QUASI-PERMANENT CHARGE-BEARING NANOFIBER AND METHOD OF FORMING THEREOF

Abstract

Provided herein is a novel formulation of a quasi-permanent charge-bearing nanofiber, and a one-step fabrication method of the nanofiber thereof. The novel formulation allows flexibility in adjusting the type of charges and crystallinity of the nanofiber product as desired, and the one-step fabrication method allows easy and cost-effective production of these nanofibers without the use of external physical charging. The charge-bearing nanofibers of the present invention also show remarkable stability under different temperature and chemical conditions, and a significant charge retention over a time period of 12 months.

Claims

1. A method of forming quasi-permanent charge-bearing nanofibers, comprising: preparing an aqueous fabrication solution comprising at least one water-soluble polymer, one charge-bearing polymer, water and acetic acid; electrospinning the aqueous solution to obtain nanofibers; and subjecting the nanofibers to ionized air to obtain quasi-permanent charge-bearing nanofibers.

2. The method of claim 1, wherein the at least one water-soluble polymer is selected from polyvinyl alcohol, polyethylene oxide, gelatin, chitosan, polycaprolactone, polylactic acid, collagen and hyaluronic acid.

3. The method of claim 1, wherein the at least one charge-bearing polymer is selected from polyacrylic acid, polyethyleneimine, polylysine or polyhexanide.

4. The method of claim 1, wherein the ionized air is produced by electrodes placed at a distance of 10-50 mm apart applying a voltage of 50-100 kV.

5. A quasi-permanent charge-bearing nanofiber fabricated using the method of claim 1.

6. The quasi-permanent charge-bearing nanofiber of claim 4, wherein the magnitude of the surface charge of the nanofiber is at least 10 mV.

7. The quasi-permanent charge-bearing nanofiber of claim 4, wherein the surface charge retention of the nanofiber 12 months after fabrication under room temperature is at least 60%.

8. The quasi-permanent charge-bearing nanofiber of claim 4, wherein the surface charge retention of the nanofiber 72 hours after fabrication under a temperature of 50 C. is at least 55%.

9. The quasi-permanent charge-bearing nanofiber of claim 4, wherein the surface charge retention of the nanofiber 72 hours after fabrication under a temperature of 20 C. is at least 60%.

10. The quasi-permanent charge-bearing nanofiber of claim 4, wherein the hydration level of the nanofiber is at least 50% higher than non-charge bearing nanofibers.

11. The quasi-permanent charge-bearing nanofiber of claim 4, wherein the total antioxidant capacity of the nanofiber is at least 300% higher than non-charge bearing nanofibers.

12. The quasi-permanent charge-bearing nanofiber of claim 4, wherein the nanofiber bears positive charge and the charge-bearing polymer in the aqueous fabrication solution comprises polyhexanide.

13. The quasi-permanent charge-bearing nanofiber of claim 4, wherein the nanofiber bears negative charge and the charge-bearing polymer in the aqueous fabrication solution comprises polyacrylic acid.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 provides a schematic diagram of the novel quasi-permanent charge-bearing nanofibers in the present invention. Both the formulation of the quasi-permanent charge-bearing nanofiber and its fabrication process is provided.

[0023] FIG. 2 shows three types of ionic nanofiber fabricated under the method and specific formulations respectively of the present invention. The physical properties of these nanofibers are tabulated, including the average diameters and surface potentials of the nanofibers respectively.

[0024] FIG. 3 shows the test results of the three types of ionic nanofibers after subjecting to high-temperature condition, low-temperature condition and prolonged (quasi-permanent) room temperature condition.

[0025] FIGS. 4A and 4B shows the performance of freshly fabricated type I ionic nanofiber. FIG. 4A shows the hydration level; while FIG. 4B shows the total antioxidation capacity.

[0026] FIGS. 5A and 5B shows the performance of the type I ionic nanofiber under different storage conditions. FIG. 5A shows the hydration level; while FIG. 5B shows the total antioxidation capacity.

