Production of Nanofibers from Plant Extracts by Electrospinning Method

Abstract

The fact that different plants grow in each climate type, that each plant has different and many benefits, and that it can obtain bio-structured, sustainable, economic, and ecological products has increased the work of researchers in this field. The long-term toxicity and harmful side effects of herbal extracts are generally less compared to synthetic drugs. Studies on the production of nanofibrous membrane structures from plant extracts are relatively limited and are an emerging field. Herbal extracts have a positive effect in electrospinning applications with their biodiversity, ability to maintain biological functionality, and wound healing effects against pathogenic microorganisms. With the creation of nanofiber structures of plants obtained from natural sources, applications in fields such as wound healing, tissue engineering, drug release are increasing day by day.

1. Introduction

Electrospinning is the most preferred method because of its low cost compared to nanofiber production methods, production of long and continuous nanofibers, controllable nanofiber diameter, and industrial processing potential. When all these properties are evaluated, it would be appropriate to produce a nanofiber for wound healing by electrospinning. On the other hand, in recent years, interest in polymer materials obtained by the electrospinning method has increased significantly. Materials such as polymers and nanofiber composites can be produced directly by electrospinning. The post-processing of electrospun fibers forms other materials, such as ceramics and carbon nanotubes [1]. Polymer nanofibers obtained by the electrospinning method have a high surface area-volume ratio, flexible in surface functions, have superior mechanical performance, and are versatile in design [2].

Because of all these advantages, the most common and simple method used for tissue framework production is electrospinning. The principle of operation is based on filling the syringe with the polymer solution or melting in the high potential area and spraying it from the tip of the syringe to the collector by applying a voltage to an electrode connected to the tip of the syringe (Figure 1). Here, since the solution sprayed from the syringe is subjected to an electrical field, it elongates at the tip of the needle, and a conical appearance called a Taylor cone is obtained. A typical electrospinning process must be between a high voltage source with positive or negative polarity and a grounded surface so that the fibers can clump together. Spraying the solution in the syringe starts when the potential difference applied from the voltage source reaches the threshold value and equalizes to the electrostatic forces, and is completed by spraying it on the grounded surface. Since the fibers collected on the surface are sprayed with a high amount of pulling, they should be in a fine and regular structure [3, 4, 5].

Figure 1.

Schematic representation of the electrospinning process.

The surface tension of the liquid (γ), and the gravitational force (Fg) affect the droplet when the solution, which is the first step of the electrospinning process, comes out of the syringe by forming a droplet. The capillary of internal radius (R), density of the liquid (ρ), and gravitational constant (g) values of the pipe through which the polymer flows are effective in the formation of the radius of the droplet (r0).

$$\left({\mathrm{r}}_0\right)={\left(3\mathrm{R}\mathrm{\gamma }/2\mathrm{\rho }\mathrm{g}\right)}^{1/3}$$E1

When a sufficiently high voltage is applied, the electric force FE, the gravitational force Fg encounter surface forces (Fγ = FE + Fg), and the radius of the droplet decreases from (r0) to r (r < r0) [6].

After droplet formation, the polymer solution overcomes the surface forces under the influence of Coloumb repulsive forces, forming a Taylor cone with an apex angle of 49.3°. Initially straight, the jet segment may become unstable over time and may show twisting and undulating movements as it passes toward the collector. The jet in this region exhibits components of predominantly non-axial electrostatic repulsion forces. Three types of instability can occur as demonstrated by the polymer jet. These instability forms are listed as classical Rayleigh instability, axisymmetric electric field current, and whipping instability. Whipping instability results in a radial torque from the center of the jet, resulting in a high degree of bending instability. The resulting radial jets push each other and separate from the main jet. The interaction between increasing charge density on the one hand and viscous and surface tension forces resisting elongation on the other determines the complexity of the resulting instability [6, 7].

