The physical/chemical characteristics of lipid particulate systems are highly complex due to the existence of a variety of lipid assembly morphologies, the morphology-dependent solubility of drug, the interconversion of assembly morphology as a function of time and chemical structure, and the simultaneous lipid digestion [47]. 3. Lipid Nanoparticles as Drug Carriers Lipid nanoparticles show interesting features concerning therapeutic purposes. Their

main characteristic is the fact that they are prepared with physiologically well-tolerated lipids [48]. During Inhibitors,research,lifescience,medical the last ten years, different substances have been entrapped into lipid nanoparticles (Table 1), ranging from lipophilic [23, 49] and hydrophilic molecules, including labile compounds, such as proteins and peptides [50]. Inhibitors,research,lifescience,medical Table 1 Examples of drugs, miscellaneous active ingredients and macrocyclic skeletons incorporated into lipid nanoparticles. 3.1. Lipid Materials for Oral Administration The term lipid is used here in a broader sense and includes triglycerides, partial glycerides, fatty acids, steroids, and waxes. However, it is required Inhibitors,research,lifescience,medical that matrix maintains the solid state at room temperature, and for this purpose, the selection of lipids

is based on the evaluation of their polymorphic, crystallinity, miscibility, and physicochemical structure [11]. Table 2 shows the main lipids employed for the preparation of lipid nanoparticles. Table 2 Lipids used for lipid nanoparticles production. Furthermore, the use of mono- and diglycerides as lipid matrix composition might increase Inhibitors,research,lifescience,medical drug solubility compared to highly pure lipids, such as monoacid triglycerides. Naturally occurring oils and fats comprise mixtures of mono-, di-, and triglycerides, containing fatty acids of varying chain buy Gefitinib length and degree of unsaturation [25, 86]. The melting point of these lipids increases with Inhibitors,research,lifescience,medical the length of the fatty acid chain and decreases with the degree of unsaturation. The chemical nature of the lipid is also important, because lipids which form highly crystalline particles with a perfect lattice (e.g., monoacid triglycerides) lead to drug expulsion during storage time. Physicochemically

stable lipid nanoparticles will be obtained only when the right surfactant and adjusted concentration have been employed [25]. 3.2. Determination of Optimal Hydrophile-Lipophile many Balance (HLB) Values for Lipid Nanoparticles Dispersions Emulsifiers are essential to stabilize lipid nanoparticles dispersions and prevent particle agglomeration [87]. The choice of the ideal surfactant for a particular lipid matrix is based on the surfactant properties such as charge, molecular weight, chemical structure, and respective hydrophile-lipophile balance (HLB). All these properties affects the stability of the emulsion [10]. The HLB of an emulsifier is given by the balance between the size and strength of the hydrophilic and the lipophilic groups.