SYSTEMS FOR FIBER GUIDANCE

Abstract

Provided herein is a system for guiding polymeric fibers using ultrasonic waves. In particular, this application discloses a system of producing fibers including an emitter, a fiber guidance system, and a collector. The emitter supplies the polymer jet into the fiber guidance system. The fiber guidance system includes a phased array of transducers and a control system. The control system directs the phased array of transducers to generate acoustic energy to create an acoustic hologram and guide the polymer jet in space to form the polymer fiber before it is collected in the collector.

Claims

1. A system for forming a polymer fiber, the system comprising: a reservoir for holding a polymer solution; an emitter for emitting a jet of the polymer solution from the reservoir to form a polymer jet, whereby the polymer jet solidifies into a fiber; and a fiber guidance system comprising a phased array of transducers and a control system, the control system configured to direct the phased array of transducers to generate acoustic energy for creating an acoustic hologram operative to guide the polymer jet in space as the polymer jet is emitted from the emitter whereby the fiber is formed to correspond with the acoustic hologram generated by the phased array of transducers.

2. The system as set forth in claim 1, wherein each of the transducers is an ultrasonic transducer.

3. The system as set forth in claim 2, wherein the acoustic hologram creates a pattern of air pressure including at least one low-pressure guide channel, the system configured to emit the polymer jet along the low-pressure guide channel.

4. The system as set forth in claim 3, wherein the low-pressure guide channel has a width, the width of the low-pressure channel being determined by a holographic aperture created by the phased array of transducers.

5. The system as set forth in claim 3, wherein the pattern of air pressure is configured to cause the polymer jet to twist as the polymer jet is emitted along the low-pressure guide channel.

6. The system as set forth in claim 1, wherein the acoustic hologram is a dynamic acoustic hologram formed by the phased array of transducers along a travel length of the polymer jet.

7. The system as set forth in claim 1, further comprising a driver configured to apply an electrostatic force to drive emission of the polymer jet from the emitter.

8. The system as set forth in claim 1, wherein the emitter is configured to emit the polymer jet along an emission axis.

9. The system as set forth in claim 8, wherein the phased array of transducers comprises at least one transducer layer comprising n transducers circumferentially spaced apart about the emission axis in spacing increments of n/360 degrees.

10. The system as set forth in claim 8, wherein the phased array of transducers comprises a plurality of layers of transducers stacked along the emission axis.

11. The system as set forth in claim 10, wherein the phased array of transducers is arranged in a rectangular pattern stacked along the emission axis.

12. The system as set forth in claim 1, wherein the fiber guidance system comprises a plurality of circuit boards, each circuit board configured to connect a subset of the transducers to the controller.

13. The system as set forth in claim 12, wherein the control system includes a microcontroller for each circuit board, each microcontroller configured to actuate the respective subset of the transducers at a plurality of phases corresponding to the acoustic hologram.

14. The system as set forth in claim 13, wherein each microcontroller comprises a gate driver connecting the respective subset of the transducers to the respective microcontroller and a transducer power supply, each microcontroller configured to signal the respective gate driver to actuate the transducers with power from the transducer power supply.

15. The system as set forth in claim 14, wherein the control system further comprises a synchronization system connected to each of the microcontrollers and configured to synchronize the plurality of phases of the microcontrollers.

16. The system as set forth in claim 1, further comprising an expressing actuator and an expressing controller, the expressing actuator configured to express the polymer from the reservoir through the emitter, the expressing controller configured to control a rate of expression of the polymer from the reservoir through the emitter.

17. The system as set forth in claim 1, wherein the emitter comprises a plurality of emitters, each of the plurality of emitters configured to emit a respective polymer jet.

18. The system as set forth in claim 17, wherein the acoustic hologram is operative to guide each of the polymer jets in space.

19. The system as set forth in claim 18, further comprising a grounding plate operable to collect the fiber once said fiber travels through space to the grounding plate.