This chapter focused that the electrospinning process, parameters affecting the process such as solution and ambient. After then, it was explained herbal extracts were used to obtain nanofibers by electrospinning method and their application areas. This chapter will provide an overview of the principles of the electrospinning process with various herbal extracts for potential applications in many fields especially biomedical areas.

2. Parameters affecting electrospinning process

There are three main parameters of the electrospinning process. These are due to the polymer solution, process, and environmental conditions. In this section, the factors affecting each parameter will be discussed in detail. These parameters and their effects in Table 1 are also shown.

Parameters	Effect of Fiber Morphology
Solution Viscosity ↑	Fiber Diameter ↑ (within the optimum range)
Surface Tension↓	Fiber Diameter ↑
Solution Conductivity ↑	Fiber Diameter ↓(wide diameter distribution)
Solution Dielectric Constant↑	Fiber Diameter ↓
Voltage ↑	Fiber Diameter ↓ later ↑
Flow Rate ↑	Fiber Diameter ↑ (if the flow rate is too high, a bead appearance occurs.)
Temperature↑	Fiber Diameter ↓ (as the viscosity will decrease)
Distance Between Tip and Collector↑	Fiber Diameter ↓ (if the distance between the tip and the collector is too short, a bead appearance occurs)
Humidity (Moisture) ↑	Fiber Diameter ↑ (with the optimum range)

Table 1.

Electrospinning parameters affecting fiber morphology.

2.1 Solution parameters

To carry out the electrospinning process, the polymer must be in liquid form, in the form of a molten polymer or polymer solution. The physical and chemical properties of the solutions play an active role in the electrospinning process and the resulting fiber morphology. During the electrospinning process, the polymer solution is drawn from the tip of the needle. For this reason, the electrical properties, surface tension, and viscosity of the solution determine the amount of stress in the solution. The evaporation rate also affects the viscosity of the solution as it is stretched. The solubility of the polymer in the solvent determines not only the viscosity of the solution but also the types of polymers that can be mixed with each other [1].

2.1.1 Solution viscosity, molecular weight, and concentration

Viscosity is the most important factor determining the flow rate of the solution. In the electrospinning process, the flow rate increases at low viscosity [8]. However, when the viscosity of the solution is too low, fluidity may occur and polymer particles may form instead of fibers. In solutions with lower viscosity, the polymer chain is generally less synthesized with each other [9], less chain entanglement occurs, and thus jet stability is lost. The fibers are collected into the collector as droplets, which first turn into spindle-like structures and then into beaded nanofibers [3]. As the viscosity increases, the formation of the bead structure decreases, and more regular nanofibers are obtained [9]. Therefore, factors that affect the viscosity of the solution also affect the electrospinning process and the resulting fibers.

The molecular weight of the polymer used in the electrospinning process has a direct effect on properties such as viscosity, surface tension, and conductivity, and this interaction determines the nanofiber formation. Molecular weight is explained as the length of the chains of the polymer from which nanofibers will be obtained [4]. The length of the polymer chain will determine the amount of entanglement of the polymer chains in the solvent [1]. Since the viscosity will be higher in polymer solutions with high molecular weight, the formation of beads decreases [10]. Although the increase in molecular weight provides regular fiber formation, if this increase is high, it causes the formation of microstrip structure [11, 12].

2.1.2 Surface tension

When a very small drop of waterfalls into the air, the droplet usually takes on a spherical shape. The liquid surface property that causes this phenomenon, which occurs when the electrical forces are around zero, is known as surface tension [1]. An excessive increase in surface tension adversely affects the electrospinning process. Some surfactants with low concentrations are used to lower the surface tension. The decrease in the surface tension of the solution ensures the formation of finer and smoother fibers and a problem-free electrospinning process [4]. The concentration change in the solutions used directly affects the surface tension [13].