[0027] FIG. 6 shows stability test results of the type II ionic nanofiber. The stability test is conducted with an HPV DNA probe of 0.6 l and a sample concentration 50 pmol.

[0028] FIGS. 7A to 7E shows the stability of hybridization membranes under different temperature and chemical environments. FIG. 7A shows the original environment; FIG. 7B shows the result after 10-minute treatment under a strongly acidic environment of pH 1; FIG. 7C shows the result after 10-minute treatment under a strongly alkaline environment of pH 14; FIG. 7D shows the result after 8-hour treatment under a temperature of 60 C.; and FIG. 7E shows the result after 24-hour treatment under a temperature of 20 C.

[0029] FIG. 8 shows stability test results of the type III ionic nanofiber in terms of anti-bacterial activity and the content and purity of the EGF released.

[0030] FIGS. 9A to 9D shows the release profile of the type III ionic nanofiber. FIG. 9A shows the release profile of the nanofiber when freshly prepared; FIG. 9B shows the release profile of the nanofiber after 12-months treatment under a temperature of 25-30 C.; FIG. 9C shows the release profile of the nanofiber after 12-months treatment under a temperature of 4-8 C.; and FIG. 9D shows the release profile of the nanofiber after 6-months treatment under a temperature of 37-40 C.

DETAILED DESCRIPTION

[0031] As used below in the specification, EGF is the abbreviation for epidermal growth factor.

[0032] As used below in the specification, quasi-permanent is defined as a time period of less than 12 months.

[0033] As used below in the specification, ionic nanofibers and charge-bearing nanofibers are used interchangeably, defined as nanofibers carrying charges. The charges carried can either be positive or negative.

[0034] While ionic nanofibers have a wide range of applications across a multitude of fields including but not limited to biomedicine, pharmaceuticals, environmental engineering and surface chemistry, the fabrication of which have proven challenging.

[0035] Attempts have been made in fabricating ionic nanofibers, including a charging mechanism requiring external power sources for charging the nanofibers as a post-fabrication treatment.

[0036] However, as discussed before, ionic nanofibers in the field of art has a shortcoming of relative low retention of charges on the nanofibers. As the specific applications and functionalities of ionic nanofibers rely heavily upon the electrostatic effect brought by the charges, a low retention of which means that more frequent replacements of ionic nanofibers would be required, thus increasing the costs.

[0037] Additionally, given the need of an external physical charging system in the existing ionic nanofiber fabrication process, scaling up production could be difficult due to the process being potentially cost-intensive and hence less economically viable.

[0038] Existing ionic nanofibers generally also have high sensitivities to environmental conditions. Special storage conditions, for example controlled temperature and pH conditions, may be required to preserve their functionality to extend shelf-life, thereby also limiting a wider range of applications.

[0039] The ionic nanofibers provided in this invention is shown, as below, to have high retention of charges under various challenging conditions, including high temperature, low temperature and extreme pH conditions, thereby allowing application in a wider variety of environments.

[0040] Specifically, the ionic nanofibers provided in this invention has quasi-permanent charge-bearing properties, which equates a significantly longer shelf-life over other existing ionic nanofibers in the art.

[0041] The novel method of fabricating the ionic nanofibers above, also provided in the present invention, is a one-step fabrication, wherein the aqueous fabrication solution pre-electrospinning contains a charge-bearing polymer. This also allows greater flexibility in controlling the crystallinity of the product by adjusting the fabrication solution before electrospinning; also, the type of charges could be customized by the choice of charge-bearing polymers.

[0042] As the production method of the ionic nanofibers in the present invention does not require external physical charging, such method is less cost-intensive and has potential for mass production.

EXAMPLES

Example 1Formulation of Ionic Nanofibers

[0043] Three formulations of ionic nanofibers are specifically developed, fabricated and tested for their performance, namely Type I, Type II and Type III.

