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Inhalation OctOber 2021 13 modulatory effect and enhanced permeation of drugs through the epithelial cell barrier. It has been suggested that they may alter membrane permea- bility by increasing the fluidity of the membrane or through Ca 2+ -dependent tight junction mech- anisms. One suggested mechanism of penetration enhancement for a medium chain fatty acid, capric acid, is by activation of phospholipase-C and an increase of intracellular calcium levels, resulting in contraction of actin microfilaments and dilation of the tight junctions [16]. Phospholipids. Phospholipids are a class of mol- ecule that has a hydrophilic "head" containing a negatively charged phosphate group, and two hydro- phobic "tails" derived from fatty acids, joined by a glycerol molecule. ey are a key component of all cell membranes and can form lipid bilayers because of their amphiphilic nature—the tail regions, being repelled by water and slightly attracted to each other, congregate, exposing the head regions to the exterior. Liposomes are biodegradable and biocompatible vesicles composed of one or more phospholipid bilayers surrounding an inner aqueous compartment. is structure enables liposomes to encapsulate drugs of different size and lipophilicity. Hydrophilic drugs are encapsulated into the aque- ous compartment, lipophilic drugs are contained inside the bilayer, and amphiphilic drugs partition themselves between these two regions. e similarity Cyclopentadecanolide. Cyclopentadecanolide is a natural macrolide lactone that is produced synthetically by ring expansion of cyclotetrade- canone, or the depolymerization of polyesters of 15-hydroxypentadecanoic acid. Macrolides consist of a large macrocyclic lactone ring, usually 14- to 16- membered. Cyclopentadecanolide is a hydropho- bic molecule that can interact with the hydrophobic chains of lipids within the cell membranes and has been shown to enhance the absorption of drugs through the nasal mucosa [14]. Diethylene glycol monoethyl ether. Diethylene glycol monoethyl ether is a hydroalcoholic sol- vent that has a long history of use as a solvent and penetration enhancer in various pharmaceutical dosage forms, and its use in liquid nasal spray for- mulations has increased in recent years. Although its mechanism of action is not fully understood, in the case of the stratum corneum, it appears to interact strongly with the water of the intercellular path, facilitating the movement of excipients and/ or active pharmaceutical ingredients (APIs) via the intercellular route [15]. Fatty acids. Fatty acids are carboxylic acids with either a saturated or unsaturated long aliphatic chain (e.g., oleic acid, capric acid). Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms—between 4 and 28 atoms. Fatty acids have shown a tight junction With enhanced chemical and biological resistance, the NGI+ is the ideal cascade impactor for nebulizer testing. Additional Features: + Extended equipment life + Enhanced corrosion resistance + Allows for more robust cleaning methods + Backwards compatible *† — upgrade your existing NGI or buy a completely new NGI * Ask for availability for your equipment † Drug and aerosol performance does not change THE NGI+ Learn more and place your order today at tsi.com/NGI-Plus With enhanced chemical and biological resistance, the NGI+ is the ideal cascade impactor for nebulizer testing. Additional Features: + Extended equipment life + Enhanced corrosion resistance + Allows for more robust cleaning methods + Backwards compatible *† — upgrade your existing NGI or buy a completely new NGI * Ask for availability for your equipment † Drug and aerosol performance does not change