2.1.3 Solution conductivity

Electrospinning is a method of obtaining nanofibers that repel the charges on the surface by stretching the solution and transfer the electric charge from the electrode to the polymer solution [1, 14]. In the electrospinning system, low electrical conductivity can form beaded fibers as it will create instability and cause the jet to not be able to extend sufficiently, while with high electrical conductivity, the polymer jet can stretch more with the loads it carries and form fibers with a smoother and finer structure [3]. For this reason, it is aimed to increase the electrical conductivity by increasing the concentration. Some additives can also be added to increase conductivity in low-concentration or insufficiently ionic solutions [4]. If the conductivity of the solution increases, the electrospinning jet can carry more charge. For example, the conductivity of the solution can be increased by the addition of ions [1]. By adding salt to an uncharged solution, although electrical neutrality is maintained, salt molecules can dissociate into independently acting positive and negative ions, thereby increasing the electrical conductivity of a solution [15, 16]. These ions can also be obtained by dissolving most drugs or proteins in water. As a result, when a small amount of salt or polyelectrolyte is added to the solution, the increased loads carried by the solution will increase the stretching of the solution and the formation of beaded fibers will be prevented [1].

2.1.4 Solution dielectric constant

The insulation constant or dielectric constant is defined as a coefficient that measures the ability of a material to store charge on it [17]. As the dielectric constant of the solutions increases, the charge distribution across the surface of the bubble formed at the needle tip will be more uniform, as there will be more net charge density. Therefore, the ordered structure of the obtained nanofiber is also increasing [3, 4]. It is thought that as the dielectric constant increases, obtaining finer and smoother fibers is due to the application of more tension force to the fluid jet [18].

2.2 Processing variables

Another important parameter affecting the electrospinning process is various external factors applied to the electrospinning jet. These factors are voltage, flow rate, temperature, collector effect, nozzle diameter, and the distance between the tip and the collector. Although these parameters are less important than solution parameters, they have a certain effect on fiber morphology.

2.2.1 Voltage

Voltage is a parameter that induces charges in the solution, overcomes electrostatic forces, and initiates the electrospinning process [1]. As the amount of applied voltage increases, the diameters of the obtained nanofibers will decrease [4]. There are three main reasons for this. The first reason is because of a higher voltage will lead to greater stretching of the solution due to the larger columbic forces in the jet and the stronger electric field. This will reduce the fiber diameter. The second factor is that by using a lower viscosity solution, at a higher voltage, the formation of secondary jets during electrospinning is achieved. Thus, the fiber diameters can become narrower. Another factor that can affect the fiber diameter is the flight time of the electrospinning jet. A longer flight time will allow more time for the fibers to stretch and elongate before being placed on the collecting plate. Therefore, at a lower voltage, the diminished acceleration of the jet and the weaker electric field can increase the flight time of the electrospinning jet, facilitating the formation of finer fibers [1].

In many studies [19, 20, 21], it was observed that the formation of beads on the surface formed with the increase of voltage increased. The increase in bead density due to tension is explained because of increased instability of the jet as it is drawn into the syringe needle in the Taylor cone [1]. Here, bead formation occurs with the excessive acceleration of voltage increase, jet movement, and evaporation [4]. It is also suggested that increasing voltage will increase bead density and at even higher voltage, beads will form fibers of thicker diameter [1].

Despite these studies that the voltage increase creates a bead surface, it has been observed that the production of nanofibers at very low voltage also creates a beaded surface [22]. In this sense, the important thing is to work at a voltage where the flow balance will be stable. With the increase in voltage, the jets coming out of the cone tip reach the collector in an orderly manner, increasing their speed in the electrical field. Here, excessive speed increase or decrease is a factor that will lead to the formation of a beaded surface. In other words, the applied voltage must have an upper and lower limit.

2.2.2 Feeding rate

The feeding rate determines the amount of feed in the electrospinning system. A certain feeding rate is needed to maintain the Taylor cone in the system. When the feeding rate increases, there will be an increase in the fiber diameter or the size of the beads formed in the fibers, as there will be more solution volume at the nozzle tip [1]. At low feeding rate, nanofiber production will not be possible because there will not be sufficient feed for the Taylor cone.

