WO2010090868A2

WO2010090868A2 - Needle-in-needle electrospinning spinneret

Info

Publication number: WO2010090868A2
Application number: PCT/US2010/021634
Authority: WO
Inventors: Kevin Bechtold; Yan Yu; Chunlei Wang
Original assignee: The Florida International University Board Of Trustees
Priority date: 2009-01-21
Filing date: 2010-01-21
Publication date: 2010-08-12
Also published as: WO2010090868A3

Abstract

A spinneret comprises at least a first needle and a second needle for delivering at least a first and a second solution, respectively, during an electro spinning or electrostatic spray deposition operation. The first needle is disposed within the second needle such that the first and second solutions can be delivered from the spinneret and mixed.

Description

NEEDLE-IN-NEEDLE ELECTROSPINNING SPINNERET CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The priority benefit of U.S. Provisional Patent Application No. 61/146,174, filed January 21, 2009, is claimed, and the entire contents thereof are hereby incorporated herein by reference.

FIELD OF THE DISCLOSURE

[0002] The present disclosure is generally directed to a nozzle for spreading multiple solutions without pre-mixing and, more particularly, to a nozzle for an electrospinning or electrostatic spray system.

BACKGROUND

[0003] Electrospinning has become a popular method for the creation of nanofibers due to the simplicity of the setup and wide selection of materials. Typically, the setup consists of a needle (or spinneret) placed perpendicularly to a substrate some distance away while an electrical potential is applied between needle and substrate. A solution is then pumped into the needle and is sprayed from the tip onto the substrate due to the large electric potential. This technique can produce fibers with diameters from nano- to sub-millimeter scales that can be used for different applications such as: gas sensors, chemical sensors, lithium ion batteries, supercapacitors, fuel cells, drug delivery, etc. Typically, single needle electrospinning is used to spray one material and requires premixing in case of multiple materials, limiting its potential for further applications.

SUMMARY

[0004] One aspect of the disclosure includes a spinneret that comprises at least a first needle and a second needle for delivering at least a first solution and a second solution, respectively. The first needle is disposed within the second needle such that the first and second solutions can be delivered from the spinneret and mixed during an electro spinning or electrostatic spray deposition operation.

[0005] In one embodiment, the first and second needles are disposed coaxially relative to each other.

[0006] In one embodiment, the first needle includes a tip that is axially offset from a tip of the second needle.

[0007] In one embodiment, the spinneret includes means for adjusting the axial position of the first tip relative to the second tip and/or means for adjusting the axial position of the second tip relative to the first tip.

[0008] In one embodiment, at least one of the first and second needles are interchangeable and replaceable with one or more replacement needles, wherein the one or more replacement needles have different dimensions than the first and second needles.

[0009] In one embodiment, the device can further include a heater connected to the second needle for heating the second needle.

[0010] Another aspect of the present disclosure includes an electro spinning or electrostatic spray deposition system, which comprises a spinneret having at least a first needle and a second needle, and at least a first pump and a second pump for independently supplying first and second solutions to the first and second needles, respectively. [0011] In one embodiment of the system, the first and second pumps can be syringe pumps.

[0012] In one embodiment of the system, the first needle of the system is disposed within the second needle such that the first and second solutions can be delivered from the spinneret and mixed during an electro spinning or electrostatic spray deposition operation.

[0013] In one embodiment system, the first and second needles of the system are disposed coaxially relative to each other.

[0014] In one embodiment of the system, the first needle includes a tip that is axially offset from a tip of the second needle.

[0015] In one embodiment of the system, the spinneret includes means for adjusting the axial position of the first tip relative to the second tip and/or means for adjusting the axial position of the second tip relative to the first tip.

[0016] In one embodiment of the system, at least one of the first and second needles are interchangeable and replaceable with one or more replacement needles, wherein the one or more replacement needles have different dimensions than the first and second needles.

