Investigation of the bee-repellent properties of cotton fabrics treated with microencapsulated essential oils

Abstract

In this study, to produce single-use bee-repellent fabrics, a variety of essential oils were encapsulated with gum arabic wall material at a 1:5 ratio of wall to the core substance. The following core substances were used: lavender oil, laurel oil, fennel oil, N, N-diethyl-3-methylbenzamide (DEET), lavender + laurel oil, lavender + fennel oil, laurel + fennel oil, lavender + fennel + laurel oil, lavender oil + DEET, fennel oil + DEET and laurel oil + DEET. Lavender, fennel and laurel oils were analyzed by high-performance liquid chromatography. In this context, 11 different microcapsules were produced. After the microencapsulation process, the microcapsules were analyzed with a light microscope and by Fourier transform infrared spectroscopy. Furthermore, an image processing application was developed and implemented to determine the particle size distribution of the microcapsules. After the analysis of the microcapsules, cotton fabric samples were treated with the microcapsules. In order to analyze the microcapsules on the fabric samples, scanning electron microscopy (SEM) was used. To analyze the bee-repellent abilities of the fabric samples, 12 different measurement cabinets made of pine tree and glass were produced. According to the results, lavender and fennel oils can be used as bee-repellent alternatives to DEET in beekeeping.

Keywords

bee repellent lavender fennel laurel DEET microencapsulation image processing

In recent decades, functional textiles have been developed to improve textile performance in order to meet customer demands and get higher added value. New ways to produce functional textiles, through research and development, and manufacture new products with high added value have been developed. Microencapsulation processes have been used for years in industries such as the agricultural, pharmaceutical, food processing, cosmetic and chemical industries; however, the process has also recently been used in the textile industry.^1,2 In recent decades, out of all functional products, microencapsulation technology concerning textiles has been a focus of research due to the long-term effects that the process can add to textiles. Microencapsulation technology can provide textiles with long-term nonflammability,^3,4 the ability to release scent,⁵ insect repellency,^6,7 antibacterial effects,⁸ thermal regulation,⁹ colorfulness,¹⁰ etc.

Around the world, beekeeping is an important agricultural activity, with the advantages of it not depending on soil, requiring less capital and using less labor compared to other agricultural activities.¹¹ However, bee stings are one of the major problems in beekeeping due to their disturbance to the beekeeper and the cause of allergic reactions. Furthermore, they may cause death in hyperallergic persons.

Researchers have reported that various essential oils can be used as mosquito repellents due to their eco-friendly and biodegradable nature, particularly the essential oils extracted from citronella,¹² oregano,¹³ rosemary,¹⁴ orange,¹⁵ thyme,¹⁶ lemon,¹⁷ and peppermint.^18,19 These essential oils can be directly applied on human skin. In addition, such oils can be encapsulated by a suitable shell material to enable them to be applied to clothes, home textiles and netting. These essential oils have also been sprayed in habitats and their insect-repellent activities investigated. Furthermore, N, N-diethyl-3-methylbenzamide (DEET) is a widespread synthetic insect repellent. Although, DEET offers long-term protection and causes the death of insects, it may cause lethargy, confusion, acute manic psychosis, headaches, ataxia, disorientation, acute encephalopathy, convulsions, tremors and seizures in humans.²⁰

The aim of this study was to produce single-use bee-repellent fabrics using natural substance alternatives to DEET. In this context, lavender fennel, and laurel oils were used and these active substances were encapsulated with gum arabic to improve the duration of the repellent effect. According to the results, the lavender and fennel oils are more repellent than DEET. Furthermore, DEET causes bee death whereas the lavender, fennel and laurel essential oils do not cause bee death.

Experiments

Materials

Gum arabic (Zag Chemical, Turkey) was used to produce the wall material in the preparation of the microcapsules. Gum arabic was used as a wall material since it is an odorless and water-soluble substance. In order to induce the coacervation process, a 25% sodium sulfate (Balmumcu Chemist, Turkey) solution was used. Glutaraldehyde (Sigma-Aldrich, Germany) was used to solidify the wall material.²¹ Furthermore, the DEET (Akdeniz University, Faculty of Science, Turkey), lavender, fennel and laurel oils (Aydın Corp., Turkey) were used as bee repellents. In a previous study, it was recognized that these essential oils have insect-repellent properties.²² The lavender, fennel and laurel essential oils were analyzed by high-performance liquid chromatography (HPLC) (Agilent Technologies, Germany, with a quaternary gradient pumping system (Agilent, G1312) for high-pressure solvent delivery, an automatic injector (Agilent, G1313A, Agilent Technologies) and a variable-wavelength ultraviolet detector (Agilent, G1314A)). The components of the oils are shown in Table 1. The chemical structure of DEET is shown in Figure 1.

