Portable Electrospinning

A portable electrospinning setup will allow nanofibers to be applied in the field and thus bringing this technology closer to end-users. Suggested application for portable electrospinning setup includes wound care and anti-fog/anti-rain/anti-glare coating. The output of a portable electrospinning setup is similar to laboratory based setup in that a nonwoven mesh of nanofibers is deposited on the target site. There are a few advantages of a portable setup over off-the-shelf electrospun nanofiber mesh,

• Control of coverage area by nanofiber
• Control of nanofiber thickness
• Adhesive may not be necessary to secure the nanofiber on the site

Electrospun mesh have been widely investigated for use as a wound care dressing due to its high porosity and relatively small pore size that serve a dual purpose of allowing the wound to dry and keeping out bacteria and other contaminants. A field operable electrospinning device will give the medical personnel a quick way of covering the wound with a highly porous "dressing" [Mouthuy et al 2015]. The contours of the injured site will not hinder or limit the application of this nanofibrous dressing. Natural adhesion of the nanofibers to the skin surface will also prevent any bacteria or contaminants entering from the edges of this dressing. Demonstrating the potential of on-site electrospinning in closing wounds, Lv et al (2016) covered simulated open head wound with electrospun N-octyl-2-cyanoacrylate (NOCA), a commercial tissue adhesive (medical glue), fibers. The NOCA nanofibrous membrane covering the hole showed no fluid leakage. A wound area of 4-9 cm² can be covered by a layer of nanofibrous membrane with 20s of electrospinning. While the setup used in their experiment was not portable, a portable version of it can potentially be used out-field for managing wound. Revia (2019) tested the potential of using a portable electrospinning setup for direct-to-skin fiber deposition to improve aesthetics of hair loss. A mouse model with shaven hair was used to compare the performance of electrospun polyacrylonitrile (PAN) mixed with dye and commercial hair thickening powder (Toppik). In terms of concealing bald patch, the electrospun colored PAN fibers provided similar aesthetics effect as the commercial powder. When a paper towel was pressed against the treated patch, none of the colored PAN fibers was transferred to the paper towel but commercial hair powder was found on the paper towel. This showed that there is better retention of colored PAN fiber compared to the powder. Zhou et al (2020) tested the use of a portable electrospinning device for treating large intestine wounds with an opening of about 1 cm. Poly-ε-caprolactone (PCL) was used as the material for electrospinning due to its good strength and that its solvent, acetone, has been used in medical settings in the human body. This in vitro study was carried out using pig large intestines where a 1 cm slit was created and deionized water was used to simulate intestinal fluid. Direct electrospinning onto the wound for 10 s was compared with suture stitching. After 3 min of suspending the water filled intestines, liquid outflow was observed through the pinholes from suture stitching. However, where the wound is covered with electrospun fibers, no liquid was seen flowing out. This demonstrated the potential use of in situ electrospinning to close wounds on internal organs. Xu et al (2022) used a handheld electrospinning device for deposition of polyvinyl alcohol (PVA) fibers containing bone marrow-derived stem cells (BMSCs) onto full-thickness skin wounds. The PVA solution was prepared using phosphate-buffered saline (PBS) and 1?x?10⁷ BMSCs were added to the solution prior to electrospinning. Cell viability test using dead/live staining showed 90.15% survival rate immediately after electrospinning. In vivo tests using SD rats demonstrated significantly faster wound healing in the PVA/cell group compared to PVA only and untreated control. On day 14, the wound covered with the PVA/cell group was almost completely closed. The epidermis was completely covered by epithelial tissue with normal skin appendages found around the wound. Healing was slower in the PVA only group with the subcutaneous tissues thinner than the PVA/cell group. The group without any intervention were still in the granulation tissue repair state with many capillaries, fibroblasts and inflammatory cells. However, to realize the use of portable electrospinning device for these purposes, there are a few obvious restrictions and requirements. Safety of the device and the nanofiber needs to be addressed before it can be put to use. While most electrospun mesh for wound dressing is based on solvent-based polymers, this is obviously a hazard for direct application on the skin. One option is to use biocompatible and water-soluble polymer which does not readily dissolve when it comes into contact with water or fluid. Polyvinyl alcohol (PVA) is known to be soluble in water at elevated temperature but less so at lower temperature. PVA may also be reinforced with additives such as cellulose nanocrystals to improve its mechanical properties and improve its stability in high humidity condition [Peresin et al 2010]. Increasing interests in green electrospinning where water-based solutions are used for producing nanofibers may also lead to the development of materials which is suitable for this application [Agarwal and Greiner 2011]. Materials that dissolve in other non-toxic solvent may also be used. 70% alcohol (ethanol or isopropyl alcohol) are being used medically for topical application. Polymer that dissolves in this solvent mixture may also be considered for this application.

