Name: solution blow spinning of polymeric nano-composite fibers for personal protective equipment
Uploaded: 2021-03-18T15:00:00.000+00:00
Duration: 7 min 8 s
Description: Watch this Scientific Journal Video about Solution Blow Spinning of Polymeric Nano-Composite Fibers for Personal Protective Equipment at JoVE.com

The authors would like to acknowledge Mr. Dwight D. Barry for his important contributions for fabrication of the solution blow spinning apparatus. Zois Tsinas and Ran Tao would like to acknowledge funding from the National Institute of Standards and Technology under Awards # 70NANB20H007 and # 70NANB15H112, respectively.

NOTE: Details related to the equipment, instrumentation, and chemicals used in this section can be found in the Table of Materials. This entire protocol should first be reviewed and approved by the institutional safety department/personnel to ensure procedures and processes specific to the institution are adhered to.
1. Preparation of polymer solution using the appropriate solvent
NOTE: Consult manufacturer/supplier safety data sheets and the institution&#39;s safety department/personnel regarding proper personal protective equipment (PPE) to use with each chemical/material.
<ol>
	<li>Use a clean small laboratory spatula, and transfer the desired amount (e.g., ~2 g) of dry polymer (poly(styrene-butadiene-styrene)) into a clean, empty, 20 mL borosilicate glass vial. Seal the vial, and store under ambient laboratory conditions. 
	NOTE: The selected concentration for poly(styrene-butadiene-styrene) in tetrahydrofuran (THF) was approximately 200 mg/mL. This concentration is used as an example throughout this protocol; the optimal concentration will depend on the polymer/solvent system used.</li>
	<li>Transfer the borosilicate glass vial containing the polymer sample into a chemical fume hood, and pipette 10 mL &#177; 0.1 mL of the desired solvent, in this case THF, into the vial to achieve the desired concentration of nominally 200 mg/mL.</li>
	<li>Seal the solvent (THF) container, and transfer it to the storage cabinet. Cap the borosilicate glass vial containing the polymer/solvent sample with the provided lid, and carefully mount it on a mixer/rotator.</li>
	<li>Agitate the mixture at room temperature using a rotator at 70 rpm until the polymer fully dissolves in the solvent. 
	NOTE: The solution appears clear and transparent after approximately 60 min, denoting complete polymer dissolution.</li>
	<li>Transfer the solution into a dissolved gas analysis (DGA) borosilicate glass syringe for SBS. 
	&#8203;NOTE: Polymer solutions can be stored and used for up to 72 h, provided that the borosilicate glass vial is securely capped, and the opening is wrapped using a paraffin wax film. However, the solutions must be agitated again before performing SBS.</li>
</ol>
2. Determination of critical overlap polymer concentration by viscosity measurement
NOTE: This step is provided here to determine the critical overlap polymer concentration, which is an important parameter that affects the overall fiber quality and morphology after SBS. See the representative results and discussion sections for details.
<ol>
	<li>Prepare eight nominal concentrations (1 mg/mL, 3 mg/mL, 5 mg/mL, 10 mg/mL, 20 mg/mL, 30 mg/mL, 40 mg/mL, 50 mg/mL) of the polymer solution in THF with an approximate volume of 10 mL. Follow the same procedure as in steps 1.1 and 1.2 to prepare the solutions.</li>
	<li>Prepare the rheometer for measurements. 
	&#8203;NOTE: Routine calibration and verification checks for torque, normal force, and phase angle should be performed on the rheometer prior to the following setup procedure.
	<ol>
		<li>Install the environmental control device on the rheometer for temperature control.</li>
		<li>Install the rheometer geometry, i.e., recessed concentric cylinders on the rheometer. First, insert and install the lower geometry (cup) into the environmental control device and then the upper geometry (bob) on the transducer shaft.</li>
		<li>Tare normal force and torque using the instrument touch screen. Zero the geometry gap using the gap control function of the rheometer software. Raise the stage to provide enough space for sample loading.</li>
	</ol>
	</li>
	<li>Load the polymer solution into the cup using a high-quality, disposable borosilicate glass pipette (minimum sample volume for the geometry ~7 mL). Set the gap to the operating gap (3.6 mm) for the measurement.</li>
	<li>Perform a shear rate sweep test from about 10 s-1 to 100 s-1 at approximately 25 &#176;C. Enable the steady-state sensing function in the rheometer software.</li>
	<li>Export the results table, and calculate the average value of the steady-shear viscosities.</li>
	<li>Plot the averaged viscosity values as a function of polymer concentration.</li>
</ol>
3. Preparation of the polymer solution/nanoparticle dispersion
NOTE: To prepare a polymer solution with added nanoparticles (NPs), work inside a nano-enclosure (high-efficiency-particulate-air-filtered) hood.
<ol>
	<li>Use a clean, small laboratory spatula, and weigh the required amount (e.g., ~0.01 g) of dry NP powder, e.g., iron oxide (Fe3O4) NPs, into a clean 20 mL borosilicate glass vial.</li>
	<li>Add the desired volume (e.g., nominally 10 mL) of solvent (e.g., THF) using a disposable borosilicate glass pipette, and cap the borosilicate glass vial containing the NPs/solvent mixture using the provided lid.</li>
	<li>Transfer the sample to a vortex mixer, and agitate thoroughly at room temperature at 3,000 rpm until the NPs are no longer visible at the bottom of the vial. Immediately transfer the vial with the sample to a bath sonicator to ensure full dispersion of the nanoparticles. To prevent sample from heating, sonicate the dispersion in ~30 min intervals, waiting for 2-5 min between each sonication step.</li>
