Herbal Extract Incorporated Nanofiber Fabricated by an

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Herbal extract incorporated nanofiber fabricated by an electrospinning technique and its application to antimicrobial air filtration Jeongan Choi, Byeong Joon Yang, Gwi-Nam Bae, and Jaehee Jung ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b07441 • Publication Date (Web): 27 Oct 2015 Downloaded from http://pubs.acs.org on November 2, 2015

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ACS Applied Materials & Interfaces

Herbal Extract Incorporated Nanofiber Fabricated by an Electrospinning Technique and its Application to Antimicrobial Air Filtration Jeongan Choi a†, Byeong Joon Yang a, b†, Gwi Nam Bae a, and Jae Hee Jung a* a

Center for Environment, Health and Welfare Research, Korea Institute of Science and Technology, Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Republic of Korea b

Department of Electric Engineering, Seoul National University of Science and Technology, Gongneung-ro, Nowon-gu, Seoul 139-743, Republic of Korea

†

Authors equally contributed to this work.

*

To whom correspondence should be addressed.

E-mail: [email protected]; Tel: 82-2-958-5718; Fax: 82-2-958-5805

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ABSTRACT Recently, with the increased attention to indoor air quality, antimicrobial air filtration techniques have been studied widely to inactivate hazardous airborne microorganisms effectively. In this study, we demonstrate herbal extract incorporated (HEI) nanofibers synthesized by an electrospinning technique and their application to antimicrobial air filtration. As an antimicrobial herbal material, an ethanolic extract of Sophora flavescens, which exhibits great antibacterial activity against pathogens, was mixed with the polymer solution for the electrospinning process. We measured various characteristics of the synthesized HEI nanofibers, such as fiber morphology, fiber size distribution, and thermal stability. For application of the electrospun HEI nanofibers, we made highly effective air filters with 99.99% filtration efficiency and 99.98% antimicrobial activity against Staphylococcus epidermidis. The pressure drop across the HEI nanofiber air filter was 4.75 mmH2O at a face air velocity of 1.79 cm/s. These results will facilitate the implementation of electrospun HEI nanofiber techniques to control air quality and protect against hazardous airborne microorganisms.

Keywords: Natural product, nanoparticles, aerosol process, antimicrobial filter, electrospinning


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INTRODUCTION Airborne microorganisms (or bioaerosols), such as bacteria, viruses, and fungi in the air can affect people’s quality of life greatly. They can pose serious health threats to the public, and cause contagious infectious diseases, acute toxicity, and allergies.1-4 Recently, with increased attention to indoor air quality (IAQ), various methods to control bioaerosols have been suggested, including the use of ultraviolet germicidal irradiation,5-7 air electric ion emission,8 thermal treatment,9-10 antimicrobial air filtration,11-12 and titanium dioxide catalysis.13-14 In particular, antimicrobial air filtration technology has been used most widely for removing bioaerosols because they are easily applied to conventional airconditioning systems. Previous studies have reported that various antimicrobial inorganic materials, such as silver (Ag),15-16 copper (Cu) nanoparticles,17 and carbon nanotubes (CNTs)18-19, are effective in controlling bioaerosols because of their excellent antimicrobial properties. These materials have been used to add the antimicrobial function to air filter media. However, many warnings regarding the health risk of exposure to inorganic nanoparticles have also been reported. For example, previous studies have indicated that Ag nanoparticles are toxic to mammalian cells and certain organs because of transcutaneous penetration of the particles20-21 and Cu oxide nanoparticles can induce DNA damage and oxidative stress in cells.22-23 Also, various toxicity mechanisms of CNTs have been reported, including penetration of the cell envelope, and oxidation of cell components.24 Moreover, long-term inhalation of these nanoparticles can lead to a reduction in respiratory function.25 Recently, antimicrobial herbal extracts have been proposed as alternative antimicrobial materials, which are typically less toxic than inorganic antimicrobial materials.26 Depending on the extract and the nature of the material, their properties can include anti-inflammatory, antiviral, and/or antimicrobial effects.27-29 Herbal extracts, such as from Melaleuca alternifolia (tea tree), Eucalyptus, and Sophora flavescens, in particular, have been used as coatings for air filters to inactivate fungal spores, bacteria, and influenza viruses.30-36 Previous studies have proposed two kinds of representative methods for antimicrobial filter fabrication: a liquid dip-coating process and an aerosol-based process. Liquid dip-