Table 1.

Lavender, fennel, and laurel oil composition obtained using HPLC analysis

Lavender Oil		Fennel Oil		Laurel Oil
Components	Percentage (%)	Components	Percentage (%)	Components	Percentage (%)
α- pinene	49.4	Limonene	8.7	1.8-cineole	54.6
β-pinene	5.8	Estragole	3.3	α-terpinil acetate	8.9
Linalool	1.0	Carvone	6.1	Sabinen	7.0
Linalyl acetate	1.1	Anisaldehyde	2.0	β-pinene	3.8
Camphor	2.1	(2)-anethole	0.3	p-cymene	2.3
Limonen	1.6	Anisketone	0.3	Terpinen-4-ol	2.3
1.8-cineole	2.2	Dill apiole	0.3	Carvacrol	2.0
δ-3-carene	16.3			Limonene	1.1
Camphene	13.0

Figure 1.

The chemical structure of N, N-diethyl-3-methylbenzamide.

In this study, 100% cotton fabric (58 ends/cm × 29 picks/cm, weighing 125 g/m²) was used for the samples.

Preparation of the microcapsules

In the preparation of the bee-repellent microcapsules, a simple coacervation technique was utilized. In order to encapsulate the core material, gum arabic was used as the wall material. Before the encapsulation of the core materials, 10 g gum arabic was dispersed into 70 ml water. Then, the core material was added to the dispersion at a 1:5 ratio of core (ml) and wall substance (ml) and mixed for 30 min by a magnetic stirrer (ULTRALAB Lab Test Instrument) at 1600 rpm. Next, 1 ml sodium sulfate solution (25%) was added in order to induce coacervation²³ and the reaction mixed for 15 min. Finally, 3 ml glutaraldehyde solution (40%) was added and the reaction mixed for 20 min. In the literature, the function of glutaraldehyde is described as separating the wall and core material.²¹ Then, the microcapsules were cooled at −18 ± 2℃ for 12 h in a freezer. This method is outlined in Figure 2.

Figure 2.

Schematic of the formation of the microcapsules via the coacervation method.

In this study, 11 different microcapsules preparations with different core substances were used, as shown in Table 2. The core materials for the mixtures were used in equal proportions.

Table 2.

Microcapsule properties

Lavender/gum arabic 1:5	Microcapsules prepared with lavender core and gum arabic wall
Laurel/gum arabic 1:5	Microcapsules prepared with laurel core and gum arabic wall
Fennel/gum arabic 1:5	Microcapsules prepared with fennel core and gum arabic wall
DEET/gum arabic 1:5	Microcapsules prepared with DEET core and gum arabic wall
Lavender + laurel/gum arabic 1:5	Microcapsules prepared with lavender + laurel core and gum arabic wall
Lavender + fennel/Gum arabic 1:5	Microcapsules prepared with lavender + fennel core and gum arabic wall
Laurel + fennel/gum arabic 1:5	Microcapsules prepared with laurel + fennel core and gum arabic wall
Lavender + laurel + fennel/gum arabic 1:5	Microcapsules prepared with lavender + laurel + fennel core and gum arabic wall
Lavender + DEET/gum arabic 1:5	Microcapsules prepared with lavender + DEET core and gum arabic wall
Laurel + DEET/gum arabic 1:5	Microcapsules prepared with laurel + DEET core and gum arabic wall
Fennel + DEET/gum arabic 1:5	Microcapsules prepared with fennel + DEET core and gum arabic wall

DEET: N, N-diethyl-3-methylbenzamide.

