Submicron Fibers Research Articles

Gold nanoparticles–gelatin hybrid fibers with bright photoluminescence

In the present work, a type of hybrid fibers—gold nanoparticles (GNPs)–gelatin fibers were designed. Spinning solutions for the sub-micron fibers were prepared by adding gelatin, ethylene diamine tetraacetic acid (EDTA) and chloroauric acid in water successively. The EDTA reduced the chloroauric acid and gave rise to in situ synthesis of GNPs in the spinning solutions. The GNPs–gelatin fibers were fabricated by electrospinning the spinning solutions. The GNPs were encapsulated in the fibers, which endowed the fibers photoluminescence (PL) characteristics. A variety of experiments were performed to characterize the structure and properties of the GNPs–gelatin fibers. This work provides new perspectives for the fabrication of functional nanocomposite fibers.

Electrospinning of poly (ε-caprolactone-co-lactide)/Pluronic blended scaffolds for skin tissue engineering

For skin tissue engineering, an ideal scaffold should mimic the natural extracellular matrix of the native skin. In this study, we reported a novel elastic sub-micron fiber scaffold blending poly (e-caprolactone-co-lactide) (PLCL) and Pluronic at different ratios by electrospinning. PLCL and Pluronic were co-electrospun with the ratio of 100/0, 99/1, 95/5, 90/10, 85/15, and 75/25. These scaffolds were evaluated in terms of fiber morphology, mechanical properties, and hydrophilicity for the purpose of culturing adipose-derived stem cells (ADSCs). Cell attachment and proliferation on the scaffolds were also evaluated to demonstrate the potential of serving as a skin graft. The results indicated that all of the electrospun fibers possessed smooth surface textures and interconnected porous structures with the average diameter ranging from approximately 750–1140 nm. The higher tensile strength was observed in 95/5 and 90/10 PLCL/Pluronic blended membranes, while further incorporation of Pluronic almost has no effect on tensile strength. The water contact angle was 85° for scaffold with the ratio of 99/1, while 0° for 90/10, 85/15, and 75/25. In addition, the elevation of Pluronic content in composition resulted in a corresponding increase in swelling behavior. Compared with PLCL, the better cell adhesion and proliferation potential of ADSCs was exhibited on all PLCL/Pluronic blended scaffolds. ADSCs on the blended scaffolds were highly elongated and well integrated with the surrounding fibers, indicating the good cytocompatibility of PLCL/Pluronic scaffolds. Thus, these blended scaffolds have the potentially high application prospect in the field of skin tissue engineering.

Occurrence and morphology of bead-on-string structures in centrifugal forcespun PA6 fibers

This research aimed at investigating the morphology and frequency of bead-on-string occurrences on forcespun nano- and sub-micron fibers. The formation of bead-on-string structures was observed on a range of fiber samples forcespun in varied conditions from PA6 solutions of different concentrations. Bead-on-string structures were characterized for morphology using SEM micrographs, and were counted on all samples. Two major factors appeared to affect both the morphology and the bead count, namely spinning solution concentration, i.e. viscosity, and spinning needle gage or diameter. Low viscosity solutions resulted in large numbers of mostly spherical beads. Solutions with higher viscosity appeared to suppress the fluid jet instability thus resulting in significantly fewer beads with exclusively elongated spindle-like shapes. Spinning needle diameter also had a significant impact on beading behavior, with the larger diameter exhibiting higher bead counts. A significant interaction between the two factors was detected and its impact on the competition between the fluid jet visco-elastic relaxation and the Rayleigh instability is discussed.