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coating is generally used for antimicrobial filter production.11 This method, which involves soaking air filters in liquid containing antimicrobial substances, is relatively fast and easy, and is therefore the most common production method. In aerosol-based processes, airborne antimicrobial particles are loaded onto the filters to achieve antimicrobial ability.37 This process works according to the same principle as the conventional air filtration mechanism, in which airborne particles are collected on the filter medium. However, while the treatment of filter surfaces with antimicrobial herbal extract is an effective method for enhancing their antimicrobial activity, such treatments suffer the drawbacks of increasing the pressure drop across the filter, which leads to a reduction in filter life and requires additional processing to coat the filters with the antimicrobial substances. Therefore, a new method for the fabrication of antimicrobial filters is necessary to facilitate low-cost, high-efficiency antimicrobial filters. Here, we demonstrate an antimicrobial, herbal extract-incorporated (HEI) air filter fabricated using a simple electrospinning technique. Generally, the electrospinning process uses a high voltage electric field to produce electrically charged jets from polymer solution or melts that, on drying (by means of evaporation of the solvent) produce nanofibers.38 Electrospinning is a versatile method for fabricating ultrathin fibers that have uniform diameters, from tens of nanometers to several micrometers.39 Because this technique has attractive features, such as its simplicity and the inexpensive nature of its mechanism, it is used widely for several applications, including filtration,40 drug delivery,41 reinforcement of composite materials,42 catalytic nanofibers,43 and fiber-based sensors,44 as well as biomaterials for wound dressings45 and tissue engineering scaffolds.46 Especially, it may be a promising technique for generating stable HEI fibers in a room temperature process. However, for antimicrobial air filtration, the fabrication of HEI fibers by an electrospinning technique has not been reported before. In this study, we generated HEI nanofibers using an electrospinning technique. As an antimicrobial herbal extract, Sophora flavescens, which has strong antibacterial activity against pathogens, was used. From various mixtures of polymer and herbal extracts, we measured the various physical characteristics of the synthesized fibers, such as morphology, fiber size distribution, and thermal stability. For the application of antimicrobial air filtration, we tested not only the antimicrobial ACS Paragon Plus Environment

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activity against a bacterial bioaerosol but also the filtration characteristics, such as the particle filtration efficiency and pressure drop. This study meets the requirements of efficient air filtration with a low pressure drop, simplicity of the manufacturing process, and a less toxic antimicrobial filter.

MATERIALS AND METHODS The experimental setup consisted of two primary components: (i) an electrospinning system for preparation of antimicrobial HEI nanofiber and (ii) a system setup for evaluating air filter performance.

Herbal plant material and extraction S. flavescens plants were purchased from Kyung-dong Oriental Herbal Market, Seoul, Korea.47 A control specimen was stored at the Functional Food Center, Korea Institute of Science and Technology, Gangneung Institute, Korea. Dried S. flavescens roots (600 g) were refluxed three times with 99% ethanol for 3 h. After filtration, the ethanol extracts were evaporated in vacuo and freeze-dried. The resulting S. flavescens powders were resuspended in pure ethanol (111727; Merck KGaA, Darmstadt, Germany) at various concentrations (2.04 wt%, 4.0 wt7%, and 6.11 wt%), and sonicated for 10 min. Insoluble residue was then removed by centrifugation (5000 × g, 20 min). The final solution was filtered with a cellulose acetate membrane filter (National Scientific Co., Rockwood, TN, USA) with a 0.45-µm pore size.

Electrospinning system for HEI nanofiber synthesis To prepare the HEI polymer solutions, polyvinyl pyrrolidone (PVP, 437190; Sigma-Aldrich, St. Louis, MO, USA) was added to herbal solutions of various concentrations (2.04%, 4.07%, and 6.11%) to 15 wt% and stirred at 120 rpm at room temperature for 5 h. Subsequently, three independently prepared HEIpolymer solutions were loaded in a 10-mL syringe (i.d. = 15.85 mm; Gastight 81620; Hamilton Co.,


