Coaxial Electrospinning Needle

Coaxial electrospinning is a process in which the polymer jets are drawn from the needle’s tip and directed to a collector. During the flight of the fibers, solvents and polymer are vaporized, and the size of the voltage difference determines the diameter. The collector can be a rotating disk or drum, or a simple aluminum plate. The fiber diameter also depends on ambient conditions, such as temperature and humidity.

Nanofibers

In a coaxial electrospinning needle, nanofibers are produced through the concentric arrangement of spinneret orifices. Most laboratories purchase commercially available spinnerets or design their own. To synthesize nanofibers, researchers modified a McIntyre cannula needle, which is commonly used for ophthalmic surgeries. These needles were adapted to produce hollow fibers of nylon 6, which are bioactive substances.

The distance between the needle tip and collector is an important factor affecting fiber morphology and bead formation. A closer distance allows a strong electrical field to develop, which makes the jet thicker. However, short distances (5 cm) do not allow the solvent to vaporize, preventing fiber formation. Increasing the concentration of the polymer solution reduces this risk, resulting in a continuous nanofiber morphology.

Electrospinning setup

The Coaxial Electrospinning needle setup comprises a 2-channel syringe pump and a coaxial stainless steel spinneret needle. This set-up allows the infusion and electrospinning of two materials simultaneously. The process can also be used to prepare core-shell fibers. The Coaxial Electrospinning needle setup is compatible with SKE E-Fiber equipment. These two components work together to create a unique fiber-spinning process.

The Coaxial Electrospinning needle setup is a flexible assembly made of four main components. A high-voltage power supply and a concentric, grounded collector are used. The polymer solution in the bowl initiates multiple jets that migrate to the edge of the cone. The droplets adhere to the surface and are stretched by electric force to form nanofibers. The solution reservoir is an alternative to needles in this process.

Fiber morphology

The morphology of the fiber formed by coaxial electrospinning is dependent on a variety of factors. This study examines the effects of four processing parameters on the fiber morphology. The distance between the needle tip and collector has a strong impact on the morphology of the fibers. A closer distance to the needle tip causes a stronger electrical field, which helps the fibers to form a thicker core. The same holds true for very close distances, where the solution jet is completely void of fiber formation.

The distance between the needle and the collector is controlled using a laboratory jack. We chose a distance of approximately 10 cm because very short distances could result in electrical arcs. However, we avoided measuring distances less than 10 cm as they are not suitable for our purposes. Additionally, we selected a constant voltage difference of 30 kV and a 15 wt% solution concentration.

Processing parameters

The process of coaxial electrospinning a polymer filament requires several variables that control the size of fibers and the morphology. The solution concentration, the distance between the needle tip and the collector, and the flow rate all influence the fiber morphology and characterization. The current work examined the effect of solution concentration on the process parameters. The results show that higher concentrations produce thicker fibers.

The initial working process of coaxial needles was based on the principle of the sheath-core separation, with the inner needle measuring 0.51 mm in diameter and the outer needle measuring 1.46 mm in diameter. The working parameters were digitally recorded and quantitatively described. The process parameters were evaluated and correlated to the nanofibers’ initial conductivity and final widths. After optimizing the parameters, we were able to fabricate the coaxial needles.

Applications

The coaxial concept has numerous applications, including the production of very thin fibers and hollow structures. Its pore formation is due to the thermally and vaporically induced phase separation of polymer molecules. This process is also suitable for the production of fibers with sensitive materials. The main drawbacks of coaxial electrospinning needles are its high cost and initial burst problem. However, there are many benefits of this technique, and it is worth exploring.

A significant advantage of coaxial electrospinning needles is that it can produce multilayered core-sheath nanofibers. The advantages of coaxial electrospinning needles are that they are easy to fabricate, and they do not require vacuum, elevated temperature, or plasma exposure. Moreover, the multifunctional properties of this process make it particularly suitable for the production of high-throughput fiber membranes.