3D Electrospun scaffolds promote a cytotrophic phenotype of cultured primary astrocytes

Astrocytes are a target for regenerative neurobiology because in brain injury their phenotype arbitrates brain integrity, neuronal death and subsequent repair and reconstruction. We explored the ability of 3D scaffolds to direct astrocytes into phenotypes with the potential to support neuronal survival. Poly-ε-caprolactone scaffolds were electrospun with random and aligned fibre orientations on which murine astrocytes were sub-cultured and analysed at 4 and 12DIV. Astrocytes survived, proliferated and migrated into scaffolds adopting 3D morphologies, mimicking in vivo stellated phenotypes. Cells on random poly-ε-caprolactone scaffolds grew as circular colonies extending processes deep within sub-micron fibres, whereas astrocytes on aligned scaffolds exhibited rectangular colonies with processes following not only the direction of fibre alignment but also penetrating the scaffold. Cell viability was maintained over 12DIV, and cytochemistry for F-/G-actin showed fewer stress fibres on bioscaffolds relative to 2D astrocytes. Reduced cytoskeletal stress was confirmed by the decreased expression of glial fibrillary acidic protein. PCR demonstrated up-regulation of genes (excitatory amino acid transporter 2, brain-derived neurotrophic factor and anti-oxidant) reflecting healthy biologies of mature astrocytes in our extended culture protocol. This study illustrates the therapeutic potential of bioengineering strategies using 3D electrospun scaffolds which direct astrocytes into phenotypes supporting brain repair. Astrocytes exist in phenotypes with pro-survival and destructive components, and their biology can be modulated by changing phenotype. Our findings demonstrate murine astrocytes adopt a healthy phenotype when cultured in 3D. Astrocytes proliferate and extend into poly-ε-caprolactone scaffolds displaying 3D stellated morphologies with reduced GFAP expression and actin stress fibres, plus a cytotrophic gene profile. Bioengineered 3D scaffolds have potential to direct inflammation to aid regenerative neurobiology.

Analysis of composition homogeneity and polarization orientation of PZT submicron fibers by micro-Raman spectroscopy

Micro-Raman spectroscopy is a convenient tool to probe individual objects with a feature size on the submicron scale. The phase, composition, and orientation of Pb(Zr,Ti)O3 fibers fabricated via hydrothermal processing have been characterized by this technique, with the working principles given in the paper. It is shown that the prepared PZT submicron fibers are of a tetragonal pervoskite phase, with Zr/(Zr + Ti) varying from 0.05 to 0.25. The spontaneous polarization has been confirmed to be along the length direction and one of its {1 0 0} planes parallel to the substrate plane.

Electrospinning of PAN nanofibers incorporating SBA-15-type ordered mesoporous silica particles

The influence of rod-like SBA-15 type ordered mesoporous silica particles, as additives, on the morphology and textural parameters of electrospun polyacrylonitrile (PAN) nanofibers has been studied. PAN charged-webs are prepared by electrospinning of a dispersion of SBA-15 particles in a solution of PAN in DMF. The effect of the applied voltage on the morphology of produced webs has been also investigated. Collected results demonstrate that when electrospinning pristine or charged PAN, the higher the voltage applied, the coarser the fiber is. As a result, sub-micron fibers of PAN charged with SBA-15 particles were obtained. An increase, to some extent, of the specific surface area and pore volume of charged fibers compared to that of pristine electrospun PAN fibers has been also observed. Thermogravimetric analyses reveal that more than 78% of SBA-15 particles are found in the dry fibers. SBA-15 loading rates of 14.3, 15.6 and 27.6wt.% were achieved. Calculations done to estimate the ratio of accessible pore of SBA-15 particles incorporated within the produced fibers show that more than 50% of accessible pores can be obtained. However, there is a saturated capacity of SBA-15 particles distribution on the surface of the nanofibers beyond 15.6wt.% loading of SBA-15.This suggests that the ratio of accessible pores within the charged fibers is also limited.

Fabrication and surface functionalization of electrospun polystyrene submicron fibers with controllable surface roughness

Polystyrene (PS) submicron fibers of 14 wt% concentration were fabricated by electrospinning using dimethylformamide (DMF)–tetrahydrofuran (THF) solvent system. The surface morphology of PS fibers was modified from smooth to rough by changing the mixing ratio of DMF and THF in the spinning solution. The electrospun PS fibers with smooth and rough surfaces were then amidomethylated by treating with N-hydroxymethyl-2-chloroacetamide. PS fibers with higher roughness incorporated more amidomethyl functional groups on their surface, as confirmed by XPS analysis. This observation was further supported by BET adsorption isotherm results which showed a significant increase in specific surface area of rough PS electrospun fibers. Interestingly, amidomethylation has altered rough electrospun PS submicron fibers from extremely hydrophobic to hydrophilic. These chemically modified electrospun PS fibers with controllable surface roughness and wettability may be utilized as a carrier for proteins, mainly enzymes and antibodies, by covalent linkage through amino groups attached to their surface.

