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 JoVE Bioengineering

Electrospinning Fundamentals: Optimizing Solution and Apparatus Parameters

1, 1,2, 3, 1,3,4

1Department of Biomedical Engineering, University of Michigan, 2State Key Laboratory of Bioelectronics, Southeast University, 3Department of Neurology, University of Michigan, 4Geriatrics Research, Education and Clinical Center, Veterans Affairs Ann Arbor Healthcare Center

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    Summary

    Electrospinning techniques can create a variety of nanofibrous scaffolds for tissue engineering or other applications. We describe here a procedure to optimize the parameters of the electrospinning solution and apparatus to obtain fibers with the desired morphology and alignment. Common problems and troubleshooting techniques are also presented.

    Date Published: 1/21/2011, Issue 47; doi: 10.3791/2494

    Cite this Article

    Leach, M. K., Feng, Z., Tuck, S. J., Corey, J. M. Electrospinning Fundamentals: Optimizing Solution and Apparatus Parameters. J. Vis. Exp. (47), e2494, doi:10.3791/2494 (2011).

    Abstract

    Electrospun nanofiber scaffolds have been shown to accelerate the maturation, improve the growth, and direct the migration of cells in vitro. Electrospinning is a process in which a charged polymer jet is collected on a grounded collector; a rapidly rotating collector results in aligned nanofibers while stationary collectors result in randomly oriented fiber mats. The polymer jet is formed when an applied electrostatic charge overcomes the surface tension of the solution There is a minimum concentration for a given polymer, termed the critical entanglement concentration, below which a stable jet cannot be achieved and no nanofibers will form - although nanoparticles may be achieved (electrospray). A stable jet has two domains, a streaming segment and a whipping segment. While the whipping jet is usually invisible to the naked eye, the streaming segment is often visible under appropriate lighting conditions. Observing the length, thickness, consistency and movement of the stream is useful to predict the alignment and morphology of the nanofibers being formed. A short, non-uniform, inconsistent, and/or oscillating stream is indicative of a variety of problems, including poor fiber alignment, beading, splattering, and curlicue or wavy patterns. The stream can be optimized by adjusting the composition of the solution and the configuration of the electrospinning apparatus, thus optimizing the alignment and morphology of the fibers being produced. In this protocol, we present a procedure for setting up a basic electrospinning apparatus, empirically approximating the critical entanglement concentration of a polymer solution and optimizing the electrospinning process. In addition, we discuss some common problems and troubleshooting techniques.

    Protocol

    1. Choose a Polymer

    1. Choose a polymer (e.g., poly-L-lactic acid (PLLA), polycaprolactone (PCL), polystyrene (PS) or nylon) based on your specifications (e.g., biodegradable, thermoplastic or cross-linkable) and a solvent of that polymer. Choose suitable personal protective equipment based on your selection.
    2. Select a substrate based on your application (e.g., glass, plastic, metal or silicon wafer).

    2. Choose a Collector

    1. Choose the collector geometry based on your specifications. Random fibers can be collected on stationary plates. Aligned fibers can be collected on rapidly rotating wheels, drums or rods, or on parallel plates.
    2. The collector must be conductive and must remain isolated from its axel in such a way that it can be grounded without also grounding adjacent objects, the table top, etc.

    3. Approximate the Critical Entanglement Concentration Empirically1

    1. Prepare several candidate polymer concentrations (e.g., 4, 10, 15, 20, 30 wt%) and choose a concentration that flows (the solution should be a viscous liquid but not a gel) to start with.
    2. Set up the electrospinning apparatus2,3,4,5 (see Figure 1)
      1. Load the syringe pump and set the pump speed such that any bead of solution wiped from the tip is immediately replaced.
      2. Ground the collector and clip the high voltage wire to the conductor plate (a small square of conductive material such as aluminum foil through which the syringe tip protrudes).
      3. Start the wheel spinning.
      4. Make sure the power supply is set to zero before turning it on.
    3. Observe the stream
      1. Ramp voltage up slowly and watch the bead of the solution at the needle tip.
      2. Adjust the voltage to obtain a long and steady stream. If a steady stream cannot be obtained, adjust the polymer solution concentration. See Table 1 for an example.