[0017] Another aspect of the present disclosure includes a kit for providing a spinneret that is customizable for a plurality of different electro spinnning or electrostatic deposition operations. The kit includes a housing and a plurality of interchangeable needles. The housing is adapted to accommodate at least two needles at a time for delivering at least two solutions to be mixed during an electro spinning or electrostatic deposition operation. The plurality of needles can include needles of different lengths, different diameters, different wall thicknesses, and/or any combination thereof. As such, the spinneret can be customized to include any combination of two or more needles to suit an intended electro spinning or electrostatic deposition operation, for example.

[0018] Another aspect of the present disclosure provides a method of forming a nanofiber. The method generally comprises positioning a spinneret relative to a substrate. Then, an electrical potential is applied between the spinneret and the substrate. While applying the electrical potential, a first solution is delivered to the substrate through a first needle of the spinneret, and a second solution is delivered to the substrate through a second needle of the spinneret simultaneously with the delivery of the first solution. Either of the first or second solutions can be continuously delivered, pulsatingly delivered, or intermittently delivered, in accordance with, for example, regular or irregular intervals.

[0019] In one embodiment, the method further includes adjusting a position of a tip of one of the first and second needles relative to a tip of the other needle prior to positioning the spinneret relative to the substrate.

[0020] In one embodiment, the method further comprises mixing the first and second solutions only immediately after, or simultaneously with, the discharge of the solutions from their respective needles.

[0021] In one embodiment, the method further comprises heating the second needle simultaneously with delivering the second solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1 is a schematic side view of one embodiment of an electro spinning or electrostatic deposition system constructed in accordance with the principles of the present disclosure; and

[0023] Fig. 2 is an exploded perspective view of one embodiment of a spinneret constructed in accordance with the principles of the present disclosure.

DETAILED DESCRIPTION

[0024] The present disclosure is directed to a nozzle for injecting multiple solutions during an electro spinning operation for creating nanofiber structures such as core-shell nanofiber structures, for example. This is achieved through the use of a spinneret with two or more needles aligned in a compact, coaxial, arrangement.

[0025] For example, Fig. 1 depicts one embodiment of an electro spinning system 10 constructed in accordance with the present disclosure. The system 10 includes a spinneret 12, a substrate 14, a first solution source 16, a second solution source 18, and an electrical circuit 20.

[0026] The spinneret 12 includes an inner needle 22, which may also be referred to as a first needle, and an outer needle 24, which may be referred to as a second needle. In the disclosed embodiment, each of the inner and outer needles 22, 24 comprises a conventional hollow hypodermic needle. In alternative embodiments, the inner and outer needles 22, 24 could include customized needles, or any other type of hollow delivery device or tubular structure, which may or may not be characterized as a "needle." The inner needle 22 includes inner and outer diameters that are smaller than inner and outer diameters of the outer needle 24. The wall thickness of the inner and outer needles 22, 24 can be the same or can be different. The inner needle 22 is disposed within the outer needle 24 and positioned in substantial coaxial alignment therewith. The inner needle 22 includes a tip 23 that is disposed offset from a tip 25 of the outer needle 24 by a distance "d." In the depicted embodiment, the tip 23 of the inner needle 22 is positioned outside of the outer needle 24, but in other embodiments, it is foreseeable that the tip 23 of the inner needle 22 could be positioned inside of the outer needle 24.

[0027] In the depicted embodiment the spinneret 12 further includes a heater 13 connected to the outer needle 24 for providing heat to the outer needle 24 to facilitate the creation of nanofiber structures. In the embodiment depicted in Figs. 1 and 2, the heater 13 can include a hollow cylindrical jacket 15, which may also be referred to as a sleeve or collar, for example, fit over a portion of the tip 25 on the outside of the outer needle 24. The jacket 15 can comprise a ceramic cylinder embedded with a wire coil for generating heat from an energy source 17, such as a battery, a power outlet, or otherwise. The wire coil can include a composite metal wire, for example, such as a nickel-chromium resistance wire, which can be referred to as a nichrome wire, or any other type of wire.