Effect of Fiber Patterns on the Fracture of Implant/Cement Interfaces

Electrospinning is a process by which fibers with micron to nanometer diameters can be obtained from an electrostatically driven jet of polymer solution. These fibers have a high surface area to volume ratio, which have numerous applications in biomedical implants such as total hip implant, dental implant. The present study is based on the hypothesis that the differences of the surface properties at titanium/cement interface due to incorporation of micro and sub-micron diameters fiber directions may have influence on the quality of titanium/cement union. The objectives of this research were to design and construct electrospinning unit for the fabrication uni- and bi-directions polycaprolactone (PCL) fiber on titanium and to measure the effect of fiber directions on the interface fracture strengths of sandwiched titanium (Ti) and poly methyl methacrylate (PMMA) cement samples with (uni-and bi-directions) and without fibers. Two groups of single edge sandwiched Ti/PMMA specimens were prepared. First group of specimen consists of Ti/PMMA sandwiched specimen without PCL fiber. Second group of specimen consists of Ti/PMMA sandwiched specimen with uni- and bi-direction PCL fibers. PCL fibers were ejected from the syringe via charged needle and deposited on two different grounded collectors to coat uni-and bi-directions PCL fibers on Ti plates. PMMA cement was poured and cured on the Ti plates with and without PCL fibers in a custom made mold to prepare Ti/PMMA samples with uni-and bi-directions fibers. Shear tests were conducted on each group of Ti/PMMA samples using Evex tensile test stage. Interface fracture toughness was calculated to determine the effect of fiber patterns on Ti/PMMA samples. This study successfully produced an electrospun unit that can produce uni- and bi- direction PCL fibers. Diameters of produced fibers were found to be in the range of 919nm ∼1.25μm. This study found that the values of KIC of Ti/PMMA with uni-direction fiber were significantly higher when compared to the values of KIC of the Ti/PMMA without fiber (p<0.05), although the values of KIC of Ti/PMMA with bi-direction fiber were significantly lower when compared to the values of KIC of the Ti/PMMA without fiber. Results indicated that the addition of the fiber to Ti improved the quality of Ti/PMMA union and fiber directions have significant effect on the strength of the Ti-PMMA union.

Physical structure behavior to wettability of electrospun poly(lactic acid)/polysaccharide composite nanofibers

Poly(lactic acid) has been electrospun into submicron fibers with embedded cassava starch matrix. The fibers had average fiber diameters between 140 and 680 nm. The starch content varied from 10 to 20% in total solids. Water contact angles were measured on sheets of these fiber materials and correlated with the fiber size and starch content. Water contact angles varied from 80 to 120° which shows that the fiber composition can control the mat properties from hydrophilic to hydrophobic. The results also showed variation in the average fiber diameters alone did not always affect sheet wettability. These results show the importance of the relationship between the electrospun fiber sheet topography and material composition to the wettability of polysaccharide electrospun nanofibers.

Preparation of Superhydrophobic Teflon® AF 1600 Sub-Micron Fibers and Yarns Using the Forcespinningtm Technique

Superhydrophobic materials combined with manufacturing processes that can increase surface roughness of the material, offer an opportunity to effectively control wetting properties. Rapid formation of Teflon® AF (TAF) fibrous mats with sub-micron fiber diameter using the Forcespinning™ technique is presented. The fiber formation technique is based on the use of centrifugal forces. SEM analysis shows uniform formation of TAF 1600 fibers with average diameter of 362±58nm. Contact angle measurement confirms the superhydrophobic nature of the mats with contact angles as high as 169° ± 3° and rolling angles of 2°. TAF 1600 mats were forcespun at a rate of 1gr/min. The relationship between the contact angle and hierarchical surface roughness of the TAF mat is also discussed. TAF yarns were also manufactured and characterized. Yarns with diameters of 156 microns withstood 17.5 MPa of engineering stress with a Young's modulus of 348 MPa in the elastic region and excellent thermal stability.