    4. Troubleshooting - the Stream:

    1. Trouble viewing the stream
      1. Use a dark matte backdrop and place a unidirectional light source (such as a flashlight) between the viewer and the stream (see Figure 2).
    2. Dripping from the syringe tip
      1. If the polymer solution is dripping straight down with no attraction to the wheel, make sure the conductor plate is making contact with the needle tip and that the collector is making contact with ground.
      2. If the drop of polymer solution at the syringe tip is leaning in the direction of the wheel but is not forming a stream, increase the voltage. The quality of the stream can be adjusted by varying the distance and the voltage until a steady stream is visible. See Figure 3 for suggested distances with corresponding voltages for a 4% PLLA solution and an 8x8 cm conductor plate.
    3. Large globs at the syringe tip
      1. When the polymer solution begins to collect and harden at the tip of the needle, swipe the glob away with a paper towel attached to a non-conductive stick.
    4. Oscillating or 'wagging' streams
      When the stream is wagging up and down rapidly, turn down the voltage or increase the distance between the syringe tip and the wheel. If the stream continues to wag use a higher concentration of polymer or add a little solvent with a slower evaporation.
    5. Short or discontinuous streams
      Visible steady streams making observable contact with the wheel set at a high rotational velocity yield the highest quality of uniformity and alignment. When the stream is short and discontinuous, increasing the polymer solution, adding more slow evaporating solvent, and adjusting the voltage will improve the length and steadiness of the stream.

    5. Troubleshooting - Fiber Morphology6,7,8 (refer to Figure 4)

    1. Beading
      When beads are discovered in the fibers, increase the polymer solution and make sure the conductor plate is making continuous contact with the needle and that the grounded wire brush is making continuous contact with the wheel.
    2. Ribbons and bleeding fibers
      When fibers are forming as ribbons or are bleeding together, use a higher concentration of polymer or a solvent with a higher rate of evaporation (more volatile).
    3. Curlicue or wavy fibers
      When fibers are forming waves or curlicues, increase the wheel speed or move the needle tip further from the collector. Also, check that the conductor plate and collector are not vibrating.
    4. Porosity9
      If pores are desired, use a rapidly evaporating solvent. If pores are not desired, try adding a small amount of co-solvent that is less volatile than the major solvent.
    5. Alignment10
      When the collector is moving at a low RPM or at rest, the alignment quality is poor. Increase the alignment by increasing the speed of the wheel.

    6. Representative Results:

    Please refer to Figure 4 for depictions of typical fiber results.

    Figure 1
    Figure 1. A typical electrospinning setup. A polymer solution (blue) is dispensed from a syringe pump (orange). A high voltage DC power supply (green) grounds a rapidly rotating wheel collector (grey) onto which aligned nanofibers are collected. The polymer jet between the syringe and collector consists of a steady streaming segment and a rapidly oscillating whipping segment.

    Figure 2
    Figure 2. The streaming jet is visible exiting the syringe tip; the whipping jet is too small to be seen.

    Approximating the critical entanglement concentration of PLLA

    PLLA (% wt/v) Observation Concentration Adjustment
    0.5 Dripping; no stream Increase
    2.0 Spitting small globs; no stream Increse slightly
    4.0 Steady stream Good
    6.0 Spitting large globs or beads Decrease slightly
    12.0 Clumping at the tip; no stream Decrease

    Table 1. An example depicting the approximation of the critical entanglement concentration of PLLA. Various polymer concentrations are tried and the resulting streaming jets observed until a steady stream is obtained.

    Figure 3
    Figure 3. The distance between the syringe tip and the collector must be balanced with the applied voltage to obtain a steady streaming jet. Excess applied voltage causes an oscillating or 'wagging' jet to form that results in less well-aligned fibers. When the voltage is too low, no jet will form and the solution will only drip from the syringe tip. The purple shaded region above represents the voltage range over which a steady streaming jet can be obtained for PLLA as a function of syringe-to-collector distance.