Application of microcapsules to the fabric samples

The microcapsules were applied to the fabric samples via a dipping method by immersing the fabric into microcapsules for 10 mins at 20℃ in an air-conditioned room. The pick-up was measured at 110% for all applications and was calculated by the following equation:

\begin{matrix} % Pick up = \frac{E_{2} - E_{1}}{E_{1}} \times 100 \end{matrix}

(1)

where Pick up is the amount of solution applied to the fabric, E₂ is the fabric weight after dipping and E₁ is the fabric dry weight. After the dipping process, the samples were dried at room temperature for 8 h in different rooms so that the odors did not mix. Since insects are quite sensitive to odors, it is essential that no mixing of odors occurs in an insect repellence mechanism.²⁴ After the drying process, the weight of samples was measured and the microcapsule pick-up was calculated at 40%.

Morphological analysis

The morphologies and particle sizes of the microcapsules were obtained using a Nikon E-200 CPD light microscope at × 40 magnification. After the microcapsules were applied to the samples, the morphological characteristics of the samples were characterized by a ZEISS/EVO 40 electron microscope at 10 kV under a high vacuum at × 5000 magnification, after being coated with gold-palladium (Au-Pl) at a thickness of 40–50 nm by a BAL-TEC SCD 005 coating device.

Particle size distribution

Particle sizes of microcapsules were determined using software located in the light microscope. In order to measure the diameters of droplets and microcapsules on light microscope pictures, an image processing application was developed and implemented, which in turn enabled the determination of the size distribution. Firstly, in the light microscope, a reference microcapsule was designated and the particle size of the reference microcapsule was measured. After this, using the image processing application, the diameters of all remaining droplets and microcapsules were computed in proportion to the diameter of the reference microcapsule. In previous literature, particle size distribution has similarly been analyzed using a light microscope and image processing software.²⁵

Fourier transform infrared spectroscopy analysis

In order to chemically characterize the microcapsules, Fourier transform infrared spectroscopy (FTIR) was used. The FTIR spectrum of the natural oils both before and after microencapsulation was determined. The FTIR analysis was carried out at a wavenumber range of 380–4000 cm⁻¹ using a PerkinElmer Inc. Spectrum BX FTIR spectrometer equipped with attenuated total reflectance.

Repellence test procedure

In order to analyze the repellent properties of the samples, a special test cabinet (Figure 3) was designed. While the structure of the cabinet was made of pine, the rest was made of glass for the purpose of observing the repellent properties. On the top of the cabinet, there were two round holes with a diameter of 5 cm to allow the bees to breathe, which were closed with wire netting to prevent the bees from escaping. The front cover of the cabinet was designed to be collapsible, which enabled the introduction of the bees into the cabinet. Separate measuring cabinets were used for each sample. Each sample was placed at the right corner of the cabinet in a petri dish. In order to prevent the mixing of a variety of sample scents together, different gloves were worn when placing each sample into the cabinets. By doing so, no contact occurred between the samples. During the measurement periods, 100 honey bees (Apis mellifera) were placed in each test cabinet. A measuring cabinet is shown in Figure 3. The measurements were conducted for 2 h, during which the measurement cabinets were photographed with a Nikon D90 Digital single-lens reflex camera every 30 min. In addition, the cabinets were videotaped for 1 min in every 10 min.

Figure 3.

A test cabinet for bee repellents.

Results and discussion

Microcapsule images

In this study, the DEET, lavender, fennel and laurel oils were encapsulated with gum arabic wall material. Figure 4 shows microscopic images of the different microcapsules.

Figure 4.

Microscopic images of microcapsules.

Figure 4 illustrates the surface characteristic shape and size of microcapsules as seen using a light microscope. The diameters of the microcapsules are shown. As seen in Figure 4, it was found that the active substances were encapsulated with gum arabic. In this study, the morphologies of the oils coated by gum arabic showed spherical shaped with various sizes ranging from 1–68 µm. The diameters of the microcapsules are probably dependent on the physical properties and concentrations of the wall and core materials.²⁶ Timilsena et al. previously demonstrated that microcapsules obtained by the coacervation method have higher encapsulation efficiency.²⁷ Higher encapsulation efficiency in coacervation-based microcapsulation results from better surface-active nature of the coacervation. Furthermore, in the literature, it has previously been mentioned that coacervates migrate to the surface of lipid droplets during emulsification and that the wall material forms a uniform layer around the oil droplets.²⁸

Particle size distributions

The particle size distributions of microcapsules are shown in Figure 5.

Figure 5.

Particle size distributions of microcapsules.