Glass fiber coalescing filter media augmented with polymeric submicron fibers and modified with angled drainage channels

Glass fiber filter media are widely used in separation of droplets from liquid aerosols. In prior works two possible enhancements to the performance of the glass fiber media were studied: (1) the capture efficiencies were increased by augmenting the glass fibers with sub-micron sized electrospun polymer fibers, and (2) the pressure drop was decreased by modifying the filter media with insertion of 45° drainage channels. In this paper we report the simultaneous application of these two enhancements on the performance of the filter media.Filters were fabricated by inserting low surface energy woven polymer fiber drainage channels at various angles within non-woven glass fiber filter media augmented with Nylon sub-micron fibers. The effects of the presence and geometry of the drainage channels on the filter performance were evaluated experimentally. The sub-micron fibers gave the filter high coalescence and separation efficiencies while the drainage channels reduced the filter pressure drop. The micro glass fiber media augmented with 100nm Nylon fibers and modified with Polypropylene fiber drainage channels at 45° downward angles had the overall best performance.

Bioactive Nanofibrous Scaffolds for Regenerative Endodontics

Here we report the synthesis, materials characterization, antimicrobial capacity, and cytocompatibility of novel antibiotic-containing scaffolds. Metronidazole (MET) or Ciprofloxacin/(CIP) was mixed with a polydioxanone (PDS)polymer solution at 5 and 25 wt% and processed into fibers. PDS fibers served as a control. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), tensile testing, and high-performance liquid chromatography (HPLC) were used to assess fiber morphology, chemical structure, mechanical properties, and drug release, respectively. Antimicrobial properties were evaluated against those of Porphyromonas gingivalis/Pg and Enterococcus faecalis/Ef. Cytotoxicity was assessed in human dental pulp stem cells (hDPSCs). Statistics were performed, and significance was set at the 5% level. SEM imaging revealed a submicron fiber diameter. FTIR confirmed antibiotic incorporation. The tensile values of hydrated 25 wt% CIP scaffold were significantly lower than those of all other groups. Analysis of HPLC data confirmed gradual, sustained drug release from the scaffolds over 48 hrs. CIP-containing scaffolds significantly (p < .00001) inhibited biofilm growth of both bacteria. Conversely, MET-containing scaffolds inhibited only Pg growth. Agar diffusion confirmed the antimicrobial properties against specific bacteria for the antibiotic-containing scaffolds. Only the 25 wt% CIP-containing scaffolds were cytotoxic. Collectively, this study suggests that polymer-based antibiotic-containing electrospun scaffolds could function as a biologically safe antimicrobial drug delivery system for regenerative endodontics.

Production of core/shell fibers by electrospinning from a free surface

Electrostatic fiber formation (“electrospinning”) is the leading technology for production of continuous fibers with submicron diameter. Applications such as drug delivery and sensors benefit from the ability to produce submicron fibers with a core/shell morphology from electrified coaxial jets of two liquids. However, low productivity of the conventional needle-based coaxial process is a barrier for commercialization. We present a novel technology that overcomes this limitation by the development of coaxial jets directly from compound droplets of immiscible liquids entrained on wires, and control of mass transfer processes to produce uniform, core/shell fibers. The enabling feature of controlled evaporation by design of solution properties is verified by a simple mass transport model. Electron micrographs confirm the formation of fibers with the desired morphology. The proposed technology creates the opportunity to produce nanofibers with core/shell morphology on an industrial scale for a wide variety of applications.

