Nonwoven Nanofibrous Mats Research Articles

Enhancing mechanical strength of electrospun nanofibers by coaxial electrospinning and thermal treatment

AbstractElectrospinning of nonwoven nanofibrous mats has received significant attention in recent years due to the high versatility and porosity of electrospun mats. However, electrospun mats generally suffer from low mechanical strength. This work reports a method to improve the mechanical strength of nanofiber mats by coaxial electrospinning combined with thermal treatment, without incurring significant dimensional shrinkage. Coaxial polyacrylonitrile (PAN)/polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) mats showed no shrinkage when tested at temperatures up to 240°C for 20 min, compared to a shrinkage of 94% for the homogenous PVDF‐HFP mats when treated at 190°C for 20 min. When treated at 178°C for up to 30 min, the coaxial fibres consistently showed changes in thickness of less than 10% and no significant change in area. The coaxial PAN/PVDF‐HFP mats showed negligible changes in average porosity after treatment at 178°C for 20 min. The mechanical strength of the coaxial samples heat treated at 178°C for 5 min was 7.72 MPa, a 22% increase from that before heating, and a 54% increase compared to the as‐spun homogenous PVDF‐HFP. Thus, the proposed technique of combining heat treatment with coaxial morphologies demonstrates significant potential for improving mechanical strength without dimensional shrinkage.

Study some specifications of copolymer (PLA-PEG)

This study about the blends of Poly Lactic Acid/ Poly Ethylene Glycol (PLA/PEG) 4000 copolymer at concentrations (9%,6%,3%,0%)) wt%) from (PEG) and (PLA) (5%) (w/w) by using casting solvent method to production films. The nonwoven nano fibrous mats were obtained by electro spinning of (PLA/PEG) solutions in chloroform, at weight ratios (70/30) (v/v), respectively. DSC is employed to measure the crystallinity difference between (PLA/PEG) blends and their nonwovens mats. the thermal properties (DSC) of (PLA/PEG) copolymer blends films and electrospun nano fiber mats such as (Tm) melting temperature, (Tg) glass transition temperature, (Tc) crystallization, Xc crystallinity rate and enthalpy . the FTIR test was done for all samples to figure the nature linking between (PLA) and (PEG),the results were that (6%) (w/w) of (PEG) was the optimized rate to apply Electrospinning method , data of DSC test defined that (Tg) and (Tm) were decreased, and that refer to occurrence physicist cross linking between the used substances (Completely miscible blend) when the electrospinning method was applied, also Xc for these nonwoven mats was decreased which has in turn an important effect on the speed of biodegradble for poly lactic acid (PLA).

How Nanofibers Carry the Load: Toward a Universal and Reliable Approach for Tensile Testing of Polymeric Nanofibrous Membranes

AbstractNanofibrous nonwovens show high versatility and outstanding properties, with reduced weight. Porous morphology, high material flexibility and deformability challenge their mechanical testing, severely affecting results reliability. Still today, a specific technical standard method to carry out tensile testing of nonwoven nanofibrous mats is lacking, as well as studies concerning tensile test data reliability. In this work, an accurate, systematic, and critical study is presented concerning tensile testing of nonwovens, using electrospun Nylon 66 random nanofibrous mats as a case study. Nanofibers diameter and specimen geometry are investigated to thoroughly describe the nanomat tensile behavior, also considering the polymer thermal properties, and the nanofibers crossings number as a function of the nanofibers diameter. Below a threshold value, which lies between 150 and 250 nm, the overall mat mechanical behavior changes from ductile to brittle, showing enhanced elastic modulus for a high number of nanofibers crossings. While specimen geometry does not affect tensile results. Stress–strain data are analyzed using a phenomenological data fitting model to better interpret the tensile behavior. The experimental results demonstrate the high reliability of the proposed mass‐based load normalization, providing a simple, effective, and universally suitable method for obtaining high reproducible tensile stress–strain curves.