	<li>Next, working inside a chemical hood, weigh and add the desired amount (e.g., ~2 g) of polymer (e.g., styrene-butadiene-styrene block-co-polymer) into the NP dispersion. Seal the borosilicate glass vial with the provided lid, and mount it securely on a rotator for mixing at 70 rpm at room temperature.</li>
	<li>Mix the polymer/NPs/solvent sample thoroughly for approximately 60 min, or until the polymer is fully dissolved. 
	NOTE: After mixing, the sample appears as a viscous liquid with uniformly dispersed NPs, and no large aggregates or precipitates are visible.</li>
	<li>Finally, transfer the mixture into a DGA borosilicate glass syringe for SBS. 
	&#8203;NOTE: It is not recommended to store the polymer NP solutions prior to SBS due to potential agglomeration or destabilization of the dispersion.</li>
</ol>
4. Solution blow spinning process (SBS)
NOTE: Suggested PPE for this process includes protective goggles, laboratory coat, and nitrile gloves; these should be donned before setting up the SBS apparatus. The setup and process should be performed inside a chemical hood. The SBS apparatus consists of a commercial airbrush unit equipped with a 0.3 mm inner nozzle (for the polymer solution) and a 1 mm head opening (for the gas), a syringe pump system, a collector, a pressurized nitrogen (N2) gas cylinder, and an aluminum enclosure. The inner nozzle protrudes approximately 0.5 mm from the head opening of the airbrush. Details on the SBS setup are given in Figure 1.
<ol>
	<li>First, adjust the height and angle of the airbrush to align with the center of the selected substrate (glass microscope slide) attached to the collector, and secure it in place. Make sure the gas cylinder is properly secured to its wall mount. Then, connect the gas inlet of the airbrush to the N2 pressurized gas cylinder.</li>
	<li>Turn on the main valve on the gas cylinder, and slowly adjust the pressure using the attacjed gas regulator valve while monitoring the pressure gauge to achieve the desired flow. Ensure there is free unobstructed flow through the system, and listen carefully for any potential gas leaks at the connection points. Use a soap and water solution to further investigate potential leaks, and if necessary, apply polytetrafluoroethylene (PTFE) tape to the fittings to eliminate any leaks. When the gas flow is adjusted properly, close the main valve on the gas cylinder to stop the gas flow.</li>
	<li>Secure the substrate on the collector using the equipped vice. Adjust the height of the collector to align perpendicular to the spray direction and pattern of the airbrush so that material will be deposited onto the substrate.</li>
	<li>Next, slide the collector to its furthest position away from the airbrush nozzle to help with identifying the optimal working distance (separation between nozzle and substrate) in the following steps.</li>
	<li>Working inside the chemical hood, carefully transfer the prepared polymer/NPs/solvent mixture from the borosilicate glass vial to a 10 mL DGA borosilicate glass syringe equipped with a stainless-steel needle.</li>
	<li>Remove any air bubbles from the sample by holding the syringe with the needle pointing up, tapping the syringe gently and slowly depressing the plunger to displace any excess air. Detach the needle, and attach the syringe to the syringe-pump unit. Secure the syringe, and connect the PTFE tubing coming from the outlet of the syringe to the appropriate inlet on the airbrush.</li>
	<li>Next, select the desired injection rate from the syringe-pump unit menu (e.g., 0.5 mL/min), and slowly open the main valve on the N2 gas cylinder to allow N2 to flow through the airbrush. Immediately start the syringe-pump unit to dispense the polymer/NPs/solvent mixture, and initiate the spraying process.</li>
	<li>Carefully observe the spraying pattern at the spray nozzle, and ensure that no clogs or partial clogs are present. Incrementally increase or decrease the injection rate until the solution is spraying freely. 
	NOTE: Very low or high injection rates are prone to clogging. The optimal injection rate is a function of the solution&#39;s viscosity and may need to be adjusted for high or low polymer solution&#39;s concentrations.</li>
	<li>Next, adjust the position of the collector to the desired working distance for the polymer/solvent system used to allow solvent evaporation by sliding it towards the airbrush until material is deposited on the substrate. 
	&#8203;NOTE: If the collector is too close to the airbrush spray nozzle, insufficient evaporation time will result in depositing liquid polymer solution onto the substrate. If the collector is too far away, very limited or no material will be deposited onto the substrate. For poly(styrene-butadiene-styrene) solutions in THF, the appropriate working distance is between 8 cm and 12 cm.</li>
	<li>When the desired amount of material is deposited on the substrate, stop the syringe-pump unit first, and then immediately close the main valve on the N2 gas cylinder.</li>
</ol>
5. Analysis of SBS fiber mats by SEM
<ol>
	<li>Use a sputter coater to coat the fiber mats with a conductive material such as Au/Pd to mitigate surface charging effects under the electron beam. 
	NOTE: A coating thickness of 4-5 nm will suffice.</li>
	<li>Load the fiber mat samples into an SEM, and image them using an accelerating voltage of 2-5 kV and a current of 0.1-0.2 nA. Apply charge neutralization settings to counter charging effects where necessary.</li>
	<li>Use a secondary electron detector, or a backscattered electron detector, to capture different features of the fiber materials.</li>
	<li>Use an energy-dispersive (EDS) detector to separate the characteristic X-rays of different elements into an energy spectrum that will allow determination of the presence of iron (Fe), indicative of iron oxide NPs embedded within the polymeric fiber mats.</li>
</ol>