    Figure 4
    Figure 4. Electrospun fibers can exhibit a variety of morphologies, including beading (A), ribbons (B), curlicues (C), porous globs (D), good alignment (E) and poor alignment (F).

    Discussion

    Note: The majority of the examples presented here deal with electrospinning poly-L-lactic acid (PLLA) nanofibers. This is simply because PLLA is the most commonly spun polymer in our laboratory. However, we have also successfully used these methods to electrospin other polymers (e.g., PLGA, PCL, PS) and believe that the techniques presented here are easily applicable to the majority of mid- to high-molecular weight polymer solutions.

    Disclosures

    No conflicts of interest declared.

    Acknowledgements

    This work was supported by NIH K08 EB003996 and the Paralyzed Veterans of America Research Foundation Grant 2573.

    Materials

    Name Company Catalog Number Comments
    High voltage DC power supply Gamma High Voltage ES40P-5W
    Syringe pump KD Scientific KDS100
    Aluminum foil Reynolds Wrap
    Blunt metal tips, 23ga Fisher Scientific 13-850-102
    Polypropylene syringe BD Biosciences 309585
    Rotating or stationary collector Custom Made
    Various alligator clips and wires
    Dimethylformamide Fisher Scientific AC11622-0010
    Chloroform Fisher Scientific AC42355-0040
    PLLA Boehringer Ingeheim Resomer L210
    PLGA 85:15 Sigma-Aldrich 43471
    Carbon tape Ted Pella, Inc. 13073-1

    References

    1. Shenoy, S.L., Bates, W.D., Frisch, H.L., & Wnek, G.E. Role of chain entanglements on fiber formation during electrospinning of polymer solutions: good solvent, non-specific polymer-polymer interaction limit. Polymer, 46, 3372-3384 (2005).
    2. Gertz, C.C., Leach, M.K., Birrel, L.K., Martin, D.C., Feldman, E.L., & Corey, J.M. Accelerated neuritogenesis and maturation of primary spinal motor neurons in response to nanofibers. Dev. Neurobiol, 70(8):589-603, 2010.
    3. Lin, D.Y., Johnson, M.A., Vohden, Jr, R.A., Chen, D., & Martin, D.C. Tailored nanofiber morphologies using modulated electrospinning for biomedical applications. Mat. Res. Soc. Symp. Proc. 736, D3.8.1-D3.8.6 (2003).
    4. Corey, J.M., Gertz, C.C., Wang, B.S., Birrell, L.K., Johnson, S.L., Martin, D.C., & Feldman, E.L. The design of electrospun PLLA nanofiber scaffolds compatible with serum-free growth of primary motor and sensory neurons. Acta. Biomater. 4, 863-875 (2008).
    5. Corey, J.M., Lin, D.Y., Mycek, K.B., Chen, Q., Samuel, S., Feldman, E.L., & Martin, D.C. Aligned electrospun nanofibers specify the direction of dorsal root ganglia neurite growth. J. Biomed. Mater. Res. A. 83, 636-645 (2007).
    6. Tan, S-H., Kotaki, M., & Ramakrishna, S. Systematic parameter study for ultra-fine fiber fabrication via electrospinning process. Polymer, 46, 16, 6128-6134 (2005).
    7. Yang, F., Murugan, R., Wang, S., & Ramakrishna, S. Electrospinning of nano/micro scale poly(L-lactic acid) aligned fibers and their potential in neural tissue engineering. Biomaterials, 26, 2603-2610, (2005).
    8. Li, W., Laurencin, C.T., Caterson, E.J., Tuan, R.S., & Ko, F.K. Electrospun nanofibrous structure: A novel scaffold for tissue engineering. J. Biomed. Mater. Res. A, 60(4), 613-621, (2002).
    9. Kim, C.H., Jung, Y.H., Kim, H.Y., & Lee, D.R. Effect of collector temperature on the porous structure of electrospun fibers. Macromol. Res., 14(1), 59-65 (2006).
    10. Wang, H.B., Mullins, M.E., Cregg, J.M., Hurtado, A., Oudega, M., Trombley, M.T., & Gilbert, R.J. Creation of highly aligned electrospun poly-L-lactic acid fibers for nerve regeneration applications. J. Neural Eng. 6, (2009).

