**2. Electrospun nanofibers**

Electrospun nanofibers (**Figure 2**) are polymeric-based structures that possess diverse customary properties that make them interesting to be used as drug carriers [13], these characteristics include biocompatibility [14, 15], biodegradability [16, 17],

**Figure 1.** *Some examples of drug carriers.*

*Novel Drug Carries: Properties and Applications DOI: http://dx.doi.org/10.5772/intechopen.106868*

**Figure 2.** *Electrospun nanofibers as drug carriers.*

high surface area [18, 19], adequate mechanical properties [20, 21], highly customizable fiber diameter and structure [22, 23], excellent porosity connectivity [24, 25], ease of handling [26, 27], functionalization [28, 29], and the ability to encapsulation of a diversity of bioactive molecules [30, 31].

Electrospinning is a versatile technique that has expanded through time, where the objective of this technique is to fabricate fibers or particles in the nanoscale range [32] creating a tridimensional scaffold that has wanted characteristics with potential use as drug carriers such as the large surface area, where this property permits a high drug loading capacity in a reduced volume range [33], low cost [10], and adaptability [33]. The electrospinning technique uses a high-voltage electrical field that charges a polymer solution breaking its surface tension when is injected with a specific rate, this polymeric solution is attracted to a conductive collector creating a liquid jet yielding nanofibers (~10–1000 nm) where the solvent evaporates in the air [18, 34].

There are different types of electrospinning techniques that help to incorporate bioactive molecules or drugs into the fibers or over their surface [35, 36]. The objective is to release the loaded drug at the target zone through the polymeric degradation of the fibers controlling its delivery rate depending on the polymer used [37]. Among the reported electrospinning techniques can be listed the blending, coaxial, emulsion, and surface modification electrospinning, each of them has a different strategy for drug incorporation. The advantage of this strategy is that improves the equilibrium between the mechanical and physicochemical characteristics of the functionalized resulting fibers. Moreover, it permits the adjusting of the proportion used of the bioactive component by altering the concentration added to the final solution [38].

One of the advantages of electrospinning is that is a one-step method because the loaded biomolecules or drug solution is dissolved or dispersed directly into the polymeric solution. In this method, it is important to choose correctly the polymeric matrix because its characteristics will determine the efficiency in the drug encapsulation, dispersion in/on the fibers, and delivery rate. It is reported that the equilibrium between hydrophilic and hydrophobic functional groups in all components of the

system (drug, polymer, solvent) will improve the optimal functionalization of the resulting fibers [39]. It's important to note that due to the hydrophobic properties of some polymers, lipophilic drugs are easier to dissolve and create a homogeneous solution and vice versa. Such is the case of the polyester's polymers, which are hydrophobic and interact very well with the hydrophobic drug rifampicin and paclitaxel, and gelatin, poly (ethylene glycol), and poly (vinyl alcohol), which are hydrophilic polymers, can dissolve hydrophilic drugs such as doxorubicin [40].

The disadvantage of this method is that some metallic bioactive molecules tend to aggregate in the polymer solution and in the resulting fibers [34]. Moreover, with this process, pharmaceutical drugs that are insoluble in water cannot be encapsulated using hydrophilic polymers [41]. To avoid this issue, cyclodextrins are used to improve the solubility of the insoluble drugs in the polymeric solution [42]. The main advantage of fibrous scaffolds proposed for drug delivery systems is that they possess a high surface area to volume ratio, which can permit high dose load and promote the solubility of the drug in an aqueous environment improving the drug efficiency [43].