[0028] While the embodiment of the heater 13 depicted in Figs. 1 and 2 includes a cylindrical jacket 15 connected to the outer needle 24, the present disclosure is not limited to such heaters. Alternatively designed heaters for heating the tip of the outer needle 24, and/or even the tip of the inner needle 22, are intended to be with in the scope of the present application. For example, it is foreseeable that in some embodiments, it may be beneficial to include separate heaters on each of the inner and outer needles 22, 24 such that the temperature thereof can be controlled independently and at the same or different temperatures. Moreover, while the embodiment of the spinneret 12 is disclosed as including a heater 13, alternative embodiments do not require a heater.

[0029] The first solution source 16 is coupled to the inner needle 22 via a first conduit 26. The second solution source 18 is coupled to the outer needle 24 via a second conduit 28. So configured, the first and second solution sources 16, 18 are adapted to deliver first and second solutions, respectively, to the inner and outer needles 22, 24. It is foreseeable that the first and second solutions can be different solutions, or the same solution, either or both could include composite solutions, depending on the desired operation being performed. Preferably, the first and second solution sources 16, 18 are independently operational such that the flow rates of the first and second solutions can be independently controlled, adjusted, etc. To achieve this objective, each of the first and second solution sources 16, 18 of the depicted embodiment includes a syringe pump. Other types of solution sources are intended to be within the scope of the present disclosure.

[0030] During operation, an electrical potential is applied between the spinneret 12 and a counter electrode region 30 of the substrate 14 via the electrical circuit 20. Generally simultaneously, the first and second solution sources 16, 18 deliver first and second solutions to the spinneret 12. As the solutions exit the spinneret 12, they mix to form a core-shell nanofiber on a fiber mat region 32 of the substrate 14. Either of the first or second solutions can be continuously delivered, pulsatingly delivered, or intermittently delivered, in accordance with, for example, regular or irregular intervals. In an embodiment that includes the heater 13 described above with reference to Fig. 1 connected to the outer needle 24, the heater 13 heats the tip 25 of the outer needle 24, thereby heating the solution delivered by the second solution source 18 prior to the first and second solutions mixing. In some embodiments, the heater 13 can heat the second solution delivered by the second solution source 18 to a temperature in the range of approximately 25 ⁰C to approximately 200 ⁰C, and, in at least one embodiment, preferably to a temperature of approximately 80 ⁰C. Heating the second solution delivered by the outer needle 24 is advantageous because it allows for precise control over experimental parameters including, but not limited to, viscosity and rate of evaporation. Depending on the types of precursor solutions used, different heating temperatures can be used.

[0031] Because of the arrangement of the inner needle 22 within the outer needle 24, the system can advantageously create or spray tubular fibers, composite fibers, and multi-layered fibers consisting of an inner core and an outer shell. That is, the first solution delivered from the inner needle 22 can be supplied from the generally hollow cylindrical passageway defined by the inner needle 22 to form a cylindrical core of a nanofiber, while the second solution can be delivered from the generally annular passageway disposed between the inner and outer needles 22, 24 to provide a generally hollow cylindrical shell around the core. Such simple, one-step, construction is not possible with prior art single-needle electro spinning or electrostatic spray deposition systems.

[0032] Referring now to Fig. 2, one embodiment of a spinneret 12 constructed in accordance with the principles of the present disclosure will be described. The spinneret 12 depicted in Fig. 2 generally includes the inner needle 22, the outer needle 24, a lower housing component 34, an upper housing component 36, a first nipple 38, and a second nipple 40. The lower and upper housing components 34, 36 are adapted to be connected to secure the inner and outer needles 22, 24 together in a working configuration, as will be described.

