Method for manufacturing nanofibers, method for manufacturing food freshness sensors, and method for manufacturing drug-supported nanofibers

Abstract

This invention provides a method for producing nanofibers that does not use highly toxic crosslinking agents and has a low environmental impact. Furthermore, it also provides a method for producing food freshness sensors and drug-supported nanofibers based on the nanofiber production method of this invention. [Solution] A method for producing nanofibers, comprising: a spinning solution preparation step of preparing a spinning solution containing a citrus-derived material obtained from citrus fruits and a water-soluble polymer that can be made into fibers; a nanofiber formation step of forming nanofibers from the spinning solution by electrospinning; and a crosslinking step of crosslinking the nanofibers.

Description

[Technical Field]

[0001] This invention relates to a method for producing nanofibers, a method for producing food freshness sensors, and a method for producing drug-supported nanofibers. [Background technology]

[0002] Conventionally, a method for producing nanofibers is known in which a spinning solution is prepared by dissolving a fiberizable water-soluble polymer in water, and nanofibers are formed from the spinning solution by electrospinning (see, for example, Patent Document 1). An example of a water-soluble polymer is polyvinyl alcohol (PVA). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2008-179629 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, nanofibers formed from water-soluble polymers have low water resistance in their original state. Therefore, in the manufacturing method of nanofibers using water-soluble polymers, crosslinking the nanofibers after formation is performed to increase their water resistance.

[0005] Crosslinking of nanofibers can be achieved by applying energy, such as heat, to the nanofibers. However, crosslinking nanofibers solely through energy application is often inefficient. Therefore, it is common practice to add a substance that promotes crosslinking (crosslinking agent) to the spinning solution.

[0006] Compounds containing acidic functional groups or aldehyde groups (formyl groups) are often used as crosslinking agents. However, many of these compounds are toxic due to their nature or their manufacturing process (impurities, etc.), and some have a high environmental impact. Therefore, in the field of nanofiber technology, there is a strong demand for nanofiber manufacturing methods that do not use highly toxic crosslinking agents and have a low environmental impact.

[0007] This invention has been made in view of the above problems, and aims to provide a method for producing nanofibers that does not use highly toxic crosslinking agents and has a low environmental impact. It also aims to provide a method for producing food freshness sensors and a method for producing drug-supported nanofibers based on the nanofiber production method of this invention. [Means for solving the problem]

[0008] [1] A method for producing nanofibers according to one embodiment of the present invention is characterized by comprising: a spinning solution preparation step of preparing a spinning solution containing a citrus-derived material obtained from citrus fruits and a fiberizable water-soluble polymer; a nanofiber formation step of forming nanofibers from the spinning solution by electrospinning; and a crosslinking step of crosslinking the nanofibers.

[0009] [2] In a method for producing nanofibers according to one embodiment of the present invention, the water-soluble polymer preferably contains at least one of polyvinyl alcohol and polyvinyl alcohol copolymer.

[0010] [3] In a method for producing nanofibers according to one embodiment of the present invention, the water-soluble polymer preferably further contains inulin.

[0011] [4] In a method for producing nanofibers according to one embodiment of the present invention, the citrus-derived material is preferably obtained from lemon fruit.

[0012] [5] In the method for producing nanofibers according to one embodiment of the present invention, it is preferable that the citrus-derived substance includes the fruit juice of the fruit and constitutes at least a part of the solvent in the spinning solution.

[0013] [6] In the method for producing nanofibers according to one embodiment of the present invention, in the spinning solution preparation step, the spinning solution is prepared by adding the water-soluble polymer to the solvent containing the citrus-derived substance, and the concentration of the citrus-derived substance in the solvent is preferably within the range of 90 to 100% by weight.

[0014] [7] In the method for producing nanofibers according to one embodiment of the present invention, in the crosslinking step, it is preferable to heat the nanofibers within the range of 80 to 100°C.

[0015] [8] The method for producing a food freshness sensor according to one embodiment of the present invention includes a spinning solution preparation step of preparing a spinning solution containing a citrus-derived substance obtained from a citrus fruit and a fiber-forming water-soluble polymer, a nanofiber forming step of forming nanofibers from the spinning solution by electrospinning, a crosslinking step of crosslinking the nanofibers, and a discoloration dye loading step of loading a discoloration dye that changes color due to a substance released upon food spoilage onto the crosslinked nanofibers.

[0016] [9] In the method for producing a food freshness sensor according to one embodiment of the present invention, it is preferable that the discoloration dye includes curcumin.

[0017]

[10] The method for producing a drug-loaded nanofiber according to one embodiment of the present invention includes a spinning solution preparation step of preparing a spinning solution containing a citrus-derived substance obtained from a citrus fruit, a fiber-forming water-soluble polymer, and a drug component, a nanofiber forming step of forming nanofibers from the spinning solution by electrospinning, and a crosslinking step of crosslinking the nanofibers.

[0018]

[11] In a method for producing drug-supported nanofibers according to one embodiment of the present invention, the drug preferably includes aloe vera. [Effects of the Invention]

[0019] In the nanofiber manufacturing method of the present invention, a citrus-derived substance obtained from citrus fruits is used as a crosslinking agent (a so-called green crosslinking agent). Citrus fruits are generally used as food products, and are considered to have low toxicity and low environmental impact. Therefore, the nanofiber manufacturing method of the present invention does not use highly toxic crosslinking agents and is an environmentally friendly method for manufacturing nanofibers.

[0020] The present invention provides a method for manufacturing a food freshness sensor that does not use highly toxic crosslinking agents and is based on a method for manufacturing nanofibers with low environmental impact. Therefore, it is a method for manufacturing a food freshness sensor that is suitable for use in close proximity to food.

[0021] The present invention provides a method for producing drug-carrying nanofibers that does not use highly toxic crosslinking agents and is based on a nanofiber production method with low environmental impact. Therefore, it is a method for producing drug-carrying nanofibers that are suitable for use both inside and outside living organisms. [Brief explanation of the drawing]

[0022] [Figure 1] This is a flowchart of the method for manufacturing nanofibers according to Embodiment 1. [Figure 2] This figure shows the morphology of PVA-DI-S in Example 1. [Figure 3] This figure shows the morphology of PVA-DI-C in Example 1. [Figure 4] This figure shows the morphology of PVA-LS in Example 1. [Figure 5] This figure shows the morphology of the PVA-LC in Example 1. [Figure 6]This figure shows the morphology of PVA-OS in Example 1. [Figure 7] This figure shows the morphology of PVA-OC in Example 1. [Figure 8] This graph shows the EDS spectrum of the nanofiber in Example 1. [Figure 9] This graph shows the TGA and DTA curves for PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1. [Figure 10] This graph shows the FT-IR spectra and XRD patterns of PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1. [Figure 11] This graph shows the XPS spectra of PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1. [Figure 12] This is a photograph showing the WCA of PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1. [Figure 13] This figure shows the water resistance of PVA-LC in Example 1. [Figure 14] This figure shows the water resistance of PVA-LC in Example 1. [Figure 15] This graph shows the EDS spectrum relating to the water resistance of PVA-LC in Example 1. [Figure 16] This graph shows the release behavior of PVA-LC in Example 1. [Figure 17] This is a radar chart showing the biodegradability of nanofibers, food freshness sensors, and drug-supported nanofibers in each example. [Figure 18] This is an SEM image taken 21 days after the start of the biodegradability test of PVA-LC in Example 1. [Figure 19] This figure shows the morphology of PVAI-LS in Example 2. [Figure 20] This figure shows the morphology of PVAI-LC in Example 2. [Figure 21] This graph shows the EDS spectrum of the nanofiber in Example 2. [Figure 22] This is an SEM image taken 21 days after the start of the biodegradability test of PVAI-LC in Example 2. [Figure 23] This figure shows the morphology of PVA-L-Cur in Example 3. [Figure 24] This figure shows the morphology of PVAI-L-Cur in Example 3. [Figure 25] This graph shows the EDS spectrum of the food freshness sensor in Example 3. [Figure 26] This graph shows the TGA and DTA curves for PVA-L-Cur and PVAI-L-Cur in Example 3. [Figure 27] This graph shows the FT-IR spectra and XRD patterns of PVA-L-Cur and PVAI-L-Cur in Example 3. [Figure 28] This graph shows the FT-IR spectrum and XRD pattern of curcumin. [Figure 29] This is an SEM image taken 21 days after the start of the biodegradability test of PVA-L-Cur and PVAI-L-Cur in Example 3. [Figure 30] This bar graph shows the pH response of PVA-L-Cur to vapor in Example 3. [Figure 31] This graph shows the pH response of PVA-L-Cur to a solution in Example 3. [Figure 32] This figure shows the elution properties of curcumin from PVA-L-Cur in Example 3. [Figure 33] This photograph shows the results of the color change test using chicken meat treated with PVA-L-Cur and PVAI-L-Cur in Example 3. [Figure 34] This graph shows the color changes in the tests using chicken meat with PVA-L-Cur and PVAI-L-Cur in Example 3. [Figure 35]This figure shows the morphology of PVA-L-AV-S in Example 4. [Figure 36] This figure shows the morphology of PVA-L-AV-C in Example 4. [Figure 37] This graph shows the EDS spectrum of the drug-loaded nanofiber in Example 4. [Figure 38] This graph shows the FT-IR spectrum and XRD pattern of PVA-L-AV-C in Example 4. [Figure 39] This graph shows the TGA curve and DTA curve of PVA-L-AV-C in Example 4. [Figure 40] This is an SEM image taken 21 days after the start of the biodegradability test of PVA-L-AV-C in Example 4. [Figure 41] This graph shows the UV spectra of PVA-LC in Example 1 and PVA-L-AV-C in Example 4. [Figure 42] These are photographs of the object to be filtered (before filtration) and the filtrate (after filtration) in Example 5. [Figure 43] This figure shows the UV spectrum of the filtrate obtained by PVA-LC in Example 5. [Modes for carrying out the invention]

[0023] The following describes the method for producing nanofibers, the method for producing food freshness sensors, and the drug-supported nanofibers of the present invention, based on the embodiments shown below.

[0024] [Embodiment 1] Embodiment 1 describes a method for producing nanofibers. Figure 1 is a flowchart of the method for producing nanofibers according to Embodiment 1.

[0025] 1. Method for producing nanofibers according to Embodiment 1 The nanofiber manufacturing method according to Embodiment 1 includes a spinning solution preparation step S1, a nanofiber formation step S2, and a crosslinking step S3, as shown in Figure 1. The nanofiber manufacturing method according to Embodiment 1 may also include steps other than those described above. Each step will be described below.