Figure 4 shows images of microcapsules obtained by a light microscope. According to Figure 4, the microcapsules were spherical and similar to those obtained in a previous work, where hexadecane was microencapsulated within soy glycinin wall material via a simple coacervation technique and the diameter of particles ranged from 101.7–157.7 µm.²⁹ In our study, the diameter of particles ranged from 1–68 µm. The principle of coacervation technique is significant to elucidate how the core/wall ratio and viscosity core material affect the particle size. In the principle of coacervation technique, it is appeared to the aggregation and subsidence tendency of the core particles surrounded by coacervate droplets that may affect the particle size.²⁹

In this study, the particle sizes of microcapsules including different core materials are similar. It is considered that the viscosity of the core material plays an important role on the particle size distribution. Furthermore, the coacervation parameters (pH, duration, temperature and stirring speed) affect the particle size distribution. By the same token, these parameters were used in the production of all microcapsules, which is why the properties of core the materials are regarded as affecting the particle size distribution.^29–30

FTIR analysis of the microcapsules

The FTIR spectra of the essential oils of lavender, fennel and laurel, DEET, gum arabic solution and different microcapsules can be seen in Figures 6 to 13.

Figure 6.

The Fourier transform infrared spectra of lavender essential oil, gum arabic solution and lavender/gum arabic 1:5 microcapsules.

Figure 7.

The Fourier transform infrared spectra of fennel essential oil, gum arabic solution and fennel/gum arabic 1:5 microcapsules.

Figure 8.

The Fourier transform infrared spectra of laurel essential oil, gum arabic solution and laurel/gum arabic 1:5 microcapsules.

Figure 9.

The Fourier transform infrared spectra of N, N-diethyl-3-methylbenzamide, gum arabic solution and N, N-diethyl-3-methylbenzamide/gum arabic 1:5 microcapsules.

Figure 10.

The Fourier transform infrared spectra of lavender and laurel essential oils, gum arabic solution and lavender + laurel/gum arabic 1:5 microcapsules.

Figure 11.

The Fourier transform infrared spectra of lavender and fennel essential oils, gum arabic solution and lavender + fennel/gum arabic 1:5 microcapsules.

Figure 12.

The Fourier transform infrared spectra of laurel and fennel essential oils, gum arabic solution, and Laurel + Fennel/Gum arabic 1:5 microcapsules.

Figure 13.

The Fourier transform infrared spectra of lavender, fennel and laurel essential oils, gum arabic solution, and Lavender + fennel + laurel/gum arabic 1:5 microcapsules.

FTIR is a very useful technique for researching intermolecular interactions since the specific interactions affect the absorption frequency.³¹ In the FTIR spectra, gum arabic absorption bands near 3260–2090 cm⁻¹ are assigned to C-H stretching group. At 1640–1690 cm⁻¹, the bands are assigned to aromatic C=C bonding. The bands near 1000–1300 cm⁻¹ are assigned to C–O bonding. At 785–540 cm⁻¹, the bands are assigned to aromatic C–Cl bonding. According to the FTIR results for DEET, lavender, laurel and fennel oil, the absorption bands near 3200–3600, 2850–3000, 1670–1820 and 600–800 cm⁻¹ are referred to as O–H, C–H, C=O and C–Cl bonding, respectively. The FTIR spectra of lavender/gum arabic, fennel/gum arabic, laurel/gum arabic and DEET/gum arabic microcapsules are similar to that of gum arabic, which provides the wall structure of the microcapsules. Similar results have previously been reported in the literature.^31–33 Absorption bands of gum arabic at 3266, 2090, 1638, 1073 and 577 cm⁻¹ were observed for the microcapsules, which indicated that gum arabic was present in the microcapsules. In addition to this, the absorption bands of the core materials were observed for the microcapsules. Furthermore, the microcapsules spectra revealed the presence of the main absorbance of gum arabic. The reason for this result was deemed to be that the density of gum arabic in the microcapsules is more dominant. Furthermore, the characteristic bands of the essential oils and DEET, particularly those of aromatic compounds are found at low intensity and may overlap other spectrum signals.³⁴ Based on the above discussion, it was concluded that intermolecular interactions between the core materials and the gum arabic wall material had formed.³¹ Moreover, the intensities of some characteristic bands of DEET, lavender, laurel and fennel oils decreased in the microcapsules, revealing that core materials were encapsulated within wall material.³⁵

Characterization of the cotton fabrics treated with the microcapsules

The cotton fabric samples were analyzed by scanning electron microscopy (SEM) after impregnation with microcapsules containing different active ingredients. Figure 14 shows the SEM micrographs of the samples.