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Reno, NV, USA) for electrospinning. A positive 15 kV DC voltage was applied at the stainless steel tubing tip (U-102; IDEX Health & Science, Oak Harbor, WA, USA) with respect to a grounded aluminum collector (a piece of flat round aluminum foil sheet) by a high-voltage generator (Korea switching Co., Seoul, Korea). The vertical distance between the stainless steel tubing tip and collector was 10 cm. Solutions were pumped to the tip with a syringe pump (KD200; KD Scientific Inc., Hollison, MA, USA) at a constant flow rate of 3 mL/h. A schematic of the electrospinning system is shown in Figure 1(a). For preparation of antimicrobial HEI nanofiber air filter, the electrospun HEI nanofibers were deposited continuously on a metallic screen filter support (o.d. = 25 mm, thickness = 0.3 mm) with various herbal extract concentrations. Weighing of prepared filter samples was performed using a microbalance (Mettler MT5; Mettler-Toledo International Inc., Seoul, Korea) to an accuracy of 1 µg.

Characterization of the synthesized HEI nanofibers The morphology and size of electrospun HEI nanofibers were investigated by scanning electron microscopy (SEM; XL30 ESEM-FEG; Philips Electron Optics, Eindhoven, The Netherlands). The nanofiber samples were coated with Pt-Pd using an ion-sputtering coater (model IB-3; Eiko Co., Ltd., Ibaraki, Japan) and analyzed under high vacuum (10-5 mbar) using the SEM. Fourier transform infrared spectroscopy (FTIR) spectra were acquired on a JASCO FTIR 4100 spectrometer (JASCO Inc., Easton, MD, USA) in the range of 500 to 4000 cm-1 to confirm the incorporation of herbal extract into the HEI nanofibers. Thermogravimetric analysis (TGA, model Q500; TA Instruments, New Castle, DE, USA) was used to measure the change in the mass of the HEI nanofibers with increasing surrounding temperature. A TGA curve was generated using a heating rate of 10°C/min under constant airflow at 50 mL/min. Samples were heated from 20 to 800°C.

Preparation of bacterial suspensions The Gram-positive Staphylococcus epidermidis (KCTC 1917) was selected as the antimicrobial test bacterium. The S. epidermidis is commonly used in bioaerosol research. Cultures of S. epidermidis were ACS Paragon Plus Environment

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grown in nutrient broth (NB; Becton Dickinson, Franklin Lakes, NJ, USA) at 37°C for 24 h. Stationaryphase organisms were harvested by centrifugation (5000 × g, 10 min).

Filtration tests Figure 1(b) shows a schematic diagram of the experimental setup for filtration tests. For bioaerosol generation, bacterial pellets were carefully washed three times with sterilized deionized water (SDW) using a centrifuge (RC-5B, Sorval Co., CT, USA; 5000 × g, 10 min) to remove residual particles, including components of the nutrient broth. SDW was also used for dilution to obtain the final bacterial suspension. A 30-mL aliquot was placed in a one-jet Collison nebulizer (BGI Inc., Butler, NJ, USA) and nebulized at an airflow rate of 1.2 L/min. Dispersed bioaerosols were passed through a diffusion dryer to remove moisture and through a

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Po neutralizer to reduce the electrical charge on the bioaerosols,

and then introduced into the filter holder where a prepared antimicrobial filter was installed. The face velocity on the filter was controlled from 1.79 to 3.59 cm/s using a mass flow controller. The pressure drop across the filter was measured using a micromanometer (FCO12; Furness Controls Ltd., Bexhill, UK). The particle size distribution and concentrations of the bioaerosols were measured upstream and downstream of the filter using an aerodynamic particle sizer (APS 3320, TSI Inc., Shoreview, MN, USA), which sizes airborne particles in the range 0.5–20 µm using a time-of-flight technique that measures aerodynamic diameter in real time. The overall particle filtration efficiency (η) is defined as η = 1- Cdown ⁄ Cup

(1)

where Cdown and Cup are the particle concentrations (particles/cm3air) of the bioaerosols measured downstream and upstream of the filter, respectively.

