Electrospinning scaffold polymers. There are currently two standard electrospinning patterns, vertical and horizontal, with three new electrospinning parameters at different angles to study the effect of gravity. Due to the growing interest in this technology, many research groups have developed more sophisticated mechanisms to fabricate more complex nanofiber structures in a more controlled and efficient manner [10, 11], see (Figure 2). For example, motorized fiber and multi-jet harvesting is a method of making a nanofiber scaffold composed of multiple layers, each made from a different type of polymer. In addition, this technology can be used to create scaffolds from polymer composites, where the fibers in each layer are a combination of different types of polymers.
The electrospinning process has been extensively studied [13]. This mechanism occurs when the surface tension of the solution is increased by an applied electric field, resulting in the creation of small sprays from the surface. Taylor [14] explained the critical voltage at which this distortion can occur:
Electrospinning scaffold polymers
Here V is an electric field, γ is the surface tension of the liquid and r is the radius of the hanging drop [15]. Taylor studied a small sample of liquids and determined an equilibrium surface tension with an equilibrium angle of 49.3 degrees using electrostatic forces. Taylor cones are essential for electrospinning because they describe the occurrence of fine speed gradients in the fiber formation process. When V > Vc, a tiny jet of solution is blown off the surface of the cone and moves towards the opposite pole, the electrode near the electrical ground. To describe it, an electrospun beam is an array of charged elements released from a viscoelastic medium with one end connected to the origin and the other end connected. When a polymer solution maintained in a surface tension capillary state is subjected to an electric field, a charge is generated on the surface of the liquid [16].
The mutual charge repulsion creates a force against the surface tension forces and shear stresses are created in the liquid. By increasing the strength of the electric field, the ions in the solution with the same polarity are forced to cluster on the surface of the droplet. The length of the stable beam increases with increasing voltage. After the viscoelastic beam begins to move away from the Taylor cone, it initially moves on a linear trajectory. The jet gradually begins to deviate from this linear path and complex shape changes can occur due to the repulsive forces in the charged elements within the electrospun jet [17]. The jet can have a significant reduction in area and spiral loops are created from this. This phenomenon is often known as flapping instability. This stretches the hemispherical surface of the solution at the end of the capillary tube, forming a cone called a Taylor cone (Figure 3). At very high electric fields (V > Vc), a charged jet of solution emerges from the apex of the Taylor cone and moves to an opposite (-) (or electrically grounded) electrode.