PRECISELY CONTROLLED FIBER DEPOSITION BY ELECTROSTATIC FIELDS

Abstract

Applications of electrospinning (ES) range from fabrication of biomedical devices and tissue regeneration scaffolds to light manipulation and energy conversion, and even to deposition of materials that act as growth platforms for nanoscale catalysis. One major limitation to wide adoption of electrospun materials is the ES hardware itself, which typically requires high voltage, electric isolation, and charged and flat deposition surfaces. In the past, fabrication of structures or materials with precisely determined mesoscale morphology has been accomplished through modification of electrode shape, use of multi-dimensional electrodes or pins, deposition onto weaving looms, hand held electrospinners that allow the user to guide deposition, or electric field manipulation by lensing elements or apertures. In this work, we demonstrate an ES system that contains multiple high voltage power supplies that are independently controlled. This system produces a novel electrostatic field that enables deposition of polymers in precise, mesoscale structures.

Claims

1. A Multiplex ES device comprising: A spinneret, which delivers a polymer; A plurality of electrodes, wherein said electrodes are each connected to an independent high voltage power supply; A means of controlling a voltage supplied to each of said electrodes by each said independent high voltage power supply to provide a high voltage electric field; wherein Manipulation of said high voltage electric field between said plurality of electrodes allows for precise control of deposition of a fiber from polymer delivered by said spinneret.

2. The Multiplex ES device of claim 1, wherein said spinneret is grounded.

3. The Multiplex ES device of claim 1, wherein said spinneret is connected to an independent high voltage power supply.

4. The Multiplex ES device of claim 1, wherein said means of controlling a voltage supplied to each of said electrodes is digitally controlled by a computer.

5. The Multiplex ES device of claim 1, wherein said means of controlling a voltage supplied to each of said electrodes is by analog or mechanical means with use of switches, knobs, buttons.

6. The Multiplex ES device of claim 1, further comprising a or a plurality of data acquisition systems.

7. The Multiplex ES device of claim 1, wherein said high voltage power supply provides between −30 kV and 30 kV.

8. The Multiplex ES device of claim 1, further comprising one or a plurality of resistors added to a circuit of said high voltage power supply.

9. The Multiplex ES device of claim 1, further comprising an isolation box, which contains said spinneret and said plurality of electrodes.

10. The Multiplex ES device of claim 1, further comprising a plurality of spinnerets.

11. The Multiplex ES device of claim 10, wherein multiple polymers are delivered to the system by said plurality of spinnerets.

12. The Multiplex ES device of claim 1, further comprised of a spinneret holder, which secures said spinneret.

13. The Multiplex ES device of claim 1, further comprised of a plurality of electrode holders, which secure said plurality of electrodes.

14. The Multiplex ES device of claim 12, further comprised of mechanical or electrical components to enable movement of said spinneret.

15. The Multiplex ES device of claim 13, further comprised of mechanical or electrical components to enable movement of said plurality of electrodes.

16. The Multiplex ES device of claim 9, wherein said isolation box is further comprised of an encasement and venting system to allow for the introduction of a gas.

17. The Multiplex ES device of claim 9, wherein said isolation box is further comprised of an encasement system to allow for polymer deposition under vacuum.

18. The Multiplex ES device of claim 1, wherein said spinneret is coaxial.

19. The Multiplex ES device of claim 1, wherein said spinneret is triaxial.

20. A method of providing precisely controlled fiber deposition during electrospinning comprising the steps of: a. delivering polymer to the Multiplex ES device of claim 1; and b. manipulating said high voltage electric field between said plurality of electrodes to precisely control deposition of said fiber.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0011] FIG. 1. Graphical representation of one configuration of the multiplex ES system. The multiplex ES system shown is comprised of four electrodes and a spinneret, each connected to an independently-controlled power supply. Independent control over each electrode enables guiding of polymer fibers or drops and deposition of defined and complex structures. Also shown in FIG. 1 is the electrical isolation box and grounded conductive tape used to prevent electric shock of the user, as well as components used to move the spinneret and/or electrodes to modify the electrostatic field during ES, ultimately resulting in polymer fibers, drops, or materials that have the desired configuration/s and properties.

[0012] FIG. 2. COMSOL Multiphysics® models representing the multiplex ES system. A. The generated model shows four electrodes placed equidistant from each other. During acquisition of the model, the high-voltage signal was supplied to electrode C as shown. B. The generated model shows the electrodes from with respect to the ES spinneret. All electrodes were placed equidistant from the spinneret in the multiplex ES system.