[0033] As mentioned above, each of the inner and outer needles 22, 24 includes a conventional hypodermic needle. More specifically, the inner and outer needles 22, 24 each comprises a cylindrically- shaped plastic reservoir 22a, 24a connected to a hollow needle 22b, 24b constructed of stainless steel, for example. As illustrated in Fig. 2, the optional heater 13, which was discussed above with reference to Fig. 1, is sized, shaped, and configured to be positioned over the hollow needle 24 of the outer needle 24. In some embodiments, the heater 13 can surround the entire hollow needle 24b, or just a portion of the hollow needle 24b adjacent to the tip 25 (shown in Fig. 1)

[0034] The lower housing 34 of the depicted embodiment includes a base cylinder 42, a male housing connector 44, and a male needle connector 46. The upper housing component 36 includes a generally cylindrical base cylinder 48 and a male needle connector 50. The male needle connector 46 of the lower housing component 34 and the male needle connector 50 of the upper housing component 36 include hollow tubes adapted to carry solution to the inner and outer needles 22, 24, respectively. For example, in the depicted embodiment, the lower housing component 34 receives the first nipple 38 into a recess 54 thereof, and the upper housing component 36 receives the second nipple 40 into a recess 56 thereof. The first nipple 38 includes a conventional hollow nipple adapted to be connected to the conduit 26 of the system of Fig. 1, for example, for delivering the first solution to the inner needle 22. Similarly, the second nipple 40 includes a conventional hollow nipple adapted to be connected to the conduit 28 of the system of Fig. 1, for example, for delivering the second solution to the outer needle 24. Therefore, the first and second nipples 38, 40 are connected in fluid communication with the male needle connector 46 of the lower housing component 34 and the male needle connector 50 of the upper housing component 36, respectively, when the spinneret 12 is assembled.

[0035] To secure the inner needle 22 to the lower housing component 34, the cylindrical reservoir 22a of the inner needle 22 is friction-fit onto the male needle connector 46 of the lower housing component 34. To secure the lower and upper housing components 34, 36 together, the male housing connector 44 of the lower housing component 34 is friction-fit within a cylindrical recess 52 in the base cylinder 48 of the upper housing component 36. So configured, the cylindrical reservoir 22a of the inner needle 22 also resides within the recess 52 of the upper housing component 36 when the lower and upper housing components 34, 36 are secured together. Furthermore, to secure the second needle 24 to the upper housing component 36, the cylindrical reservoir 24a of the outer needle 24 is friction-fit onto the male needle connector 50 of the upper housing component 36. While the inner and outer needles 22, 24 have been described as being friction-fit onto their respective male needle connectors 46, 50, in other embodiments, each of the needles 22, 24 can be connected to the respective male needle connectors 46, 50 with an industry standard connector such as a Luer-Lok™ connector, or some other standard connector. It should be appreciated that, because the hollow needle 22b of the inner needle 22 is narrower and longer than the hollow needle 24b of the outer needle 24 (as shown in Fig. 1, for example), the hollow needle 22b of the inner needle 22 extends through the male needle connector 50 of the upper housing component 36 and out of the hollow needle 24b of the outer needle 24.

[0036] In a preferred embodiment, the inner and outer needles 22, 24 are sealed from each other such that no solution from the inner needle 22 will mix with the solution in the outer needle 24 (or vice versa) until both solutions exit the spinneret 12. This seal can be achieved by the placement of an O-ring 58, for example, within the recess 52 of the upper housing component 36 at a location between the cylindrical reservoir 22a of the inner needle 22 and the upper housing component 36. This O-ring 58 can prevent the flow of fluid from the second nipple 40 from backing up into the recess 52 and entering the cylindrical reservoir 22a of the inner needle 22.

[0037] While each of the components of the spinneret 12 have thus far been described as being friction-fit together, it should be appreciated that they could alternatively be secured together by some fastening means. For example, they may be secured together with an adhesive, with male and female threads, or any other means.

[0038] One advantageous feature of the present disclosure is that the design also makes it possible to adjust the length of the inner needle 22, thereby allowing the needle tips to be offset or not, as described above with respect to Fig. 1. In one embodiment, the spinneret and/or other components of the system can be provided in a kit that includes a plurality of inner and/or outer needles 22, 24, each being easily interchangeable within the lower and upper housing components 34, 36. The plurality of interchangeable needles 22, 24 can have different lengths, different diameters, different wall thicknesses, and/or any combination thereof. This means that the inner diameter, the outer diameter, and the wall thickness of any nanofiber ultimately manufactured with the disclosed system can be controlled as a function of the particular needles employed, the flow rate of the solution(s), and/or other factors.