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The full description of the procedures used in this paper requires the identification of certain commercial products and their suppliers. The inclusion of such information should in no way be construed as indicating that such products or suppliers are endorsed by NIST or are recommended by NIST or that they are necessarily the best materials, instruments, software or suppliers for the purposes described.

The method described herein provides a protocol for producing polymer elastomer nanocomposite fiber mats via a relatively new technique known as solution blow spinning. This technique allows the fabrication of fibers in the nanoscale and has several advantages over other well-established techniques, such as the electrospinning process, as it can be carried out under atmospheric pressure and room temperature27. Furthermore, SBS is not highly susceptible to local environmental changes (temperature o...

Many light-weight, ballistic, protective armor systems are currently constructed using high-modulus and high-strength polymeric fibers, such as oriented, ultra-high molar mass polyethylene fibers or aramids, which provide outstanding ballistic resistance1,2. These fibers are used in combination with an elastic resin material (binder) that can penetrate to the filament level and secure the fibers in a 0&#176;/90&#176; configuration to form a non-woven, unidirectional laminate. The percentage of the polymer elastomer resin (binder) should not exceed 13% of the total weight of the unidirectional laminate to maintain the structural integrity and antiballistic properties of the laminate structure3,4. The binder is a very important component of the armor as it keeps the high-strength fibers properly oriented and tightly packed within each laminate layer3. Elastomer materials commonly used as binders in body armor applications have very low tensile modulus (e.g., ~17.2 MPa at ~23 &#176;C), low glass transition temperature (preferably below -50 &#176;C), very high elongation at break (as high as 300%) and must demonstrate excellent adhesive properties5.
To improve the performance of these polymer elastomers, SBS was performed to create fibrous elastomer materials that can be used as binders in body armor applications. SBS is a relatively new, versatile technique allowing the use of different polymer/solvent systems and the creation of different end products6,7,8,9,10,11,12,13. This simple process involves the rapid (10x the rate of electrospinning) deposition of conformal fibers onto both planar and nonplanar substrates to fabricate sheets or webs of fibers that encompass&#160;nano and micro length scales14,15,16,17,18. SBS materials have numerous applications in medical products, air filters, protective equipment, sensors, optical electronics, and catalysts14,19,20. Developing small diameter fibers can drastically increase the surface area to volume ratio, which is very important for several applications, especially in the personal protective equipment field. The diameter and morphology of the fibers generated by SBS depend&#160;on the molar mass of the polymer, polymer concentration in the solution, viscosity of the solution, polymer solution flow rate, gas pressure, working distance, and diameter of the spray nozzle14,15,17.
An important characteristic of the SBS apparatus is the spray nozzle consisting of an inner and a concentric outer nozzle. The polymer dissolved in a volatile solvent is pumped through the inner nozzle while a pressurized gas flows through the outer nozzle. The high-velocity gas exiting the outer nozzle induces shearing of the polymer solution flowing through the inner nozzle. This forces the solution to form a conical shape when exiting the spray nozzle. When the surface tension at the tip of the cone is overcome, a fine stream of polymer solution is ejected, and the solvent rapidly evaporates causing polymer strands to coalesce and deposit as polymer fibers. The formation of a fibrous structure, as solvent evaporates, strongly depends on the polymer molar mass and the solution concentration. Fibers are formed by chain entanglement, when polymer chains in solution begin to overlap at a concentration known as the critical overlap concentration (c*). Therefore, it is necessary to work with polymer solutions above the c* of the polymer/solvent system selected. Also, an easy strategy to attain this is to choose polymers with relatively high molar mass. Polymers with higher molar mass have increased polymer relaxation times, which is directly related to an increase in the formation of fibrous structures, as described in the literature21. As many of the parameters used in SBS are strongly correlated, the goal of this work is to provide guidance to develop tunable, and flexible polymeric fiber nanocomposites to be used as alternatives for typical binder materials found in body armor applications by incorporating nanoparticles in the fibrous polymer-elastomer matrix.

