of nanofibers The morphological characterization techniques briefly discussed herein are: optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). These methods characterize the morphology and determine fiber diameter, pore size and porosity, all of which are necessary to evaluate the various production parameters. The techniques for characterization of order/disorder of molecular structures using X-ray diffraction (XRD) are also covered in this section. Furthermore, mercury porosimetry, a special technique for porosity measurement, is introduced.
Separation and Purification Technology, Oct 1, 2017
Lignin-zeolite composite nanofiber membranes were prepared by the electrospinning technique. The ... more Lignin-zeolite composite nanofiber membranes were prepared by the electrospinning technique. The membranes were characterized in terms of morphology, mechanical properties, hydrophilicity, permeation, and particulate separation performance. The experimental results indicated that lignin-zeolite composite nanofiber membranes exhibited significant differences in surface properties and mechanical properties because of the addition of inorganic particles. Adding one weight percent of zeolite nanoparticles improved the tensile strength, tensile modulus, hydrophilicity, permeability, and separation factor of the membranes. However, the addition of higher weight percent of zeolite nanoparticles resulted in the decline of mechanical properties, permeability, and particulate retention.
The authors describes the composite sheet with Fe<sub>3</sub>O<sub>4</sub>... more The authors describes the composite sheet with Fe<sub>3</sub>O<sub>4</sub> particles as inclusions in polymer based nanofibers by using the electrospinning technique . The spinning dopes were prepared by sonication of the iron oxide nanoparticles in Dimethylformamide (DMF, Sigma-Aldrich) for 24 hrs . Polyvinylidene Fluoride (PVDF, Kynar) of 20 wt .% to DMF were then added to the prepared Fe<sub>3</sub>O<sub>4</sub>/DMF mixture . The solutions mixtures were stirred for 24 hrs with 5, 10 and 20 wt .% of Fe<sub>3</sub>O<sub>4</sub> in PVDF before the electrospinning at 90 <sup>0</sup>C, respectively . The spinning dope of 5 ml was transferred to a syringe for electrospinning.
Porous carbon materials derived from plant biomass offer great promise towards developing sustain... more Porous carbon materials derived from plant biomass offer great promise towards developing sustainable and advanced renewable materials for energy applications. Lignin is as an abundant and renewable aromatic biopolymer with high carbon content and chemical functionality for crosslinking, which make lignin a promising alternative for environmentally-friendly carbon aerogel production. In this study, carbon aerogels were produced using an industrial softwood kraft lignin isolated from renewable forest resources. Crosslinked lignin gels were synthesized using an epoxy compound and converted into carbon aerogels with subsequent sol-gel processing, supercritical drying and pyrolysis steps. The effect of lignin-to-crosslinker ratio on the chemical, physical and structural properties of resulting carbon aerogels were investigated. The bulk density of carbon aerogels increased as the lignin content increased from 56 wt% to 87 wt% and ranged from 0.45 to 0.83 g/cm3, respectively. FTIR result...
We report herein the structural and mechanical properties and in-vitro cellular response of hydro... more We report herein the structural and mechanical properties and in-vitro cellular response of hydroxyapatite/alginate nanocomposite fibrous scaffolds mimicking the mineralized collagen fibrils of bone tissue. The biomimetically "engineered" nanocomposites, fabricated by electrospinning and in-situ synthesis strategy, were compared with pure alginate nanofibers and micrometer-level HAp/alginate composite fibers. The tensile strength and elastic modulus of the nanocomposites increased by 79.3% and 158.4%, respectively, compared to those of the alginate. The uniform nucleation and HAp nanocrystal growth on the alginate nanofibers resulted in such enhancement of the mechanical properties via a stress-transfer effect. Rat calvarial osteoblasts were stably attached and stretched more extensively on the nanocomposites' surface than the pristine alginate. The controlled deposition of the HAp nanophase contributed to a much faster cell proliferation rate on the nanocomposites than the others. The improved structural stability and osteoblast interactions suggest the fibrous nanocomposite scaffold's potential advantages for bone tissue regeneration.