[0044] For Type I ionic nanofiber, the aqueous fabrication solution comprises 8-25% polyethylene oxide (PEO), 0.5-5% -tocopherol and 0.5-5% Span-80.

[0045] Accordingly, the type I ionic nanofiber fabrication solution is prepared by first adding -tocopherol and Span-80 into water and stirred vigorously. PEO is then added to the solution and stirred over a period of time. The fabrication solution is then used to fabricate nanofiber by electrospinning under optimized parameters of 15-30 C., 15-40% RH, 50-100 kV applied voltage, spinning distance at 120-250 mm.

[0046] For type II ionic nanofiber, the aqueous fabrication solution comprises 1-10% poly(vinyl alcohol) (PVA), 15-30% poly(acrylic acid) (PAA) and 0-10% citric acid.

[0047] Accordingly, the type II ionic nanofiber fabrication solution is prepared by mixing PVA and PAA in a mixture of water and acetic acid. The fabrication solution is then electrospun into nanofiber at conditions of 15-30 C., 5-25% RH, 50-100 kV applied voltage, spinning distance at 120-250 mm.

[0048] For type III ionic nanofiber, the aqueous fabrication solution comprises 5-20% poly(caprolactone) (PCL), 0.5-5% poly(vinyl alcohol) (PVA), 0.5-5% gelatin, 0-2% polyhexanide and 0-1% epidermal growth factor (EGF).

[0049] Accordingly, the type III ionic nanofiber fabrication solution is prepared by dissolving PCL and polyhexanide are dissolved in acetic/formic acid mixture, and dissolving PVA and gelatin in water/acetic acid mixture. These two precursor polymer solutions are mixed together under vigorous stirring. EGF solution is then added under vigorous stirring to the PCL/PVA/gelatin/polyhexanide mixture solution. Nanofibers are then electrospun under the condition: 15-30 C., 15-30% RH, 50-100 kV applied voltage, spinning distance at 120-250 mm.

Example 2Performance Tests

[0050] Referring to FIG. 2, the diameters of the nanofibers can be adjusted, as shown in the three types of ionic nanofibers fabricated with different formulations having different nanofiber diameters.

[0051] The type of charges, positive or negative, could also be altered by adjusting the charge-bearing polymer in the fabrication solution. It should be noted that while the nanofibers of the present invention have a general surface potential of at least 10 mV, Type I ionic nanofiber displays a significantly higher surface potential of nearly 25,000 mV.

[0052] The three types of ionic nanofibers are subjected to storage simulating summer, winter and on-shelf storage conditions respectively. For simulation of summer conditions, the ionic nanofibers fabricated are placed under a temperature of 50 C. for 72 hours. For simulation of winter conditions, the ionic nanofibers fabricated are placed under a temperature of 20 C. for 72 hours. For simulation of on-shelf storage conditions, the ionic nanofibers are stored under a room temperature of 20-25 C. for 12 months. Both the diameter of nanofibers and their surface potentials are measured. Results are tabulated as shown in FIG. 3.

[0053] Across all three types of ionic nanofibers, their surface potential reached a retention of at least 60% under summer storage conditions, at least 55% under winter storage conditions, and at least 60% under on-shelf storage conditions.

[0054] Meanwhile, for all three types of ionic nanofibers, their nanofiber diameters have a retention of at least 40% under summer storage condition, at least 35% under winter condition and at least 35% under on-shelf storage conditions.

2.1 Stability of Type I Ionic Nanofiber

[0055] The type I ionic nanofibers are further tested for their hydration level and total antioxidation capacity level. Referring to FIGS. 4A and 4B, it is observed that the type I ionic nanofibers have a hydration level 54.5% higher than the control non-ionic nanofiber (FIG. 4A), and a total antioxidant capacity 374% higher than the control non-ionic nanofiber (FIG. 4B).