[0039] In another embodiment, instead of (or in addition to) having replaceable, interchangeable needles to adjust the length of the inner needle 22, it is foreseeable that the first male connector 44 of the lower housing component 34 could be disposed in threaded engagement with the recess 52 formed in the upper housing component 36. So configured, the axial position of the tip 23 of the inner needle 22, as depicted in Fig. 1, could be adjusted by simply turning one of the lower and upper housing components 34, 36 relative to the other. In one embodiment, either or both of the lower and upper housing components 34, 36 could also have markings to indicate the precise distance "d" between the respective tips 23, 25 of the inner and outer needles 22, 24. In another embodiment, either or both of the cylindrical reservoirs 22a, 24a of the inner and outer needles 22, 24 could be disposed in threaded engagement with their respective male needle connectors 46, 50 to effectuate axial adjustment of the tips 23, 25.

[0040] Being able to adjust the dimensions of the needles, whether it be through interchanging the needles with different needles, or simply adjusting the axial position of either or both of the inner and outer needles 22, 24, for various applications can also be advantageous when working with highly viscous solutions, or solutions that contain particles that tend to clump. A prior solution to accommodating such solutions was to dilute the solutions. Dilution, however, is not always a viable option due to various constraints that may be placed on any desired application. [0041] While the present disclosure has described a spinneret 12 having two coaxially aligned needles, it should be appreciated that alternative embodiments could have generally any number of coaxially aligned needles such as three, four, five, etc.

[0042] The needle-in-needle approach to electro spinning provides a simple yet effective method to encapsulate nanoparticles within nanofibers. This design has proven to be both easy and economical. Because any number of different solutions can be combined and used, the design is adaptable to a wide variety of applications making the system very flexible. The needle-in-needle nozzle cannot only be used in electro spinning, electrostatic spray deposition, but also in other dispensing systems where dispensing needles are used to spread solutions without pre-mixing.

[0043] For example, in various tests conducted with the disclosed system, the following fibrous materials have been fabricated: carbon fibers, metal oxide fibers (such as: SnO, TiO, FeO, CuO, MnO, etc) and metal oxide composite fibers (such as: SnO-Ag composite), core-shell structured fibers (such as: Si-C), polymer-metal, polymer- polymer, semiconductor-metal oxide wires, etc. The present disclosure can therefore have a substantial impact on energy-related materials, electrochemical and biological sensors, drug delivery, etc.

[0044] In one example test study, a system constructed in accordance with Fig. 1 was used to fabricate Si particles in carbon nanofibers using an ESD method. First, 1 wt% Si was dissolved in 1 wt% PAN to form a suspension used for the first solution to be delivered from the inner needle 22, and 10 wt% PAN dissolved in DMF to obtained precursor solution for the second solution to be delivered from the outer needle 24. Both mixtures were then loaded into two plastic syringes such as the syringe pumps depicted in Fig. 1. A needle with an internal diameter of 0.3 mm was used as the inner needle 22, and a needle with an internal diameter of 1.6 mm was used as the outer needle 24. The spinneret 12 was attached to a high- voltage power supply, capable of generating direct- current voltages up to 30 kV. The grounding electrode from the same power supply was attached to a piece of aluminum foil which was used as the collector plate and was placed approximately 15-20 cm below the tip of the needle. Upon the application of a high voltage ranging between 15 and 20 kV across the needle and the collective plate, a fluid jet was ejected from the nozzle. The typical ejection rate of solution from the syringe was 0.5-4 mL/h, and the deposition time is 10 hours. As-deposited, the Si particles in PAN nanofibers carbonized under the atmosphere of 95% N₂ and 5% H₂ at 600 °C~900 ⁰C for 2 hours. This technique made it possible to embed Si nanoparticles inside carbon nanofibers.