Figure 14.

Scanning electron microscopy micrographs of cotton fabric samples.

According to the SEM micrographs, individual microcapsule particles were observed in the structures of the cotton samples. Microcapsules made with gum arabic walls had generally spherical and smooth surfaces. These characteristics desirable of the microcapsules are because the integrity of the microcapsules leads to good core retention and lower permeability of water vapor and oxygen.^36–39 Furthermore, SEM images showed that core material was coated completely by the wall coating agents. Moreover, the SEM micrographs showed no observable fractures, cracks or pores.

Repellent properties

Figures 15 to 26 show the repellent results of the samples. The repellent properties of the samples were monitored at 10 min intervals over 2 h.

Figure 15.

Bee-repellent properties of the control sample.

According to the results, in Figure 15, the bees came into contact with the cotton sample that was used in beekeeping. The cotton fabric had no bee repellent properties, so the bees attacked it.

Figure 16 shows the repellent properties of the sample treated with the lavender/gum arabic 1:5 microcapsules. The result showed that the bees stayed off the sample, so the sample had bee-repellent properties. According to the HPLC results, the lavender oil consists of α-pinene, β-pinene, camphene, δ-3-carene, limonene, 1.8-cineole, camphor, linalool and linalyl acetate, which are known insect repellents.^40–44 These components cause the repellent property of the microcapsules that contain lavender oil. In literature, it has previously been mentioned that lavender essential oil is an effective insect repellent.⁴⁵

Figure 16.

Bee-repellent properties of the sample treated with the lavender/gum arabic 1:5 microcapsules.

Figure 17 shows the bee-repellent activity of the sample treated with the fennel/gum arabic 1:5 microcapsules. The HPLC analysis of the fennel essential oil shows that it contains limonene, estragole, carvone, (2)-anethole, anisaldehyde, anis ketone and dillapiole. These components are known insect repellents.^46–48 Furthermore, in previous research, fennel essential oil has been described as an effective insect repellent. It has previously been reported that the active ingredients in fennel oil lead to fennel oil having insect-repellent properties.²²

Figure 17.

Bee-repellent properties of the sample treated with the fennel/gum arabic 1:5 microcapsules.

According to Figure 18, the bees were aggressive in the cabin and attacked the sample treated with the laurel/gum arabic 1:5 microcapsules. However, the HPLC results of the laurel oil show that laurel oil includes repellent ingredients.^44,46,49 In the literature, laurel essential oil has previously been reported as an insect-repellent essential oil due to its active ingredients.⁵⁰ In this cabinet, the laurel odor at the dose applied caused bee irritation. It is understood that an overdose of laurel essential oil causes aggression instead of repellence. The laurel oil stimulated an alarm response, and this caused the aggression and clustering of bees onto the sample. This indicates that the dose of laurel oil should be decreased.^51,52

Figure 18.

Bee-repellent properties of the sample treated with the laurel/gum arabic 1:5 microcapsules.

Figure 19 shows the repellent properties of the sample treated with DEET microcapsules. According to the results, the bees did not contact the sample but instead stayed a short distance away from the sample. Bee deaths started at 80 min in this measurement cabin, and a total of five bees had died after 120 min. The bees died because of the intense stress and insecticide effect of DEET.

Figure 19.

Bee-repellent properties of the sample treated with the N, N-diethyl-3-methylbenzamide/gum arabic 1:5 microcapsules.

In the literature, DEET has been widely described as an insect repellent since its discovery more than five decades ago. It is effective against mosquitoes and other insects of medical and veterinary importance, and is used worldwide. In spite of the effectiveness of DEET and its history of seemingly safe use, some studies have mentioned the unacceptably high potential health risks of DEET. Furthermore, DEET has been recognised as being quite deadly for all types of insect.^53–55

Figure 20 demonstrates the bee-repellent behavior of the sample treated with the lavender + fennel/gum arabic 1:5 microcapsules. The sample shows high bee-repellent properties. This result is believed to be caused by the bee-repelling components in the lavender and fennel oils.

Figure 20.