[0056] Similarly, the hydration level and total antioxidation capacity level is extended to the different simulation conditions. For simulation of summer conditions, the ionic nanofibers fabricated are placed under a temperature of 50 C. for 72 hours. For simulation of winter conditions, the ionic nanofibers fabricated are placed under a temperature of 20 C. for 72 hours. For simulation of on-shelf storage conditions, the ionic nanofibers are stored under a room temperature of 20-25 C. for 12 months. Results are shown in FIGS. 5A and 5B.

[0057] Apart from the lowered total antioxidation capacity which is expected from a greater difficulty to maintain antioxidation capacity due to an intrinsically higher tendency of oxidation under high temperature, the type I ionic nanofibers exhibited no significant differences in hydration levels and total antioxidation capacities across different storage conditions.

2.2 Stability of Type II Ionic Nanofiber

[0058] FIG. 6 shows the results of stability test on type II ionic nanofiber performance for storage under 2-8 C. for 15 months (on the right; freshly fabricated type II ionic nanofiber on the left).

[0059] An HPV DNA probe is used with a probe volume of 0.6 l and sample concentration of 50 pmol is used.

[0060] After the said low-temperature storage for 15 months, a 50 pmol DNA sample was detected successfully and the color of the dots are still apparently visible.

[0061] Similar tests are extended to the type II ionic nanofiber under different chemical and thermal challenges. As shown in FIGS. 7A to 7E, FIG. 7A shows the original environment; FIG. 7B shows the result after 10-minute treatment under a strongly acidic environment of pH 1; FIG. 7C shows the result after 10-minute treatment under a strongly alkaline environment of pH 14; FIG. 7D shows the result after 8-hour treatment under a temperature of 60 C.; and FIG. 7E shows the result after 24-hour treatment under a temperature of 20 C.

[0062] It can be observed across the images that the stability of the hybridization membrane after different chemical and thermal challenges remained high, with no significant deterioration detected.

2.3 Stability of Type III Ionic Nanofiber

[0063] The stability of type III ionic nanofiber is tested for its anti-bacterial activities and controlled release properties under different conditions as part of the stability test. Referring to FIG. 8, the different conditions under which the test is repeated include 12-months treatment under a temperature of 25-30 C.; 12-months treatment under a temperature of 4-8 C.; and 6-months treatment under a temperature of 37-40 C.

[0064] It is observed that the anti-bacterial activities of the type III ionic nanofibers across all test conditions remain stable.

[0065] The controlled release properties of the type III ionic nanofibers are tested with the controlled release of EGF. Tests are conducted on the released EGF contents and purities, which show that all type III ionic nanofibers across the three test groups show a performance level of at least 90% in terms of both the content and purity of the EGF released, in comparison to the freshly fabricated control group.

[0066] Turning to FIGS. 9A to 9D, FIG. 9A shows the EGF release profile of the nanofiber when freshly prepared; FIG. 9B shows the release profile of the nanofiber after 12-months treatment under a temperature of 25-30 C.; FIG. 9C shows the release profile of the nanofiber after 12-months treatment under a temperature of 4-8 C.; and FIG. 9D shows the release profile of the nanofiber after 6-months treatment under a temperature of 37-40 C.

[0067] The EGF release profile of the type III ionic nanofibers do not show significant differences across the test groups, thereby evidencing a stability of performance of the type III ionic nanofibers under different storage conditions.

[0068] Throughout this specification, unless the context requires otherwise, the word comprise or variations such as comprises or comprising, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. It is also noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as comprises, comprised, comprising and the like can have the meaning attributed to it in U.S. Patent law; e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the present invention.

[0069] Furthermore, throughout the specification and claims, unless the context requires otherwise, the word include or variations such as includes or including, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0070] References in the specification to one embodiment, an embodiment, an example embodiment, etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0071] Other definitions for selected terms used herein may be found within the detailed description of the present invention and apply throughout. Unless otherwise defined, all other technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the present invention belongs.

[0072] It will be appreciated by those skilled in the art, in view of these teachings, that alternative embodiments may be implemented without undue experimentation or deviation from the spirit or scope of the invention, as set forth in the appended claims. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.