As the applied voltage changes, the resulting Taylor cone will also change. At low applied voltages, a hanging drop forms at the tip of the array. The Taylor cone is then formed at the tip of the array. However, as the applied voltage increases (moving from left to right), the volume of the hanging drop decreases until a Taylor cone is formed at the tip of the array. Increasing the applied voltage results in the ejection of the spray through the syringe, which is associated with an increase in bead formation [5].

2.2.3 Temperature

The temperature parameter consists of three environmental variables: melt temperature, solution temperature, and ambient temperature. As the melt temperature increases, less tension is required due to the decrease in viscosity and fiber diameters decrease [7]. Similar to melt temperature, the temperature of a solution has the effect of both increasing the evaporation rate and reducing the viscosity of the polymer solution. This is because the solution has a lower viscosity and greater solubility of the polymer in the solvent, allowing the solution to be stretched more evenly. With a lower viscosity, Columbic forces can exert a greater tensile force on the solution, thus resulting in smaller diameter fibers [1].

2.2.4 Effect of the collector

There must be an electric field between the source and the collector (collector) for the electrospinning process to start. Therefore, in most electrospinning systems, the collector plate is made of a conductive material such as aluminum foil, which is electrically grounded such that there is a constant potential difference between the source and the collector. If a non-conductive material is used as a collector, charges from the electrospinning jet will quickly build upon the collector, resulting in less fiber deposition. Fibers collected on non-conductive material generally have a lower packing density than those collected on a conductive surface. This is due to the repulsive forces of the loads that build upon the collector as more fibers accumulate. For a conductive collector, the loads on the fibers are distributed so that more fibers are drawn into the collector. As a result, the fibers can be wrapped closely together [1].

The most commonly used collector types in the electrospinning method are generally flat plates, grids and frames. Apart from these, rotating cylinder, rotating disc, rotating cones, parallel rings, liquid bath and wrapper, pyramid-shaped platform, conveyor belt, two parallel frames, rotor, and thin conductive rod are listed as [7].

2.2.5 Nozzle (needle) diameter

The nozzle diameter has a certain effect on the electrospinning process. As the nozzle diameter gets smaller, it provides clogging of the diameter and reduces the amount of beads on the nanofibers. The reduction in occlusion is due to less exposure of the solution to the atmosphere during electrospinning. The decrease in the inner diameter of the hole causes a decrease in the diameter of the nanofibers. As the size of the droplet at the tip of the hole decreases, the surface tension of the droplet increases. It reduces jet acceleration when the same amount of voltage is applied, allowing more time for the solution to stretch and stretch before the collector. The nanofibers formed in this way are finer [1].

The nozzle could be blockage when electrospinning with electrospinning chloroform solutions of PLA. When more than one nozzle is formed, the solvent density may increase, but this will increase the difficulty of solvent removal and nozzle cleaning and compose the deposition of nonwoven fiber in thicknesses >10 mm [23].

2.2.6 Distance between tip and collector

The distance between the needle tip and the collector provides the necessary time for the solvent in the polymer jet sprayed from the nozzle tip to evaporate [4]. Changing the distance between the tip and the collector has a direct effect on both the flight time and the electric field strength. As the distance between the tip and the collector decreases, the jet will have a shorter distance to travel before reaching the collector plate. In addition, the electric field strength will increase at the same time, which will increase the acceleration of the jet going to the collector. As a result, there may not be enough time for solvents to evaporate when they hit the collector. When the distance is too low, excess solvent causes the fibers to coalesce where they come into contact [1].

2.3 Environmental conditions

Environmental conditions in the electrospinning process are the factors affecting the electrospinning process. In this sense, humidity, atmospheric type, and pressure cause physical and morphological changes in the formed fibers.