[0045] In light of the foregoing, it should be appreciated that the device of the present disclosure has many advantages, such as being leak proof, providing easy cleaning, and having replaceable and interchangeable components. These components include commercially available standard parts such as: nipples, O rings, and needles. The entire assembly is easy to disassemble making it possible to replace these parts, as shown in Fig. 2 and discussed above, for example. The design also makes it possible to select or adjust the inner needle and/or outer needle length allowing the needle tips to be offset at different distances. The experimenter can incorporate syringe pumps, which allow for the simultaneous control the flow rates of the inner and outer solutions. This means that the inner diameter, outer diameter, and wall thickness of the nanofiber can be controlled.

Claims

What is claimed is:

1. A device for performing an electro spinning or electrostatic spray deposition operation, the device comprising: a spinneret comprising: a first needle for delivering a first solution; and a second needle for delivering a second solution, the first needle being disposed within the second needle such that the first and second solutions can be delivered from the spinneret during an electro spinning or electrostatic spray deposition operation and mixed after delivery.

2. The device of claim 1, further comprising: a first solution source coupled to the first needle for supplying the first solution to the first needle; and a second solution source coupled to the second needle for supplying the second solution to the second needle, the first and second pumps independently supplying the first and second solutions to the first and second needles, respectively.

3. The device of any one of the preceding claims, wherein the first and second needles are disposed coaxially relative to each other.

4. The device of any one of the preceding claims, wherein the first needle includes a tip that is axially offset from a tip of the second needle.

5. The device of claim 4, wherein the tip of the first needle is disposed outside of the second needle.

6. The device of any one of the preceding claims, further comprising means for adjusting the axial position of the first tip relative to the second tip and/or means for adjusting the axial position of the second tip relative to the first tip.

7. The device of any one of the preceding claims, further comprising a threaded connection between the first needle and the second needle for enabling adjustment of the axial position of the first tip relative to the second tip and/or means for adjusting the axial position of the second tip relative to the first tip.

8. The device of any one of the preceding claims, wherein at least one of the first and second needles are interchangeable and replaceable with one or more replacement needles, wherein the one or more replacement needles have different dimensions than the first and second needles.

9. The device of any one of claims 2 to 8, wherein at least one of the first and second solution sources comprises a pump.

10. The device of any one of claims 2 to 9, wherein at least one of the first and second solution sources comprises a syringe pump.

11. The device of any one of the preceding claims, further comprising a heater connected to the second needle for heating the second needle.

12. A kit for providing a spinneret that is customizable for a plurality of different electro spinnning or electrostatic deposition operations, the kit comprising: a housing; and a plurality of interchangeable needles, the housing being adapted to accommodate at least two needles at a time for delivering at least two solutions during an electro spinning or electrostatic deposition operation to be mixed after delivery, the plurality of needles comprising needles of different lengths, different diameters, different wall thicknesses, and/or any combination thereof, the spinneret being customizable to include any combination of two or more needles to suit an intended electro spinning or electrostatic deposition operation.

13. A method of forming a nanofiber, the method comprising: positioning a spinneret relative to a substrate; applying an electrical potential between the spinneret and the substrate; delivering a first solution to the substrate through a first needle of the spinneret while applying the electrical potential; and delivering a second solution to the substrate through a second needle of the spinneret simultaneously with the delivery of the first solution.

14. The method of claim 13, wherein delivering at least one of the first and second solutions includes delivering at least one of the first and second solutions either continuously, pulsatingly, or intermittently.

15. The method of claim 14, wherein intermittently delivering at least one of the first and second solutions comprises delivering at least one of the first and second solutions intermittently in accordance with regular or irregular intervals.

16. The method of any one of claims 13 to 15, further comprising adjusting a position of a tip of one of the first and second needles relative to a tip of the other needle prior to positioning the spinneret relative to the substrate.

17. The method of any one of claims 13 to 16, further comprising mixing the first and second solutions immediately after, or simultaneously with, the discharge of the solutions from their respective needles.

18. The method of any one of claims 13 to 17, further comprising heating the second needle simultaneously with delivering the second solution.