Bee-repellent properties of the sample treated with the lavender + fennel/gum arabic 1:5 microcapsules.

Figure 21 shows the bee-repellent properties of the sample treated with the lavender + laurel/gum arabic 1:5 microcapsules. The results show that the bees are not on the sample but instead fly a short distance away from the sample. It was also observed that the bees appear nervous. A possible reason for this observation is that the odor of the lavender and laurel essential oil mixture irritates the bees.^51,52

Figure 21.

Bee-repellent properties of the sample treated with the lavender + laurel/gum arabic 1:5 microcapsules.

Figure 22 shows the bee-repellent behavior of the sample treated with the laurel + fennel/gum arabic 1:5 microcapsules. According to the results, the bees do not contact the sample and are positioned a great distance from the sample. The mixture of the laurel and fennel oils repels the bees. The reason for this observation is that the fennel essential oil is believed to suppress the irritating effect of the laurel oil.

Figure 22.

Bee-repellent properties of the sample treated with the laurel + fennel/gum arabic 1:5 microcapsules.

According to Figure 23, the sample treated with the lavender + fennel + laurel/gum arabic 1:5 microcapsules has a bee-repellent effect. The lavender, fennel and laurel oils consist of bee-repellent ingredients. It is for this reason that the sample treated with the lavender + fennel + laurel/gum arabic 1:5 microcapsules repels the bees.

Figure 23.

Bee-repellent properties of the sample treated with the lavender + laurel + fennel/gum arabic 1:5 microcapsules.

Figures 24 to 26 show the bee-repellent properties of the samples treated with the DEET + lavender/gum arabic 1:5, DEET + fennel/gum arabic 1:5 and DEET + laurel/gum arabic 1:5 microcapsules, respectively. The results show that these samples cause death of the bees in the cabinet. The number of dead bees from the sample treated with the DEET + lavender/gum arabic microcapsules was more than those of the samples treated with DEET + fennel/gum arabic and DEET + laurel/gum arabic microcapsules. The mixture of the DEET and lavender oil causes the bees to secrete a stress hormone more than in the presence of the mixtures of DEET/fennel oil and DEET/laurel oil. A possible reason that the DEET and lavender oil mixture had an insecticide effect on bees could be due to a cumulative overdose. Furthermore, the addition of the essential oils to DEET reduced bee deaths and enhanced the repellent effect of the DEET.

Figure 24.

Bee-repellent properties of the sample treated with the N, N-diethyl-3-methylbenzamide + lavender/gum arabic 1:5 microcapsules.

Figure 25.

Bee-repellent properties of the sample treated with the N, N-diethyl-3-methylbenzamide + fennel/gum arabic 1:5 microcapsules.

Figure 26.

Bee-repellent properties of the treated with the N, N-diethyl-3-methylbenzamide + laurel/gum arabic 1:5 microcapsules.

Compared to the repellent effect of the DEET and lavender combination, the repellent effect of the fennel and laurel oil combination is higher. Moreover, the lavender, fennel and laurel oils did not lead to the death of bees, so these essential oils can be used as alternatives to DEET, which is a synthetic insect repellent. The results show that lavender and fennel essential oils are good alternatives to chemical insecticides or repellents.

Conclusion

The aim of this study was to facilitate the production of bee-repellent fabric produced from natural materials. Within this scope, microcapsules containing gum arabic shell with different core substances were fabricated with via a simple coacervation method. The microcapsules were initially analyzed by light microscope and subsequently analyzed by FTIR after the microcapsules were applied to cotton fabrics via a dipping method. In addition, the transfer of capsules to the fabrics was analyzed by SEM. The bee-repellent properties of the samples were analyzed in separate cabinets. The light microscope results show that the core materials were encapsulated with gum arabic. Furthermore, it was observed that the microcapsules were applied to cotton fabric samples successfully. According to bee-repellent measurements, the microcapsules made from lavender and fennel oils had optimal bee-repellent properties compared to the other microcapsules. The samples that consisted of DEET caused bee deaths. As a result, we conclude that the microcapsules produced with essential oils such as lavender and fennel oils can be used to manufacturing bee suits with bee-repellent properties. Furthermore, the microencapsulation of essential oils delivers long-term effect, lowering the costs of long-term use.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Ministry of Science, Industry, and Technology in Turkey under Grant Number 0897.STZ.2015.

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