Coaxial electrospinning of PVA/Nigella seed oil nanofibers: Processing and morphological characterization
Introduction
“The Coaxial Electrospinning“ is a versatile electrospinning technique to produce “core/shell” structures in which two or more dissimilar solutions are injected independently from two different coaxial capillary channels with a strong electrostatic field [1]. Coaxially spun core/shell structured nanofibers of the order of 80–120 nm diameter have attracted considerable attention in self-healing, drug/gene delivery and biomedical and tissue engineering [2], [3], [4], [5], [6]. It has been shown that nanofibers are the perfect intermediary platforms for drug delivery and tissue applications [7]. In this regard, nanofiber mats provide a platform for tissue cells; thus, tissue cells may multiply and differentiate for the tissue that they aimed to form [8].
There have been a growing number of investigations utilizing the coaxial electrospinning technique for such biomedical applications. Electrospun nanofibers have been the focus of attention for their excellent properties as high surface-to-volume ratios, adequate porosity, cost-effectiveness, tunable fiber diameters and ability of controlled degradation for applications in drug delivery and wound healing. They are widely used as excellent carriers for anticancer drugs, antibiotics, proteins, DNA, wound healing and skin treatment agents. In this regard, many bioactive substances and compounds can be filled/encapsulated and enshrouded in electrospun nanofibers for the drug delivery process and their proper release to the target [9].
Coaxial electrospinning technique, also called “two-fluid electrospinning” is adopted and employed effectively by many researchers due to its ease of production, cost-effectiveness, versatility, straightforward and simple setup [1], [10], [11], [12], [13]. A coaxial electrospinning set-up consists of two different solutions inside two different coaxial capillary injectors, releasing the materials in the form of core/shell (sheath) structure from the joint injector due to a strong electrostatic field starting at the tip. Moreover, due to their different properties and characteristics of solutions, such as different concentrations, conductivity and viscosity, their spinning behavior is different for the same parameter set [14]. In this technique, which was described in details elsewhere [1], [2], [3], [4], [15], [16], the voltage difference between needle and collector is used to create an electrical area that affects the droplet formation at the tip of the needle and draws nanofibers of the order of 80–120 nm from the tip to the grounded collector [13]. In this instant, the droplet at the needle changes its shape from spherical to a distorted specific form of conical “Taylor cone” and flows down to form fibrous geometry resulting in nano/microfibers spinning down to the collector [17]. During the formation of the “Taylor cone,” firstly, a hemispherical droplet forms at the tip of the metallic needle and eventually distorts into a conical shape under the mixed effects of electrostatic forces, including internal repulsion and external coulombic attraction [9]. Processing coaxial electrospinning parameters may include the following parameters: the applied voltage, flow rate, solution concentrations, molecular weights, viscosity, the distance between two electrodes and state of the collector along with other conditional parameters (e.g., temperature, humidity and airflow) [18].
Various polymeric solutions have been utilized for producing coaxially electrospun nanofibers as the shell structure, such as polyolefins, polyamides, polyesters, polyurethanes, polypeptides, polysaccharides and polyvinylalcohol (PVA) (19). Among these, particularly PVA has the following superior merits for being the right choice for coaxial electrospinning:
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good fiber-forming characteristics and thermal stability,
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non-toxic and water-soluble,
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biocompatible, biodegradable and safe,
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good mechanical properties (abrasion resistance) and chemical (e.g., alkali) resistance,
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ease of functionalization,
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low cost.
Based on these advantages, electrospun PVA nanofibers are coaxially blended with the bioactive compounds, such as therapeutic agents, enzymes and plant extracts (e.g., the extract of J. chinesis and A. muricatawas and others), iodine (for wound cleansing and debridement) and the variety of other bioactive compounds (proteins and probiotics) has been reported in many biomedical applications to develop nanofibrous mats for antimicrobial/antibacterial and healing activities [9], [18], [19], [20], [21]. Electrospun PVA nanofibers incorporated with liposomes have also been shown as drug delivery carriers for tissue engineering [22]. As indicated in many relevant studies, encapsulation/enshrouding of bioactive compounds through the electrospinning process is highly effective and useful to maximize the therapeutic potential by enhancing bioavailability and provides a steady concentration of drugs/enzymes/seed extracts to the targeted wounds [18]. As other recent examples of relevant studies, the following works can be summarized as follows: H. Jiang et al. embedded bovine serum albumin (BSA) containing dextran into polycaprolactone (PCL) nanofibers as an example of a drug delivery system [23]. W. Chen et al. used the coaxial electrospinning technique to incorporate chitin-derived glucosamine sulfate into nanofibers for cartilage regeneration [24]. L. Zhu et al. reported asiaticoside-loaded coaxially electrospun nanofibers of alginate, polyvinyl alcohol (PVA) and chitosan (alginate/PVA/chitosan) and also their effects on deep partial-thickness burn injury [25]. M. He et al. employed coaxial electrospinning technique to fabricate metronidazole (MNA)-loaded poly (e-caprolactone) (PCL)/zein core/shell nanofibers for guided tissue regeneration [26]. J-M. Yang et al. investigated drug/zein composite fibers prepared using a modified coaxial electrospinning process. They reported that composite fibers with unspinnable acetic acid as shell liquid and zein and ferulic acid (FA) as core fluid improved drug release profiles [27]. A. Cuvellier et al. reported submicron core–shell fibers with a polymer shell that encapsulated the liquid monomers for use in a vascular self-healing epoxy. A two-component epoxy-amine was used for the cores and a polysaccharide for the shell [28].