<table><tbody><tr><td>45 MM Toolmaker Vise</td><td>Tormach Inc.</td><td>32547</td><td>To secure substrate onto the collector</td></tr><tr><td>ARES-G2 Rheometer</td><td>TA Instruments</td><td>401000.501</td><td>Rheometer</td></tr><tr><td>Branson Ultrasonics M Series - Ultrasonic Cleaning Bath</td><td>Fisher Scientific</td><td>15-336-100</td><td>To disperse nanoparticles</td></tr><tr><td>Cadence Science&amp;nbsp;Micro-Mate Interchangeable Syringe</td><td>Fisher Scientific</td><td>14-825-2A</td><td>Glass Syringe 5mL in 1/5mL, Luer Lock Tip</td></tr><tr><td>Chemical hood</td><td>Any company</td><td></td><td></td></tr><tr><td>Corning - Disposable Pasteur Glass Pipette</td><td>Sigma Aldrich</td><td>CLS7095D5X-200EA</td><td>Non-Sterile</td></tr><tr><td>DWK Life Sciences&amp;nbsp;Wheaton - Glass Scintillation Vial</td><td>Fisher Scientific</td><td>03-341-25G</td><td>20 mL with cap</td></tr><tr><td>FEI Quanta 200 Scanning Electron Microscope (SEM)</td><td>FEI</td><td></td><td>For imaging samples</td></tr><tr><td>Iron Oxide Nanopowder/Nanoparticles</td><td>US Research Nanomaterials, inc.</td><td>US3320</td><td>Fe3O4, 98%, 20-3- nm, Silicon oil Coated</td></tr><tr><td>KD Scientific Legato 100 Single-Syringe Pump</td><td>Sigma Aldrich</td><td>Z401358-1EA</td><td>Single syringe infusion pump</td></tr><tr><td>Master Airbrush - Model S68</td><td>TCP Global</td><td>MAS S68</td><td>Nozzle/needle diameter: 0.35 mm</td></tr><tr><td>Mettler Toledo AB265-S/FACT Scale</td><td>Cole-Parmer Scientific</td><td>EW-11333-14</td><td>For weighing polymer and&amp;nbsp; Nanoparticles</td></tr><tr><td>N2 Gas Regulator</td><td>Any company</td><td></td><td></td></tr><tr><td>Nanoenclosure</td><td>Any company</td><td></td><td></td></tr><tr><td>Optical Microscopy Glass Slides</td><td>Fisher Scientific</td><td>12-550-A3</td><td>Used as a substrate for fiber mat deposition</td></tr><tr><td>OSP Slotted Bob, 33 mm</td><td>TA Instruments</td><td>402796.902</td><td>Bob, upper geometry</td></tr><tr><td>OSP Slotted Double Gap Cup, 34 mm</td><td>TA Instruments</td><td>402782.901</td><td>Double wall cup, lower geometry</td></tr><tr><td>Oxford BenchMate Digital Vortex Mixer</td><td>Pipette</td><td>VM-D</td><td>Rated up to 4,200 rpm, for mixing solutions</td></tr><tr><td>Oxford Benchmate Tube Roller</td><td>Pipette</td><td>OTR-24DR</td><td>Sample mixer/rotator</td></tr><tr><td>Polystyrene-block-polybutadiene-block-polystyrene</td><td>Sigma Aldrich</td><td>432490-1KG</td><td>styrene 30 wt. %, Mw ~ 185,000 g/mol</td></tr><tr><td>SEM Pin Stub Specimen Mount</td><td>Ted Pella Inc.</td><td>16119</td><td>18 mm diameter x 8 mm height</td></tr><tr><td>Spatula</td><td>VWR</td><td>82027-532</td><td>To load test materials</td></tr><tr><td>Tetrahydrofuran (THF)</td><td>Fisher Scientific</td><td>T425-1</td><td>solvent, HPLC grade</td></tr><tr><td>TRIOS</td><td>TA Instruments</td><td>v4.3.1.39215</td><td>Rheometer software</td></tr></tbody></table>

solution blow spinning of polymeric nano-composite fibers for personal protective equipment