Hexagonal braiding technology is a kind of state-of-the-art braiding method, which uses hexagonal... more Hexagonal braiding technology is a kind of state-of-the-art braiding method, which uses hexagonal horngears to driveyarn carriers and make yarns intertwined into fabrics. In terms of hexagonal braiding principles, the braiding parameterslike initial arrangement of yarn carriers, yarn number and horngears sequence were defined, and then the movementpaths of yarn carriers in hexagonal braiding process and stitch length were obtained, which could be converted intocoordinates on the xoy plane and the coordinates along z-axis. In that case, a group of spatial coordinates were got tocreate the yarn trajectories and fabric structures in Matlab. And then, B-spline curve was utilized to fit the yarntrajectories. Considering the compactness of hexagonal fabric, the coordinates conversion algorithm and conversionmatrix were utilized to optimize the fabric structure, so a more compact fabric structure was established. The braidingangle variation and volume fraction of fabric showed that after c...
Carbon nanofibers (CNFs) have attracted much attention as effective materials for energy storage ... more Carbon nanofibers (CNFs) have attracted much attention as effective materials for energy storage devices. Here, silver nanoparticles (AgNPs) were in situ synthesized on the cellulose nanofibers containing vapor grown carbon nanofibers (VGCNFs) for producing carbon nanofibers with desirable properties toward electrochemical applications. Carbon nanofibers were fabricated by electrospinning of cellulose acetate solution containing 0.5 wt% VGCNFs followed by deacetylation and carbonization. Dopamine as a carbon source with high amine content was introduced as poly-functional compound that served as a reducing, adhesive, binding and stabilizing agent for production of silver nanoparticles as well as forming a carbon layer with high nitrogen content on CNF surfaces after heat-treatment. The carbon nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction, X-ray
Nanocrystalline cellulose (NCC) is a sustainable material with excellent mechanical properties an... more Nanocrystalline cellulose (NCC) is a sustainable material with excellent mechanical properties and can potentially be used as a reinforcement agent. The objective of this work was to test the effects of NCC incorporation on the mechanical properties of electrospun polyacrylonitrile (PAN) nanofibers. Methods: Eleven percent in weight of PAN (molecular weight 150 kD) in a dimethylformamide (DMF) solution was electrospun at 14.6 kV. Nonfunctionalized NCC was added to the solution at 1%, 2%, or 3 wt% (NCC/PAN). Suspensions were mixed and sonicated for 2 h before spinning. Strips (5 0.5 cm) were cut from the spun mat, parallel and perpendicular to the rotational direction of the fiber collection drum. Tensile tests were performed, and ultimate tensile strength (UTS), yield strength (YS; 0.3%), elastic modulus (E), and elongation at maximum stress (EMS, %) were calculated from stress-strain plots. Data were analyzed by multiple t tests and one-way ANOVA (α = 0.05). Results: Among all groups, samples with 3 wt % NCC loading had significantly superior mechanical properties. The fiber mats showed anisotropic behavior.
Conventional electrospinning is an effective and versatile method employed for fabricating nanofi... more Conventional electrospinning is an effective and versatile method employed for fabricating nanofibers. However, the relatively low production rate is the major challenge of electrospinning as an economic and scalable method. Recently, several approaches have been developed to ensure the high production rate of nanofibers. This paper has reviewed the latest developed electrospinning methods, such as multi-jet, needleless, bubble, centrifuge and electro-centrifuge systems. Furthermore, the jet formation in centrifugal spinning, as well as electro-centrifuge systems, was investigated through experimental and numerical analysis.
The phase structure and dynamic mechanical properties of poly(acrylonitrile-co-methyl acrylate) (... more The phase structure and dynamic mechanical properties of poly(acrylonitrile-co-methyl acrylate) (P(AN-co-MA)) nanofibers collected in the form of twisted yarn via the two-nozzle conjugated electrospinning method were investigated to study the effects of solution concentration and take-up velocity on the relaxation behavior of nanofibers yarn. The wide-angle X-ray diffraction analyses of P(AN-co-MA) nanofibers show a two-phase structure of nanofibers consisting of crystalline and amorphous phases and polymorphic transition from hexagonal to orthorhombic. Heating P(AN-co-MA) nanofibers at over the glass transition temperature led to an increased degree of both crystallinity and crystallite size with no polymorphic change. Three transitions (tan δ peaks) were observed in nanofibrous yarn prepared at different spinning dope concentrations and take-up speeds, except for the specimen prepared at a concentration of 14 wt% and collecting speed of 8 cm/min, wherein no α transition was observed due to improved molecular orientation. The temperature dependence of the dynamic Young’s modulus of nanofibrous yarn at different spinning dope concentrations was mainly affected by the diameter of the nanofiber as the morphological property and molecular orientation. Take-up speed was found to affect the γ and α transitions more than the β transition. Moreover, the maximum storage modulus was obtained at a take-up speed of 8 cm/min at all over recorded temperatures.