Antimicrobial tests Bioaerosols were deposited continuously onto filters for a period of 5 min in all experiments to obtain identical loading on all filters. Approximately 106 cells were inoculated onto the test filter and incubated for a contact time of 30 min at room temperature.48 Each filter was removed from the filter holder ACS Paragon Plus Environment

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immediately after bioaerosol sampling and placed into a Petri dish (o.d. = 55 mm) with a bacteria residence time of 30 min. Each filter was then soaked in a 50-mL conical tube containing 5 mL of a phosphate-buffered saline (PBS, pH 7.4) with 0.01% Tween 80. Samples in extraction fluid were vortexed for 2 min. Samples in solution then underwent an agitation step in an ultrasonic bath with ice for 10 min. Aliquots of the 0.1-mL extract suspensions were serially diluted with PBS, plated on nutrient agar, and incubated at 37°C for 24 h. After incubation, the colonies that formed on the plates were counted. The inactivation rate was calculated using the following equation: Bacterial viability (%) =

CFU experiment CFU control

×100% ,

(2)

Inactivation rate (%) = 100 − bacterial viability (%)

(3)

where CFUexperiment and CFUcontrol are the number of bacterial colonies derived from the HEI nanofiber and control filters, respectively.

RESULTS AND DISCUSSION Characteristics of the electrospun HEI nanofibers The SEM images in Figure 2(a) show the morphology of electrospun HEI nanofibers. Both nanofibers containing herbal extract (HE) and the control fibers (without HE) exhibited showed a smooth and clear surfaces without small beads or any other damage. Although the electrospinning process produces nanofibers ranging in size from several hundred nanometers to micrometers, the overall fiber diameter of the HEI nanofibers was smaller than that of the control fibers. The normalized fiber size distribution of the electrospun HEI nanofibers is shown in Figure 2(b). The average fiber diameter and the cut-off diameter (d50) were 1.49 ± 0.461 µm and 1.42 µm for the control fibers and 0.47 ± 0.291 µm and 0.35 µm for the HEI nanofibers containing the 6.11% herbal extract, respectively (Table 1). The size distributions of the HEI nanofibers in Figure (b) show bimodal distributions, with peaks at ~ 0.3 and ~ 1 ACS Paragon Plus Environment

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µm. In Figures (b-1), (b-2), and (b-3), the overall distribution shifted to the left, and more nanofibers (d 3 µm of particle size, the HEI nanofiber filter showed > 95% FFE over the entire size range. Furthermore, total particle filtration efficiencies of the HEI nanofiber and control filters were 99.9 ± 0.01% and 96.7 ± 0.03%, respectively. Quantitative analysis of air penetration of the filter was carried out by investigating the filter pressure drop with various face air velocities (Fig. 6(c)). As the face velocity of airflow increased from 1.79 to 3.59 cm/s (0.4 to 0.8 L/min of airflow rate), the pressure drop of the control filter increased linearly from 4.6 ± 0.08 to 9.4 ± 0.18 mmH2O, compared with the HEI nanofiber filter (4.7 ± 0.01 to 10.5 ± 0.05 mmH2O). Also, the pressure drop difference between both filters increased from ∆3.9% (1.79 cm/s) to ∆13% (3.59 cm/s) under the test conditions of face air velocity. The theoretical pressure drop, ∆Pth, can be calculated for a fibrous filter based on the cumulative drag on the fibers in the filter:58 ∆Pth =

16αηUL ( d 2f )( Ku )

(4)

where, α is the solidity or packing density of the filter, η is the air viscosity, U is the face velocity at the filter surface, L is the filter depth or thickness, d f is the fiber diameter, and Ku is the hydrodynamic factor, or Kuwabara number ( Ku = −0.5ln α − 0.75 + α − 0.25α 2 in viscous flow through a bed of cylinders oriented perpendicular to the flow).59 From equation (4), the pressure drop increases ACS Paragon Plus Environment

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with increasing packing density of the filter ( α ) and decreasing fiber diameter ( d f ). According to our results, shown in Figures 6(b) and (c), the HEI nanofiber air filter, which has a smaller average fiber diameter and higher packing density than the control filter, showed superior filtration efficiency performance, while its pressure drop was slightly higher than that of the control filter. In the present study, a flat panel-type filter was used for the filtration performance tests, such as filtration efficiency and filter pressure drop. In real situations, however, folded filter media are typically used to enlarge the filtration area, such that the pressure drop can be decreased.