20. The system as set forth in claim 19, further comprising a non-conductive collector positioned below the grounding plate, whereby the grounding plate includes an aperture for the fiber to pass through the grounding plate to the non-conductive collector.

Description

DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a schematic illustration of a system for forming structured fiber material in accordance with the present disclosure;

[0008] FIG. 2 is a perspective of an assembly two stacked circuit boards of an embodiment of a system for forming structured fiber material in which layers of ultrasound transducers have 24 transducers per layer;

[0009] FIG. 3 is an enlarged view of a portion of FIG. 2;

[0010] FIG. 4 is a top plan view of the assembly of FIG. 2;

[0011] FIG. 5 is a side elevation of the assembly of FIG. 2;

[0012] FIG. 6 is an end elevation of the assembly of FIG. 2;

[0013] FIG. 7 is a bottom plan view of the assembly of FIG. 2;

[0014] FIG. 8 is a cross section of a system for forming structured fiber material formed from a stack of assemblies taken along line A-A in FIG. 7;

[0015] FIG. 9A is an image of a simulation of the acoustic energy generated by the phased array of transducers of an embodiment in accordance with the present disclosure;

[0016] FIG. 9B is an enlarged view of area B within the image of 9A;

[0017] FIG. 10 is a schematic of an annular grounding plate usable in a system for forming structured fiber material in accordance with the present disclosure to form the structured fiber material from electrically conductive polymer;

[0018] FIG. 11 is a perspective of a rectangular phased array of transducers according to an alternative embodiment in accordance with the present disclosure;

[0019] FIG. 12 is a photograph showing fiber material formed on a foil collector using conventional electrospinning;

[0020] FIG. 13 is a photograph similar to FIG. 12 but showing fiber material formed on foil collector using an embodiment of the system for forming structured fiber material in accordance with the present disclosure; and

[0021] FIG. 14A is a scanning electron micrograph (SEM) image of fiber material formed using conventional electrospinning at 500 magnification;

[0022] FIG. 14B is a SEM image of fiber material formed using conventional electrospinning at 2,500 magnification;

[0023] FIG. 15A is a SEM image of fiber material formed by the fiber guidance system in accordance with the present disclosure at 500 magnification; and

[0024] FIG. 15B is a SEM image of fiber material formed by the fiber guidance system in accordance with the present disclosure at 2,500 magnification.

[0025] Corresponding parts are given corresponding reference numbers throughout this disclosure.

DETAILED DESCRIPTION

[0026] One challenge with electrospinning is fiber guidance. Conventional electrospinning techniques produce an essentially random structure of fibers on the grounding plate. But to maximize the utility of the fibers, it would be beneficial to have a mechanism for guiding the fibers as they travel from the emitter toward the grounding plate. This would facilitate the formation of fiber materials with improved fiber morphologies, which could have numerous applications in many industries. A fiber guidance system coupled with electrospinning mechanisms makes it possible to produce fibers with different morphologies by utilizing acoustic hologram patterns to alter the structure of the fiber. Furthermore, the fiber guidance system may increase the capacity to output nanofiber or microfiber material on an industrial scale by controlling the deposition of the fibers and the uniformity of the fibers. For example, the directed deposition of the fibers can achieve the desired porosity of electrospun mats which is critical for tissue engineering, filtration membranes, and drug delivery systems.

[0027] Referring now to FIG. 1, the inventor has devised a new system for forming structured fiber material, which is shown schematically and generally indicated at reference number 10. This disclosure specifically contemplates that the system 10 will be used for small-diameter fibers, e.g., nanofibers or microfibers. The system 10 includes the basic components of an electrospinning system, but in addition, includes a fiber guidance system 12 for guiding the fibers as they are emitted in order to form more structured fiber material than is possible using conventional electrospinning techniques.

