Electrospinning for Nanofiber Applications

Pharmaceutical Resonance 2020 Vol. 2 - Issue 2

EXPERT COMMENTS

ELECTROSPINNING FOR NANOFIBER APPLICATIONS

Ajinkya Shitole Symbiosis School of Biological Sciences, Pune- 411004

1. INTRODUCTION : polymer solution from the spinneret at a constant flow rate. When a high voltage is applied, the drop of As the diameters of polymeric fiber materials are the polymer formed at the nozzle of spinneret shrunk from micrometers to submicrons or becomes highly electrified, this induces the drop with nanometers, there appear several amazing two major forces: electrostatic repulsions between characteristics as compared to their bulk form. surface charges and coulombic force exerted by Nanofibers, as a result of its desirable properties have external electric field. Under the influence of these found wide range of applications in tissue forces, liquid drop forms a Taylor cone. Once the engineering, medical devices, wound healing, drug electric field surpasses the threshold value, an release, barrier textile, as sensors, carrier for catalyst electrostatic force overcomes the surface tension of and enzymes, for energy storage, filtration the polymer solution, thus ejecting a fluid jet. This applications, etc. Nanofibers have small diameters, charged fluid jet is collected on a collecting device as exhibit high surface area, and have highly porous a result of difference of electrical potential between structure with interconnected pores. They may exhibit the polymer solution at the tip of the syringe or different morphologies such as porous-surface nozzle and the collector. The whipping motion of the nanofibers, side-by-side structure, core/shell polymer jet that takes place between the needle and structure, etc and have been produced using various the collecting device allows for the solvent to synthetic or natural polymers. evaporate. This results in the collection of a polymer fiber mat on the collecting device. The resulting fiber Several methods have been employed to fabricate mat consists of non-woven, random oriented or nanofibers, such as, self-assembly, template aligned fibers that can vary in diameter from synthesis, melt-blown, phase separation, and micrometres to tens of nanometres depending upon electrospinning. Electrospinning has been recognized the processing parameters. as simple, inexpensive and efficient technique for the fabrication of polymeric nanofibers with micro- to 3. Factors that may influences the electrospun nano-meter range diameters and with controlled product surface morphology. Various natural or synthetic polymers have been successfully electrospun to The factor that influence the process of generate ultrafine fibers in recent years. electrospinning or more precisely the final electrospun product include: Solution parameters 2. Electrospinning Process such as: solution properties (viscosity, surface tension, conductivity), molecular weight of the The major components of the electrospinning setup polymer and molecular weight distribution; Applied include, a collecting device, high voltage power process parameters such as: flow rate of the solution, source (DC) and a spinneret. The spinneret is applied electric potential, distance between spinneret connected to the syringe in which the polymer is and collector, motion and speed of collector, etc. loaded. A syringe pump is used to release the Thus, these parameters must be optimized in order to control the fibre diameter. The collector geometry may be selected based on the Ajinkya Shitole desired nanofibers morphology for an intended Symbiosis School of Biological Sciences application. A stationary plate may be used for Pune - 411 004 Email : [email protected] collecting randomly oriented fibers; while a high Contact : +91 80801 11543 speed rotating wheel or drum or rod may be used for generating aligned nanofibers. The collector used in electrospinning must be conductive; it must remain © Published by DYPIPSR, Pimpri, Pune - 411 018 ( MH ) INDIA 1 Pharmaceutical Resonance 2020 Vol. 2 - Issue 2 isolated from its axel, and must be grounded. The choice of substrate used for deposition of nanofibers may depend on the intended application. Various materials such as glass, metal, plastic, or silicon wafer may be explored as substrate material. 4. Troubleshooting of Electrospun nanofibers Dripping of polymer solution might occur from the syringe tip. In such instance it is necessary to make sure that the conducting plates are making contact with the ground. The distance between the tip and collector and the applied voltage might influence the quality of the stream ejected from the tip. The voltage needs to be adjusted in case the polymer solution at the syringe tip is leaning in the direction of the wheel but is not forming a stream. At higher voltage and lower distance between the tip- collector, the stream might undergo wagging, moving up and down rapidly. Wagging and formation of short or discontinuous stream might also occur as a result of use of lower concentration of the polymer. Using a higher concentration of polymer or adding a solvent with slower evaporation rate might help in overcoming this issue. Large globs might be formed at the syringe tip due to deposition of solution and further causing its hardening at the tip. This might be removed by using a tissue paper attached to a non- conductive stick. Beading might occur in the fibers when there is lower voltage or when the solution concentration is lower or when the distance between the tip-collector is lower. Adjusting these parameters along with verifying the proper contact between the tip of needle and the conducting plate, and the collector with the grounded wire might be helpful in overcoming beading. In case if the porous morphology of the nanofibers is desired, a solution with rapid rate of evaporation might be used. Wavy or curly fibers might be observed when the distance between the tip-collector, and when the speed of collector is low. Adjusting the parameters might be helpful in overcoming these issues. In case of formation of ribbon like structure or blending of fibers together, the use of increased concentration of polymer solution or the use of solvent with higher rate of evaporation might be helpful. Aligned nanofibers may be achieved at high speed rotation of the mandrel, while at lower speed or using a stationary collector, randomly oriented nanofibers may be achieved.