Antimicrobial performance of HEI nanofiber filter The antimicrobial effects of HEI nanofiber air filters were evaluated in terms of the reduction of bacterial viability on filters against S. epidermidis bioaerosols. Figure 7 shows the variation in the S. epidermidis viability on HEI nanofiber filters. The HEI nanofiber filter with 6.11% of the herbal extract concentration showed a ~99.98% bacterial inactivation rate. Previous studies also showed that the antimicrobial activity of filters increased with the quantity of S. flavescens nanoparticles deposited on the filter surface.37, 47 The major chemical compounds in S. flavescens extract have biological activities: sophoraflavanone G displays antibacterial, anti-inflammatory, and anticancer effects,60-61 while kurarinone induces apoptosis in tumor cells and exhibits antioxidant and phytoestrogenic effects.62-64

CONCLUSIONS The HEI nanofibers was fabricated using a simple electrospinning technique. Various physical characteristics of the HEI nanofibers, such as morphology, fiber size distribution, and thermal stability were studied by SEM and TGA analyses. The HEI nanofibers had a smooth surface, thermal stability, and better packing density than the control fibers. As a demonstration of HEI nanofibers use in antimicrobial air filtration, the filtration efficiency and antimicrobial activity of the HEI nanofiber air filter were 99.9% and 99.5%, respectively, against S. epidermidis bioaerosols. The herbal ACS Paragon Plus Environment

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extract/polymer hybrid nanofiber in air filtration may have the potential to control indoor air quality against hazardous bioaerosols.

ACKNOWLEDGMENTS This research was supported by the Railway Technology Research Project, funded by the Ministry of Land, Infrastructure, and Transport (15RTRP-B082486-02), Republic of Korea, and was partially supported by the KIST Institutional Program.


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44. Wang, X.; Drew, C.; Lee, S.-H.; Senecal, K. J.; Kumar, J.; Samuelson, L. A., Electrospun nanofibrous membranes for highly sensitive optical sensors. Nano Lett. 2002, 2 (11), 1273-1275. 45. Khil, M. S.; Cha, D. I.; Kim, H. Y.; Kim, I. S.; Bhattarai, N., Electrospun nanofibrous polyurethane membrane as wound dressing. J. Biomed. Mater. Res. B 2003, 67 (2), 675-679. 46. Li, W. J.; Laurencin, C. T.; Caterson, E. J.; Tuan, R. S.; Ko, F. K., Electrospun nanofibrous structure: a novel scaffold for tissue engineering. J. Biomed. Mater. Res. 2002, 60 (4), 613-621. 47. Jung, J. H.; Lee, J. E.; Bae, G.-N., Use of electrosprayed Sophora flavescens natural-product nanoparticles for antimicrobial air filtration. J. Aerosol Sci. 2013, 57, 185-193. 48. Jung, J. H.; Hwang, G. B.; Park, S. Y.; Lee, J. E.; Nho, C. W.; Lee, B. U.; Bae, G.-N., Antimicrobial air filtration using airborne Sophora flavescens natural-product nanoparticles. Aerosol Sci. Technol. 2011, 45 (12), 1510-1518. 49. Kuroyanagi, M.; Arakawa, T.; Hirayama, Y.; Hayashis, T., Antibacterial and antiandrogen flavonoids from Sophora flavescens. J. Nat. Prod. 1999, 62 (12), 1595-1599. 50. Kang, T. H.; Jeong, S. J.; Ko, W. G.; Kim, N. Y.; Lee, B. H.; Inagaki, M.; Miyamoto, T.; Higuchi, R.; Kim, Y. C., Cytotoxic lavandulyl flavanones from Sophora flavescens. J. Nat. Prod. 2000, 63 (5), 680-681. 51. Angammana, C. J.; Jayaram, S. H., Analysis of the effects of solution conductivity on electrospinning process and fiber morphology. IEEE T. Ind. Appl. 2011, 47 (3), 1109-1117. 52. Uyar, T.; Besenbacher, F., Electrospinning of uniform polystyrene fibers: The effect of solvent conductivity. Polymer 2008, 49 (24), 5336-5343. 53. Lin, T.; Wang, H.; Wang, H.; Wang, X., The charge effect of cationic surfactants on the elimination of fibre beads in the electrospinning of polystyrene. Nanotechnology 2004, 15 (9), 1375. 54. Demir, M. M.; Yilgor, I.; Yilgor, E.; Erman, B., Electrospinning of polyurethane fibers. Polymer 2002, 43 (11), 3303-3309. 55. Suganya, S.; Senthil Ram, T.; Lakshmi, B.; Giridev, V., Herbal drug incorporated antibacterial nanofibrous mat fabricated by electrospinning: an excellent matrix for wound dressings. Journal of Applied Polymer Science 2011, 121 (5), 2893-2899. 56. Peng, C.; Hou, Z.; Zhang, C.; Li, G.; Lian, H.; Cheng, Z.; Lin, J., Synthesis and luminescent properties of CaTiO 3: Pr 3+ microfibers prepared by electrospinning method. Optics Express 2010, 18 (7), 7543-7553. 57. Kim, G.-M.; Le, K. H. T.; Giannitelli, S. M.; Lee, Y. J.; Rainer, A.; Trombetta, M., Electrospinning of PCL/PVP blends for tissue engineering scaffolds. Journal of Materials Science: Materials in Medicine 2013, 24 (6), 1425-1442.