[0028] In the presently described embodiment, the system 10 comprises a reservoir 14 for holding polymer solution, an emitter 16 for emitting a jet of the polymer solution from the reservoir, and a grounded collector 18 (e.g., a plate with a grounded metal surface) on which the polymer collects after solidifying into a fiber material. The fiber guidance system 12 comprises a phased array of transducers 20 and a control system 22 configured to direct the array of transducers to generate acoustic energy for creating an acoustic hologram (e.g., a pattern of acoustic energy made up of interfering acoustic signals) along the path of the polymer jet from the emitter 16 to the collector 18. The acoustic hologram created by the fiber guidance system 12 guides the polymer jet in space as the polymer jet is emitted from the emitter 16 toward the collector 18. The polymer jet naturally undergoes plastic stretching and is further manipulated by the fiber guidance system 12 as it travels to the collector 18. Thus, the fiber is formed to have a structure that corresponds with the acoustic hologram generated by the phased array of transducers.

[0029] In general, the emitter 16 is configured to emit the jet of polymer solution along an emission axis EA toward the collector 18. In an exemplary embodiment, the emitter 16 is electrically charged through application of an electric field with high voltage. The application of the electric field may vary with factors such as material viscosity and travel distance. In some cases, for example, the voltage applied may be between 10-130 kV, however other voltages may be used without departing from the scope of the present disclosure. When the applied electric field strength overcomes the surface tension of the solution at the tip of the emitter 16, a polymer jet is emitted from the emitter 16.

[0030] In the illustrated embodiment, the reservoir 14 comprises a syringe barrel and the emitter 16 comprises a capillary tip. In one or more embodiments, the system 10 comprises a driver 24 configured to apply an electrostatic force to the emitter 16 to drive emission of the jet of polymer solution. In FIG. 1, the driver 24 is depicted as connecting the conductive emitter 16 to a power supply 26. In certain embodiments, the system 10 further comprises an expressing actuator 28 and an expressing controller 30. The expressing actuator 28 is configured to express the polymer from the reservoir 14 through the emitter 16, and the expressing controller 30 is configured to control a rate of expression of the polymer from the reservoir 14 through the emitter 16. Suitably, the expressing actuator 28 can comprise a linear actuator configured to depress a plunger 32 of the syringe along the barrel 14. As the polymer jet travels to the grounded collector 18, the fiber guidance system 12 acts upon the fiber as the polymer jet while solvent is evaporating to form a solid fiber.

[0031] To produce fibers, various polymer solutions may be employed. These solutions typically comprise a polymer dissolved in a solvent. Common polymers utilized include, but are not exclusively limited to, polyethylene oxide (PEO), polyvinyl alcohol (PVA), polycaprolactone (PCL), polyacrylonitrile (PAN), polyvinylidene fluoride and poly(lactic-co-glycolic acid) (PLGA), each offering distinct advantages in terms of bio-compatibility and mechanical strength. The solvents used in the polymer solution must effectively dissolve the polymer and evaporate at a rate that makes it possible to effectively form fibers. Examples of solvents include water, ethanol, chloroform, acetone and dimethylformamide (DMF).

[0032] Turning now to the fiber guidance system 12 as shown in FIG. 1, the phased array of transducers 20 is arranged to extend circumferentially about the emission axis EA of the emitter 16. For example, in one or more embodiments, the array forms a cylindrical or rectangular wall about the emission axis EA. In FIG. 1, the phased array of transducers 20 is shown in schematic cross-section. In one or more embodiments, each of the transducers 20 is an ultrasonic transducer (broadly, an acoustic transducer) configured to output an ultrasonic wave (broadly, acoustic energy) in the space surrounded by the array.

