Lipids are used as vehicles for the preparation of various formulations prescribed for administrations, including emulsions, ointments, suspension, tablets, and suppositories. The first parental nano-emulsion was discovered from the 1950s when it was added to the intravenous administration of lipid and lipid-soluble substances. Lipid-based drug delivery systems are important nowadays. Solid nanoparticles (SLN) and Nanostructured lipid carriers (NLC) are very proficient due to the ease of production process, scale-up capability, bio-compatibility, the biodegradability of formulation components and other specific features of the proposed route. The administration or nature of the materials must be loaded into these delivery systems. The main objectives of this review are to discuss an overview of second-generation nanoparticles, their limitations, structures, and route of administration, with emphasis on the effectiveness of such formulations. NLC is the second generation of lipid nanoparticles having a structure like nanoemulsion. The first generation of nanoparticles was SLN. The difference between both of them is at its core. Both of them are a colloidal carrier in submicron size in the range of 40-1000 nm. NLC is the most promising novel drug delivery system over the SLN due to solving the problem of drug loading and drug crystallinity. Solid and liquid lipids combination in NLC formation, improve its quality as compare to SLN. NLC has three types of structures: random, amorphous, and multiple. The random structure containing solid-liquid lipids and consisting crystal and the liquid lipid irregular in shape; thereby enhance the ability of the lipid layer to pass through the membrane. The second is the amorphous structure. It is less crystalline in nature and can prevent the leakage of the loaded drug. The third type is multiple structures, which have higher liquid lipid concentrations than other types. The excipients used to form the NLC are bio-compatible, biodegradable and non-irritating, most of which can be detected using GRAS. NLC is a promising delivery system to deliver the drug through pulmonary, ocular, CNS, and oral route of administration. Various methods of preparation and composition of NLC influence its stability Parameters. In recent years at the educational level, the potential of NLC as a delivery mechanism targeting various organs has been investigated in detail.