2.3.1 Humidity (moisture)

The increase in humidity in the environment adversely affects the electrospinning process. High humidity causes circular pores to form on the nanofiber surfaces obtained. The pore depth increases with increasing humidity. However, the depth, diameter, and number of pores remain constant above a certain humidity [1]. It is not possible to carry out the electrospinning process at very high humidity values [3]. As the humidity level decreases, volatile solvents evaporate quickly, causing drying and making the electrospinning process difficult [9]. For this reason, keeping the humidity level at an optimum level is an important factor.

2.3.2 Type of atmosphere

The type of atmosphere in which the electrospinning process takes place is very important for the smooth running of the process. Different gases have different behavior under the high electrostatic field. For example, helium decomposes under a high electrostatic field and therefore electrospinning is not possible [1]. For another example, with excessively volatile solvents the Taylor cone could dry out. To prevent evaporation in the cone, it is feasible to introduce a local stream of solvent-saturated gas around the cone [23]. The decrease in pressure in the environment adversely affects the electrospinning process [1].

2.3.3 Pressure

Pressure changes in the electrospinning process make it difficult to ensure the stability of the drafting process. The reduction in pressure surrounding the electrospinning jet adversely affects the electrospinning process. When the ambient pressure drops below atmospheric pressure, the polymer solution in the syringe will have a greater tendency to flow through the needle, resulting in an unstable spray start. As the pressure decreases, rapid solution foaming occurs at the needle tip. At very low pressure, electrospinning is not possible due to the direct discharge of electric charges [1].

3. Herbal extracts used to obtain nanofibers by electrospinning method

Reasons such as health problems, population density, environmental pollution, and increased consumption have encouraged people to seek natural solutions. The use of herbal products in the field of health for their healing properties is increasing day by day. In recent years, plants derived from natural substances such as flavonoids, terpenoids, steroids have received considerable attention due to their different pharmacological properties, including antibacterial, antioxidant, and anticancer activity.

The olive leaf plant, which draws attention with its biocompatible, biodegradable, antioxidant, and antimicrobial properties, has been used by many researchers [24, 25, 26, 27] in the electrospinning process for use in the biomedical field. Similarly, because of its biocompatible, biodegradable and antimicrobial properties, and rosemary plant [28, 29] has been used as a bioactive packaging material and to obtain nanofibers by electrospinning for use in the biomedical field. Many plant extracts such as aloe vera [30, 31], thyme [10], grape seed [32], chamomile [33], green tea [34], grewia mollis [35], gotu kola [36], calendula [37], mangosteen [38], lavender [39] are mixed with different polymers and used in the production of nanofibers for use in the medical field.

4. Application areas of nanofibers obtained from plant extracts by electrospinning method

The fact that different plants grow in every geography, each plant has different and many effects and the ability to obtain biocompatible, sustainable, organic, and environmentally friendly products have encouraged researchers to work in this field. The use of plants obtained from natural sources as active agents is increasing day by day in areas such as wound healing, tissue engineering, and drug release.

4.1 Wound healing

The skin forms the largest part of body weight and is very vulnerable to external forces and effects such as tissue traumas and injuries. Today, wound dressings play a vital role in the healing of such wounds, and wound healing depends on several factors such as selection of wound dressing, physiological state of the wound, and degree of damage. An ideal wound dressing should facilitate wound healing, remove exudates from the wound bed, be non-toxic and allergenic, and act as a barrier against microbes [4, 30]. Conventional wound dressings are generally used to close the wound and absorb the excess discharge. Although in previous studies, it was stated that the dressing should keep the wound dry, it is known that a warm and moist environment on the wound increases the healing of the wound [40]. However, it is a fact that excessive moisture causes wetting and softening of the scar tissues and prolongs the wound healing process [4]. Keeping the humidity level at an optimum level is very important for wound treatment. In addition to the ideal moisture level of modern wound dressings, effective oxygen circulation, air permeability, and low bacterial contamination are the essential qualities sought [40].