[0013] FIG. 3. A. Graphical representation of polymer deposition path and order of deposition during multiplex ES of woven fiber mats. During deposition, polymer deposition follows the electrode exhibiting the highest voltage (strongest electrostatic force). In instances 2, 4, and 6, the polymer jet jumps exterior to the center woven mat in order to avoid disrupting the woven material and enabling true weaving of the fibers to occur. B. SEM micrograph showing the precisely woven polymer fiber pattern graphically represented in A. C. is a digital light microscopy image shows the bulk three-dimensional configuration of the woven ES mats.

[0014] FIG. 4. Part A-C shows images of electrospun, polymer tori patterns fabricated using multiplex ES. Electrospun tori were removed from the system and placed in a light box prior to acquisition of images, which were thresholded with ImageJ. Parts D-F show corresponding images demonstrating the tori fiber mats after a threshold had been applied in ImageJ. Tori and images were collected in triplicate, and dimensions from these images were used to provide mathematical understanding of the fiber mat that would result when specific ES parameters were used.

DETAILED DESCRIPTION OF THE INVENTION

[0015] In general, use of the Multiplex-ES system 100 involves delivery of solvent dissolved or melted liquid polymer into a spinneret 120 via a pump. Once polymer is forced to the tip of the spinneret 120, electric voltage initiated in the electrodes 130 creates an electrostatic field within the Multiplex-ES system 100. The electrostatic force begins to stretch a polymer bead at the tip of the spinneret 120. The polymer then enters a chaotic region where polymer whips around and results in evaporation of solvent used to dissolve the polymer during preparation. Control over the voltage supplied to a plurality of electrodes guides deposition of polymer beads or fibers to a specific electrode, sequential electrodes, and/or in between electrodes to produce a precisely desired configuration of the deposited polymer beads or fibers. Using the device and methods described herein, precise weaving of fibers has been achieved as demonstrated in FIG. 3. Similarly, electrospun tori patterns have been achieved as shown in FIG. 4. One familiar with the art would recognize that multiple polymer specifications could be supplied to the system. In one embodiment, polymer supplied to the system is comprised of polymer dissolved in solvent. In another embodiment, polymer supplied to the system is melted. In yet another embodiment, polymer supplied to the system is comprised of semi conducting or conducting properties. In yet another embodiment, multiple polymers are supplied to the system through multiple spinnerets and delivery means where such delivery means would include pumps, syringes, and gravity fed.

[0016] The multiplex ES system 100 (FIG. 1) was assembled inside an isolation box 110 assembled from ⅛-in-thick acrylic sheets and equipped with a momentary safety switch 111. The safety switch 111 was integrated into the system via LabVIEW and programmed to force a connected data acquisition system (DAQ) output to 0 kV, should the door 112 of the isolation box 110 be opened. The DAQ system used for this work were USB-6008 and USB-6009 12-bit resolution National Instruments digital acquisition DAQs that regulated direct current (DC) and alternating current (AC) input signals. One familiar with the art would recognize that various data acquisition systems of various specifications could be utilized to practice the invention and data acquisition systems of alternative specifications are contemplated within the disclosure herein. Aluminum tape 113 was placed at the corners 114 of the isolation box 110 and grounded 115 to prevent buildup of electrical charge on the surfaces of the isolation box 110. In another embodiment, said isolation box is equipped with an encasement and ventilation system to allow for the introduction of a gas to the system.

[0017] At a first end 116 of the isolation box 110, a photopolymer resin spinneret holder 122 was used to hold a spinneret 120 in place. The spinneret is connected to a high voltage source via contact with a metal pogo pin 121. The spinneret may also be grounded. One familiar in the art would recognize that multiple spinnerets could be incorporated into the system to supply multiple polymers for ES and also said spinnerets could be comprised of various characteristics such as being coaxial or triaxial to produce fibers of differing characteristics. Electrode holders 131 were fabricated with a Formlabs Form2 405 nm SLA resin 3D printer. The photocatalytic resin was used in place of fused deposition modelling printing to prevent formation of trapped air spaces that can become charged by the power supplies and interrupt the electric field distribution in the multiplex ES system 100. In another embodiment, said spinneret holder 122 and electrode holders 131 are further comprised of mechanical or electrical components, which are utilized to move said spinneret 120 and electrodes 130 to further precisely alter the electric field shape, size, and/or strength.