Light-weight, protective armor systems typically consist of high modulus (&#62;109 MPa) and high-strength polymeric fibers held in place with an elastic resin material (binder) to form a non-woven, unidirectional laminate. While significant efforts have focused on improving the mechanical properties of the high-strength fibers, little work has been undertaken to improve the properties of the binder materials. To improve the performance of these elastomeric polymer binders, a relatively new and simple fabrication process, known as solution blow spinning, was used. This technique is capable of producing sheets or webs of fibers with average diameters ranging from the nanoscale to the microscale. To achieve this, a solution blow spinning (SBS) apparatus has been designed and built in the laboratory to fabricate non-woven fiber mats from polymer elastomer solutions.
In this study, a commonly used binder material, a styrene-butadiene-styrene block-co-polymer dissolved in tetrahydrofuran, was used to produce nanocomposite fiber mats by adding metallic nanoparticles (NPs), such as iron oxide NPs, that were encapsulated with silicon oil and thus incorporated in the fibers formed via the SBS process. The protocol described in this work will discuss the effects of the various critical parameters involved in the SBS process, including the polymer molar mass, the selection of the thermodynamically appropriate solvent, the polymer concentration in solution, and the carrier gas pressure to assist others in performing similar experiments, as well as provide guidance to optimize the configuration of the experimental setup. The structural integrity and morphology of the resultant non-woven fiber mats were examined using scanning electron microscopy (SEM) and elemental X-ray analysis via energy-dispersive X-ray spectroscopy (EDS). The goal of this study is to evaluate the effects of the various experimental parameters and material selections to optimize the structure and morphology of the SBS fiber mats.

In this study, non-woven fiber mats consisting of poly(styrene-butadiene-styrene) fibers in the nano- and micro-scale, were synthesized with and without the presence of iron oxide NPs. To form fibers, the SBS parameters must be carefully selected for the polymer/solvent system used. The molar mass of the dissolved polymer and the solution concentration are critical in controlling the morphology of the structures produced by the SBS process. In this study, a poly(styrene-butadiene-styrene) block-co-polymer (styrene 30 wt....

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Solution Blow Spinning of Polymeric Nano-Composite Fibers for Personal Protective Equipment

The primary goal of this study is to describe a protocol to prepare polymeric fiber mats with consistent morphology via solution blow spinning (SBS). We aim to use SBS to develop novel, tunable, flexible polymeric fiber nanocomposites for various applications, including protective materials, by incorporating nanoparticles in a polymer-elastomer matrix.

Light-weight, protective armor systems typically consist of high modulus (&#62;109 MPa) and high-strength polymeric fibers held in place with an elastic ...

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Research

JoVE Journal

Engineering

2.7K Views.  Material Measurement Laboratory, National Institute of Standards and Technology. Dit zelfprotocol omvat enkele van de belangrijkste parameters en stappen die betrokken zijn bij het blazen van oplossingen van polymere nanocomposietvezels, waaronder polymeer molaire massaselectie van thermodynamisch geschikte oplosmiddelen, polymere concentratie in oplossing, opname van nanomaterialen, dragergasdruk en werkafstand. SPS is een relatief nieuwe techniek die een grote veelzijdigheid biedt met betrekking tot het polymeer oplosmiddelsysteem en het eindproduct. Bovendien kan het w...

Video: Solution Blow Spinning of Polymeric Nano-Composite Fibers for Personal Protective Equipment

Microfluidic Fabrication of Polymeric and Biohybrid Fibers with Predesigned Size and Shape

A &#8220;sheath&#8221; fluid passing through a microfluidic channel at low Reynolds number can be directed around another &#8220;core&#8221; stream and used to dictate the shape as well as the diameter of a core stream.&#160;Grooves in the top and bottom of a microfluidic channel were designed to direct the sheath fluid and shape the core fluid.&#160;By matching the viscosity and hydrophilicity of the sheath and core fluids, the interfacial effects are minimized and complex fluid shapes can be formed.&#160;Controlling the relative flow rates of the sheath and core fluids determines the cross-sectional area of the core fluid.&#160;Fibers have been produced with sizes ranging from 300 nm to ~1 mm, and fiber cross-sections can be round, flat, square, or complex as in the case with double anchor fibers. Polymerization of the core fluid downstream from the shaping region solidifies the fibers.&#160;Photoinitiated click chemistries are well suited for rapid polymerization of the core fluid by irradiation with ultraviolet light.&#160;Fibers with a wide variety of shapes have been produced from a list of polymers including liquid crystals, poly(methylmethacrylate), thiol-ene and thiol-yne resins, polyethylene glycol, and hydrogel derivatives. Minimal shear during the shaping process and mild polymerization conditions also makes the fabrication process well suited for encapsulation of cells and other biological components.

Two adjacent fluids passing through a grooved microfluidic channel can be directed to form a sheath around a prepolymer core; thereby&#160;determining both shape and cross-section. Photoinitiated polymerization, such as thiol click chemistry, is well suited for rapidly solidifying the core fluid into a microfiber with predetermined size and shape.