Early morning condensation on car windscreen.

Liu et al (2018) tested the feasibility of using a hand-held portable electrospinning apparatus, HHE-1 from Qingdao Junada Technology Co., Ltd for deposition of fibers on a wound. This simple electrospinning apparatus ejects the solution through a syringe manually by the user's thumb. A disk covering the solution exit presumably to direct the electrospinning jet. Liu et al (2018) used polymers, poly(vinyl pyrrolidone) (PVP) and poly(vinyl butyral) (PVB) as the polymer carrier with iodine and iodine complex as anti-bacterial agents for electrospinning onto wound. PVP and PVB were both soluble in ethanol thus safe to use for direct application on wound. Comparison of the anti-bacterial properties of iodine-based electrospun membranes against E. coli and S. aureus showed that PVP with iodine had the best inhibition property and PVB/poly(vinylpyrrolidone)-iodine complex the least. The portable hand-held electrospinning device was able to deposit a layer of fibers on a hand and the fibers were sufficiently compact such that the deposited membrane may be peeled off from the hand.

The handheld electrospinning apparatus (a) and the in situ electrospinning process (b). The electrospinning jets can be seen from the spinneret [Liu et al 2018]

Electrospun coating on transparent surfaces for anti-rain, anti-fog or anti-glare purpose has been suggested as a possible application for portable electrospinning device. Although scientific reports on this property of electrospun nanofiber mesh are lacking or not available, this has been suggested in patent [Liu et al 2010] and presented in conferences. This product works by using the portable electrospinning device to spray a layer of fibers on the window, mirror or car windscreen to prevent water droplets from forming on them. Since the nanofibers are not applied on skin, the range of materials that can be used is wider although it should not be toxic and harmful to the user. Raut et al (2013) used electrospinning to coat a layer of SiO₂ on glass substrate for anti-glare function using a laboratory setup. The initial SiO₂ precursor used for electrospinning has to be sintered at high temperature for conversion to SiO₂. Coating on one side and both sides of the glass substrate was able to yield transmittance of 94% and 96% respectively. The minimum reflectance of the glass substrate with one side and both sides coating was 5.1% and 2.7% respectively. This compares well to the reflectance of glass without coating at 8.61%. This provides evidence of the potential use of electrospun fibers as anti-glare coating. Jaafar and Aldabbagh (2019) conducted an accelerated weathering study on a glass surface coated with electrospun polystyrene (PS), polymethylmethacrylate (PMMA), silicon rubber (Si) and with TiO₂ added to the polymer. The specimens were subjected to ultraviolet lights, high temperature up to 50°, humidity and rain for 6 months. The contact angle was taken before and after the accelerated weathering test. Electrospun PS and Si coating with and without TiO₂ showed significant drop in contact angle from values above 100° to about 90°. In particular, electrospun PS and PS/TiO₂ coating has an initial contact angle of 160° and 154° respectively and their reduction is most significant. Electrospun PMMA and PMMA/TiO₂ has initial contact angle of 152° and 125° respectively and after accelerated weathering, has contact angle of 134° and 124° respectively. Of these materials, PMMA/TiO₂ is the most promising coating with a minor drop in hydrophobicity.