Evaluation of gallic acid loaded zein sub-micron electrospun fibre mats as novel active packaging materials

The applicability of gallic acid loaded zein (Ze-GA) electrospun fibre mats towards potential active food packaging material was evaluated. The surface chemistry of the electrospun fibre mats was determined using X-ray photon spectroscopy (XPS). The electrospun fibre mats showed low water activity and whitish colour. Thermogravimetric analysis (TGA) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy revealed the stability of the fibre mats over time. The Ze-GA fibre mats displayed similar rapid release profiles, with Ze-GA 20% exhibiting the fastest release rate in water as compared to the others. Gallic acid diffuses from the electrospun fibres in a Fickian diffusion manner and the data obtained exhibited a better fit to Higuchi model. L929 fibroblast cells were cultured on the electrospun fibres to demonstrate the absence of cytotoxicity. Overall, the Ze-GA fibre mats demonstrated antibacterial activity and properties consistent with those considered desirable for active packaging material in the food industry.

Quantitative characterization of functionally modified micron–submicron fibers for tissue regeneration: a review

Tissue regeneration relies on building carefully crafted scaffold material in the micron–submicron scale and imparting specific functionality in order to best mimic the in vivo environment in terms of chemical composition, morphology, and surface functional groups. Fibrous meshes with structural features at the micron to submicron level for ideal three-dimensional tissue regeneration scaffolds can be an inexpensive scale-up option. Bio-inert polymers lack the functional motifs for specific bioactivity; however, functionalization of the scaffolds can provide biological functions to actively induce tissue regeneration and promote cell adhesion by targeting specific cell–matrix interactions. It is therefore important to characterize the scaffolds and understand the relationship between the efficacy of the functionalization, the surface properties of the scaffolds, and their biological performance. This paper is a comprehensive review of the current understanding in functionalization and characterization of fibrous scaffolds and their biological efficacy. We begin with a compilation of various functionalization schemes including physical adsorption, co-electrospinning, wet chemical techniques, and surface graft polymerization methods and their application to fibers. After a critical literature review, the state of the art for characterization of these functionalized nano-fibers is then discussed. We emphasize the importance of covalent binding of biomolecules and the subsequent need for characterization of functional group distribution, or local density of functionalization, on the scaffold surface. Current challenges and future directions are outlined so that quantitative characterization of scaffold surfaces can aid in the development of next generation scaffolds.

Electrospinning of poly (3-hydroxybutyric acid) and gelatin blended thin films: fabrication, characterization, and application in skin regeneration

A tissue engineering scaffold should mimic the structure and biological function of native extracellular matrix proteins. Electrospinning is a simple and versatile method to produce ultrathin fibers for tissue engineering. Blended submicron fibers of poly (3-hydroxybutyric acid) and gelatin were electrospun using 1,1,1,3,3,3 hexafluoro-2-propanol as solvent. Cross linking of fibers was achieved using glutaraldehyde, and the resultant fibers were tested and analyzed using scanning electron microscopy (SEM), differential scanning calorimetry, thermogravimetric analysis, X-ray diffraction, and Fourier transformed infrared spectroscopy (FTIR).The fibers were found to exhibit good tensile strength. Degradation studies were performed and analyzed using SEM and FTIR and proved the stability of fibers for tissue engineering applications. The fibrous scaffold supported the growth and rapid proliferation of human dermal fibroblasts and keratinocytes with normal morphology, thus proving its reliability in using it as a potential scaffold for skin regeneration.

Fibrous Polymeric Composites Based on Alginate Fibres and Fibres Made of Poly-ε-caprolactone and Dibutyryl Chitin for Use in Regenerative Medicine

This work concerns the production of fibrous composite materials based on biodegradable polymers such as alginate, dibutyryl chitin (DBC) and poly-ε-caprolactone (PCL). For the production of fibres from these polymers, various spinning methods were used in order to obtain composite materials of different composition and structure. In the case of alginate fibres containing the nanoadditive tricalcium phosphate (TCP), the traditional method of forming fibres wet from solution was used. However in the case of the other two polymers the electrospinning method was used. Two model systems were tested for biocompatibility. The physicochemical and basic biological tests carried out show that the submicron fibres produced using PCL and DBC have good biocompatibility. The proposed hybrid systems composed of micrometric fibres (zinc and calcium alginates containing TCP) and submicron fibres (DBC and PCL) meet the requirements of regenerative medicine. The biomimetic fibre system, the presence of TCP nanoadditive, and the use of polymers with different resorption times provide a framework with specific properties on which bone cells are able to settle and proliferate.