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Table Legend TABLE 1. Size characteristics of the electrospun HEI nanofibers.

Figure Legends FIGURE 1. Experimental configuration of (a) the electrospinning system for generating the herbal extract-incorporated (HEI) nanofibers and (b) the air filtration test system including bioaerosol generation. FIGURE 2. Morphology and size distribution of control fibers and synthesized HEI nanofibers (2.04%, 4.07%, and 6.11%): (a) scanning electron microscope (SEM) images and (b) fiber size distributions. FIGURE 3. FTIR spectra of (a) control fibers, (b) herbal extract and (c) HEI nanofibers (6.11%). FIGURE 4. Variation in the relative weight loss (%) of the herbal extract powder, control fibers, and HEI nanofibers (6.11%) as determined by thermogravimetric analyses: (a) TGA curve and (b) DTA curve. FIGURE 5. Preparation of antimicrobial air filters using HEI nanofibers (6.11%): (a) pictures of entire filter area (~5.1 cm2) and (b) SEM images. FIGURE 6. Filtration performance of HEI nanofiber air filters: (a) particle size distribution of S. epidermidis bioaerosols, (b) fractional filtration efficiency (%), and (c) filter pressure drop of control and HEI nanofiber filters (6.11%). FIGURE 7. Variation of bacterial viability on HEI nanofiber filter with various herbal extract concentrations.


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TABLE 1. Size characteristics of the electrospun HEI nanofibers.

Mean ± SDa [µm]

CVb

d50c [µm]

0 wt% (n = 288)d

1.49 ± 0.461

0.308

1.424

2.04 wt% (n = 271)

0.68 ± 0.387

0.569

0.697

4.07 wt% (n = 243)

0.58 ± 0.402

0.693

0.394

6.11 wt% (n = 251)

0.47 ± 0.291

0.619

0.350

Sample Control fiber

HEI nanofiber

a

Mean ± Standard deviation of the measured fibers

b

Coefficient of variation

c

Cut-off fiber diameter at a cumulative number concentration of 50%

d

Number of fibers measured by SEM


20

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FIGURE 1


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

FIGURE 2


22

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FIGURE 3

% of Arbitrary Transmittance Units

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1598 2955

1286

1651 1422

2341

1047

(a) Control fibers

(b) Herbal extract

(c) HEI nanofibers

4000

3500

3000

2500

2000

Wave number cm

1500 -1


23

1000


FIGURE 4

(a) 100 Heat rate : 10oC/min N2 Condition

Weight (%)

80 60 40 HE powder Control fiber HEI nanofiber

20 0 0

200

400

600

800

o

Temperature ( C)

(b) 2.0

HE powder Control fiber HEI nanofiber

o

Derivation of weight (%/ C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.5

1.0

0.5

0.0 0

200

400

600 o

Temperature ( C)


24

800

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FIGURE 5


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

FIGURE 6


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FIGURE 7 100 S. epidermidis

Bacterial viablity (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10

5.51%

1

0.84%

0.1 0.02%

0.01 0

1

2

3

4

5

6

Concentration of herbal extract (%)


27

7


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85x43mm (300 x 300 DPI)


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Herbal Extract Incorporated Nanofiber Fabricated by an

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