[0026] 1-1. Spinning solution preparation process S1 The spinning solution preparation step S1 is a step of preparing a spinning solution containing a citrus-derived material obtained from citrus fruits and a fiberizable water-soluble polymer. In this specification, "citrus-derived material" includes both primary derived materials obtained from citrus fruits by pressing, shredding, extraction, centrifugation, etc., and processed materials obtained by processing the primary derived materials (e.g., concentration, freezing, liquefaction, etc.). In this specification, "fiberizable water-soluble polymer" refers to a polymer (high molecular weight substance) that is soluble in water (including hot water) and can form a fibrous structure by electrospinning.

[0027] The citrus-derived material is preferably obtained from lemon fruit. Lemons are rich in citric acid (about 5-6%). Since citric acid is thought to promote crosslinking of water-soluble polymers, lemon fruit is particularly suitable as a material for the citrus-derived material. However, the citrus-derived material in this invention is not limited to that obtained from lemon fruit, and materials obtained from the fruits of plants belonging to the genus Citrus and Fortunella (e.g., oranges, limes, yuzu, mandarins, etc.) can also be used.

[0028] The citrus-derived material preferably contains fruit juice. Furthermore, the citrus-derived material preferably constitutes at least a portion of the solvent in the spinning solution. In this case, in the spinning solution preparation step S1, the spinning solution is prepared by adding the polymer to a solvent containing the citrus-derived material, and it is preferable that the concentration of the citrus-derived material in the solvent is in the range of 90 to 100% by weight (see Example 1 described later). It is even more preferable to use only the citrus-derived material as the solvent for the spinning solution.

[0029] The water-soluble polymer preferably contains at least one of polyvinyl alcohol (PVA) and a polyvinyl alcohol copolymer. The molecular weight and degree of saponification of the polyvinyl alcohol and polyvinyl alcohol copolymer are not particularly limited. Furthermore, the water-soluble polymer in this invention is not limited to polyvinyl alcohol and polyvinyl alcohol copolymer; other water-soluble polymers may also be used.

[0030] Furthermore, the water-soluble polymer may further contain other water-soluble polymers in addition to water-soluble polymers that can be fiberized on their own (e.g., polyvinyl alcohol). For example, the water-soluble polymer may preferably further contain inulin.

[0031] Furthermore, the spinning solution may also contain substances other than citrus-derived materials and water-soluble polymers (other components).

[0032] 1-2. Nanofiber formation process S2 The nanofiber formation step S2 is a step in which nanofibers are formed from a spinning solution by electrospinning. Except for using the spinning solution prepared in the spinning solution preparation step S1, various conventionally known methods can be used for the electrospinning method in the nanofiber formation step S2.

[0033] 1-3. Crosslinking step S3 Crosslinking step S3 is a step in which the nanofibers are crosslinked. In crosslinking step S3, it is preferable to heat the nanofibers in the range of 80 to 100°C. However, in crosslinking step S3, treatments other than heating may be performed for crosslinking.

[0034] Through the above process, crosslinked (water-resistant) nanofibers can be manufactured. Nanofibers manufactured by the nanofiber manufacturing method according to this embodiment can be used as a material for manufacturing various high-performance products, such as liquid filtration filters (see Example 5 described later).

[0035] 2. Effects of the Nanofiber Manufacturing Method According to Embodiment 1 In the nanofiber manufacturing method according to Embodiment 1, a citrus-derived substance obtained from citrus fruits is used as the crosslinking agent (a so-called green crosslinking agent). Citrus fruits are generally used as food products and are considered to have low toxicity and low environmental impact. Therefore, the nanofiber manufacturing method according to Embodiment 1 does not use highly toxic crosslinking agents and is an environmentally friendly method for manufacturing nanofibers.

[0036] Furthermore, in the nanofiber manufacturing method according to Embodiment 1, the water-soluble polymer preferably contains at least one of polyvinyl alcohol and polyvinyl alcohol-based copolymer. In this case, according to the nanofiber manufacturing method of Embodiment 1, it is possible to manufacture nanofibers with various expected applications using a polyvinyl alcohol-based polymer as a raw material (see Example 1 described later).

[0037] Furthermore, in the nanofiber manufacturing method according to Embodiment 1, it is preferable that the water-soluble polymer further contains inulin. In this case, the nanofiber manufacturing method according to Embodiment 1 makes it possible to manufacture nanofibers with different characteristics than those produced using only a polyvinyl alcohol-based polymer (see Example 2 described later).

[0038] Furthermore, in the nanofiber manufacturing method according to Embodiment 1, it is preferable that the citrus-derived material is obtained from lemon fruit. In this case, according to the nanofiber manufacturing method according to Embodiment 1, it is possible to use lemon fruit that is commonly cultivated and distributed, and to insolubilize the nanofibers without special processing such as concentrating the fruit juice (see Example 1 described later).

[0039] Furthermore, in the nanofiber manufacturing method according to Embodiment 1, it is preferable that the citrus-derived material includes fruit juice and constitutes at least a portion of the solvent in the spinning solution. In this case, according to the nanofiber manufacturing method of Embodiment 1, the manufacturing process can be simplified by using the citrus-derived material (fruit juice) as the solvent in the spinning solution.

[0040] Furthermore, in the nanofiber manufacturing method according to Embodiment 1, in the spinning solution preparation step S1, the spinning solution is prepared by adding a water-soluble polymer to a solvent containing citrus-derived material, and it is preferable that the concentration of citrus-derived material in the solvent is in the range of 90 to 100% by weight. In this case, according to the nanofiber manufacturing method according to Embodiment 1, it is possible to further promote the crosslinking of nanofibers by increasing the proportion of citrus-derived material in the solvent.

[0041] Furthermore, in the nanofiber manufacturing method according to Embodiment 1, it is preferable to heat the nanofibers in the crosslinking step S3 within the range of 80 to 100°C. This temperature range is lower than the general heat treatment temperature. In this case, according to the nanofiber manufacturing method according to Embodiment 1, by performing the crosslinking step S3 at a temperature lower than the general heat treatment temperature, it is possible to suppress excessive deterioration (deactivation) of the nanofibers and the components supported or added to the nanofibers.

[0042] [Embodiment 2] Embodiment 2 describes a method for manufacturing a food freshness sensor. In this specification, a "food freshness sensor" comprises a color-changing pigment that changes color due to substances released as food spoils, and nanofibers that support (including adsorption and binding) the color-changing pigment. The food freshness sensor according to Embodiment 2 is for determining the freshness of protein-rich foods (for example, meat and fish). The food freshness sensor may be placed directly on the surface of the food, or it may be placed near the food (for example, on the food packaging or container).

[0043] In this specification, "discoloration pigment" may be a substance that changes color by directly reacting with substances released as food spoils, or it may be a substance that changes color due to environmental changes (e.g., changes in pH) associated with substances released as food spoils.

[0044] The method for manufacturing a food freshness sensor according to Embodiment 2 is basically the same as the method for manufacturing nanofibers according to Embodiment 1. However, the method for manufacturing a food freshness sensor according to Embodiment 2 includes a step of supporting a color-changing pigment on crosslinked nanofibers, in which a color-changing pigment that changes color due to substances released as food spoils is supported.

[0045] The discoloration dye loading process can be carried out, for example, by immersing crosslinked nanofibers in a solution containing a discoloration dye, and then removing the solvent from the solution (drying it) (see Example 3 described later).

[0046] The color-changing pigment preferably contains curcumin. Curcumin can be obtained as a natural extract from turmeric and is well known as a natural antibacterial and antioxidant agent. Curcumin changes state between the structure shown in the following chemical formula (1) (keto form) and the structure shown in the following chemical formula (2) (enol form) due to interaction with ammonia and changes in pH, and the color changes accordingly. [ka]

[0047] In addition, substances other than curcumin can be used as color-changing pigments. Any color-changing pigment that causes discoloration due to substances released as food spoils is acceptable. Examples of color-changing pigments that can be used include polyaniline (emeraldine), anthocyanin, alizarin, shikonin, betalain, phenolphthalein, bromocresol purple, bromocresol green, methyl orange, and methyl red.

[0048] The method for manufacturing a food freshness sensor according to Embodiment 2 does not use highly toxic crosslinking agents and is based on a method for manufacturing nanofibers that has a low environmental impact. Therefore, it is a method for manufacturing a food freshness sensor that is suitable for use in close proximity to food.

[0049] Furthermore, in the method for manufacturing a food freshness sensor according to Embodiment 2, it is preferable that the color-changing pigment contains curcumin. In this case, the method for manufacturing a food freshness sensor according to Embodiment 2 makes it possible to manufacture a food freshness sensor that can accurately and easily determine the freshness of protein-rich foods (see Example 3).

[0050] [Embodiment 3] Embodiment 3 describes a method for manufacturing drug-carrying nanofibers. In this specification, "drug-carrying nanofiber" refers to a nanofiber on which a drug is carried that is separated from the basic structure (matrix) of the nanofiber and released. In this specification, "drug" refers to any substance that has some medicinal effect on living organisms, and is not limited to so-called "pharmaceuticals."

[0051] The method for producing drug-supported nanofibers according to Embodiment 3 is basically the same as the method for producing nanofibers according to Embodiment 1. However, in the spinning solution preparation step of the method for producing drug-supported nanofibers according to Embodiment 3, a spinning solution is prepared containing a citrus-derived material obtained from citrus fruits, a fiberizable water-soluble polymer, and a drug component.

[0052] The medicinal ingredient preferably contains aloe vera. Aloe vera is a succulent plant belonging to the genus Aloe and is thought to have various medicinal properties, such as efficacy against acne vulgaris (commonly known as "pimples").

[0053] Of course, the active ingredient is not limited to aloe vera; any type and amount of drug can be used as long as it does not inhibit the fiber formation and crosslinking of the water-soluble polymer.

[0054] The method for producing drug-carrying nanofibers according to Embodiment 3 is a method based on a nanofiber manufacturing method that does not use highly toxic crosslinking agents and has a low environmental impact, and therefore is a method for producing drug-carrying nanofibers that are suitable for use both inside and outside living organisms.

[0055] Furthermore, in the method for producing drug-supported nanofibers according to Embodiment 3, the drug preferably contains aloe vera. In this case, the method for producing drug-supported nanofibers according to Embodiment 3 makes it possible to produce drug-supported nanofibers that release the drug component slowly (see Example 4 described later).

[0056] [Examples] The inventors of the present invention actually manufactured nanofibers by carrying out the nanofiber manufacturing method according to Embodiment 1 described above, and analyzed their morphology and other characteristics. Furthermore, the inventors of the present invention manufactured various products using the manufactured nanofibers and confirmed their morphology and other characteristics and practicality. The following describes the analysis, test content, and results related to the nanofiber manufacturing method according to Embodiment 1 as examples.

[0057] In each example, the analysis and experiments were carried out using the following materials and equipment. General-purpose instruments and equipment are not described.