In this study, the aqueous solution of PVA (as the shell structure) and Nigella (Nigella sativa) Seed Oil (as the core liquid) were used to produce core/shell structured nanofiber mats with antibacterial effects for wound dressing and other potential applications. Nigella seed oil has been known as a traditional herbal medicine to offer many health and cosmetic benefits, such as aiding weight loss, improving skin conditions, and even treating cancer and diabetes. It is also known as “Black Cumin” and “Black Onion Seeds.” Nigella seed oil has been used as an ointment for dermatitis, eczema, skin rashes, tissue impairment, wound healing and swollen joints along with many other applications, such as anti-oxidant, anti-bacterial, food ingredient and ailments for asthma, hypertension, diabetes, kidney or liver afflictions, cough, fever and influenza. Nigella sativa seeds and oil components consist of proteins, carbohydrates, fibers, ashes, moisturizers, linoleic, oleic, palmitic, dihomolinoleic and eicosadienoic acids [29], [30], [31], [32], [33], [34], [35].
Experimental parameters of the coaxial electrospinning process investigated in this work were as follows: PVA solution concentrations, flow rate, applied voltage, spinning distance, nanofibers diameters, morphology, alignment and structure of PVA nanofibers filled/enshrouded using Nigella seed oil.
Section snippets
Materials and methods
Polyvinylalcohol (PVA) was selected as the electrospinning polymeric solution for the shell structure owing to its inexpensive price and its solvent availability, which was distilled water. Polyvinylalcohol (PVA, Mw = 85000–124000) was purchased from Sigma-Aldrich and used without further purification. High purity Nigella sativa (Nigella seed oil) –as the core solution- was purchased from the local market, and its brand name is “Extrem NaturalTM”.
Results and discussion
As pointed out in many studies, electrospinning is quite a simple, practical and versatile technique except that it has not been shown to be an adaptable and practical method for industrial production of mass scale [1]. The coaxial electrospinning process employed in this study looked over the following processing parameters affecting fiber size and fiber morphology:
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Applied voltage;
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Spinning distance (which was held constant in this work);
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Flow rate (polymer feeding rate);
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Injector(s)’ diameter;
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Conclusion
The coaxial electrospinning using double injectors aligned into a common needle technique is employed for investigating the processing parameters for the PVA/Nigella seed oil solutions. Results showed that the processing parameters, such as the flow rate, solution concentrations, and the voltage difference have significant effects on the core/shell nanofiber morphology. SEM micrographs revealed randomly oriented, smooth and homogeneous, lesser bead nanofibers using 18 to 20% PVA concentrations
Data availability statement
The datasets generated during and/or analysed during this current study are available from the corresponding author on reasonable request.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to thank the Istanbul Development Agency for their support through the funding of Project No. İSTKA TR10/15/YNK/056.
References (41)
- et al.
Filtr. Sep.
(2002) - et al.
Electrospun Nanofibers, in book: Electrospun Nanofibers
Publisher: WOODHEAD PUBLISHING
(2017) - et al.
Trends Food Sci. Technol.
(2017) - et al.
Compos. Sci. Technol.
(2003) - et al.
Mater. Sci. Eng. C
(2017) - et al.
Polymer (Guildf)
(2008) - et al.
Biotechnol. Adv.
(2010) - et al.
Mater. Sci. Eng., C
(2017) - et al.
Carbohydr. Polym.
(2020) - et al.
J. Colloid Interface Sci.
(2017)
Colloids Surf., B
Polym. Test.
J. Ethnopharmacol.
Integr Med Res
J. Ethnopharmacol.
Bioorg. Med. Chem. Lett.
Plant Physiol. Biochem.
Appl. Therm. Eng.
Compos. Sci. Technol.
Polymer (Gu ildf)
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