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Electrospinning

Electrospinning is a method of preparing ultrafine fibers from polymer solution or polymer melt by means of electrostatic and capillary forces. Using this method has been spun about 100 kinds of polymers, both natural and synthetic.
The electrospinning process is used to create a high voltage electrically charged stream of polymer solution or melt. A capillary, nozzle or spinning collector is connected to an electrode with high voltage (tens of kilovolts) and it polarises the polymer solution.

schematic diagram of an electrospinning set up

Schematic diagram of an electrospinning set-up.

 

The opposite pole in the eelectrostatic field is a conductive collector shaped as a plate, mesh, metallic tip or cylinder which is grounded or connected to an opposite high voltage electrode.
Electrospinning occurs when electrical forces at the surface of polymer solutions overcome the surface tension, and cause an electrically charged jet to be ejected. Due to a bending instability, the jet is subsequently enormously stretched to form continuous, ultrathin fibres.

struktura nanovlakenne vrstvy

The structure of the nanofiber layer prepared by classical spinning. Picture from scanning electron microscope.



 

Coaxial electrospinning

Coaxial electrospinning is a unique sophisticated method, and an alternative route to produce composite functionalized nanofibres with nearly strictly organized core-shell structure. The shell of a nanofibre is most commonly a polymeric material, while the core can consist of other polymer of another encapsulated mass including liquids. From the technological point of view, the fibre shell has to originate from electrospun-able fluid while the core fluid may or may not be electrospun-able, since the physics of electrospin-ability is mostly governed by jet surface. Core-shell fibres possessing a combination of mechanical properties not seen in any other fibre.
Like common electrospinning, its core-shell variant also occurs when electrical forces at the surface of polymer solutions overcome the surface tension, and cause an electrically charged jet to be ejected. Due to a bending instability, the jet is subsequently enormously stretched to form continuous, ultrathin fibres.

tryska pro koaxialni zvlaknovaniThe nozzle used for coaxial electrospinning, (1) Input of the core polymer (2) Input of the shell polymer.

 

In comparison with the classical electrospinning technology different types of electrodes - nozzles are used in the case of coaxial electrospinning. The critical component of a core-shell electrospinning setup is a composite spinneret comprising of two separately fed chambers that culminate into co-axial capillary orifice, i.e. small capillary tubes with one inside the other.
Core-shell electrospinning is appropriate for processing materials, which are difficult or impossible to spin into nanofibres by conventional fibre-forming techniques or by classic electrospinning. This technique can also be employed to incorporate active substances such as anesthetics, antibiotics, immunosuppressants, natural substances, but also growth factors within the core of core-shell biodegradable nanofibers in higher concentration than in the case of conventional nanofibers and sometimes even nanoparticles. Incorporated active substances are subsequently targeted and controlled release, which is preferably used for applications of nanofibrous layers in topical treatments and cosmetics.

struktura rezu nanovlakenne vrstvy

Cross-sectional imaging of tnanofibrous layer prepared by coaxial electrospinning.



 

AC spinning

AC spinning is a new experimental method used to produce nanofibres which again utilises an electrostatic field, but with an alternating current with a frequency of tens Hz. This idea allows for the most productive preparation of nanofibres among the methods using electrostatic field – involving spitting of a parallelised nanofibrous “cloud”. When using the alternating current, the created fibres are able to self-organise thanks to the carried alternating charge and to travel to some extent in a free space, thus it is not necessary to use the collecting antielectrode which facilitates the production of fibres simpler.

nanovlakenna prize

Nanofiber yarn produced by the method of alternating spinning. Picture from the scanning electron microscope.

 

Another positive effect is the possibility to deposit the nanofibre flow in a more targeted manner. This method is currently successfully used for the production of core yarns and classic yarns, which is another interesting possibility in the field of controlled drug release and targeted delivery to the required site.
Thus the indisputable benefit of this method is relatively good productivity compared to electrostatic methods, however this technique is still new and thus it is only being used within a limited group of polymers, such as polylactic acid (PLA), polyamide (PA), polyvinylbutyrale (PVB) and their copolymers or blends.

formovani svazku vlaken

Formation of a fiber bundle in a free space.