A &#8220;sheath&#8221; fluid passing through a microfluidic channel at low Reynolds number can be directed around another &#8220;core&#8221; stream and ...

Bioengineering

Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity.
In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties.
In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

A protocol to expose bare fibers on the composite surface by eliminating resin rich area is presented. The fibers are exposed during fabrication of the composites, not by the post surface treatment. The exposed carbon composites exhibit high electrical conductivity in the through-thickness direction and high mechanical property.

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional ...

Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to diversify the fiber choices in the United States body armor market, copolymer fibers based on the combination of 5-amino-2-(p-aminophenyl) benzimidazole (PBIA) and the more conventional PPTA were introduced. Little is known regarding the long-term stability of these fibers, but as condensation polymers, they are expected to have potential sensitivity to moisture and humidity. Therefore, characterizing the strength of the materials and understanding their vulnerability to environmental conditions is important for evaluating their use lifetime in safety applications. Ballistic resistance and other critical structural properties of these fibers are predicated on their strength. To accurately determine the strength of the individual fibers, it is necessary to disentangle them from the yarn without introducing any damage. Three aramid-based copolymer fibers were selected for the study. The fibers were washed with acetone followed by methanol to remove an organic coating that held the individual fibers in each yarn bundle together. This coating makes it difficult to separate single fibers from the yarn bundle for mechanical testing without damaging the fibers and affecting their strength. After washing, fourier transform infrared (FTIR) spectroscopy was performed on both washed and unwashed samples and the results were compared. This experiment has shown that there are no significant variations in the spectra of poly(p-phenylene-benzimidazole-terephthalamide-co-p-phenylene terephthalamide) (PBIA-co-PPTA1) and PBIA-co-PPTA3 after washing, and only a small variation in intensity for PBIA. This indicates that the acetone and methanol rinses are not adversely affecting the fibers and causing chemical degradation. Additionally, single fiber tensile testing was performed on the washed fibers to characterize their initial tensile strength and strain to failure, and compare those to other reported values. Iterative procedural development was necessary to find a successful method for performing tensile testing on these fibers.

The primary goal of the study is to develop a protocol to prepare consistent specimens for accurate mechanical testing of high strength copolymer aramid fibers, by removing a coating and disentangling the individual fiber strands without introducing significant chemical or physical degradation.

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to ...

Chemistry

Electrospun Nanofiber Scaffolds with Gradations in Fiber Organization

The goal of this protocol is to report a simple method for generating nanofiber scaffolds with gradations in fiber organization and test their possible applications in controlling cell morphology/orientation. Nanofiber organization is controlled with a new fabrication apparatus that enables the gradual decrease of fiber organization in a scaffold. Changing the alignment of fibers is achieved through decreasing deposition time of random electrospun fibers on a uniaxially aligned fiber mat. By covering the collector with a moving barrier/mask, along the same axis as fiber deposition, the organizational structure is easily controlled. For tissue engineering purposes, adipose-derived stem cells can be seeded to these scaffolds. Stem cells undergo morphological changes as a result of their position on the varied organizational structure, and can potentially differentiate into different cell types depending on their locations. Additionally, the graded organization of fibers enhances the biomimicry of nanofiber scaffolds so they more closely resemble the natural orientations of collagen nanofibers at tendon-to-bone insertion site compared to traditional scaffolds. Through nanoencapsulation, the gradated fibers also afford the possibility to construct chemical gradients in fiber scaffolds, and thereby further strengthen their potential applications in fast screening of cell-materials interaction and interfacial tissue regeneration. This technique enables the production of continuous gradient scaffolds, but it also can potentially produce fibers in discrete steps by controlling the movement of the moving barrier/mask in a discrete fashion.

Here, we present a protocol to fabricate electrospun nanofiber scaffolds with gradated organization of fibers and explore their applications in regulating cell morphology/orientation. Gradients with regard to physical and chemical properties of the nanofiber scaffolds offer a wide variety of applications in the biomedical field.

The goal of this protocol is to report a simple method for generating nanofiber scaffolds with gradations in fiber organization and test their possible ...

Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial applications. Here we describe how electrospinning or electrospraying a polymer mixture containing a biodegradable, biocompatible aliphatic polyester (e.g., polycaprolactone and poly(lactide-co-glycolide)), as the major component, doped with a hydrophobic copolymer composed of the polyester and a stearate-modified poly(glycerol carbonate) affords a superhydrophobic biomaterial. The fabrication techniques of electrospinning or electrospraying provide the enhanced surface roughness and porosity on and within the fibers or the particles, respectively. The use of a low surface energy copolymer dopant that blends with the polyester and can be stably electrospun or electrosprayed affords these superhydrophobic materials. Important parameters such as fiber size, copolymer dopant composition and/or concentration, and their effects on wettability are discussed. This combination of polymer chemistry and process engineering affords a versatile approach to develop application-specific materials using scalable techniques, which are likely generalizable to a wider class of polymers for a variety of applications.