[0058] The compost growing medium, raw chicken meat, aloe vera, lemon fruit, orange fruit, and turmeric powder were all commercially available products purchased from a store near the Ueda Campus of Shinshu University, a national university corporation. Polyvinyl alcohol (PVA, saponification degree 87-89%, Mw=85,000-124,000), phosphate-buffered saline (PBS), agar, and ethyl alcohol (99.8% or higher, anhydrous) were purchased from Sigma-Aldrich Japan LLC. Inulin (enzyme synthesis, Mw=6179) was purchased from Tokyo Chemical Industry Co., Ltd. Acetic acid (99.7%) and aqueous ammonia (10%) were purchased from Fujifilm Wako Chemical Co., Ltd. The buffer solutions (pH=5 and 10) were purchased from Dojin Chemical Laboratories Co., Ltd. Deionized water (DI) was produced using the Milli-Q system.

[0059] For Fourier transform infrared spectroscopy (FT-IR), we used the IRPrestige-21 from Shimadzu Corporation. The wavenumber range was 4000-600 cm⁻¹. -1 That's what I decided. For the X-ray photoelectron spectrometer (XPS), we used the Axis-Ultra HSA SV from Kratos Analytical (UK). A Rigaku Miniflex 300 X-ray diffractometer (XRD) was used. The diffraction angle was set in the range of 2θ = 20 to 80°. A scanning electron microscope (SEM) JSM-6010LA from JEOL Ltd. was used. The acceleration voltage was set to 10kV. For the transmission electron microscope (TEM), we used the JEM-2100 from JEOL Ltd. ImageJ (software version 19 1.4.3.) was used as the image analysis software for statistical measurements from SEM images. For thermogravimetric analysis (TGA), we used the TG-8120 thermal analyzer manufactured by Rigaku Corporation. For measuring hydrophobicity (surface water contact angle), we used the Digidrop (contact angle analyzer) from GBX (France).

[0060] [Example 1] Production and analysis of nanofibers using PVA In Example 1, nanofibers were actually manufactured by carrying out the nanofiber manufacturing method according to the embodiment. The morphology and properties of the manufactured nanofibers were also analyzed. In Example 1, PVA was used as the polymer.

[0061] 1. Manufacturing of nanofibers Before carrying out the spinning solution preparation process, citrus-derived materials were prepared. First, lemons were manually chopped and squeezed to obtain lemon juice. Next, the lemon juice was purified by filtration, centrifugation (30 minutes), and re-filtration to obtain high-purity lemon extract. Orange extract was also obtained using the same procedure as for the lemon extract. In subsequent experiments, lemon extract and orange extract were used as citrus-derived materials.

[0062] In the spinning solution preparation step in Example 1, a spinning solution was prepared by adding PVA (10%, w / w) to lemon extract or orange extract and stirring at 70°C for 6 hours. For comparison, a spinning solution was also prepared by adding PVA (10%, w / w) to deionized water.

[0063] In the nanofiber formation process in Example 1, nanofibers were formed from each spinning solution by electrospinning. The electrospinning conditions were: voltage: 17kV, flow rate: 0.3mL / h, tip-collector distance (TCD): 15cm, temperature: 25℃, and humidity: 40%.

[0064] The above nanofiber formation process made it possible to produce uniform nanofibers without bead-like structures. Since the nanofibers produced in Example 1 had a nonwoven fabric-like form, it could also be said that "a nanofiber nonwoven fabric was produced" in Example 1. Hereafter, nanofibers formed using lemon extract will be referred to as "PVA-LS", nanofibers formed using orange extract will be referred to as "PVA-OS", and nanofibers formed using deionized water will be referred to as "PVA-DI-S".

[0065] In the crosslinking process in Example 1, PVA-LS, PVA-OS, and PVA-DI-S were crosslinked by heating at 90°C for 18 hours. Hereafter, nanofibers produced by crosslinking PVA-LS will be referred to as "PVA-LC", nanofibers produced by crosslinking PVA-OS will be referred to as "PVA-OC", and nanofibers produced by crosslinking PVA-DI-S will be referred to as "PVA-DI-C".

[0066] Furthermore, the 90°C temperature used in the crosslinking process was considerably lower than the temperatures reported in previous literature (120-160°C). This is thought to be due to the accelerated esterification of PVA with ultra-high purity citric acid (CA).

[0067] 2. Analysis of nanofibers First, the morphology of the nanofibers PVA-DI-S, PVA-DI-C, PVA-LS, PVA-LC, PVA-OS, and PVA-OC in Example 1 was analyzed using SEM, EDS, and TEM.

[0068] Figure 2 shows the morphology of PVA-DI-S in Example 1. Figures 2(a) and 2(b) are SEM images of PVA-DI-S, Figure 2(c) is a graph showing the distribution of fiber diameter of PVA-DI-S, and Figure 2(d) is a TEM image of PVA-DI-S. Figure 3 shows the morphology of PVA-DI-C in Example 1. Figures 3(a) and 3(b) are SEM images of PVA-DI-C, Figure 3(c) is a graph showing the fiber diameter distribution of PVA-DI-C, and Figure 3(d) is a TEM image of PVA-DI-C.

[0069] Figure 4 shows the morphology of the PVA-LS in Example 1. Figures 4(a) and 4(b) are SEM images of the PVA-LS, Figure 4(c) is a graph showing the distribution of fiber diameter of the PVA-LS, and Figure 4(d) is a TEM image of the PVA-LS. Figure 5 shows the morphology of the PVA-LC in Example 1. Figures 5(a) and 5(b) are SEM images of the PVA-LC, Figure 5(c) is a graph showing the distribution of fiber diameter of the PVA-LC, and Figure 5(d) is a TEM image of the PVA-LC.

[0070] Figure 6 shows the morphology of PVA-OS in Example 1. Figures 6(a) and 6(b) are SEM images of PVA-OS. Figure 7 shows the morphology of PVA-OC in Example 1. Figures 7(a) and 7(b) are SEM images of PVA-OC. Figure 8 is a graph showing the EDS spectrum of the nanofibers in Example 1. Figure 8(a) is a graph for PVA-DI-S, Figure 8(b) is a graph for PVA-DI-C, Figure 8(c) is a graph for PVA-LS, and Figure 8(d) is a graph for PVA-LS. In the graphs in Figure 8, the vertical axis represents counts (×1000) and the horizontal axis represents energy (unit: keV).

[0071] First, SEM images of PVA-DI-S formed using deionized water confirmed that it had a smooth morphology with an average fiber diameter of 313.9 ± 47.87 nm (see Figures 2(a) to 2(c)). Furthermore, it was observed that heating PVA-DI-S to form PVA-DI-C increased the diameter by 2.64%, reaching 322.2 ± 55.67 nm (see Figures 3(a) to 3(c)).

[0072] On the other hand, PVA-LS formed using lemon extract had an average fiber diameter of 428.3 ± 91.05 nm, showing a 36.45% increase in diameter compared to PVA-DI-S (see Figures 4(a) to 4(c)). Furthermore, it was confirmed that heating (crosslinking) PVA-LS to form PVA-LC increased the diameter by 2.78%, to 440.2 ± 82.03 nm (see Figures 5(a) to 5(c)).

[0073] The diameter increase rates in PVA-LC were 2.78%, 40.24%, and 36.62% compared to PVA-LS, PVA-DI-S, and PVA-DI-C, respectively. This increase in diameter is thought to be due to the physiologically active compounds contained in the lemon extract and the chemical changes during crosslinking.

[0074] Furthermore, TEM imaging confirmed that the surface roughness of PVA-LC was slightly rougher compared to other nanofibers, indicating the effect of crosslinking (see Figures 2(d), 3(d), 4(d), and 5(d)).

[0075] Furthermore, the formation and crosslinking of nanofibers were confirmed in PVA-OS and PVA-OC formed and manufactured using orange extract (see Figures 6 and 7). As will be discussed later, unfortunately, PVA-OC did not have sufficient water resistance, but it was confirmed that the direction of using citrus-derived materials is promising.

[0076] Furthermore, elemental mapping analysis confirmed that carbon (C), oxygen (O), and sodium (Na) elements were uniformly distributed on the surfaces of PVA-DI-S and PVA-DI-C. On the other hand, potassium (K) and magnesium (Mg) were additionally detected in PVA-LS and PVA-LC, confirming that these elements, which are thought to originate from lemon extract, were incorporated into the nanofibers.

[0077] In summary, the analysis results above show that heating (90°C for 18 hours) resulted in an increase in diameter, changes in morphology (roughness), and changes in color in the PVA-LC. These changes suggest that the nanofibers in the PVA-LC were cross-linked, improving rigidity and stability in water (water resistance).

[0078] The above analysis confirmed that the nanofiber manufacturing method according to Embodiment 1 makes it possible to produce crosslinked nanofibers using environmentally friendly and sustainable resources.

[0079] Next, to verify the thermal stability, TGA curves and DTA curves were obtained for the nanofibers PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC used in Example 1.

[0080] Figure 9 is a graph showing the TGA curve and DTA curve for PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1. Figure 9(a) is a graph showing the TGA curve, and Figure 9(b) is a graph showing the DTA curve. In Figure 9(a), the vertical axis shows the degree of weight loss (in %), and the horizontal axis shows the temperature (in °C). In Figure 9(b), the vertical axis shows differential heat (DTA) (in eV), and the horizontal axis shows the temperature (in °C).

[0081] As a result, multi-stage decomposition was observed in the TGA curves for all nanofibers in Example 1: PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC (see Figure 9(a)). In PVA-DI-S, multi-stage decomposition (20-200°C) was observed. Initial decomposition was observed around 17°C, showing a weight loss of 5.8%. In the second and third stages of decomposition, weight losses of 77.32% and 15% were observed, respectively. This weight loss is thought to be due to the decomposition of the PVA polymer chain by cleaving hydrogen bonds and the release of low-molecular-weight substances such as water and carbon dioxide. In PVA-LC, an overall weight loss of 98.12% was observed.

[0082] Furthermore, in PVA-DI-C, the initial weight loss was 5.64%, which is thought to be due to the evaporation of water. In the second and third stages of decomposition, weight losses of 66.79% and 18.2% were observed, respectively, resulting in an overall weight loss of 72.43%.

[0083] Furthermore, PVA-LS showed weight losses of 6.91%, 47.99%, and 29.23% at all three stages of thermal decomposition. This is thought to be due to the release of water and the decomposition of PVA and organic matter. Overall, PVA-LS showed a total weight loss of 94.74%.

[0084] Furthermore, in the PVA-LC, an initial weight loss of 9.34% was observed at around 17°C, which is thought to be due to the loss of moisture. In the second and third stages of decomposition, weight losses of 65.63% and 24.73% were observed, respectively. Overall, the PVA-LC showed a total weight loss of 99.70%. In conclusion, a decrease in thermal stability due to the crosslinking effect was observed in the PVA-LC.