Effect of alkyl derivatization of gellan gum during the fabrication of electrospun membranes

Electrospun nanofibers based on polysaccharides represent a consolidated approach in Tissue Engineering and Regenerative Medicine (TERM) and nanomedicine as a drug delivery system (DDS). In this work, two chemical derivatives of a low molecular weight gellan gum (96.7 kDa) with aliphatic pendant tails were processed by electrospinning technique into non-woven nanofibrous mats. In order to generate spinnable blends, it was necessary to associate poly vinyl alcohol (PVA). The relationships between the physicochemical properties and the processability via electrospinning technique of gellan gum alkyl derivatives (GG-C8 and GG-C12 having a degree of alkyl chain derivatization of 17 mol % and 18 mol %, respectively) were investigated. The deposition of nanometric fibers (212.4 nm ± 60.0) was achieved by using the blend GG-C8/PVA spinned at 5% w/v in water. The use of a binary solvent composed of water and ethanol in a volumetric ratio 95:5 improved further spinnability obtaining similar nanofiber diameters (218.0 nm ± 96.0). The rheological analysis has allowed to highlight the role of the alkyl portion (C8 and C12) on the spinnability of the blended polymers.

PVA/CA based electrospun nanofibers: Influence of processing parameters in the fiber diameter

Recently, the electrospinning technique has been explored as a natural and synthetic polymer processing tool due to its versatility and potential to generate complex structures at a nanoscale. In this work, non-woven nanofibrous mats were electrospun, with a structure resembling the extracellular matrix, for prospective biomedical uses. Poly (vinyl alcohol) (PVA) and cellulose acetate (CA) based electrospun nanofibrous meshes were prepared at different ratios 100/0, 90/10, 80/20 and 70/30 and characterized in terms of fiber diameter. The process was kept as green as possible by resorting to a combination of acetic acid and distilled water as solvents. Optimal conditions for PVA/CA processing were established at 29 kV, feeding rate of 0.8 mL/h and distance between needle and collector of 17 cm. These allowed for the most uniform fibers with the smallest diameters to be produced.

Fast dissolving moxifloxacin hydrochloride antibiotic drug from electrospun Eudragit L-100 nonwoven nanofibrous Mats

Antimicrobial electrospun nonwoven Eudragit L-100 nanofibrous mats containing Moxifloxacin hydrochloride (MOX-HCL) were fabricated for fast dissolving drug delivery systems (DDSs) associated with wound infection. The morphological characterization of nanofibers using ESEM revealed that the average diameter of non-woven nanofibrous mats ranges 200‐600 nm. The nanofiber showed cylindrical shape with crack on the surface. Differential scanning calorimetric (DSC) and Wide Angle X-ray diffraction (WAXRD) demonstrate that the drug exists in an amorphous state in the nanofibers. Nanofibrous mats were also tested for mechanical strength, contact angle, swelling assay, haemolysis and disintegration test. In vitro disintegration tests demonstrated that the dissolution of Eudragit L-100 fiber mats was within 25 s which was higher compared to the pure drug. The Eudragit nanofibers showed pH-dependent drug release profiles, with slow release at pH 1.2 and burst release (around 30 s) at pH 6.8. The in-vitro quantitative and qualitative antimicrobial assay showed that the developed Eudragit L-100 nanofibrous mats with MOX-HCL concentration of 1%, 5% and 15 wt% exhibited antibacterial activities against both gram positive (Staphylococcus aureus) and gram negative (Escherichia coli) bacteria. The in-vitro cytotoxicity assay using mouse fibroblast NIH/3T3 cells demonstrated significant biocompatibility of nanofiber mats. As per the results of biological evaluation, Eudragit L-100 nanofibrous mats with 1wt% MOX-HCL could be a suitable substrate for biomedical applications. Eudragit L-100 nanofibrous mats containing Moxifloxacin hydrochloride (MOX-HCL) showed immediate DDSs for localized drug release in the wound infection at slightly acidic or alkaline conditions where faster drug release rate is required for wound healing.