[0033] As explained more fully below, the control system 22 is configured to control the ultrasonic transducers 20 to generate an acoustic hologram (e.g., a pattern of interference between the acoustic waves output by the transducers), which creates a pattern of air pressure including at least one low-pressure guide channel 35. That is, the transducers 20 are controlled so that the ultrasonic waves output from the array interfere in a predetermined pattern creating static or dynamic acoustic holograms that may change along the length of the polymer jet travel path. Those skilled in the art will recognize that interference between acoustic waves can be used to establish a corresponding pattern of air pressure in space, e.g., alternating regions of low and high pressure. In this disclosure, the fiber guidance system 12 uses the correlation between acoustic wave interference and air pressure to form one or more low pressure channels inside the array. The system 10 is configured so that the emitter 16 emits the polymer jet along a low-pressure guide channel 35 and the polymer jet follows the low-pressure guide channel 35. In this way, the acoustic hologram generated by the array is capable of guiding the polymer jet in space. Further, the fiber material that collects on the collector 18 forms a structure that corresponds to the acoustic hologram because of the effect the acoustic hologram had on the polymer jet in flight.

[0034] As shown, the phased array of transducers 20 preferably comprises a plurality of transducer layers stacked along the emission axis EA. Each layer comprises n transducers circumferentially spaced apart about the emission axis EA in spacing increments of n/360 degrees. In certain embodiments, each transducer layer includes at least 12 transducers (n12) circumferentially spaced apart about the emission axis EA. In a presently preferred embodiment, each transducer layer comprises 96 transducers circumferentially spaced apart about the emission axis EA. In the illustrated embodiment, the transducers 20 in adjacent layers are circumferentially offset from one another such that the array defines an alternating honeycomb pattern. Suitably, each layer of transducers can be mounted on an appropriately designed printed circuit board. In an example, an appropriately designed printed circuit board comprises a plastic frame configured to align the transducers 20 on the printed circuit board 100 such that the transducers 20 are mounted and soldered to the side of the printed circuit boards 100. As explained in further detail below, the printed circuit boards 100 are configured to connect the control system 22 to each of the transducers 20. An exemplary embodiment of a printed circuit board 100 for a fiber guidance system 12 is shown in FIGS. 2-7. In FIGS. 2-7, each circuit board 100 is configured to connect 24 ultrasound transducers 20 to the control system 22. (FIG. 8 shows a complete fiber formation system 10 assembled from a stack of the circuit boards 100). While the current preferred embodiment demonstrates compatibility with 96 ultrasound transducers, it should be understood that the design is not limited to a specific quantity. The circuit board design could be adapted to accommodate a wide range of ultrasound transducer arrays, ranging from smaller arrays comprising tens of transducers to larger arrays incorporating thousands of transducers. It should further be noted that the system of the present disclosure may be adapted for use with two transducers, or with a single transducer used in combination with a reflector.

[0035] Referring to FIG. 1, the control system 22 includes one or more microcontrollers 40 for controlling the transducers 20. In FIG. 1, the control system 22 is schematically depicted as having one microcontroller 40 per transducer layer, but many of the microcontrollers are omitted for clarity. In the 24-transducer-per-layer circuit board embodiment of FIGS. 2-7, one microcontroller 40 having a plurality of I/O ports controls the transducers 20 of two transducer ring layers. In the 96-transducer-per-layer circuit board embodiment, every two layers includes a microcontroller 40 such that 15 microcontrollers control 30 layers of transducer rings. Regardless of the circuit board configuration, each microcontroller 40 is configured to actuate the respective subset of the transducers 20 at an activation frequency or phase corresponding to the desired acoustic hologram. Dynamic acoustic holograms may be employed by the fiber guidance system 12 to manipulate the polymer jet along the length of the travel distance from the emitter 16 to the grounded collector 18. Dynamic acoustic holograms form complex 3D pressure patterns in space, the phase and amplitude of each transducer 20 are controlled to alter acoustic wavefronts and create interference patterns along the emission axis EA of the phase array of transducers.

