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Developing and testing a (Matlab) program to analyze the thickness non-uniformity of electrospun fibers

Introduction

To fabricate and deposit micro and nanosized (polymer) fibers, a method called electrospinning is used. A typical electrospinning setup is depicted in Figure 1.

Figure 1: A schematic drawing of an electrospinning setup. The blue part in the syringe shows the electrospinning mixture

An electrospinning setup typically comprises of a capillary which is fluidically connected to an electrospinning mixture feed mechanism and is electrically connected to a high voltage (HV) power supply. The power supply changes the electrical potential of the capillary with respect to the grounded substrate, which is located approximately 10 cm below the capillary. The electrospinning mixture is pumped through the capillary (for example by means of a syringe pump) and forms a droplet at the end of the capillary. If the local electric field near the end of the capillary is strong enough, a thin fiber emanates from this droplet and moves towards the substrate [1].

Assignment

A Scanning Electron Microscope (SEM) micrograph of an electrospun fiber mat is shown in Figure 2. In the image, the unaligned fibers of non-uniform thickness are clearly visible.

Figure 2: A SEM micrograph of an electrospun fiber mat. The fibers show a very non-uniform thickness and are not aligned.

The stability of electrospinning processes is usually determined by measuring the fiber thickness non-uniformity, which should be low if the electrospinning process is stable. To determine the thickness non-uniformity, the SEM micrographs are manually analyzed by determining the fiber thickness at random locations of the micrograph. The analysis becomes more accurate if the amount of fiber thickness measurements at random locations in the micrograph increases. For this reason, accurate thickness non-uniformity measurements are very time-consuming. When the electrically conductive substrate is completely covered by the non-conductive fibers, the contrast of the SEM micrograph is poor and determining the fiber thickness is becoming difficult. Because it is preferential to electrospin a fiber mat consisting of aligned fibers, also the angle of the fiber (with respect to a reference angle) is important information that could be extracted from the micrographs.

Depending on the application, the fibers and/or substrate could be electrically isolating. For this reason, the contrast in the SEM micrographs can be insufficient to accurately determine the edge of a fiber. Therefore, the student should start with investigating how a program could enhance the contrast between adjacent fibers and/or the contrast between fiber and substrate: Only with a proper contrast, the program could automatically detect the edges of the fibers. Next, the program should extract the fiber angle and fiber thicknesses at multiple locations within the SEM micrograph. In the last step, the program should be able to autonomously perform a statistical data analysis of the gathered data. After the program is written, the student will test or benchmark the developed program by analyzing real SEM micrographs.

We would like to stress that this project is only suitable for students who have an affinity with image analysis and statistics.

More information

Are you interested in this attractive project or do you have any questions about the project? Do not hesitate to contact either Prof. Dr. Han Gardeniers (j.g.e.gardeniers@utwente.nl) or Bjorn Borgelink (b.t.h.borgelink@utwente.nl).

REFERENCES

[1] J. J. Feng. “The stretching of an electrified non-Newtonian jet: A model for electrospinning”. In: Physics of fluids 14.11 (2002), pp. 3912–3926.