Chemically and mechanically isolated nanocellulose and their self-assembled structures

Cellulose nanocrystals (CNCs) and nanofibrils (CNFs) have been isolated from pure rice straw cellulose via sulfuric acid hydrolysis, mechanical blending and TEMPO-mediated oxidation to 16.9%, 12% and 19.7% yields, respectively. Sulfuric acid hydrolysis produced highly crystalline (up to 90.7% CrI) rod-like (3.96–6.74nm wide, 116.6–166nm long) CNCs with similarly negative surface charges (−67 to −57mV) and sulfate contents but decreasing yields and dimensions with longer hydrolysis time. Mechanical defibrillated CNFs were 82.5% crystalline and bimodally distributed in sizes (2.7nm wide and 100–200nm long; 8.5nm wide and micrometers long). TEMPO mediated oxidation liberated the most uniform, finest (1.7nm) and micrometer long, but least crystalline (64.4% CrI) CNFs. These nanocellulose self-assembled into submicron (153–440nm wide) fibers of highly crystalline (up to 90.9% CrI) cellulose Iβ structure upon rapid freezing (−196°C) and freeze-drying. The self-assembling behaviors were analyzed based on nanocellulose dimensions, specific surfaces and surface chemistries.

Modified electric fields to control the direction of electrospinning jets

Electrospinning is a well known process for fabricating sub-micron size fibers. A high voltage potential is used in electrospinning to launch a polymer jet from a droplet of polymer solution towards a grounded collector. Most of the electrospun fibers collect on the grounded collector, but depending on the design of the electrospinning apparatus and the environment, some of the fibers drift away from the collector and are captured on other objects.In this work we apply the hypothesis that the electrospinning jet follows the path of the electric field's current density lines. By controlling the direction of the current density lines one can control the path of the electrospinning jet and hence can control the location of where the fibers are collected.The current density lines are determined by the gradient of the static electric potential field. The electric field is modified in this work by positioning charged electrodes that change the potential field and hence change the potential gradient and the path of the current density lines. In this way, the jet, following the current density lines, can be directed towards desired locations and away from undesired locations. The static electric field was modeled by numerically solving Laplace's equation for the potential field. Electrospinning experiments were conducted with the same geometric arrangement of electrodes for comparison. The results show the center of mass of the electrospinning jets generally followed the current density lines. This work shows it is possible to direct the electrospinning jets away from undesired objects by use of secondary electrodes.

Photoluminescent electrospun submicron fibers of hybrid organosiloxane and derived silica

Silica fibers are of technological significance in view of their applications in sensing, photocatalysis, filtration, biological scaffolds, photoluminescence, composites, etc. A combination of electrospinning and sol–gel technique has been employed to synthesize inorganic or ceramic sub-micron fibers starting from a novel oligomeric pre-ceramic precursor, Poly(methylhydrosiloxane) (PMHS). The composite fibers were calcined at temperatures in the range of 550 °C to 1400 °C to obtain slica fibers. The electrospun pre-ceramic fibers and derived silica sub-micron fibers were characterized by FESEM, TEM, XRD, Raman spectroscopy and FTIR. Calcination transformed the smooth pre-ceramic fibers to compact silica fibers that consist of nano-sized silica particles. Calcinations at lower temperatures yielded more amorphous silica fibers, but calcination at 1400 °C yielded a polymorph of crystalline silica, α-cristobalite. Building up of an ordered Si–O network with increased temperature was verified by Infra-Red and Raman Spectroscopy. Photoluminescence (PL) study of the electrospun fibers showed their potential as blue, green and red light emitters at room temperature at different excitation wavelengths, and a blue/violet emission with the UV excitation not seen previously. Although calcination of PMHS fibers decreased PL intensity, a close correspondence in both the emission and excitation PL spectra along with the PL life times of differently calcined fibers is probably owing to the presence of similar defect centers. Tuning of PL should allow potential applications in optoelectronics, medical nanoprobes and bio-labeling and sensing.