[0036] In an exemplary embodiment, each microcontroller 40 comprises a gate driver 42 connecting the respective subset of the transducers 20 to the respective microcontroller and a transducer power supply 26. Each microcontroller 40 is configured to signal the respective gate driver 42 to actuate the transducers 20 with power from the transducer power supply 26. The illustrated control system 22 further comprises a synchronization system 44 connected to all of the microcontrollers 42. The synchronization system 44 is configured to synchronize the activation frequencies of the microcontrollers 40 so that the microcontrollers fire the respective transducers 20 at the correct time to generate the desired acoustic hologram. The synchronization system 44 is configured to continuously execute a synchronization feedback loop with each of the microcontrollers 40 to ensure that the synchronization frequencies of the microcontrollers remain calibrated and accurate

[0037] In general, the control system 22 is configured for adjusting the phase of the ultrasound wave output from each transducer 20 so that the transducers collectively create the desired acoustic hologram. In one example, the phase of a transducer 20 is based on the angle formed between that transducer, the center of the array (e.g., the emission axis EA), and a transducer of the same layer chosen to be 0 degrees for the layer. In the case of an array of transducers set so that there are 96 transducers per layer and wherein the layers are laid out in an alternating honeycomb pattern, the zero-position transducer for each layer is incremented by 360/192 degrees for each double layer from the bottom because there are 192 transducer positions about the emission axis EA. In this example there are fifteen double layers of stacked transducers.

[0038] Using the control system 22, the phase of the ultrasound wave outputted from each transducer 20 can be adjusted to create an acoustic hologram which creates a sufficiently defined pattern of air pressure to noticeably alter the typically random path of polymer jet emission. The transducers 20 facing each other produce an interference pattern, and when in phase, a high pressure is produced at the center point. Adjusting one transducer to be out of phase by 180 from an oppositely positioned transducer, produces a low-pressure channel and modulating the phase over time produces a dynamic acoustic hologram. Within the low-pressure channel, the polymer jet is guided to the collector as the combination of stretching and solvent evaporation causes the polymer jet to solidify into a fiber. It is possible to vary the holographic aperture by changing the Vortex Number, which in turn, alters the width of the low-pressure channel. The Vortex Number indicates how many 360 degree phase rotations are completed by the phased array of transducers around the perimeter of the low-pressure channel. The ring of the of transducers 20 may be divided by radial segmentation into sectors. The Vortex Number increases with the number of sectors and the number of phase changes within the ring which results in an increase of the diameter of the holographic aperture. Contrariwise, decreasing the Vortex Number constricts the holographic aperture and reduces the size of the low-pressure channels.

[0039] The system 10 guides the emitted polymer jet to generally follow the path of the low-pressure guide channel(s) 35 created by the dynamic interference of ultrasonic waves. Accordingly, the system 10 can be employed to create structured fiber material that is guided by the acoustic hologram, whereby the fiber material has a structure that is not random, but rather has characteristics that correspond to the acoustic hologram. Furthermore, the density and alignment of the fibers collected may be modified with the fiber guidance system 12, by altering the acoustic hologram and precisely controlling the feed rate of the emitter 16. The system 10 can be configured to produce microfibers, nanofibers and fiber materials of various desired shapes. For example, in one or more embodiments, the system 10 is configured (by adjusting the acoustic hologram) to produce twisted fibers. Those skilled in the art will appreciate that twisted fibers (e.g., twisted nanofibers or microfibers) would be useful for applications such as tissue scaffolding because they have extremely high surface area. Different morphological structures may be created such as smooth cylindrical fibers, flat fibers, porous fibers, hollow fibers and bead-on-string structures. The fiber diameter may range from nanometers to micrometers.