Physico- and bio-activities of nanoscale regenerated cellulose nonwoven immobilized with lysozyme

Lysozyme-cellulose conjugates are of wide interest for food packaging, tissue scaffolding, wound healing, and antimicrobial applications. Here a recycled cotton-based source of regenerated cellulose in combination with carboxylated carbon nanotubes and graphene oxide was configured as nonwoven nanofibrous mats through electrospinning and utilized to immobilize lysozyme. Scanning electron microscopy, Fourier transform-infrared spectra, thermal-gravimetric analysis, tensile test, and antibacterial assessments were conducted to characterize and determine physical and bioactive properties of the nonwoven nanofibrous mats. The resulted cellulose-lysozyme conjugates were found to have robust bioactivity with no indication of cell cytotoxicity. The study confirmed that the carbon-nanoparticle-modified cellulose nonwoven mats revealed a high antimicrobial activity after immobilization of lysozyme.

Aqueous electrospinning of poly(2-ethyl-2-oxazoline): Mapping the parameter space

Recently, poly(2-oxazoline)s have regained significant interest and research has especially been focusing on biomedical applications. As non-woven nanofibrous mats show appealing features in this respect, the potential and limitations of electrospinning aqueous solutions of poly(2-ethyl-2-oxazoline) (PEtOx), the only poly(2-oxazoline) produced on industrial scale (i.e. Aquazol®) so far, was evaluated. The polymer molecular weight appeared to be the dominant factor defining the optimal concentration range for successful nanofiber production. The molar mass distribution, i.e. the dispersity (Ð), is relevant as well. However, it is not a limiting factor as defined PEtOx (Ð<1.2) could be electrospun without major adaptations to the electrospinning procedure that was optimized for the commercial grades of Aquazol® with Ð of 3–4. By varying the PEtOx molecular weight and concentration, a broad range of fiber diameters can be targeted. Furthermore, we demonstrated the transferability of the PEtOx electrospinning parameters and the reproducibility of the resulting fiber diameters by repeating the experiments on an independent mononozzle electrospinning device, by a different operator. In order to fulfil all prerequisites for industrialization, we also demonstrated the feasibility for upscaling the PEtOx nanofiber production process using a pilot scale multinozzle electrospinning set-up.

Optimized Nanostructured TiO2 Photocatalysts

Titania is the most widely studied photocatalyst. In it’s mixed-phase configuration (anatase-rutile form) -as manifested in the commercially available P25 Degussa material- titania was previously found to exhibit the best photocatalytic properties reported for the pure system. A great deal of published research by various workers in the field have not fully explained the underlying mechanism for the observed behavior of mixed-phase titania photocatalysts. One of the prevalent hypothesis in the literature that is tested in this work involves the presence of small, active clusters of interwoven anatase and rutile crystallites or “catalytic “hot-spots””. Therefore, non-woven nanofibrous mats of titania were produced and upon calcination the mats consisted of nanostructured fibers with different anatase-rutile ratios. By assessing the photocatalytic and photoelectrochemical properties of these samples the optimized photocatalyst was determined. This consisted of TiO2 nanostructures annealed at 500˚C with an anatase /rutile content of 90/10. Since the performance of this material exceeded that of P25 complete structural characterization was employed to understand the catalytic mechanism involved. It was determined that the dominant factors controlling the photocatalytic behavior of the titania system are the relative particle size of the different phases of titania and the growth of rutile laths on anatase grains which allow for rapid electron transfer between the two phases. This explains how to optimize the response of the pure system.

Immobilization of trypsin onto poly(ethylene terephthalate)/poly(lactic acid) nonwoven nanofiber mats

Mixed solutions of poly(ethylene terephthalate) (PET) and three types of poly(lactic acid) (PLA; a commercial sample and two branched PLAs) were used to prepare nonwoven nanofibrous mats by electrospinning. These mats were used as supports for trypsin immobilization, with the aim of an application in whey protein hydrolysis. Covalent attachment of crosslinked trypsin aggregates to amine-derivatized PET/PLA mats, followed by reduction with sodium cyanoborohydride, gave the best immobilized trypsin activity and showed no enzyme leaching. The activity of immobilized trypsin was higher than that of free trypsin at pH 6, a pH value representative of sweet whey. The PET/PLA mats with immobilized trypsin could be stored at 4°C in water for at least 30 days, and could be reused 8 times without loosing activity and without enzyme leaching.