Modern wound dressings are composed of water-absorbent granular hydrocolloids, alginate containing mannuronic and guluronic acids, and hydrogel, in which water-absorbing polymers are structured into a three-dimensional network [40]. In recent years, with the rapid development of tissue engineering, nanofiber-based ECM (extracellular matrix) scaffold structures have become widespread [4]. ECM is a collagenous substance commonly found in skin, tendons, cartilage, and bone [11]. Compared to other wound dressings, nanofiber wound dressings have advantages such as hemostasis, high porosity, good fluid absorption capacity, small pore sizes, and large surface area [4]. Hyaluronic acid, collagen, chitosan-based nanofibers are generally used in new generation nanofiber-containing bioactive wound dressings due to their biocompatible, biodegradable, and antibacterial properties [40]. Thus, it ensures the healing of the wound by releasing the active substance in the nanofiber structure onto the wound in a controlled manner.

In recent studies [24, 29, 41, 42, 43], herbal extracts seem to be helpful in fighting infection and accelerating the wound healing process. The use of herbal extracts as wound dressings can nourish the wound site with healing properties such as antimicrobial, anti-inflammatory, analgesic, and tissue regeneration [30]. The long-term toxicity and harmful side effects of herbal extracts are generally insignificant compared to synthetic drugs. The main disadvantage of herbal medicines is that they need to be used in higher dosages than synthetic medicines. Large amounts of herbal medicines extracted from plants reduce their solubility in water or other chemical solvents. Therefore, dissolution of plant extracts almost never occurs in polymer-carriers such as capsules, nanofiber mats, and casting films containing herbal medicines. This may cause adverse effects in applications such as drug release behavior. Despite these problems, herbal drugs promise great success compared to chemical drugs due to their superior performance in wound treatments [10]. The important point here is to extract the herbal extracts in a suitable solvent, to obtain a biocompatible polymer and a nanofibrous structure that preserves its existing effects such as anti-inflammatory and antibacterial and supports the repair of opened wounds.

4.2 Tissue engineering

Tissue engineering is a field that aims to heal damaged or diseased tissues/organs, to maintain, regenerate and develop the functions of normal tissues/organs, and to form tissue scaffolds with repair capability for this purpose. Electrospinning is an application with high potential in many tissue engineering fields such as vasculature, bone, neural, and tendon/ligament. With the electrospinning process, the ability to form aligned scaffolds for anisotropic mechanical and biological properties in the field of vascular grafts, as well as the ability to inhibit smooth muscle cell migration, is provided. In addition, possibilities have been presented to improve vascular grafts with tissue scaffolds that can be obtained by tissue engineering [5, 44].

Nanofibers in tissue engineering must have such as biocompatible, biodegradable (with an acceptable shelf life), tissue-appropriate degradation rate, tissue-appropriate mechanical (strength, stiffness, and modulus) and structural (pore sizes, shape, and structure) properties, and sterilizability [45]. Tissues consist of multiple cell types and works in conjunction with the cell-surrounding extracellular matrix (ECM), which is the tissue scaffold, concealed by regular, micro-sized cells. The ECM is responsible for providing the cells with the needed mechanical support and protecting the cells. The materials used in tissue engineering applications should allow a certain interaction with the cell, the cell’s attachment, proliferation, change, ECM production, and proper progression of this process should be ensured. It should form a supporting function in the formation of new tissues [3, 44].

Approximately, 25% of current prescription drugs are derived from trees, medicinal plants, shrubs, and herbs in nature. The use of herbal extracts with nanofibers produced by electrospinning provides a good potential to form scaffolds for skin regeneration [46]. For example, it has been seen that the nanofibrous structure of the chamomile plant supports collagen fiber accumulation and tissue formation in the dermis [33], and the olive leaf plant has a good potential for tissue scaffolding in biomedical applications thanks to its high antioxidant effect [3]. There are studies on tissue scaffolds containing edible, non-toxic, biocompatible, biodegradable plant extracts with many different contents. It is thought that the applications of plant-based tissue scaffolds will increase in future studies.