[0085] Furthermore, DTA analysis of PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1 revealed exothermic peaks around 200-500°C in each nanofiber (see Figure 9(b)). PVA-DI-S and PVA-DI-C showed sharp exothermic peaks around 450-500°C. On the other hand, PVA-LS showed a sharp peak around 400-460°C, as well as an additional exothermic peak around 210-350°C. In addition, PVA-LC showed the same exothermic peaks as PVA-LS, but the peak positions around 50-310°C and 320-350°C were lower. These changes in peak positions may be due to the effects of crosslinking and crystallization.

[0086] Next, to investigate the structural properties, FT-IR spectra, XRD patterns, and XPS spectra were obtained for the nanofibers PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1.

[0087] Figure 10 is a graph showing the FT-IR spectra and XRD patterns of PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1. Figure 10(a) is a graph showing the FT-IR spectra, and Figure 10(b) is a graph showing the XRD patterns. In Figure 10(a), the vertical axis represents absorbance (unit: au), and the horizontal axis represents wavenumber (unit: cm). -1 Figure 10(b) shows the intensity (unit: au) on the vertical axis and 2θ (unit: degrees) on the horizontal axis. Figure 11 is a graph showing the XPS spectra of PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1. Figure 11(a) is a graph showing the XPS spectrum for the entire measurement range, while Figures 11(b) and 11(b) are graphs showing the XPS spectrum for a specific range. In Figure 11, the vertical axis represents intensity (unit: au), and the horizontal axis represents binding energy (unit: eV).

[0088] First, the FT-IR spectrum of PVA-DI-S is 1731, 3313, 2840~3000 cm⁻¹. -1 In the first stage, stretching vibrations were observed, confirming the presence of stretching vibrations of the C=O, OH, and CH groups (see Figure 10(a)). On the other hand, in the second stage, PVA-LS showed an increase in the intensity of peaks related to the C=O, OH, and CH groups, confirming the effect of lemon extract. Furthermore, the OH stretching peak decreased in the third stage. In addition, a decrease in the intensity of stretching vibrations of the C=O, CC, and CO groups was also observed. This is thought to be due to the formation of ester bonds and is strong evidence of successful crosslinking in the third stage.

[0089] Note that CO base (1650~1780 cm) -1 ) and COOH groups (2300~2400 cm) -1The absorption associated with ) indicates that the lemon extract contains a carboxylic acid. Therefore, it is thought that this carboxylic acid promoted crosslinking. In conclusion, the significant difference in the FT-IR spectra between PVA-LC and PVA-DI-C is strong evidence of the successful crosslinking of nanofibers using lemon extract (citrus-derived material), and it can be said that citrus-derived materials can be a sustainable and environmentally friendly crosslinking agent that replaces conventional crosslinking agents.

[0090] Furthermore, the XRD pattern of PVA-DI-S confirmed that it is amorphous, with broad peaks around 2θ=15.8° and 2θ=19.6°, and an area under the curve (AUC) of 38279.9 (see Figure 10(b)). In PVA-DI-C, the intensity increased at the same peak positions, and an increase in AUC (44371.4) was observed (15.9%), indicating improved crystallinity.

[0091] On the other hand, PVA-LS showed a unique crystal structure compared to PVA-DI-S and PVA-DI-C, as indicated by the peak at 2θ=19.3°, and its AUC (55908.6) was significantly increased. In PVA-LS, an increase in AUC of 46.1% and 26% was observed compared to PVA-DI-S and PVA-DI-C, respectively. When PVA-LC was compared to PVA-LS, a decrease in peak intensity and AUC (23.2% and 42924.75) was observed, suggesting the effects of decreased crystallinity and crosslinking.

[0092] Furthermore, XPS spectroscopy revealed that each nanofiber exhibited a consistent and significant peak throughout (see Figure 11(a)). These peaks corresponded to carbon (C) and oxygen (O).

[0093] Furthermore, no changes due to the lemon extract were observed in the PVA-LC XPS spectrum. This result was further clarified by high-resolution scanning (deconvolution) of the PVA-LC spectrum. The binding energy (C,1S) of each nanofiber was observed to be around 282 eV (see Figure 11(b)). The C(1S) spectrum was further deconvolved into subpeaks (CC,CO,C=O). The C(1S) peak of PVA-DI-S showed an intensity of 61,638, while that of PVA-DI-C increased to 90,935 (47.53%).

[0094] On the other hand, in PVA-LS, the above peak showed an intensity of 87,118 (a 41.33% increase compared to PVA-DI-C). Furthermore, in PVA-LS, the above peak showed an intensity of 102,117, which was an increase of 65.67%, 12.30%, and 17.22% compared to PVA-DI-S, PVA-DI-C, and PVA-LS, respectively. In addition, the AUC of C(1S) in PVA-DI-S, PVA-DI-C, PVA-1S, and PVA-LC was observed to be 150671, 251522, 227839, and 261850, respectively.

[0095] Furthermore, a detailed comparative study focusing on the O(1S) photoelectron spectrum revealed significant changes. While the binding energy (O,1S) of each nanofiber was observed to be around 529 eV, interestingly, heating, the use of lemon extract, and crosslinking resulted in an increase in the intensity of the O(1S) peak for nanofibers other than PVA-DI-S compared to PVA-DI-S (see Figure 11(c)). The difference in peak intensity between PVA-LC and PVA-DI-S indicates that the electron density of the hydroxyl oxygen atom is lower in PVA-LC.

[0096] Furthermore, the AUC of O(1S) in PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC was observed to be 130412, 263192, 241650, and 255422, respectively.

[0097] Next, the water-to-air interaction (WCA) with water (droplets) was measured for the nanofibers PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1 at residence times of 100, 300, 500, 700, 900, and 1000 milliseconds.

[0098] Figure 12 is a photograph showing the WCA of PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC in Example 1. The numbers in the upper row of Figure 12 indicate the residence time (in milliseconds).

[0099] At an initial residence time of 100 milliseconds, the contact angle was 44.17° for PVA-DI-S (the smallest) and 87.53° for PVA-LC (the highest). Because PVA is hydrophilic and easily wettable, the contact angle decreased more significantly over time for nanofibers other than PVA-LC (see Figure 12).

[0100] On the other hand, PVA-LC consistently exhibited the best contact angle, confirming its superior resistance to wetting. Crosslinking increased the hydrophobicity of PVA-LC by 24.71-39.41% compared to PVA-LS. Even with a long residence time (1000 milliseconds), the WCA was 45.89° for PVA-LS, while it was 75.74° for PVA-LC. This result suggests that crosslinking significantly improved the hydrophobicity of PVA-LC.

[0101] Next, water resistance analyses were performed on the nanofibers PVA-DI-S, PVA-DI-C, PVA-LS, PVA-LC, PVA-OS, and PVA-OC from Example 1.

[0102] Figure 13 shows the water resistance of the PVA-LC in Example 1. Figures 13(a) and 13(b) are SEM images of the PVA-LC after 5 minutes of exposure to deionized water, and Figure 13(c) is a graph showing the distribution of fiber diameter of the PVA-LC after 5 minutes of exposure to deionized water. Figure 14 shows the water resistance of the PVA-LC in Example 1. Figures 14(a) and 14(b) are SEM images of the PVA-LC after 4 days of exposure to deionized water, and Figure 14(c) is a graph showing the distribution of fiber diameter of the PVA-LC after 4 days of exposure to deionized water. Figure 15 is a graph showing the EDS spectrum relating to the water resistance of PVA-LC in Example 1. Figure 15(a) is a graph of PVA-LC after 5 minutes of exposure to deionized water, and Figure 15(b) is a graph of PVA-LC after 4 days of exposure to deionized water. In the graphs of Figure 15, the vertical axis represents counts (×1000), and the horizontal axis represents energy (unit: keV). Figure 16 is a graph showing the release behavior of PVA-LC in Example 1. The vertical axis of Figure 16 represents the amount of elution (AUC), and the horizontal axis represents time (in minutes).

[0103] The water resistance of each nanofiber was observed by exposing each nanofiber to deionized water. The sample size (size of the nanofiber nonwoven fabric) for each nanofiber was 3 cm x 5 cm. The water resistance tests were conducted at room temperature (25°C). The water resistance of each nanofiber was confirmed visually and by SEM imaging (after 5 minutes and 4 days). As a result, all nanofibers except PVA-LC dissolved rapidly in water.

[0104] In PVA-LC, dissolution in water was not observed, but swelling behavior was seen due to interaction with deionized water (see Figures 13 and 14). The average fiber diameter of PVA-LC increased by 19.53% after 5 minutes of immersion and by 24.04% after 4 days.

[0105] Furthermore, EDS analysis revealed that C, O, Na, and K were observed 5 minutes after immersion, and C, O, Mg, and Ca were observed 4 days after immersion (see Figure 15). This is thought to be due to differences in the binding strength between Na and K and Mg and Ca in PVA-LC. It should be noted that Na, K, Mg, and Ca are thought to have originated from the lemon extract.

[0106] Furthermore, to confirm the release behavior of PVA-LC, PVA-LC was immersed in PBS solution for 24 hours, and samples were taken after immersion at specified times (5 minutes, 15 minutes, 30 minutes, 60 minutes, 180 minutes, 360 minutes, 720 minutes, and 1440 minutes). Time-dependent release was confirmed by UV spectroscopy, suggesting that surface elements such as Na, K, Mg, and Ca were released continuously and gradually. The time-dependent release of components from PVA-LC was confirmed by AUC calculated from the UV spectrum (see Figure 16). As a result, it was suggested that in PVA-LC, the maximum release occurred 15 minutes after the start of immersion.

[0107] Next, the nanofibers PVA-DI-S, PVA-DI-C, PVA-LS, and PVA-LC used in Example 1 were analyzed for their antibacterial and biodegradable properties. Figure 17 is a radar chart showing the biodegradability of nanofibers, food freshness sensors, and drug-supported nanofibers in each example. The radial axis in the radar chart shown in Figure 17 represents the weight loss rate (in %). Figure 18 shows an SEM image of the PVA-LC in Example 1 21 days after the start of the biodegradability test.

[0108] The antibacterial activity of each nanofiber was qualitatively measured using the agar disk diffusion method with Gram-positive bacteria (Escherichia coli) and Gram-negative bacteria (Staphylococcus aureus), in accordance with AATCC147-1998 standard test 11. Furthermore, the antibacterial activity of each nanofiber was evaluated by placing the sample in a composite culture medium and observing SEM images and measuring the weight loss rate (%) after 7, 14, and 21 days.

[0109] The antibacterial test evaluates the ability to inhibit the growth of target bacteria. Nanofibers other than PVA-LC were dissolved on agar plates, similar to the analysis for water resistance. On the other hand, PVA-LC did not dissolve on agar plates. Furthermore, because it contains physiologically active components derived from lemon extract, it showed significant antibacterial activity against Escherichia coli and Staphylococcus aureus. It is thought that lemon extract inhibits bacterial growth by inducing oxidative stress and damaging the bacterial cell membrane.