Immobilized Furanone Derivatives as Inhibitors for Adhesion of Bacteria on Modified Poly(styrene-co-maleic anhydride)

The ability of brominated furanones and other furanone compounds with 2(3H) and 2(5H) cores to inhibit bacterial adhesion of surfaces as well deactivate (destroy) them has been previously reported. The furanone derivatives 4-(2-(2-aminoethoxy)-2,5-dimethyl-3(2H)-furanone and 5-(2-(2-aminoethoxy)-ethoxy)methyl)-2(5H)-furanone were synthesized in our laboratory. These furanone derivatives were then covalently immobilized onto poly(styrene-co-maleic anhydride) (SMA) and electrospun to fabricate nonwoven nanofibrous mats with antimicrobial and cell-adhesion inhibition properties. The electrospun nanofibrous mats were tested for their ability to inhibit cell attachment by strains of bacteria commonly found in water ( Klebsiella pneumoniae Xen 39, Staphylococcus aureus Xen 36, Escherichia coli Xen 14, Pseudomonas aeruginosa Xen 5, and Salmonella tymphimurium Xen 26). Proton nuclear magnetic resonance spectroscopy ((1)H NMR), electrospray mass spectroscopy (ES-MS), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used to confirm the structures of the synthesized furanones as well as their successful immobilization on SMA. To ascertain that the immobilized furanone compounds do not leach into filtered water, samples of water, filtered through the nanofibrous mats were analyzed using gas chromatography coupled with mass spectroscopy (GC-MS). The morphology of the electrospun nanofibers was characterized using scanning electron microscopy (SEM).

Electrospun chitosan–gelatin nanofiberous scaffold: Fabrication and in vitro evaluation

In this study, chitosan and gelatin solutions were blended at five different ratios. Samples were fed into electrospinning apparatus to produce non-woven nanofibrous mats. Scanning electron microscopy (SEM) showed that the low-viscosity sample with 30% chitosan and 70% gelatin (sample 30/70) formed the least amount of beads and droplets and yielded fibers with the highest morphological uniformity. To examine the effect of processing parameters on fibers morphology and nanofibers diameter, flow rate, voltage and distance between needle to the collector were changed in the sample 30/70. SEM revealed that high voltages (25 kV) and flow rates (1.5 ml·h⁻¹) decrease the uniformity of fibers and lead to bead and droplet formation. It has also shown that the distance between the tip and the collector have no significant effect on fibers' structure. The values of 15 kV (voltage), 0.2 ml·h⁻¹ (flow rate) and the fixed distance of 15 cm were identified as the optimal electrospinning conditions, which produce fibers with a mean diameter of 180±20 nm. Fourier transform infrared (FTIR) experiment revealed an increase in N-H bending and decrease in C-O stretching vibration in both chitosan and gelatin at 1060 and 1148 cm⁻¹. The in vitro biocompatibility tests performed with human skin fibroblasts showed excellent cell proliferation (MTT assay) and attachment (SEM) on these scaffolds confirming its highly acceptable biological properties.

Preparation of the chitosan containing nanofibers by electrospinning chitosan–gelatin complexes

AbstractElectrospinning is an interesting technique, which provides a facile and an effective mean in producing nonwoven fibrous materials; however, for producing nanofibers, investigation of the electrospinning conditions is very important. In this study, chitosan, gelatin, and their polyelectrolyte complexes (PECs) were electrospun to prepare nonwoven nanofibrous mats. The concentrations of chitosan and gelatin solutions and electric field (kV/cm) were optimized. The solutions were then blended in different ratios (0–100%) to get electrospun nanofibrous mats. Solution concentration and electric field showed pronounced effect on the electrospinnability and fiber diameter of these systems. Mostly large beads coexisted with the fibers were observed for chitosan at 1 wt% solution concentration, which then showed good electrospinnability at 2 wt% (nanofiber diameter was 145 and 122 nm at 15 and 20 kV/10 cm, respectively), whereas gelatin showed no electrospinnability below 15 wt% solution concentration and a homogenous fibers network at 15 wt% (149 nm at 20 kV/10 cm). The morphology and diameter of chitosan–gelatin PEC nanofibers varied with the chitosan/gelatin ratio. The crystallinity of chitosan was also observed to reduce with electrospinning and addition of gelatin. POLYM. ENG. SCI. 50:1887–1893, 2010. © 2010 Society of Plastics Engineers