Two- and three-dimensional superhydrophobic polymeric materials are prepared by electrospinning or electrospraying biodegradable polymers blended with a lower surface energy polymer of similar composition.

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial ...

Synthesis of Keratin-based Nanofiber for Biomedical Engineering

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of these porous nanofibers is of great interest due to their unique physiochemical properties. Here we elaborate on the fabrication of keratin containing poly (&#949;-caprolactone) (PCL) nanofibers (i.e., PCL/keratin composite fiber). Water soluble keratin was first extracted from human hair and mixed with PCL in different ratios. The blended solution of PCL/keratin was transformed into nanofibrous membranes using a laboratory designed electrospinning set up. Fiber morphology and mechanical properties of the obtained nanofiber were observed and measured using scanning electron microscopy and tensile tester. Furthermore, degradability and chemical properties of the nanofiber were studied by FTIR. SEM images showed uniform surface morphology for PCL/keratin fibers of different compositions. These PCL/keratin fibers also showed excellent mechanical properties such as Young&#39;s modulus and failure point. Fibroblast cells were able to attach and proliferate thus proving good cell viability. Based on the characteristics discussed above, we can strongly argue that the blended nanofibers of natural and synthetic polymers can represent an excellent development of composite materials that can be used for different biomedical applications.

Electrospun nanofibers have a high surface area to weight ratio, excellent mechanical integrity, and support cell growth and proliferation. These nanofibers have a wide range of biomedical applications. Here we fabricate keratin/ PCL nanofibers, using the electrospinning technique, and characterize the fibers for possible applications in tissue engineering.

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of ...

Fabricating Degradable Thermoresponsive Hydrogels on Multiple Length Scales via Reactive Extrusion, Microfluidics, Self-assembly, and Electrospinning

While various smart materials have been explored for a variety of biomedical applications (e.g., drug delivery, tissue engineering, bioimaging, etc.), their ultimate clinical use has been hampered by the lack of biologically-relevant degradation observed for most smart materials. This is particularly true for temperature-responsive hydrogels, which are almost uniformly based on polymers that are functionally non-degradable (e.g., poly(N-isopropylacrylamide) (PNIPAM) or poly(oligoethylene glycol methacrylate) (POEGMA)). As such, to effectively translate the potential of thermoresponsive hydrogels to the challenges of remote-controlled or metabolism-regulated drug delivery, cell scaffolds with tunable cell-material interactions, theranostic materials with the potential for both imaging and drug delivery, and other such applications, a method is required to render the hydrogels (if not fully degradable) at least capable of renal clearance following the required lifetime of the material. To that end, this protocol describes the preparation of hydrolytically-degradable hydrazone-crosslinked hydrogels on multiple length scales based on the reaction between hydrazide and aldehyde-functionalized PNIPAM or POEGMA oligomers with molecular weights below the renal filtration limit. Specifically, methods to fabricate degradable thermoresponsive bulk hydrogels (using a double barrel syringe technique), hydrogel particles (on both the microscale through the use of a microfluidics platform facilitating simultaneous mixing and emulsification of the precursor polymers and the nanoscale through the use of a thermally-driven self-assembly and cross-linking method), and hydrogel nanofibers (using a reactive electrospinning strategy) are described. In each case, hydrogels with temperature-responsive properties similar to those achieved via conventional free radical cross-linking processes can be achieved, but the hydrazone cross-linked network can be degraded over time to re-form the oligomeric precursor polymers and enable clearance. As such, we anticipate these methods (which may be generically applied to any synthetic water-soluble polymer, not just smart materials) will enable easier translation of synthetic smart materials to clinical applications.

Protocols are described for the fabrication of degradable thermoresponsive hydrogels based on hydrazone cross-linking of polymeric oligomers on the bulk scale, microscale, and nanoscale, the latter for preparation of both gel nanoparticles and nanofibers.

While various smart materials have been explored for a variety of biomedical applications (e.g., drug delivery, tissue engineering, bioimaging, etc.), ...

Melt Electrospinning Writing of Three-dimensional Poly(&#949;-caprolactone) Scaffolds with Controllable Morphologies for Tissue Engineering Applications

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology with great potential for biomedical applications. The technique facilitates the direct deposition of biocompatible polymer fibers to fabricate well-ordered scaffolds in the sub-micron to micro scale range. The establishment of a stable, viscoelastic, polymer jet between a spinneret and a collector is achieved using an applied voltage and can be direct-written. A significant benefit of a typical porous scaffold is a high surface-to-volume ratio which provides increased effective adhesion sites for cell attachment and growth. Controlling the printing process by fine-tuning the system parameters enables high reproducibility in the quality of the printed scaffolds. It also provides a flexible manufacturing platform for users to tailor the morphological structures of the scaffolds to their specific requirements. For this purpose, we present a protocol to obtain different fiber diameters using melt electrospinning writing (MEW) with a guided amendment of the parameters, including flow rate, voltage and collection speed. Furthermore, we demonstrate how to optimize the jet, discuss often experienced technical challenges, explain troubleshooting techniques and showcase a wide range of printable scaffold architectures.

