Nanotechnology has profound applications in healthcare and has improved healthcare research to a large extent. The therapeutic benefits of nanotechnology in the field of medicine have resulted in new areas, such as nanomedicine, nanobiotechnology, etc. Researchers in the field are attempting to find an effective nanoformulation to deliver growth factors, supplements or drugs safely and in a sustained manner at the required site. Their task is to attempt a different drug nanoformulation of existing blockbuster drugs that brings improved efficacy and a therapeutic breakthrough. Thus the ultimate objective of these nanotechnological drug-delivery systems is to fine tune the normal profile of potent drug molecules in the body following their administration to significantly improve their efficacy and also minimize potential intrinsic severe adverse effects. For treatment of breast cancer and non-small-cell lung cancer, Abraxane® (paclitaxel) is employed as a nanoparticular formulation, which increases drug delivery up to 70% in comparison with solvent-based paclitaxel delivery. In this novel nanoformulation, Abraxis Bio Sciences have used Bristol-Meyers Squibb’s blockbuster drug paclitaxel (Taxol) and a very common globular protein bovine serum albumin (BSA). There are numerous nanotechnology-based drug-delivery systems such as nanocrystals, nanoemulsions, lipid or polymeric nanoparticles, liposomes and nanofibers. While nanoemulsions and liposomal formulations did not make significant advances, despite huge research spending, the polymeric nanoparticulate systems show more promise. Nanoparticles of a polymeric nature find application as drug-delivery systems and are advantageous due to their scalability, cost, controlled and targeted delivery, compatibility, degradability, etc. Natural biopolymers are even better than the synthetic polymers in terms of biocompatibility and biodegradability. Nanoparticulate drug formulations alter the pharmokinetic profile of the therapeutic entity and program the release of the drug in sustained or controlled manner. Thus, nanoparticle or nanoformulated drugs outperform conventional systemic delivery in terms of delivery of an encapsulated drug and its sustained release. Slowly and surely nanoformulated drugs are coming onto the market, surpassing systemic delivery, which is believed to be the only mode of administration for a wide range of active pharmaceutical ingredients. Nanofibrous drug-delivery systems are being developed as potential scaffolds in tissue regeneration, wound healing and cancer drug-delivery applications. In this chapter we are going to discuss two promising nanotechnology-based drug-delivery tools, namely electrospun micro- and nanofibers and electrosprayed micro- and nanoparticles, which have a common synthetic procedure mediated by an electrical potential difference.

This chapter introduces the fundamental general equations of the dynamics of free liquid jets in Sections 3.1 and 3.2. The applications of these equations encompass practically all fiber-forming processes from melt spinning, as was sketched out in Section 1.2 in Chapter 2 to melt- and solution blowing, and electrospinning of polymer micro- and nanofibers discussed in detail in Chapters 4 and 5, or drawing of optical fibers outlined in Section 6.5 in Chapter 6. They also form the framework for description of several types of instabilities characteristic of the hydrodynamics of free liquid jets in general and of fiber-forming processes in particular. These include capillary instability (Section 3.3), aerodynamically driven bending instability (Section 3.4) and buckling of liquid impinging onto a wall (Section 3.5).

Mass, momentum and moment-of-momentum balance equations

The dynamics of free liquid jets moving in air, which are characteristic of fiber-forming processes, involve growth of various perturbations. The most notable are driven by surface tension and the dynamic interaction with the surrounding air, as well as electrically driven effects. Theoretical/numerical description of the jet evolution in general, and of perturbed jets in particular, is hindered by the fact that such problems typically involve a three-dimensional, time-dependent evolution of flows with free surfaces, the locations in time of which should also be established. Solving such problems in the framework of the rigorous equations of fluid mechanics, say the Navier–Stokes equations, in most cases would be prohibitively time-consuming, even using super-computers. Additional complicating factors arise due to the rheological complexity of polymer solutions used in fiber forming, as well as the temperature-dependent variation of material properties in nonisothermal situations. Accounting for all these factors together in the framework of the rigorous equations of non-Newtonian fluid mechanics would be tremendously difficult. However, these difficulties can be relatively easily overcome in the framework of a quasi-one-dimensional description of liquid motion in the bending jets. In the works of Entov and Yarin (1980, 1984a) and Yarin (1983, 1993) the general quasi-one-dimensional equations of the straight and bending jets were derived from the integral balances of mass, momentum and moment of momentum, as well as by averaging the three-dimensional equations of hydrodynamics over the jet cross-section.