[0018] At a second end 117 of the isolation box 110, four electrodes 130a, 130b, 130c, and 130d were held in place with said photopolymer resin electrode holders 131 to keep each electrode 130a, 130b, 130c, and 130d isolated and connected to each electrode's high voltage source by corresponding electrode metal pogo pins 132. The four deposition electrodes 130a, 130b, 130c, and 130d used were cut from 1/64 in thick Cu sheets. Each electrode 130a, 130b, 130c, and 130d was connected to an external National Instruments DAQ (data acquisition) system, which was connected to a corresponding independent electrostatic discharge electromagnetic compatible 20-kV/1-mA high-voltage power supply 140a, 140b, 140c, and 140d. The DAQ has both analog and digital input/outputs and enables both control over the high voltage power supplies, as well as provides a user with real-time voltage readings as the electrospinning process occurs. Control over the power supplies is fed from LabView through the DAQ and signal feedback is fed from the high voltage power supplies through the DAQ and can be read in LabView. One familiar with the art would recognize that various data acquisition systems and power supplies of various specifications could be utilized to practice the invention and data acquisition systems and power supplies of alternative specifications are contemplated within the disclosure herein. Feedback from said four power supplies was monitored by a Tektronix TDS 2004C oscilloscope.

[0019] The Multiplex-ES system 100 provides precise deposition of electrospun fibers 200 and mesoscale morphology control by manipulation of the high voltage electric field. The point of high voltage in the system 100 is moved from one electrode to another, thereby guiding fiber deposition as the polymer fiber lays down where the electric field is strongest. In FIG. 2, a COMSOL Multiphysics model is shown. In FIG. 2, the point of high voltage in the system 100 is electrode C 130c. Therefore, in the theorized instance shown in FIG. 2, electrospun polymer would preferably deposit on electrode C 130c. In the preferred embodiment, voltage supplied to each electrode is digitally controlled by a computer, which receives information from a or a plurality of DAQ's. Therefore by manipulating voltages to said electrodes simultaneously, fiber deposition can be precisely moved to any point within the four independently controlled electrodes 130a, 130b, 130c, and 130d. See FIGS. 3A and B. While the preferred means of controlling the voltages supplied to the electrodes is digital via a computer programming based on data from a DAQ, one familiar with the art would recognize that voltages could be controlled by analog or mechanical means with use of switches, knobs, buttons, and similar means. Similarly, while four electrodes were utilized in the herein disclosed embodiment, one familiar with the art would recognize that any plurality of electrodes could be utilized depending on the fiber deposition characteristics to be achieved.

[0020] Through control over electric field strength at specific locations within the system, fiber deposition is precisely controlled and can be utilized to fabricate highly accurate specified materials. FIG. 2 shows a COMSOL model used to visualize the multiplex ES system 100 when the highest voltage was supplied to one electrode (electrode C 130c). In this instance (FIG. 2), fiber deposition would preferentially deposit on electrode C 130c. If the highest voltage is directed to switch from a first electrode to a second electrode, fiber deposition follows the path between the first electrode and the second. See FIG. 3A. If two electrodes are supplied with similar high voltages, fiber deposition will occur between the electrodes rather than on them. Fiber deposition also occurs between electrodes as the polymer stream moves from one electrode or space to the next electrode or space within the system as shown on FIG. 3A.

[0021] One limiting factor to control over fiber deposition controlled by a computational system is response time of the power supplies to the computational input. In this system, the response time was improved up to 65% through manipulation of the impedance of the Multiplex-ES system by the addition of resistors to the high voltage circuit.

[0022] In other embodiments the Multiplex-ES system may be equipped with a high-resolution camera for real time viewing of the processes of the system. The Multiplex-ES system may be equipped with one or a plurality of lasers to aid in process control and feedback. The Multiplex-ES system may be equipped with one or a plurality of collimated light sources. The Multiplex-ES system may be equipped for electrical isolation. Interlock technology may be incorporated into the system. Safety shutoff technology may be utilized within the system. One familiar in the art would recognize the system could be configured so that polymer deposition is guided to a surface other than conductive electrodes or surfaces; polymer deposition is guided to a non-conductive surface; or where polymer deposition is guided to a conductive surface. Furthermore, the system is capable of scaling in size from handheld systems to large systems for large scale industrial applications. All are considered within the scope of the present disclosure.

[0023] It is contemplated that the device and methods described herein would include but not be limited to the following: fabrication of materials for medical applications; electrical applications; coating applications, chemistry applications; biological applications; fabrication of solid therapeutic materials, including medications; fabrication of powdered therapeutic materials, including medications; and fabrication of liquid therapeutic materials, including medications.

[0024] It is understood that the foregoing examples are merely illustrative of the present invention. Certain modifications of the disclosed device and/or methods may be made and still achieve the objectives of the invention. Such modifications are contemplated as within the scope of the claimed invention.