    Comments

    15 Comments

    a great video and explanation!
    Reply

    Posted by: AnonymousJuly 25, 2011, 1:27 PM

    How much this system costs?
    Reply

    Posted by: AnonymousOctober 13, 2011, 8:08 AM

    have any documents concerning the theory of electrospinning,

    of course light theory (very simple model )
    Reply

    Posted by: AnonymousJanuary 19, 2012, 11:33 AM

    hello my name is Luis, a province of Argentina tucuman, I would like to know q is the source model to buy an equal, q I have my project done in a university graduation electrospinning, please expect a response, thank you very much
    Reply

    Posted by: AnonymousMarch 19, 2012, 9:14 AM

    Gamma High Voltage model: ES40P-5W and Hipotronics HV DC (for the -²kV).
    Reply

    Posted by: Michelle L.March 19, 2012, 10:30 AM

    thank you very much, is very helpful for me, more consultation, which approximate current consumed by the system
    Reply

    Posted by: AnonymousMarch 20, 2012, 8:55 AM

    The current is very low, although we have never attempted to measure it, I believe it to be in the microamp or lower range.
    Reply

    Posted by: Michelle L.March 21, 2012, 11:39 AM

    sorry for the inconvenience, I am doing my graduation thesis and consists of manufacturing scaffold with the technique of electrospinning, I ask as I get the PLLA polymer, if you will make technical q how often? or you can buy, I thank you very much is being very helpful for me
    Reply

    Posted by: AnonymousMarch 20, 2012, 5:19 PM

    We purchase our polymers. Currently, we are using Resomer L²10 PLLA by BŒhringer Ingelheim. I believe this polymer is now available on Sigma. We also purchase our PLGA (85:15) from Sigma.
    Reply

    Posted by: Michelle L.March 21, 2012, 11:42 AM

    sorry for the inconvenience, I am doing my graduation thesis and consists of manufacturing scaffold with the technique of electrospinning, I ask as I get the PLLA polymer, if you will make technical q how often? or you can buy, I thank you very much is being very helpful for me
    Reply

    Posted by: AnonymousMarch 20, 2012, 6:37 PM

    Hello, you PLLA solvent used for? , And the substrate used, do they work? , Thank you very much
    Reply

    Posted by: AnonymousMarch 30, 2012, 4:52 PM

    Hi Luis- Please email me directly so we can speak in more detail. mkleach @ umich . edu
    Reply

    Posted by: Michelle L.March 30, 2012, 4:57 PM

    hola yo de nuevo, disculpen las molestias,
    Que informacion podria darme sobre la temperatura que debe haber en el ambiente para la optima fabricacion del scaffolds, hay que cuidar la temperatura de la aguja
    Por favor agradeceria cualquier informacion al respecto
    GRACIAS!!
    Reply

    Posted by: AnonymousMarch 30, 2012, 5:50 PM

    Hi, I'm an MArch student at Architectural Association in London and I am doing some research in electrospinning, so please if You could explain me how to use high voltage power supply, can it be connected to mains, what are the amps you used, etc. I don't know anything about electricity and for now it sound kind of scary thing to do. How difficult is to install the equipment and how isolated should the whole process be? My email is dica.aadrl@gmail.com. Best, Dimitrije
    Reply

    Posted by: dica a.October 2, 2012, 10:19 AM

    Hello, I am a Research Assistant for a PhD student and my job is to set up the electrospinning apparatus. I have no idea of what i'm doing, so please I would just like for someone to explain it to me in layman's terms. Also I would like to know if it is possible to collect the nanofibres on the surface of a circular filter that is about 2-3 mm in diameter? At what frequency should you set the rotating collector??
    Reply

    Posted by: Ose A.February 10, 2014, 5:12 PM

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