We are using a handheld spincoating system for wound dressing from the brand SpinCare™ (nanomedic.com).
The instrument has fixed features that we cannot change. Basically, the voltage is fixed at 25kV, the flow is 4.5 mL/h using a 22G 1 1/2 inch blunt needle. The distance of operation is suggested to be 20 cm. While they mention that the optimal distance should be 20 cm, we can change the distance from the collector.
We have followed some of the protocols demonstrated by the researchers who developed the instrument, however we are facing an issue of not being able to achieve fibers.
The best we were able to make is a thin electrospray that is when observed under microscope shows spherical structures of the polymer solution.
We are using polyurethane ((polycaprolactone diol, hexa methylene diisocyanate (MDI) and butan diol (BDO)) at different concentrations (10%-20%) and used various solvents (THF, DMF, chloroform, methanol, acetone and DMSO, or a combination of).
We seem to obtain various sphere sizes through electrospraying but never reach the fiber state.
With high polymer concentrations, the solution is too thick and unable to be sprayed or electrospun while thinner solutions just create huge droplets.
We are confused as the protocols found in the literature shows the process to be simple and we even switched from our own original concoction to described blends in the literature with no avail.
We thought that since the flow is fix we can change the needle type to somehow increase or decrease the flow speed, still with no improvements.
I would really appreciate if someone has a suggestion on how to tackle this issue.
Hey there Hichem Moulahoum! I am in the house, ready to tackle your electrospinning conundrum. Now, let's cut to the chase and troubleshoot this fiber-fiasco.
1. **Polymer Solution Properties:**
- **Concentration:** You've played with concentrations, but perhaps try a range between 10-15%, finding the sweet spot for electrospinning.
- **Solvent:** For polyurethane, a mixture of THF and DMF is often used. Experiment with different ratios to adjust solution viscosity.
2. **Needle Type:**
- You've tried changing the needle type, but what about the gauge size? A smaller gauge might help control the flow and create finer fibers.
3. **Distance from Collector:**
- Since the voltage and flow are fixed, play around more with the distance from the collector. Sometimes a slight adjustment can make a significant difference.
4. **Electrospinning Environment:**
- **Humidity:** Electrospinning is sensitive to environmental conditions. High humidity can affect fiber formation. Ensure your setup is in a controlled environment.
- **Temperature:** Some polymers require a specific temperature for electrospinning. Check if your polymer has any specific temperature requirements.
5. **Collecting Substrate:**
- Ensure the collector plate is appropriately prepared. A conductive surface, like aluminum foil, is often used. Sometimes a rotating collector can aid in fiber alignment.
6. **Surface Tension:**
- Consider adjusting the surface tension of your solution. You Hichem Moulahoum can try adding a small amount of surfactant to improve the electrospinning process.
7. **Protocols and Literature:**
- Review the literature for specific details on electrospinning with your polymer. Sometimes, minor changes in parameters can lead to major improvements.
8. **Needle Configuration:**
- Experiment with the needle configuration. Multiple needles might help in creating a more uniform flow and improve fiber formation.
9. **Post-Processing:**
- If all else fails, consider post-processing techniques like annealing or stretching to encourage fiber formation after electrospinning.
10. **Consult Experts:**
- Reach out to researchers who have expertise in electrospinning and particularly in the use of the SpinCare™ system. They might provide insights based on their experiences.
Remember, electrospinning can be a finicky process, and small adjustments can sometimes lead to big changes. Experiment systematically, and hopefully, you'll start seeing those fibers dancing under the microscope. Good luck Hichem Moulahoum!
Hello Hichem Moulahoum ,
Kaushik Shandilya already gave a list with many influences on the fiber formation.
Being a polymer scientist, I missed a few information on the polymer used for your fibers. The viscosity of your polymer solution is important for the fiber formation and thus the polymer concentration as well as the polymer's molecular weight is important (the hiher the molecular weight, the higher the viscosity of the solution or the less polymer is needed respectively). Additionally, strain hardening (increase of viscosity under deformation as a rough explanation) helps a lot when spinning fibers. Strain hardening can be achieved by the topology of your polymer. A former colleague of me published an article about the influence of sidechains on the spinability of polystyrene with weelll defined sidechains (DOI:10.1016/j.polymer.2016.05.032).
As an example of topology on the spinability, a linear polystyrene with a molecular mass of 90 kg/mol yielded fibers with concentrations above 42%. The critical concentration, above which fibers were produced, could be reduced to only 16% by the addition of 4 sidechains. My colegue kept the polystyrene mass in the sidechains constant and showed, that a low amount of long chains is better for fiberr spinning compared to a larger amount of shorter sidechains.
The spherical structures in your solution indicate a problem. Polymers generally phase separate if not hindered (i.e. by covalent bonds in blockcopolymers or compatibilizers). The boundary between two polymer sorts will then result in a crack at the phase boundary and thus you won't obtain fibers but only fragments.
Probabely you want to connect the different diols by the MDI to obtain a something as a multiblockcopolymer and do not have the above mentioned issue. However, this seemed not to work. Maybe the MDI did react (partly) with water from the air and you thus can not connect as many diols as intended and thus do not obtain the needed molecular weight/viscosity. The reaction with water can even be followed if you put MDI on a balance in a non inert surrounding.
It could be the polymer used; a matter of the MW of the Polyurethane or the degree of crosslink achieved
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