[0110] Regarding biodegradability, all nanofibers except PVA-LC were completely decomposed after 21 days (see Figure 17). The weight loss rate of PVA-DI-S was 0% after 7 days, 58% after 14 days, and 100% after 21 days. The weight loss rate of PVA-DI-C was 10% after 7 days, 46% after 14 days, and 100% after 21 days. On the other hand, PVA-LS showed significant degradation after 7 days (weight loss rate of 57%) and was completely decomposed after 14 days.

[0111] The weight loss rate of PVA-LC was 0% after 7 days, 9% after 14 days, and 15% after 21 days (see Figures 17 and 18). This is thought to be due to increased hydrophobicity in PVA-LC. Furthermore, crosslinking enhances the stability of the polymer, suppresses the effects of microorganisms and enzymes, and reduces biodegradability.

[0112] The above analysis confirmed that it is possible to manufacture nanofibers with high water resistance that can be used for various applications by using citrus-derived materials (lemon extract).

[0113] [Example 2] Production and analysis of nanofibers using PVA and inulin 1. Manufacturing of nanofibers In Example 2, PVA and inulin were used as polymers. In the spinning solution preparation step in Example 2, 1.2 g of inulin powder was added to the spinning solution using lemon extract (PVA, 10 wt%) from Example 1 and stirred at 70°C for 6 hours to prepare the spinning solution. The nanofiber formation step and crosslinking step in Example 2 are the same as those in Example 1, except for the use of the spinning solution described above, so a description will be omitted.

[0114] Hereafter, the nanofibers formed by the nanofiber formation process in Example 2 will be referred to as "PVAI-LS," and the nanofibers produced by crosslinking PVAI-LS will be referred to as "PVAI-LC."

[0115] 2. Analysis of nanofibers First, the morphology of the nanofibers PVAI-LS and PVAI-LC in Example 2 was analyzed using SEM, EDS, and TEM.

[0116] Figure 19 shows the morphology of PVAI-LS in Example 2. Figures 19(a) and 19(b) are SEM images of PVAI-LS, Figure 19(c) is a graph showing the distribution of fiber diameter of PVAI-LS, and Figure 19(d) is a TEM image of PVAI-LS. Figure 20 shows the morphology of the PVAI-LC in Example 2. Figures 20(a) and 20(b) are SEM images of the PVAI-LC, Figure 20(c) is a graph showing the distribution of fiber diameters of the PVAI-LC, and Figure 20(d) is a TEM image of the PVAI-LC. Figure 21 is a graph showing the EDS spectra of nanofibers in Example 2. Figure 21(a) is a graph for PVAI-LS, and Figure 21(b) is a graph for PVAI-LC. In the graphs in Figure 21, the vertical axis represents counts (×1000), and the horizontal axis represents energy (unit: keV).

[0117] SEM images revealed that PVAI-LS exhibited a smooth surface morphology, with an average fiber diameter of 653.8 ± 124 nm (see Figure 19). Furthermore, PVAI-LS showed a 34.94% increase in average fiber diameter compared to PVA-LS. This is thought to be due to strong intermolecular interactions between PVA and inulin.

[0118] On the other hand, in PVAI-LC, the average fiber diameter decreased by 6.03% to 614.4 ± 120 nm due to the effect of crosslinking (see Figure 20). Furthermore, TEM images from PVAI-LS and PVAI-LC confirmed that the surface of the nanofibers was smooth (see Figures 19(d) and 20(d)).

[0119] Furthermore, elemental mapping in PVAI-LS and PVAI-LC revealed the presence and uniform distribution of carbon (C), oxygen (O), and potassium (K) on the surface (see Figure 21).

[0120] Next, the nanofibers PVAI-LS and PVAI-LC used in Example 2 were analyzed for their antibacterial and biodegradable properties. The tests for antibacterial and biodegradable properties were conducted using the same method as in Example 1. Figure 22 shows an SEM image of PVAI-LC 21 days after the start of the biodegradability test in Example 2.

[0121] In the antimicrobial activity test, PVAI-LS dissolved on the agar plate, while PVAI-LC did not. PVAI-LC maintained a clear surface after the test, demonstrating good antimicrobial properties. In conclusion, PVAI-LC was confirmed to be sensitive to both negative and positive bacteria.

[0122] In biodegradation tests, PVAI-LS showed a moderate weight loss rate compared to PVA-LS (27% after 7 days, 78% after 14 days, and 100% after 21 days), and eventually decomposed completely (see Figure 17). This decomposition is thought to be due to the hydrophilicity (water absorption promotion) of inulin and the decomposition of the PVA matrix.

[0123] PVAI-LC showed a similar degradation pattern to PVA-LC (see Figure 17), but the weight loss rate of PVAI-LC was slightly higher after 7 days (5% after 7 days, 8% after 14 days, and 16% after 21 days; see Figure 22).

[0124] Based on the above analysis and tests, it was confirmed that the nanofiber manufacturing method according to the embodiment is effective even when PVA and inulin are used as polymers.

[0125] [Example 3] In Example 3, food freshness sensors based on PVA-LC and PVAI-LC were actually manufactured, analyzed, and evaluated.

[0126] 1. Manufacturing of food freshness sensors First, a mixture of 20 g of turmeric powder and 200 mL of ethanol was stirred under an air atmosphere (70°C, 3.5 hours). The mixture was then cooled to room temperature and vacuum filtered to obtain a turmeric extract. The extraction rate of curcumin (Cur) from turmeric was calculated to be 4.2%. Next, PVA-LC and PVAI-LC were immersed in the turmeric extract (30°C, 5 minutes). Finally, each of the resulting nanofibers was dried at 60°C for 5 hours to produce food freshness sensors. The produced food freshness sensors were stored in a desiccator.

[0127] Of the food freshness sensors manufactured as described above, those based on PVA-LC will be referred to as "PVA-L-Cur," and those based on PVAI-LC will be referred to as "PVAI-L-Cur." In drawings, PVA-L-Cur may be referred to as "PVA-LC-Cur," and PVAI-L-Cur may be referred to as "PVAI-LC-Cur."

[0128] 2. Analysis of food freshness sensors First, the morphology of PVA-L-Cur and PVAI-L-Cur, which are food freshness sensors in Example 3, was analyzed using SEM, EDS, and TEM.

[0129] Figure 23 shows the morphology of PVA-L-Cur in Example 3. Figures 23(a) and 23(b) are SEM images of PVA-L-Cur, Figure 23(c) is a graph showing the distribution of fiber diameter of PVA-L-Cur, and Figure 23(d) is a TEM image of PVA-L-Cur. Figure 24 shows the morphology of PVAI-L-Cur in Example 3. Figures 24(a) and 24(b) are SEM images of PVAI-L-Cur, Figure 24(c) is a graph showing the distribution of fiber diameter of PVAI-L-Cur, and Figure 24(d) is a TEM image of PVAI-L-Cur. Figure 25 is a graph showing the EDS spectrum of the food freshness sensor in Example 3. Figure 25(a) is a graph related to PVA-L-Cur, and Figure 25(b) is a graph related to PVAI-L-Cur. In the graphs of Figure 25, the vertical axis represents counts (×1000), and the horizontal axis represents energy (unit: keV).

[0130] First, SEM images of PVA-L-Cur showed an average fiber diameter of 665 ± 154 nm, confirming a homogeneous and smooth surface (see Figure 23). In PVA-L-Cur, the average fiber diameter increased by 33.83% compared to PVA-LC, suggesting that curcumin was incorporated. Furthermore, magnified images of PVA-L-Cur showed no curcumin aggregation, and uniform loading was observed.

[0131] Furthermore, EDS spectroscopy and elemental mapping of PVA-L-Cur revealed a uniform distribution of carbon (C) and oxygen (O) on the nanofiber surface (see Figure 25(a)). This distribution of carbon and oxygen supports the successful loading of curcumin.

[0132] Furthermore, TEM images revealed that PVA-L-Cur exhibited a smoother surface compared to PVA-LC due to the curcumin coating (see Figure 23(d)). Coating rough nanomaterials with active dyes is highly effective in developing efficient food freshness sensors (colorimetric sensors) for food safety.

[0133] Next, in PVAI-L-Cur, a decrease in average fiber diameter was observed compared to PVAI-L-Cur, due to the effect of curcumin coating (see Figure 24). In PVAI-L-Cur as well, a uniform curcumin coating was suggested, and no aggregation was observed.

[0134] Furthermore, the EDS spectrum and elemental mapping of PVAI-L-Cur showed a uniform distribution of carbon (C), oxygen (O), and potassium (K) on the surface (see Figure 25(b)). In PVAI-L-Cur, an increase in the element carbon (C) was observed compared to PVAI-LC. This supports the successful loading of curcumin. In addition, TEM images of PVAI-L-Cur showed a smooth nanofiber surface due to the curcumin coating, with no surface roughness or aggregation observed (see Figure 24(d)).

[0135] Next, to verify thermal stability, TGA curves and DTA curves were obtained for the food freshness sensors PVA-L-Cur and PVAI-L-Cur used in Example 3.

[0136] Figure 26 is a graph showing the TGA curve and DTA curve of PVA-L-Cur and PVAI-L-Cur in Example 3. Figure 26(a) is a graph showing the TGA curve of PVA-L-Cur, Figure 26(b) is a graph showing the DTA curve of PVA-L-Cur, Figure 26(c) is a graph showing the TGA curve of PVAI-L-Cur, and Figure 26(d) is a graph showing the DTA curve of PVAI-L-Cur. In Figures 26(a) and 26(c), the vertical axis shows the degree of weight loss (in %), and the horizontal axis shows the temperature (in °C). In Figures 26(b) and 26(d), the vertical axis shows differential heat (DTA) (in eV), and the horizontal axis shows the temperature (in °C).

[0137] First, TGA analysis of PVA-L-Cur and curcumin revealed that curcumin exhibited a multi-stage degradation pattern (see Figures 26(a) and 26(b)). For curcumin, a weight loss of 27.33% was observed around 110–250°C, with weight losses of 36.37% and 30.12% observed in the second and third stages, respectively. Curcumin showed a total weight loss of 99.95%.

[0138] Furthermore, PVA-L-Cur exhibited a multi-stage decomposition pattern similar to PVA-LC. In the initial stage, PVA-L-Cur showed a weight loss of 7.45% (around 200°C). This is usually due to the evaporation of adsorbed water molecules. In the second stage, the weight loss escalated significantly to 60.98%, which is thought to correspond to the decomposition of lemon extract. The weight loss in the third stage was 14.38%, which is thought to be due to the decomposition of PVA (main chain) and curcumin. In addition, the ash content of PVA-L-Cur was 17.55%. In conclusion, it was confirmed that PVA-L-Cur has improved thermal stability compared to PVA-LC.

