## 1 Introduction  
The inhalation of aerosols has played a pivotal role in the vistas of pulmonary drug delivery since ancient times, as a way of relieving respiratory diseases [1; 2; 3]. From a medical perspective, \"aerosol therapy\" is medical terminology, which is used to describe a variety of treatment techniques, including the delivery of a variety of drugs that may be administered via inhalation, targeting lung tissues and airway secretions in the upper, central, and peripheral airways [4; 5]. These drug-delivery strategies have several advantages compared with conventional methods of oral administration. First, aerosol methods have the advantages of a direct and simple delivery of medication to the site where action is required [6]. This produces a more rapid therapeutic effect. In addition, another important benefit of these strategies is that less medication can be used to obtain the same therapeutic effects, compared to systemically-delivered medication. As a consequence, inhalation therapy can be an extremely effective method in the field of drug delivery systems [7; 8; 9]. In practice, these drug delivery techniques developed rapidly in the 1950s, with the development of nebulizers and pressurized metered-dose inhalers. In addition, there have been advances in the development of new nebulizers that hold promise in improving aerosol drug delivery in patients with pulmonary diseases [10; 11; 12]. Nebulizer therapy is a traditional and common instrumental therapeutic method consisting of supplying a drug to a patient's air-passages in the form of an aerosol, namely, the supply of tiny solid particles suspended in gas or liquid [13; 14; 15; 16]. Generally, there are three types of conventional nebulizer equipment: jet nebulizers, ultrasonic nebulizers, and mesh nebulizers. Air-jet nebulizers generate drug aerosols by using the energy provided by compressed gas [17]. The jet stream generated by high-speed gas is passed through a narrow Venturi tube and an area of negative pressure, where the air jet emerges and draws liquid from a reservoir, up a feed tube. However, jet nebulization causes the formation of solvent vapor, which saturates outgoing air. The generated solvent vapor cools down the nebulizer fluid and results in an increase in solute concentration in the residual fluid [18]. The drawback of this method is the need for a source of compressed gas and its inherent inefficiency. Ultrasonic nebulizers generate aerosols using a high-frequency vibrating piezoelectric crystal, producing a fountain at the air-liquid interface. However, excessive frequency energy is converted to heat, causing the temperature of the liquid within the nebulizer to increase [19; 20]. Therefore, this method can lead to serious thermal denaturalization of therapeutic agents. Practically, traditional ultrasonic nebulizers are also inefficient for delivering suspensions and viscous liquids [8; 21]. To overcome these problems, new types of vibrating-mesh nebulizers have been developed in recent years. In this method, a piezoelectric crystal within the nebulizer induces vibrations that are transmitted to an adjacent mesh with multiple apertures [22]. This result causes the extrusion of fluid through the apertures to generate aerosols [22]. Commercial products using this technology include Aeroneb (Aerogen, Galway, Ireland), MicroAir (Omron, Vernon Hills, IL, USA), eFlow (PARI, Midlothian, VA, USA), and I-neb (Respironics, Murrysville, PA, USA) [23]. A silicone-based mesh has also been introduced recently [24]. This new technology offers many features and practical advantages, such as an increased fine particle fraction due to standardized micro-perforations, a higher output rate of inhaled medication, improved portability, and easier handling [25]. However, the vibrating mesh nebulizers require daily cleaning and sanitization protocols to keep the meshes from becoming clogged over time, which can change the aerosol output rate and aerosol droplet size distribution [26].