AB.S_IXA.CE A new type of braided fiber seal has been developed for high temperature engine appli... more AB.S_IXA.CE A new type of braided fiber seal has been developed for high temperature engine applications. Development work performed in this study includes seal design, fabrication, leakage flow testing, and flow resistance modeling. This new type of seal utilizes the high flow resistance of tightly packed fibers and the conformability of textile structures. The seal contains a core part with aligned fibers, and a sheath with braided fiber layers. Seal samples are made by using the conventional braiding process. Leakage flow measurements are then performed. Mass flow rate versus the simulated engine pressure and preload pressure is recorded. The flow resistance of the seal is analyzed using the Ergun equation for flow through porous media, including both laminar and turbulent effects. The two constants in the Ergun equation are evaluated for the seal structures. Leakage flow of the seal under the test condition is found to be in the transition flow region. The analysis is used to predict the leakage flow performance of the seal with the determined design parameters.
This work presents a continuous roll-to-roll electrochemical coating system for producing silver/... more This work presents a continuous roll-to-roll electrochemical coating system for producing silver/silver chloride (Ag/AgCl)-coated yarns, and their application in e-textile electrodes for biosignal monitoring. Ag/AgCl is one of the most preferred electrode materials as an interface between the conductive backbone of an electrode and skin. E-textile Ag/AgCl-coated multi-filament nylon yarns offer stable, flexible, and breathable alternatives to standard rigid or flexible film-based Ag/AgCl electrodes. The developed system allows for highly controlled process parameters to achieve stable and uniform AgCl film deposition on Ag-coated nylon yarns. The electrical, electrochemical properties, and morphology of the coated yarns were characterized. Dry electrodes were fabricated and could measure electrocardiogram (ECG) signals with comparable performance to standard gel electrodes. Ag/AgCl e-textile electrodes demonstrated high stability, with low average polarization potential (1.22 mV/ min) compared with Ag-coated electrodes (3.79 mV/min), low impedance (below 2 MΩ, 0.1-150 Hz), and are excellent candidates for heart rate detection and monitoring. Biosignals can be detected and monitored from various locations of the body, by employing electrode sensors. Electrodes used for biosignal monitoring function by transducing ionic current (i.e., sodium, potassium, calcium, chloride ions) from the skin surface, into electron current, through metallic wires of a given recording system/ instrument 1,2 . Electrodes made from conductive metals or polymer films are commonly being used, but tend to have high sensitivity to motion artifacts, produce fluctuations in potential, and cause signal distortion over time, owing to the absence of an electrolyte layer 3 . However, sweat and moisture that develops on the skin surface over time is thought to act as an electrolyte layer, thereby reducing skin impedance 4 . While these distortions in features can be corrected by signal processing methods, it is more ideal to develop materials with polarization potential stability, to reduce interference with the collected signal . Other considerations to be made when developing electrode materials for biosignal monitoring include low electrical resistance of the electrode compared with that for skin surface 7 , skin contact, conformability, and biocompatibility 8 . Silver/Silver chloride (Ag/AgCl) electrode material is the gold standard for biosignal acquisition (electrocardiogram, electroencephalography, endodermal activity etc.), owing to its low and stable half-cell potential 2 . The most commonly used electrode for biosignal monitoring includes a pellet of sintered high purity silver and silver chloride, with a thin layer of conductive gel electrolyte coating on its top surface. This configuration provides good electric contact with the skin, and a metallic salt coating acts as an intermediate bridge between electrode to and electrolyte, thereby reducing skin-electrode impedance, which translates to good signal quality. It is desirable for electrode-electrolyte materials to be electrochemically reversible and stable, with minimal fluctuations in potential over time . Efforts have been devoted to developing dry electrodes for biosignal monitoring, such as printed Ag/AgCl-based inks on flexible substrates or textiles . Work by Xu et al. 11 and Haddad et al. 12 have demonstrated the fabrication of Ag/AgCl based e-textiles comparable with Ag/AgCl solid gel electrodes for biosignal monitoring. Ag/AgCl coated yarn is the key element in developing e-textile electrodes. A wide range of Ag coated yarns made from a variety of core materials, fibre diameter, Ag film thickness, and quality are available on the market
International Journal of Biological Macromolecules, Mar 1, 2021
Pectin has been regarded as a drug carrier accelerating the healing process due to its bioactivit... more Pectin has been regarded as a drug carrier accelerating the healing process due to its bioactivities, abundance and lower cost of resources. However, a big challenge related to its practical application is its poor mechanical strength. In this study the modified Cu-based MOF containing Folic acid was synthesized and incorporated in the suitable pectin electrospun nanofibers which not only improved the copper ions release behavior but also made the fiber mat stronger, antibacterial and induce angiogenesis, fibroblast migration, and proliferation due to loaded copper ions and folic acid. The nanofibers composing of 75% pectin and 4000 kDa -PEO were chosen after morphological and mechanical characterization. Finally, the effect of MOF incorporation on the nanocomposite samples was characterized in terms of morphological, physiochemical and biological properties. The nanofibrous mats were evaluated by tensile testing, antibacterial and cytotoxicity. The release behavior of copper ions and folic acid was controlled and their burst release alleviated reducing cytotoxicity in vitro. It was found that the Young's moduli of the pectin nanofibers were improved to 19.13 MPa by the addition of Cu-based MOFs. Moreover, nanocomposite pectin nanofibers were found to be antibacterial and biocompatible. These results demonstrate that MOF-contained pectin nanofibers are promising for biomedical applications.
