**1. Introduction**

Presently, drug carriers can be incorporated in several systems that are available in the market in different presentations such as tablets, syrups, and shots that the patients swallow, chew, or are inoculated administering specific doses of the medical compound. However, children, geriatrics, and patients with specific conditions have still difficulty obtaining the recommended doses through these administration routes and medical presentations [1–4]. Until now, oral administration has been the preferred administration route for its easiness of administration [5–7].

Innovative drug carriers can include several micro and nanostructures such as micelles, nanoparticles, liposomes, emulsions, and nanofibers, among others [8]. The most important technical advantages of drug carriers can be reported as the high stability, high carrying capacity, the feasibility of several administration routes, and

the capacity to be used with hydrophilic and hydrophobic molecules. The intention to use drug carriers is to control the drug release using these polymeric matrices and reduce or avoid secondary effects [9].

One of the main properties needed for a drug carrier is biocompatibility, which is the absence or decrease of adverse tissue reactions against the implanted or administered biomaterials avoiding immune response. Biomaterials can include natural and synthetic polymers, ceramics, metals, and a combination of them [10]. However, biomaterials that are applied as a drug carrier need to develop a bioactive role in the tissue such as to respond to chemical, physical, or external stimuli and possess a therapeutic effect [11].

Drug carriers can include nanogels, micelles, mucoadhesives, bacteriophages, magnetic nanoparticles, graphene, dendrimers, carbon-based materials, viral-based nanoparticles, nanofibers, liposomes, films, bacterial vesicles, metal-organic frameworks, and carbon nanotubes, among others [12]. **Figure 1** shows some examples of nanocarriers.

For all the above, this chapter discusses the electrospun nanofibers' properties applied as drug delivery systems, some characteristics of the main polymers used, describing their advantages and disadvantages. Some electrospinning strategies are also compared.