4.3 Drug delivery systems

Drug delivery systems aim to deliver the drug to the unhealthy region in a controlled and regular manner and to ensure its effectiveness in this region. While drug delivery is generally associated with the delivery of therapeutic agents for the treatment of certain disease states such as cancer, the delivery systems for tissue engineering applications can also apply to the delivery of bioactive agents such as proteins and DNA [5].

In conventional drug delivery systems, successive doses of the drug cause a fluctuating profile of the drug concentration in the blood throughout the treatment period. Therefore, at certain times, concentrations may exceed the recommended maximum (Cmax) concentration with the risk of biotoxicity or fall below the minimum concentration (Cmin), limiting the therapeutic effect. To obtain the highest therapeutic value from the drug, the optimum concentration (C), (Cmin < C < Cmax) in body tissue should be maintained throughout the entire treatment period. Via controlled delivery techniques, the bioavailability of the drug has been designed throughout to be close to this optimum value. In addition, the amount of drug required to be administered is relatively lower in the controlled release mode, minimizing potential side effects [6].

In tissue engineering, the design of the polymer scaffold requires the release of growth factors and other bioactive substances into the growing tissue over a period of time. In nanofiber applications such as wound dressings or artificial leather, the local controlled release of antibiotic substances can aid the healing process. Polymer-based delivery systems can produce controlled drug release by diffusion or chemical bioerosion of the matrix or biodegradation of the linkages connecting the drug to the matrix [6]. These advantages are of great importance in their preference and use.

Polymer-based drug delivery systems; nano or microparticles, hydrogels, micelles, and fibrillar systems. Fibrillated systems form nanofiber-based drug release systems [3]. The release kinetics of the drug is controlled by the morphology of the polymer/drug composite as well as the semi-crystalline structure of the polymer. First, the drug is dissolved at the molecular level in the polymer matrix. The drug is separated as crystalline or amorphous particles in the polymer matrix [6, 47].

The use of herbal-based nanofiber structures in drug delivery systems has increased in recent years. There are different applications such as designing coaxial nanofibers by using olive leaf extract as a bioactive agent [25], producing nanofiber membranes containing aloe vera [48], using nanofibers prepared using the bark of Tecomella undulate (rohida) plant in in-vitro drug release [49]. It is expected that nanofiber drug delivery systems containing herbal extracts will increase therapeutic efficacy, reduce toxicity and ensure compatibility with patients by delivering drugs to the affected area at a controlled rate for a certain period.

5. Conclusion

Electrospinning is a nanofiber production method that is the most preferred because it is simple, economical, and environmentally friendly, and has many production parameters including solution, process, and environmental conditions. Production of nanofibers by electrospinning process; It is a subject that draws attention with its applications in many fields such as tissue engineering, drug release, filtration, automotive, energy, food industry, cosmetics, agriculture, biosensing. Although polymer contents with synthetic infrastructures are generally preferred in these applications, approaches to using natural agents with few side effects, biocompatible, sustainable, economical, biodegradable, and free from toxic components are increasing [10, 27, 33, 41, 42]. The use of natural components containing active agents in the production of nanofibers is becoming more and more common in the fight against potential health problems that may occur due to the rapidly increasing world population and environmental pollution. Herbal extracts are promising in electrospinning applications with their biodiversity, ability to maintain their biological functionality even after exposure to high electrical voltage, and wound healing effects against pathogenic microorganisms. In addition, it is thought that the use of herbal extracts in different applications in the field of health will become widespread, as they have fewer side effects, and versatile therapeutic properties compared to chemical agents.

Conflict of interest

The authors declare no conflict of interest.