Knowing the basic properties of nanofibers (such as morphology, molecular structure and mechanica... more Knowing the basic properties of nanofibers (such as morphology, molecular structure and mechanical properties) is crucial for the scientific understanding of nanofibers and for the effective design and use of nanofibrous materials. In order to evaluate and develop the manufacturing process, the composition, structure and physical properties must be characterized to decide whether the produced fibers are suitable for their particular application. Evaluation of the various production parameters in processes such as electrospinning is a critical step towards production of nanofibers commercially. Many common techniques used to characterize conventional engineering materials, as well as some not so common techniques, have been employed in the characterization of nanofibers. Table 6.1 shows the scales of fibers and the corresponding characterization techniques. To provide an overall understanding, some of the general characterization techniques for structural, chemical, mechanical, thermal and other properties will be introduced in this chapter. Structural characterization of nanofibers The morphological characterization techniques briefly discussed herein are: optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). These methods characterize the morphology and determine fiber diameter, pore size and porosity, all of which are necessary to evaluate the various production parameters. The techniques for characterization of order/disorder of molecular structures using X-ray diffraction (XRD) are also covered in this section. Furthermore, mercury porosimetry, a special technique for porosity measurement, is introduced.
Separation and Purification Technology, Oct 1, 2017
Lignin-zeolite composite nanofiber membranes were prepared by the electrospinning technique. The ... more Lignin-zeolite composite nanofiber membranes were prepared by the electrospinning technique. The membranes were characterized in terms of morphology, mechanical properties, hydrophilicity, permeation, and particulate separation performance. The experimental results indicated that lignin-zeolite composite nanofiber membranes exhibited significant differences in surface properties and mechanical properties because of the addition of inorganic particles. Adding one weight percent of zeolite nanoparticles improved the tensile strength, tensile modulus, hydrophilicity, permeability, and separation factor of the membranes. However, the addition of higher weight percent of zeolite nanoparticles resulted in the decline of mechanical properties, permeability, and particulate retention.
The authors describes the composite sheet with Fe<sub>3</sub>O<sub>4</sub>... more The authors describes the composite sheet with Fe<sub>3</sub>O<sub>4</sub> particles as inclusions in polymer based nanofibers by using the electrospinning technique . The spinning dopes were prepared by sonication of the iron oxide nanoparticles in Dimethylformamide (DMF, Sigma-Aldrich) for 24 hrs . Polyvinylidene Fluoride (PVDF, Kynar) of 20 wt .% to DMF were then added to the prepared Fe<sub>3</sub>O<sub>4</sub>/DMF mixture . The solutions mixtures were stirred for 24 hrs with 5, 10 and 20 wt .% of Fe<sub>3</sub>O<sub>4</sub> in PVDF before the electrospinning at 90 <sup>0</sup>C, respectively . The spinning dope of 5 ml was transferred to a syringe for electrospinning.
Porous carbon materials derived from plant biomass offer great promise towards developing sustain... more Porous carbon materials derived from plant biomass offer great promise towards developing sustainable and advanced renewable materials for energy applications. Lignin is as an abundant and renewable aromatic biopolymer with high carbon content and chemical functionality for crosslinking, which make lignin a promising alternative for environmentally-friendly carbon aerogel production. In this study, carbon aerogels were produced using an industrial softwood kraft lignin isolated from renewable forest resources. Crosslinked lignin gels were synthesized using an epoxy compound and converted into carbon aerogels with subsequent sol-gel processing, supercritical drying and pyrolysis steps. The effect of lignin-to-crosslinker ratio on the chemical, physical and structural properties of resulting carbon aerogels were investigated. The bulk density of carbon aerogels increased as the lignin content increased from 56 wt% to 87 wt% and ranged from 0.45 to 0.83 g/cm3, respectively. FTIR result...