An interesting use of electrospun fibers is in anti-corrosion protective coating. Electrospun membrane from hydrophobic polymer is known to exhibit greater hydrophobicity than the same material in the form of film. Since the presence of water generally increases the rate of corrosion of metal, an electrospun hydrophobic layer on the metal surface will help to protect the underlying metal substrate from corrosion. Iribarren et al (2019) demonstrated the protective benefit of electrospun polyvinyl chloride (PVC) with nanoparticles of a corrosion inhibitor like ZnO on aluminum alloy 6061T6. Aluminum with electrospun PVC coating with and without ZnO nanoparticles showed reduction in corrosion current density by two orders of magnitude. Heat treatment was carried out to improve adhesion of electrospun coating to the metal substrate. Electrospun coatings with and without heat treatment showed a minimum water contact angle of 120° (at heat treatment temperature of 120°C) with higher heat treatment temperature lead to a corresponding reduction in its water contact angle. The reduction in water contact angle with increasing heat treatment temperature may be due to increased fusion between fibers and lowers the surface roughness. Interestingly, electrospun pure PVC fibers heated to 80°C (Tg) showed protection efficiency of 99.01%. However, the same temperature treatment on PVC/ZnO has a protection efficiency of 95.12%. While increasing the heat treatment temperature of electrospun pure PVC fibers to 100°C reduces the protection to 97.38%, the same heat treatment on PVC/ZnO increases the protection to 99.19%. The reduction of protection in the heat treated pure PVC fibers may be attributed to reduction in its water contact angle. In the presence of ZnO nanoparticles, the same molecular relaxation may improve the distribution of ZnO nanoparticles within the PVC matrix, hence increasing the level of protection.

A few portable electrospinning devices have been reported and these uses batteries to generate the required high voltage for initiating electrospinning from a cartridge filled with the solution. Mouthuy et al (2015) described the details of their portable electrospinning device which have been shown to be capable of producing nanofibers from a wide range of polymers such as polycaprolactone, polyvinyl alcohol, polyethylene oxide and poly(vinyl butyral) to name a few. Their battery powered device is able to run for 100 minutes at 13 kV. Feasibility of the device in depositing fibers on skin was demonstrated on human volunteers and pig skin [Mouthuy et al 2015]. Safety of the portable device is a very important consideration due to the high voltage generated for electrospinning. At a low current, high voltage would only cause a static shock and is unlikely to cause death. In Revia et al (2019) design, the current is deliberately limited to 2 mA and a 2-mA fuse was used to provide overcurrent protection. The HV circuits were also isolated from mains-powered devices and the amount of current it can sraw is limited to 2 mA. However, prevention of electrical shock is more challenging as dielectric breakdown of air may occur and causes a shock to the user without he/she touching the circuit. Therefore, secondary measures or personal protective equipment (PPE) is needed to mitigate this hazard.

Portable electrospinning device. Photo credit: P-A Mouthuy, University of Oxford, UK

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With a heat source, a portable melt electrospinning setup may be assembled. Yan et al (2017) showed that using a simple alcohol lamp, a temperature range from 120 to 255 °C can be applied to the charging barrel which contains the polymer, by varying the distance between flame and the charging barrel. A hand generator, rechargeable battery and high voltage converter supplies the high voltage required to charge the molten polymer. With this setup, polycaprolactone (PCL), poly(lactic acid) (PLA) and polyurethane (PU) were electrospun successfully into fibers with diameters of 13 to 60 µm.

A more convenient portable melt electrospinning device is to have a heating source as part of the setup. However, the challenge is to insulate the heating element from the high voltage. In a laboratory setup, it is possible to physically isolate the heating element from the high voltage. In a portable device, the space constraints means that both parts will be at close proximity to one another. A unique material which has excellent heat conductivity but electrically insulating property is the key to construct a portable melt electrospinning device. This allows the heat to be conducted close to the nozzle tip where the high voltage is applied while insulating the heating element from the high voltage source. Aluminum nitride (AlN) is one such material with good electrical insulation and heat transfer capacity. Zhao et al (2020) showed that with an AlN tube to conduct the heat within the setup, they were able to melt electrospin poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), and hot-melt adhesive. The device was tested on a mouse for direct fiber deposition on a cut wound. The PCL fiber mesh that was melt electrospun on the wound was able to prevent blood from spilling out.

Optical pictures showing the process of melt e-spinning PCL fibers directly onto the skin producing by the hand-held melt e-spinning apparatus in 5 min and SEM images of fibers with various polymer materials produced by the hand-held melt e-spinning apparatus to further test the performances of the apparatus. (a) The apparatus was operated by one hand and the other hand received the PCL fibers. (b) Magnified view of spinning jet. (c) Comparison of two hands with or without fiber membrane. (d) The picture shows the e-spun fiber membrane has good flexibility and the inset SEM picture is the e-spun fibers. e PLA fibers. f PLGA fibers. g hot-melt adhesive fibers [Zhao et al 2020].

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