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
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).
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.
1. Choose a Polymer
2. Choose a Collector
3. Approximate the Critical Entanglement Concentration Empirically1
4. Troubleshooting - the Stream:
5. Troubleshooting - Fiber Morphology6,7,8 (refer to Figure 4)
6. Representative Results:
Please refer to Figure 4 for depictions of typical fiber results.
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. 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|
|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. 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. 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).
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.
No conflicts of interest declared.
This work was supported by NIH K08 EB003996 and the Paralyzed Veterans of America Research Foundation Grant 2573.
|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|
|PLLA||Boehringer Ingeheim||Resomer L210|
|Carbon tape||Ted Pella, Inc.||13073-1|