[0040] The system 10 can be scaled to produce greater outputs of fiber material. For example, instead of using a cylindrical array of ultrasound transducers 20, the system could use a rectangular or hexagonal array. An exemplary embodiment of a rectangular phased array of transducers is shown in FIG. 11. In the case of a rectangular array, the plurality of emitters 16 may be spaced apart along both the length and width of the transducer array (e.g., a 1010 or an 8080 grid of emitters positioned above the array). The rectangular array of transducers 20 could be configured to generate an acoustic hologram that creates low pressure channels for each respective emitter 16, whereby the system could be configured to produce 100 (in the case of a 1010 grid of emitters) the amount of structured fiber material as the single emitter system in the same amount of time. Similarly, the 8080 rectangular phased array of transducers 20 can be configured to produce 6400 the amount of structured fiber material as the single emitter system in the same amount of time without the fibers colliding during deposition. Hexagonal arrays, similar to rectangular arrays, may prove useful for industrial applications while permitting equidistant spacing of the polymer jets.

[0041] Turning now to FIGS. 9A and 9B, the images show a top view of a simulation of multiple holographic apertures (broadly referred to as low-pressure guide channels 35) with a hexagonal phased array of transducers. As seen in FIG. 9B, the holographic apertures are darker areas surrounded by lighter shaded areas of higher acoustic energy. These quiet zones are the low-pressure guide channels 35 generated within the array in which the polymer jet may travel along the emission axis EA of the fiber guidance system 12. The low-pressure channels 35 can be dynamically altered along the emission axis by the multiple layers of transducers 20 as the polymer jet travels from the emitter 16 to the grounded collector 18.

[0042] One strategy of scaling the system 10, involves increasing the quantity of transducers in the array, in an example, a circular array of 192 transducers in each layer may be employed. Depending on the scale of the equipment and the production needs, thousands of emitters may be employed within a phased array to increase the output of fibers. In one larger scale embodiment, 3,600 emitters are employed with 21,000 transducers within a phased array. Further, multiple emitters with the larger phased array may produce a cabled fiber without any additional post processing of the fibers. The emitters may be placed upon a robotic head or gantry system to more accurately place and move the emitters for directed deposition and fiber manipulation within the phased array.

[0043] It is envisioned that any number of layers of transducers 20 may be employed to generate an acoustic hologram over a distance adequate to shape the polymer jet as it is traveling from the emitter 16. Additionally, the system may employ high-frequency arrays to achieve a reduction in acoustic wavelength. These high frequency arrays may be configured to operate within a frequency spectrum spanning from approximately 300 kHz-1 MHz. It should be understood that this frequency range is illustrative and non-limiting, as the system may be adapted to utilize frequencies outside this range as necessitated by specific application requirements or technological advancements.

[0044] Referring to FIG. 10, the inventor further envisions that the system 10 could be adapted for making conductive fiber material. With conventional electrospinning, it is very difficult to use conductive polymer. If highly conductive polymer is emitted from the emitter of a conventional electrospinning system, as soon as the conductive polymer solution jet contacts the grounding plate, the jet effectively becomes a conductive wire carrying the high voltage applied at the emitter to ground. This instantly destroys the delicate polymer jet. However, with the fiber guidance system of the present disclosure, it is possible to guide the polymer jet in space such that it lands on a non-conductive collector, instead of a conductive grounding plate. Accordingly, as shown in FIG. 10, in one or more embodiments, a system for forming conductive polymer fibers in the scope of this disclosure, comprises an annular grounding plate 18 with a central aperture 180. In this embodiment, the fiber guidance system 12 is configured to guide the conductive polymer jet to pass through the aperture 180 onto a non-conductive collector 19 located below the annular grounding plate 18. It can be seen, therefore, that the low-pressure fiber guidance channel produced by the fiber guidance system 12 is used to steer the jet away from the grounding plate so that the conductive polymer never closes a circuit between the high voltage emitter 16 and ground. Additional mechanisms may be used for unobstructed fiber passage through the aperture 180. A combination of compressed air directed at the annular grounding plate 18 and vacuum applied beneath it can be used to manage fiber accumulation in unwanted areas of the system and prevent fiber accumulation from interfering with the acoustic hologram.