We report herein the structural and mechanical properties and in-vitro cellular response of hydro... more We report herein the structural and mechanical properties and in-vitro cellular response of hydroxyapatite/alginate nanocomposite fibrous scaffolds mimicking the mineralized collagen fibrils of bone tissue. The biomimetically "engineered" nanocomposites, fabricated by electrospinning and in-situ synthesis strategy, were compared with pure alginate nanofibers and micrometer-level HAp/alginate composite fibers. The tensile strength and elastic modulus of the nanocomposites increased by 79.3% and 158.4%, respectively, compared to those of the alginate. The uniform nucleation and HAp nanocrystal growth on the alginate nanofibers resulted in such enhancement of the mechanical properties via a stress-transfer effect. Rat calvarial osteoblasts were stably attached and stretched more extensively on the nanocomposites' surface than the pristine alginate. The controlled deposition of the HAp nanophase contributed to a much faster cell proliferation rate on the nanocomposites than the others. The improved structural stability and osteoblast interactions suggest the fibrous nanocomposite scaffold's potential advantages for bone tissue regeneration.
Hexagonal braiding technology is a kind of state-of-the-art braiding method, which uses hexagonal... more Hexagonal braiding technology is a kind of state-of-the-art braiding method, which uses hexagonal horngears to driveyarn carriers and make yarns intertwined into fabrics. In terms of hexagonal braiding principles, the braiding parameterslike initial arrangement of yarn carriers, yarn number and horngears sequence were defined, and then the movementpaths of yarn carriers in hexagonal braiding process and stitch length were obtained, which could be converted intocoordinates on the xoy plane and the coordinates along z-axis. In that case, a group of spatial coordinates were got tocreate the yarn trajectories and fabric structures in Matlab. And then, B-spline curve was utilized to fit the yarntrajectories. Considering the compactness of hexagonal fabric, the coordinates conversion algorithm and conversionmatrix were utilized to optimize the fabric structure, so a more compact fabric structure was established. The braidingangle variation and volume fraction of fabric showed that after c...
Carbon nanofibers (CNFs) have attracted much attention as effective materials for energy storage ... more Carbon nanofibers (CNFs) have attracted much attention as effective materials for energy storage devices. Here, silver nanoparticles (AgNPs) were in situ synthesized on the cellulose nanofibers containing vapor grown carbon nanofibers (VGCNFs) for producing carbon nanofibers with desirable properties toward electrochemical applications. Carbon nanofibers were fabricated by electrospinning of cellulose acetate solution containing 0.5 wt% VGCNFs followed by deacetylation and carbonization. Dopamine as a carbon source with high amine content was introduced as poly-functional compound that served as a reducing, adhesive, binding and stabilizing agent for production of silver nanoparticles as well as forming a carbon layer with high nitrogen content on CNF surfaces after heat-treatment. The carbon nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction, X-ray
Nanocrystalline cellulose (NCC) is a sustainable material with excellent mechanical properties an... more Nanocrystalline cellulose (NCC) is a sustainable material with excellent mechanical properties and can potentially be used as a reinforcement agent. The objective of this work was to test the effects of NCC incorporation on the mechanical properties of electrospun polyacrylonitrile (PAN) nanofibers. Methods: Eleven percent in weight of PAN (molecular weight 150 kD) in a dimethylformamide (DMF) solution was electrospun at 14.6 kV. Nonfunctionalized NCC was added to the solution at 1%, 2%, or 3 wt% (NCC/PAN). Suspensions were mixed and sonicated for 2 h before spinning. Strips (5 0.5 cm) were cut from the spun mat, parallel and perpendicular to the rotational direction of the fiber collection drum. Tensile tests were performed, and ultimate tensile strength (UTS), yield strength (YS; 0.3%), elastic modulus (E), and elongation at maximum stress (EMS, %) were calculated from stress-strain plots. Data were analyzed by multiple t tests and one-way ANOVA (α = 0.05). Results: Among all groups, samples with 3 wt % NCC loading had significantly superior mechanical properties. The fiber mats showed anisotropic behavior.
Uploads
Papers by Frank Ko