[0139] Next, TGA analysis of PVAI-LS, PVAI-LC, and PVAI-L-Cur revealed that all nanofibers and food freshness sensors exhibited a multi-stage degradation pattern (see Figure 26(c)). PVAI-LS, PVAI-LC, and PVAI-L-Cur showed their initial weight loss around 20–140°C. In the case of PVAI-LS, an initial weight loss of 6.38% was observed around 20°C. This is thought to be due to the removal of adsorbed water and the modification of the nanofiber's bonds. In the second and third stages, PVAI-LS showed weight losses of 77.33% (110–310°C) and 9.16% (310–400°C), respectively. Overall, PVAI-LS showed a weight loss of 92.87% (20–600°C).

[0140] In PVAI-LC, an initial weight loss of 7.14% was observed around 20°C, followed by weight losses of 82.92% (140–310°C) and 4.31% (310–400°C), respectively. Overall, PVAI-LC showed a weight loss of 94.37% (20–600°C).

[0141] In PVAI-L-Cur, an initial weight loss of 14.73% was observed around 20°C. The weight losses in the second and third stages were 69.9% (120-200°C) and 3.08% (200-350°C), respectively. The overall weight loss in PVAI-L-Cur (20-400°C) was 99.95%.

[0142] Furthermore, in DTA analysis, PVAI-LS, PVAI-LC, and PVAI-L-Cur showed two exothermic peaks around 150-450°C (see Figure 26(d)). In PVAI-LS, two exothermic peaks were observed around 300°C and 450°C. This is thought to be due to the loss of water and the denaturation of PVA and inulin.

[0143] In addition, PVAI-L-C also showed the same exothermic peak at the same position as PVAI-L-S, but the intensity increased. Furthermore, in PVAI-L-Cur, a shift in the peak position and intensity was observed. In PVAI-L-Cur, the first exothermic peak was observed around 200 °C, and the second exothermic peak was observed around 320 °C. This is considered to be due to the decrease in thermal stability caused by crosslinking and the loading of curcumin.

[0144] Next, to investigate the structural characteristics, FT-IR spectra and XRD patterns were obtained for PVA-L-Cur and PVAI-L-Cur, which are food freshness sensors in Example 3.

[0145] Figure 27 is a graph showing the FT-IR spectra and XRD patterns of PVA-L-Cur and PVAI-L-Cur in Example 3. Figure 27(a) is a graph showing the FT-IR spectrum of PVA-L-Cur, Figure 27(b) is a graph showing the XRD pattern of PVA-L-Cur, Figure 27(c) is a graph showing the FT-IR spectrum of PVAI-L-Cur, and Figure 27(d) is a graph showing the XRD pattern of PVAI-L-Cur. The vertical axis in Figures 27(a) and 27(c) indicates absorbance (unit: a.u.), and the horizontal axis indicates wavenumber (unit: cm -1 ). The vertical axis in Figures 27(b) and 27(d) indicates intensity (unit: a.u.), and the horizontal axis indicates 2θ (unit: degree). Figure 28 is a graph showing the FT-IR spectrum and XRD pattern of curcumin. Figure 28(a) is a graph showing the FT-IR spectrum, and Figure 28(b) is a graph showing the XRD pattern.

[0146] First, the FT-IR spectrum of curcumin showed stretching vibrations at 1628 cm -1 and 3200 - 3500 cm -1 , and the presence of alkene groups (C=C), carbonyl groups (C=O), and -OH groups was confirmed (see Figure 28(a)). Also, 1427 cm -1 and 1512 cm -1A peak due to aromaticity appeared, confirming the presence of C=C in curcumin. Also, at 1277 cm -1 The bending vibration is due to the phenol group.

[0147] On the other hand, in the FT-IR spectrum of PVA-L-Cur, at 2000 cm⁻¹ -1 The peak intensity in the vicinity is slightly increased, which typically indicates stretching vibrations of the C=O group (see Figure 27(a)). Furthermore, at 1000 cm -1 The peaks identifiable in this region are presumed to be due to CO stretching vibrations common to the phenol group of curcumin and the ether group of PVA. In PVA-L-Cur, the intensity of this peak is enhanced compared to PVA-LC, supporting the successful immobilization of curcumin. Furthermore, in the FT-IR spectrum of PVA-L-Cur, the intensity of the OH group is slightly increased compared to PVA-LC, suggesting interaction or binding between curcumin and the PVA-LC matrix. Based on these results, it is considered that the immobilization of curcumin onto PVA-LC was successful.

[0148] Furthermore, the effect of curcumin on the structure of PVA-L-Cur was evaluated by XRD analysis. In the case of curcumin, a characteristic diffraction peak indicating crystallinity was observed at 20° (see Figure 28(b)). On the other hand, in the XRD pattern of PVA-L-Cur, a prominent peak with an intensity of 2470 and an area under the curve (AUC) of 3607 was observed at approximately 19.4° (see Figure 27(b)). This peak indicates the interplanar spacing in the crystal structure of PVA-L-Cur and shows a structural change caused by curcumin loading (functionalization).

[0149] Furthermore, peaks with intensities of 408, 271, and 257, and AUCs of 1775, 1027, and 517 were observed at 26.4°, 57.8°, and 69.4°, respectively. Overall, the AUC of PVA-L-Cur was 6925. Compared to PVA-LC (peak position: 19.4°, intensity: 1975.8, AUC: 42924.75), a significant decrease in intensity and AUC was observed in PVA-L-Cur. The broadening of the peak width may be due to the interaction between curcumin and the PVA-LC matrix, which may suggest an increase in crystallite size or a decrease in lattice strain.

[0150] Next, the FT-IR spectra of PVAI-LS, PVAI-LC, and PVAI-L-Cur are described. Compared to PVA-LS, PVAI-LS showed increased intensity of peaks related to the stretching vibrations of the OH, C=O, and CO groups, confirming the presence of inulin in the complex (see Figure 27(c)). In addition, the FT-IR spectrum of PVAI-LS showed peaks of 3200-3600 cm² due to OH stretching vibrations. -1 (Center: 3302cm -1 A broad peak was observed, confirming the presence of inulin in PVAI-LS. This result indicates that PVAI-LS is more hydrophilic than PVA-LS.

[0151] Furthermore, 2800-3000cm -1 (Center: 2925cm -1 A peak related to the stretching vibration of the CH functional group was observed at ). Also, at 1730 cm -1 A strong peak indicating stretching vibration of the carbonyl (C=O) group was observed in the vicinity. Also, at 1000-1300 cm -1 Peaks were observed in the CO stretching vibrations of PVA and inulin. Therefore, characteristic peaks were confirmed in both PVA and inulin according to the FT-IR spectrum of PVAI-LS, confirming that the introduction of inulin into the PVA matrix was successful.

[0152] The FT-IR spectrum of PVAI-LC revealed a 3302 cm² vibration related to OH stretching vibrations, similar to that observed in PVA-LC. -1 A phenomenon of decreased peaks in the vicinity was observed. This is due to bridge bridging. Furthermore, a decrease in the intensity of stretching vibrations related to C=O and CO groups was observed.

[0153] In PVAI-L-Cur, no additional peaks were observed compared to the curcumin data. This suggests that curcumin may be physically adsorbed rather than chemically bound to the nanofibers. In addition, the peak intensity related to the CO group increased slightly in PVAI-L-Cur. Furthermore, a slight change in the peak intensity related to C=O was observed, which was attributed to the presence of curcumin on the nanofibers. Based on these results, it can be concluded that the loading of curcumin onto PVAI-LC was successful.

[0154] Furthermore, the structures (amorphous and crystalline) of PVAI-LS, PVAI-LC, and PVAI-L-Cur were evaluated by XRD analysis (see Figure 27(d)). PVAI-LS showed a peak around 19.2° with an intensity of 3156 and an AUC of 46390. In addition, PVAI-LS showed an increase in peak intensity compared to PVA-LS, which is thought to be due to the presence of inulin.

[0155] Furthermore, PVAI-LC showed a slight shift in the peak position around 19.5°, with an intensity of 3865 and an AUC of 47009. This is thought to indicate successful crosslinking and a change in functional groups due to interaction with lemon extract.

[0156] Furthermore, in PVAI-L-Cur, a slight shift in peak position (19.6°), a decrease in intensity (2470), and a decrease in AUC (28780) were observed. In conclusion, XRD analysis confirmed the presence of inulin in the nanofibers and the success of crosslinking, and structural changes due to the loading of lemon extract and curcumin were observed.

[0157] Next, the food freshness sensors PVA-L-Cur and PVAI-L-Cur used in Example 3 were analyzed for their antibacterial and biodegradable properties. The tests for antibacterial and biodegradable properties were conducted using the same method as in Example 1. Figure 29 shows SEM images of PVA-L-Cur and PVAI-L-Cur 21 days after the start of the biodegradability test in Example 3. Figure 29(a) is an SEM image of PVA-L-Cur, and Figure 29(b) is an SEM image of PVAI-L-Cur.

[0158] In antimicrobial activity tests, PVA-L-Cur showed a significant antimicrobial activity against Staphylococcus aureus, exhibiting an 18 mm inhibitory area. PVA-L-Cur also showed sensitivity (clear surface) against Escherichia coli. PVAI-L-Cur also showed a clear surface, demonstrating good antimicrobial properties. In conclusion, it was confirmed that both PVA-L-Cur and PVAI-L-Cur are sensitive to both Gram-negative and Gram-positive bacteria.

[0159] In biodegradation tests, PVA-L-Cur showed significant weight loss rates of 12%, 21%, and 35% at 7, 14, and 21 days, respectively, and was not completely degraded even after 21 days (see Figures 17 and 29(a)). This may be due to the hydrophobic and anti-inflammatory properties of curcumin. PVAI-L-Cur was also not completely degraded after 21 days (see Figures 17 and 29(b)), but the overall weight loss rate was slightly lower compared to PVA-L-Cur (10% at 7 days, 17% at 14 days, and 30% at 21 days).

[0160] Next, the reactivity of PVA-L-Cur, the food freshness sensor in Example 3, to alkaline and acidic vapors was confirmed. Bacterial protein degradation is associated with the release of amino acids and other nitrogen compounds (volatile organic compounds, VOCs), resulting in the generation of nauseating odors. Important parameters for a food freshness sensor are sensitivity to vapors and pH solutions, real-time responsiveness, and reversibility.

[0161] Figure 30 is a bar graph showing the pH responsiveness of PVA-L-Cur to vapor in Example 3. Figure 30(a) is a bar graph showing the RGB values ​​of the color exhibited by PVA-L-Cur, and Figure 30(b) is a bar graph showing the pH responsiveness of PVA-L-Cur. In Figure 30(a), the vertical axis shows the magnitude of the RGB values, and the horizontal axis shows the type of vapor (N: ammonia vapor, A: acetic acid vapor) and the number of times (1: 1st time, 2: 2nd time, 3: 3rd time). In Figure 30(b), the vertical axis shows the total color difference (unit: ΔE), and the horizontal axis shows the type of vapor and the number of times. Note that the square photograph superimposed on the graph in Figure 30(b) shows the color of PVA-L-Cur and is not part of the graph. Also, in Figure 30(b), the sensitivity (SRGB) graph is shown to the right of the total color difference (ΔE). Figure 31 is a graph showing the pH response of PVA-L-Cur to a solution in Example 3. The vertical axis of Figure 31 shows the total color difference (unit: ΔE), and the horizontal axis shows the type of solution. In addition, a small graph of RGB values ​​is included in the upper right space of Figure 31. Furthermore, in Figure 31, a graph of sensitivity (SRGB) is placed to the right of the total color difference (ΔE).