[0045] Turning now to the experimental efforts to produce fibers with the system 10, two examples of fiber production are discussed. In the field of electrospinning, the presence of beads along fiber lengths is generally considered a defect. These beads are undesirable because they introduce inconsistencies in fiber morphology and can alter the mechanical properties of the resultant fibers. Smooth, uniform fibers are typically preferred. The fiber guidance system 12 has shown an improvement in fiber morphology, including the elimination of beads during experimentation.

Example I

[0046] FIGS. 12 and 13 show a comparison of a nanofiber material M1 generated without ultrasound guidance and another nanofiber material M2 generated under the similar conditions with ultrasound guidance. In the first test, a polymer solution with 5% polyacrylonitrile (PAN) combined with dimethylformamide (DMF) was placed on a magnetic stirrer at 450 rpm for 4 hours at 25 C. The expressing actuator was set to 5 mL/hr. The electrospinning process was conducted without the use of the phased array transducers.

[0047] In the second test, a polymer solution with 10% polyvinylidene fluoride, 63% dimethylformamide, and 27% acetone was placed on a magnetic stirrer at 450 rpm for 4 hours at 55 C. The expressing actuator was set to 1 mL/hr. The electrospinning process was conducted with the phased array of transducers set to 20V. In both cases, the nanofiber material M1, M2 appears as a whitish residue on a circular foil sheet. The foil was placed on the collector during each respective test. As can be seen, the material M2 is more structured that the material M1. Whereas the material M1 is randomly distributed across most of the foil sheet, the material M2 is focused on two relatively small areas in the center of the plate. The location of the fiber deposition changed after several minutes. In the second test, nanoscale and uniform fibers were observed with no beads.

[0048] The inventor believes this focused formation of structured nanofiber material M2 occurred because the jet of polymer was guided through a low-pressure guide channel created by the acoustic hologram produced by the fiber guidance system. Additionally, the uniformity of the fibers improved and the beads of polymer were eliminated by using the fiber guidance system during electrospinning. The location of fiber deposition changed during the second test due to noise in synchronization signal disrupting normal operation of the phased array of transducers, resulting in irregularities in the acoustic hologram.

Example II

[0049] FIGS. 14A,B and 15A,B are micrographs from a scanning electron microscope showing fibers made from two slightly different tests. In the first test, a polymer solution with 5% Polyacrylonitrile (PAN) combined with Dimethylformamide (DMF) was placed on a magnetic stirrer at 450 RPM for 4 hours at 25 C. The expressing actuator was set to 5 mL/hr. The electrospinning process was conducted without the use of the phased array transducers. As shown in FIGS. 14A and 14B, the resulting nano-scale fibers had sporadic beads and non-uniform fiber morphology. During the first test, fibers landed throughout the machine, leaving stray fibers in undesirable locations within the machine.

[0050] In the second test the same polymer solution preparation and expressing actuator settings were used, and in this case, the phased array of transducers was used during the electrospinning process. The images in FIGS. 15A and 15B show the resulting fibers at 500 magnification and 2,500 magnification respectively. The resulting fibers had fewer beads compared to the first test. Additionally, less stray fibers landed on the transducers, as the fibers were better directed toward the collection plate.

[0051] As seen in FIGS. 15A and 15B, the use of the fiber guidance system led to reduced bead formation and increased fiber uniformity. In conclusion, the reduced bead formation within the fibers may be a result of fiber manipulation with the acoustic hologram produced by the phased array of transducers. The fiber guidance system may also prevent stray fibers from landing outside the targeted collection area.

[0052] When introducing elements of the present disclosure or the preferred embodiment(s) thereof, the articles a, an, the and said are intended to mean that there are one or more of the elements. The terms comprising, including and having are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0053] In view of the above, it will be seen that the several objects of the disclosure are achieved and other advantageous results attained.

[0054] As various changes could be made in the above products and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.