This protocol serves as a comprehensive guideline to fabricate scaffolds via electrospinning with polymer melts in a direct writing mode. We systematically outline the process and define the appropriate parameter settings for achieving targeted scaffold architectures.

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology ...

Fabrication and Characterization of Griffithsin-modified Fiber Scaffolds for Prevention of Sexually Transmitted Infections

Electrospun fibers (EFs) have been widely used in a variety of therapeutic applications; however, they have only recently been applied as a technology to prevent and treat sexually transmitted infections (STIs). Moreover, many EF technologies focus on encapsulating the active agent, relative to utilizing the surface to impart biofunctionality. Here we describe a method to fabricate and surface-modify poly(lactic-co-glycolic) acid (PLGA) electrospun fibers, with the potent antiviral lectin Griffithsin (GRFT). PLGA is an FDA-approved polymer that has been widely used in drug delivery due to its outstanding chemical and biocompatible properties. GRFT is a natural, potent, and safe lectin that possesses broad activity against numerous viruses including human immunodeficiency virus type 1 (HIV-1). When combined, GRFT-modified fibers have demonstrated potent inactivation of HIV-1 in vitro. This manuscript describes the methods to fabricate and characterize GRFT-modified EFs. First, PLGA is electrospun to create a fiber scaffold. Fibers are subsequently surface-modified with GRFT using 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS)chemistry. Scanning electron microscopy (SEM) was used to assess the size and morphology of surface-modified formulations. Additionally, a gp120 or hemagglutinin (HA)-based ELISA may be used to quantify the amount of GRFT conjugated to, as well as GRFT desorption from the fiber surface. This protocol can be more widely applied to fabricate fibers that are surface-modified with a variety of different proteins.

This manuscript describes the procedure to fabricate and characterize Griffithsin-modified poly(lactic-co-glycolic acid) electrospun fibers that demonstrate potent adhesive and antiviral activity against human immunodeficiency virus type 1 infection in vitro. Methods used to synthesize, surface-modify, and characterize the resulting morphology, conjugation, and desorption of Griffithsin from surface-modified fibers are described.

Electrospun fibers (EFs) have been widely used in a variety of therapeutic applications; however, they have only recently been applied as a technology to ...

Vapor Phase Deposition of Electroactive Poly(3,4-ethylenedioxythiophene) onto Electrospun Commodity Polymer Nanofibers

This study investigates the preparation of polyacrylonitrile (PAN) nanofibers through electrospinning to create highly porous and strong materials for applications in water purification, electrocatalysis, and biomedicine. The uniformly white PAN nanofiber mats were cut into 2 cm x 2 cm coupons to ensure consistency. After electrospinning, these nanofibers were coated with an electroactive polymer (EAP) using chemical vapor deposition, with iron (III) chloride (FeCl3) serving as an oxidant for polymerizing 3,4-ethylenedioxythiophene (EDOT) into poly(3,4-ethylenedioxythiophene) (PEDOT). The study examined the impact of different FeCl3 concentrations on PEDOT deposition on the PAN coupons. PEDOT deposition led to an increase in coupon weight. Scanning electron microscopy (SEM) revealed increases in the diameter of the nanofibers treated with increasing FeCl3 oxidant concentration, although higher FeCl3&#160;concentrations caused inter-fiber bridging, implying a concomitant decrease in inter-fiber spacing. Energy dispersive X-ray spectroscopy (EDS) was used to confirm the presence of Fe, Cl, and S in the nanofibers, with sulfur content rising with FeCl3&#160;concentration used, suggesting increased PEDOT deposition efficiency with increasing oxidant concentration. Mechanical testing showed that PEDOT-coated PAN fibers had improved tensile strength and toughness in the hydrated state compared to pure PAN nanofibers. These results highlight the crucial role of FeCl3&#160;concentration in influencing the morphology and properties of PAN-PEDOT composites, enhancing their suitability for applications such as water purification, tissue engineering, biosensing, catalysis, and energy storage.

This paper describes a simple technique for coating electrospun PAN nanofibers with electroactive polymers using vapor deposition. The effects of the oxidant FeCl&#8323; on the deposition of poly(3,4-ethylenedioxythiophene) coatings on PAN were investigated to understand and optimize polymer growth, fiber diameter, and overall mechanical strength of the nanofiber mats.

This study investigates the preparation of polyacrylonitrile (PAN) nanofibers through electrospinning to create highly porous and strong materials for ...

Solution Blow Spinning of Polymeric Nano-Composite Fibers for Personal Protective Equipment

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