[0162] The color change of the food freshness sensor was measured using a circular sample with a diameter of 16 mm. Images of the food freshness sensor were recorded simultaneously with the occurrence of the color change, and the results were calculated using the Windows Pixie program and the following formulas (1) and (2).

number

[0163] Here, in Equation 1, ΔE represents the total color difference (change in color from the initial state), L1 is the lightness of the initial (reference) color, L2* is the lightness of the color after the test (after the change from the initial state), a1 is the color value for green / magenta of the initial color, a2* is the color value for green / magenta of the color after the test, b1 is the color value for blue / yellow of the initial color, and b2* is the color value for blue / yellow of the color after the test.

[0164] Furthermore, in equation 2, sRGB represents sensitivity, and R, G, B and R * ,G * ,B * These represent the initial and final values ​​(red, green, blue) of the hue of the food freshness sensor, respectively. Note that "SRGB" is written as "Srgb" or "S" in the diagram. RGB It is sometimes written as "".

[0165] First, PVA-L-Cur was exposed to 80 ml of ammonia buffer and acetate buffer vapors. The responsiveness and reversibility of PVA-L-Cur were observed after 3 minutes of exposure to each vapor. When exposed to ammonia vapor, PVA-L-Cur turned reddish (ΔE=55.1, 48.1, 46.2), and when exposed to acetate vapor, it returned to a yellow color similar to its initial color (ΔE=13.88, 16.25, 23.96) (see Figure 30). From these results, it was confirmed that PVA-L-Cur has high sensitivity (SRGB) and functions well even after multiple (3) exposures to acidic and basic vapors.

[0166] Furthermore, PVA-L-Cur showed a clear color change (from yellow to red) in response to solutions with different pH levels (pH=5 and 10) (see Figure 31). The solution temperature was room temperature (25°C), and the immersion time was 1 minute. These are relevant to the guidelines for use as a food freshness sensor, namely, yellow (indicating freshness) and reddish (indicating spoilage). PVA-L-Cur showed a total color difference (ΔE) of 50.69 in alkaline solutions (pH=5) and a total color difference (ΔE) of 14.21 in acidic solutions.

[0167] Therefore, PVA-L-Cur has shown great potential for applications in the chemical and environmental industries in detecting ammonia gas.

[0168] Next, the elution properties of PVA-L-Cur, the food freshness sensor used in Example 3, were confirmed in a food simulation liquid.

[0169] Figure 32 shows the elution of curcumin from PVA-L-Cur in Example 3. Of the photographs in Figure 32, the upper photograph was taken 5 minutes after immersion in the food simulation solution, and the lower photograph was taken 10 minutes after immersion in the food simulation solution.

[0170] Deionized water (DI), acetic acid (Ac.Acid, 3%), and ethanol (Eth, 50% and 95%) were used as food simulants. These food simulants are considered to resemble foods with pH values ​​of 5.8, 2.9, 5.3, and 6.4, respectively. The tests were conducted at room temperature (25±2℃) with time intervals of 5 minutes and 10 minutes.

[0171] As a result, a slight color change was observed in PVA-L-Cur after 10 minutes of immersion in 50% ethanol (see Figure 32). Furthermore, a more pronounced color change occurred after 5 minutes of immersion in 95% ethanol, and the color change intensified further after 10 minutes. A strong color change was observed after 10 minutes of immersion in acetic acid. On the other hand, because curcumin is hydrophobic, no color change was observed even after 10 minutes of immersion in deionized water (pure water).

[0172] Next, tests were conducted using chicken meat to examine the color changes of the food freshness sensors PVA-L-Cur and PVAI-L-Cur, which were used in Example 3.

[0173] Figure 33 is a photograph showing the color change test using chicken meat treated with PVA-L-Cur and PVAI-L-Cur in Example 3. Figure 33(a) is a photograph of PVA-L-Cur, and Figure 33(b) is a photograph of PVAI-L-Cur. In Figures 33(a) and 33(b), two photographs are shown side by side; the left photograph is from the start of the test, and the right photograph is from the end of the test (4 days later). Figure 34 is a graph showing the color changes in the tests using chicken meat treated with PVA-L-Cur and PVAI-L-Cur in Example 3. In the graph in Figure 34, the total color difference (ΔE) is represented by a line graph, and the sensitivity (SRGB) is represented by a bar graph. The vertical axis of the graph in Figure 34 represents the total color difference (ΔE) or sensitivity (SRGB), and the horizontal axis represents time (in days).

[0174] In the experiment using chicken, 200g of chicken was prepared and placed in a plastic bowl. Food freshness sensors (PVA-L-Cur and PVAI-L-Cur) were then placed on the lid of the bowl and 3cm above the chicken (see Figure 33). The chicken was stored at 25°C for 4 days, and real-time monitoring of spoilage of the chicken using the food freshness sensors was attempted.

[0175] There is a link between the spoilage of animal proteins and the release of VOCs (ammonia, dimethylammonium, trimethylamine, etc.). The release of VOCs leads to an increase in pH, which ultimately triggers a color change in food freshness sensors (from initial yellow to red, indicating spoilage).

[0176] First, PVA-L-Cur showed a significant and visible color change from yellow to red over four days (ΔE = 72.99) (see Figure 34). Within 12 hours, the total color difference (ΔE) of PVA-L-Cur reached 29.66, indicating the initial change was detected. This color change is comparable to that of conventionally known food freshness sensors. Therefore, it was confirmed that PVA-L-Cur can be used as a food freshness sensor for real-time monitoring of food freshness.

[0177] Furthermore, PVAI-L-Cur was found to exhibit a tendency towards higher overall color difference and sensitivity compared to PVA-L-Cur. PVAI-L-Cur showed an improvement in sensitivity (48.28%) after 12 hours, followed by a consistent increase in overall color difference. Therefore, these findings highlight the potential of PVAI-L-Cur in food safety.

[0178] [Example 4] In Example 4, drug-loaded nanofibers based on PVA-LC were actually manufactured, analyzed, and evaluated.

[0179] 1. Manufacturing of drug-carrying nanofibers The method for producing drug-supported nanofibers in Example 4 is basically the same as the method for producing nanofibers according to Embodiment 1 (the method using lemon extract), but differs in that 1 g of aloe vera (hereinafter referred to as "AV") is further added to the spinning solution in the spinning solution preparation step, and the solution is stirred for 6 hours without heating.

[0180] Regarding the drug-loaded nanofibers manufactured as described above, the drug-loaded nanofibers before crosslinking will be referred to as "PVA-L-AV-S," and the drug-loaded nanofibers manufactured by crosslinking PVA-L-AV-S will be referred to as "PVA-L-AV-C."

[0181] 2. Analysis of drug-carrying nanofibers First, the morphology of the drug-carrying nanofibers PVA-L-AV-S and PVA-L-AV-C in Example 4 was analyzed using SEM, EDS, and TEM.

[0182] Figure 35 shows the morphology of PVA-L-AV-S in Example 4. Figures 35(a) and 35(b) are SEM images of PVA-L-AV-S, Figure 35(c) is a graph showing the distribution of fiber diameter of PVA-L-AV-S, and Figure 35(d) is a TEM image of PVA-L-AV-S. Figure 36 shows the morphology of PVA-L-AV-C in Example 4. Figures 36(a) and 36(b) are SEM images of PVA-L-AV-C, Figure 36(c) is a graph showing the distribution of fiber diameter of PVA-L-AV-C, and Figure 36(d) is a TEM image of PVA-L-AV-C. Figure 37 is a graph showing the EDS spectrum of the drug-supported nanofiber in Example 4. Figure 37(a) is a graph for PVA-L-AV-S, and Figure 37(b) is a graph for PVA-L-AV-C. In the graphs in Figure 37, the vertical axis represents counts (×1000), and the horizontal axis represents energy (unit: keV).

[0183] PVA-L-AV-S exhibited a smooth surface morphology, with an average fiber diameter of 383 ± 68.34 nm (see Figure 35). The average fiber diameter of PVA-L-AV-S was 11.75% lower compared to PVA-LS. This is thought to be due to the decrease in the viscosity and surface tension of the solution caused by the addition of AV to the PVA solution.

[0184] Furthermore, PVA-L-AV-C showed a slight increase in average fiber diameter (2.6%) compared to PVA-L-AV-S, and a flatter surface morphology was observed (see Figure 36). In addition, PVA-L-AV-C had a 14.9% decrease in average fiber diameter compared to PVA-LC.

[0185] Furthermore, EDS analysis showed that carbon (C), oxygen (O), sodium (Na), and potassium (K) elements were uniformly distributed on the surface of PVA-L-AV-S (see Figure 37(a)). On the other hand, sodium (Na) was absent in PVA-L-AV-C (see Figure 37(b)). Because PVA-L-AV-C does not contain sodium, it is less likely to cause skin inflammation and dryness, and is considered particularly suitable for the treatment of acne vulgaris.

[0186] Furthermore, TEM images revealed that PVA-L-AV-S and PVA-L-AV-C possessed a smooth surface morphology (see Figures 35(d) and 36(d)). In conclusion, it was confirmed that the introduction of AV significantly affects the morphological properties of nanofibers, resulting in a decrease in fiber diameter both before and after crosslinking.

[0187] Next, to investigate its structural properties, FT-IR spectra and XRD patterns were obtained for PVA-L-AV-C, the drug-supported nanofiber in Example 4.

[0188] Figure 38 is a graph showing the FT-IR spectrum and XRD pattern of PVA-L-AV-C in Example 4. Figure 38(a) is a graph showing the FT-IR spectrum, and Figure 38(b) is a graph showing the XRD pattern. In Figure 38(a), the vertical axis shows absorbance (unit: au), and the horizontal axis shows wavenumber (unit: cm). -1 Figure 38(b) shows the intensity (unit: au) on the vertical axis and 2θ (unit: degrees) on the horizontal axis.

[0189] In PVA-L-AV-C, peaks associated with functional groups (C=O, OH, and CH) were observed to be significantly increased compared to PVA-LC (see Figure 38(a)). Furthermore, PVA-L-AV-C showed a significant increase in peaks associated with OH groups and CH2 groups, respectively, at 3100-4000 cm⁻¹ compared to PVA-LC. -1 (Center: 3400cm -1 ) and 2800cm -1 A strong absorption peak was observed during this period. This is thought to be due to the carbohydrate monomers of AV (uronic acid, mannose, galacturonic acid, and phenolic components such as aloin and emodin).