This chapter outlines several applications of electrospun and solution-blown nanofibers and their mats. In the case of filters and membranes (Section 9.1), industrial application has already begun, but a number of research questions are still open. Applications of nanofiber mats as fluffy electrodes beneficial for fuel cells and Li-ion batteries have recently attracted significant attention and are the focus of Section 9.2. Two recent approaches based on nanofibers were proposed in the field of cooling of high-heat flux microelectronics (Section 9.3) and nanofluidics (Section 9.4).

Filters and membranes

Filter materials are used for air, water and blood filtration, while membranes are used in separation processes, in particular, for bioseparation and pathogen removal for direct blood transfusion. Filters can remove particles, droplets, bacteria, viruses or even individual molecules from a carrier fluid flowing through them, or, in principle, possess advanced detection and response features that are practically absent in today’s products (see Chapter 10).

Chemical warfare differs from conventional warfare, such as explosives, in the sense that the toxicity of the chemicals used is very dangerous to the combatants in the battlefield, or to the civil population being affected during a war or as a result of a terrorist attack. The threat is amplified by concealment and low cost and relatively easy production of these agents, which renders them weapons of mass destruction. It becomes essential in such a situation that soldiers wear protective clothing, respirators, face masks, gloves, etc. Initially German troops unleashed chemical warfare agents, such as mustard agent, HD, during World War I in 1915, and this resulted in much more concern during World War II. Thus research on decontamination of chemical and biological warfare agents (CWAs) has been the subject of serious interest in many research laboratories since World War II. Mustard gas or bis(2-chloroethyl) sulfide is one of the highly cytotoxic, readily methylating CWAs that are regulated under the 1993 Chemical Weapons Convention (CWC). It covalently binds to DNA bases or forms disulfide bonds with the thiol groups. This readily leads to programmed cell death or the mutated DNA leads to cancer. The simultaneous danger associated with this toxic agent is its high skin penetration owing to its high lipophilicity, which results in immediate blister formation and huge uptake through skin within a short duration of exposure (Ivarsson et al. 1992).

Conventional modes of decontamination involve activated charcoal or other such heavy physical adsorbants of the contaminant. When compared with technologies employing conventional catalysts and reactive sorbents, which are specific and sometimes time-consuming, nanotechnology-based nanomaterials are highly reactive, nonselective and multifunctional in character. Current development of nanoparticles such as MgO, Al2O3, Fe2O3, ZnO and TiO2 and their incorporation into nanofibers impart enhanced catalytic, disinfection and sensing capabilities, photo-protection capability, and stain-resistance and self-cleaning properties. The testing of these materials in textiles and protective clothing against CWAs showed that they have potential as replacement technology in such applications.

Preface

Fiber-forming processes and the resulting fibers have become a key element in many modern technologies. Today, practically everyone is directly or indirectly using these fibers. Manmade macroscopic fibers are widely used in our garments and many other items of everyday life. On the other hand, much smaller microscopic and, especially, nanofibers are only beginning their path to prominence. The chemical, physical and technological aspects of manufacturing of such fibers are still weakly linked and not fully understood. Two main processes associated with formation of micro- and nanofibers are melt- or solution blowing and electrospinning. They require concerted interaction of synthetic chemistry, responsible for polymers used as raw materials, polymer physics, providing a link to their viscoelastic behavior, rheological characterization of flow properties, non-Newtonian fluid dynamics of polymer solutions and melts, aerodynamics, associated with gas blowing, and electrohydrodynamics, in the case of electrospinning. The key element of the fiber-forming processes is a thin jet of polymer solution or melt, which rapidly changes its three-dimensional configuration under the action of the aerodynamic or electric forces applied to its surface and the internal viscous and elastic stresses. There is a definite and imperative need to interpret and rationalize these phenomena, which requires acquisition of extensive experimental data and establishment of an appropriate theoretical framework as an essential element in the further technological design and optimization. In addition to the above-mentioned broad spectrum of disciplines, this involves different aspects associated with materials science, such as the methods developed in polymer crystallography, and elasticity and plasticity theory. Although many aspects of fiber-forming processes can today be considered as uncovered and well described, either experimentally or theoretically/numerically, numerous important details are still to be explored. The importance of this subject is attested by an exponential increase in scientific publications devoted to microscopic and nanofibers and a broad involvement of the industries associated with fiber media, nonwovens, nano-textured materials, novel biomedical and healthcare products and optical fibers, as well as defense applications.