[0190] Furthermore, the presence of AV-derived proteins and polysaccharides results in 1730cm -1 A strong absorption peak associated with the carbonyl (C=O) group was observed. Furthermore, at 1200 cm² -1 An increase in CO-related peak intensity was also observed at 760-870 cm, which may be due to the presence of saccharides. -1 Nearby vibration band (center: 830cm) -1 ) is the out-of-plane vibration of CH (mannose and pyranose rings) and -CH 2 This is due to the twisting of the structure. Also, CO(1650~1780cm -1 ) and COOH (2300~2400cm -1The significant increase in intensity associated with the absorption peak of ) suggested the possibility of the presence of a carboxylic acid. From these results, it was confirmed that the manufactured PVA-L-AV-C contains AV.

[0191] Furthermore, analysis of the XRD pattern of PVA-L-AV-C revealed a diffraction pattern somewhat different from that of PVA-LC (see Figure 38(b)). In PVA-L-AV-C, a clear peak was observed at 19.8°, with decreased intensity (414) and decreased AUC (4281.6). This is thought to be due to the presence of AV in the PVA matrix resulting in a structure closer to amorphous.

[0192] Furthermore, a peak with an intensity of 240 and an AUC of 1367.6 was detected at 57.9°. This peak suggests a complex structural change caused by both AV support and crosslinking by lemon extract, and is thought to be due to the formation of a new crystalline phase. Overall, the AUC of PVA-L-AV-C was 5649.2. In conclusion, PVA-L-AV-C showed the effects of AV support and a decrease in AUC (an 86.8% decrease compared to PVA-LC), indicating a decline in crystallinity.

[0193] Next, to verify the thermal stability, TGA and DTA curves were obtained for PVA-L-AV-C, the drug-supported nanofiber used in Example 4. Figure 39 is a graph showing the TGA curve and DTA curve of PVA-L-AV-C in Example 4. The vertical axis of Figure 39 shows the degree of weight loss (in %) and differential heat (DTA) (in eV), and the horizontal axis shows the temperature (in °C).

[0194] PVA-L-AV-C exhibited multi-stage decomposition, similar to PVA-LC (see Figure 39). Initially, a weight loss of 6.12% (around 17°C) was observed, which is thought to be due to the removal of moisture. In the second and third stages, weight losses of 58.16% and 25.76% were observed, respectively. Overall, a weight loss of 90.04% was observed for PVA-L-AV-C. Therefore, it can be said that PVA-L-AV-C has improved thermal stability compared to PVA-LC.

[0195] The reduction in weight loss is thought to be due to the presence of AV, which has a high water content and is gel-like. In other words, AV is thought to have exerted a certain degree of protective effect (masking effect) during heat treatment, ultimately leading to a reduction in weight loss (overall decomposition rate). Furthermore, DTA analysis of PVA-L-AV-C revealed two exothermic peaks. PVA-L-AV-C showed the first exothermic peak at approximately 300°C. A significant shift was also observed in the second exothermic peak (a sharp peak, approximately 350-400°C). These results also confirmed that PVA-L-AV-C has improved thermal stability compared to PVA-LC.

[0196] Next, the drug-carrying nanofibers PVA-L-AV-S and PVA-L-AV-C from Example 4 were analyzed for their antibacterial and biodegradable properties. The tests for antibacterial and biodegradable properties were conducted using the same method as in Example 1. Figure 40 is an SEM image of PVA-L-AV-C 21 days after the start of the biodegradability test in Example 4.

[0197] In the antimicrobial activity test, PVA-L-AV-S was dissolved in agar medium because it is hydrophilic and susceptible to water. On the other hand, PVA-L-AV-C showed a clear surface (no growth of Staphylococcus aureus) and exhibited a clean surface against both types of bacteria. This is thought to be due to the effects of lemon extract and the bioactive component (AV). In conclusion, PVA-L-AV-C was found to be susceptible to both Gram-negative and Gram-positive bacteria.

[0198] Furthermore, the degradation of PVA-L-AV-C was 13% after 7 days, 17% after 14 days, and 33% after 21 days, indicating that it was not completely degraded even after 21 days (see Figures 17 and 40). Therefore, it was suggested that the addition of AV contributed to promoting biodegradation.

[0199] Next, an analysis was conducted on the release of the drug (AV) from PVA-L-AV-C, the drug-carrying nanofiber in Example 4. Figure 41 is a graph showing the UV spectra of PVA-LC in Example 1 and PVA-L-AV-C in Example 4. Figure 41(a) is the graph for PVA-LC, and Figure 41(b) is the graph for PVA-L-AV-C. In the graphs of Figures 41(a) and 41(b), the vertical axis represents absorbance (unit: au), and the horizontal axis represents wavelength (unit: nm). Note that Figures 41(a) and 41(b) show multiple results (curves), which are arranged from bottom to top in order of test time.

[0200] For the analysis of the release of the drug (AV), PVA-LC and PVA-L-AV-C were immersed in PBS solution, and samples were taken at predetermined times (5 minutes, 15 minutes, 30 minutes, 60 minutes, 180 minutes, 360 minutes, 720 minutes, and 1440 minutes). UV spectroscopy was used for evaluation, and UV spectra were obtained for each sample.

[0201] From the UV spectrum, a time-dependent increase in absorbance was observed in PVA-L-AV-C with respect to the AV-related peak (280 nm) (see Figure 41(b)). Compared to the case of PVA-LC (see Figure 41(a)), an increase in absorbance intensity in the UV spectrum was observed, which is due to the emission of AV from PVA-L-AV-C.

[0202] Furthermore, in PVA-L-AV-C, the AUC of the UV spectrum also increased over time (14.19 after 5 minutes, 15.04 after 15 minutes, 16.61 after 30 minutes, 16.76 after 60 minutes, 20.21 after 180 minutes, 21.47 after 360 minutes, 22.74 after 720 minutes, and 27.5 after 1440 minutes). In addition, a rapid increase in release was observed in PVA-L-AV-C during the first 5 minutes of immersion in PBS compared to PVA-LC. In conclusion, PVA-L-AV-C was found to be suitable for application in the field of drug delivery.

[0203] [Example 5] In Example 5, PVA-LC was used as a filter for filtration, and analysis and evaluation were performed.

[0204] Figure 42 shows photographs of the material to be filtered (before filtration) and the filtrate (after filtration) in Example 5. Figure 42(a) is a photograph of the material to be filtered, which is water mixed with soil; Figure 42(b) is a photograph of the material to be filtered, which is oil mixed with soil; Figure 42(c) is a photograph of the filtrate after filtering Figure 42(a); and Figure 42(d) is a photograph of the filtrate after filtering Figure 42(b). Figure 43 shows the UV spectrum of the filtrate obtained by PVA-LC in Example 5. The vertical axis of Figure 43 represents absorbance (unit: au), and the horizontal axis represents wavelength (unit: nm).

[0205] The PVA-LC in Example 5 is the same as the PVA-LC in Example 1. In Example 5, the PVA-LC was cut into a circular shape to fit the inner diameter of a syringe and set in the syringe to form a syringe filter. The materials used for filtration were water mixed with soil (particulate pollutants) (see Figure 42(a)) and oil mixed with soil (see Figure 42(b)). The oil used in Example 5 was cooking oil (so-called waste oil).

[0206] As a result, it was confirmed that using PVA-LC as a filter could purify both water and oil to the point where no visible foreign matter (soil) was present in the filtrate (see Figures 42(c) and 42(d)). In addition, it was confirmed that the color of the oil itself had become lighter. Furthermore, UV spectroscopy of the filtrate of water confirmed that particulate pollutants (soil) were effectively removed (see Figure 43). These results indicate that PVA-LC has potential as a powerful liquid purification medium.

[0207] Although the present invention has been described above based on the embodiments and examples, the present invention is not limited to the embodiments and examples described above. It can be implemented in various forms without departing from the spirit of the invention, and for example, the following modifications are also possible.

[0208] (1) The substances and numerical values ​​described in the above examples are not limiting to the present invention. Other substances and numerical values ​​may be used as long as they do not impair the effects of the present invention.

[0209] (2) In Embodiment 2 described above, the color-changing dye was supported on the crosslinked nanofibers, but the present invention is not limited thereto. The color-changing dye may also be added to the spinning solution.

[0210] (3) In Embodiment 3 described above, the drug component was added to the spinning solution, but the present invention is not limited thereto; the drug component may be supported on the crosslinked nanofiber.

Claims

1. A spinning solution preparation step involves preparing a spinning solution containing a citrus-derived material obtained from citrus fruits and a water-soluble polymer that can be made into fibers. A nanofiber formation step in which nanofibers are formed from the spinning solution by electrospinning, A method for producing nanofibers, characterized by including a crosslinking step of crosslinking the nanofibers.

2. The method for producing nanofibers according to claim 1, characterized in that the water-soluble polymer comprises at least one of polyvinyl alcohol and a polyvinyl alcohol copolymer.

3. The method for producing nanofibers according to claim 2, characterized in that the water-soluble polymer further comprises inulin.

4. The method for producing nanofibers according to claim 1, characterized in that the citrus-derived material is obtained from lemon fruit.

5. The method for producing nanofibers according to claim 1, characterized in that the citrus-derived material includes the juice of the fruit and constitutes at least a portion of the solvent in the spinning solution.

6. In the spinning solution preparation step, the spinning solution is prepared by adding the water-soluble polymer to a solvent containing the citrus-derived substance. The method for producing nanofibers according to claim 5, characterized in that the concentration of the citrus-derived substance in the solvent is within the range of 90 to 100% by weight.

7. The method for producing nanofibers according to claim 1, characterized in that the crosslinking step involves heating the nanofibers within a range of 80 to 100°C.

8. A spinning solution preparation step involves preparing a spinning solution containing a citrus-derived material obtained from citrus fruits and a water-soluble polymer that can be made into fibers. A nanofiber formation step in which nanofibers are formed from the spinning solution by electrospinning, A crosslinking step for crosslinking the nanofibers, A method for manufacturing a food freshness sensor, characterized by comprising a step of supporting a color-changing pigment on the cross-linked nanofiber, the color-changing pigment being affected by substances released as food spoils.

9. The method for producing a food freshness sensor according to claim 8, characterized in that the color-changing pigment contains curcumin.

10. A spinning solution preparation step involves preparing a spinning solution containing a citrus-derived material obtained from citrus fruits, a fiberizable water-soluble polymer, and a pharmaceutical component. A nanofiber formation step in which nanofibers are formed from the spinning solution by electrospinning, A method for producing drug-supported nanofibers, characterized by including a crosslinking step of crosslinking the nanofibers.

11. The method for producing drug-carrying nanofibers according to claim 10, characterized in that the drug component includes aloe vera.

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