Nanostructured lipid carrier system: A compendium of their formulation development approaches, optimization strategies by quality by design, and recent applications in drug delivery

The lipid-based colloidal carriers, such as nanostructured lipid carriers (NLCs), solid lipid nanoparticles (SLNs), nanocapsules, liposomes, and microemulsion, are the latest and significant entrants in the development of drug delivery systems owing to their myriad advantages. The NLCs are second-generation SLNs having unstructured matrix, have high drug loading, and provide long-term drug stability in comparison to SLNs and other colloidal systems, which show lower drug loading and experience burst release/drug expulsion during storage. This review is aimed to summarize the formulation development and optimization strategies for NLCs as reported in the literature collected from authentic databases. Various types of NLCs, formulation components, methods of preparation, characterization parameters, optimization (statistical designs) strategies, toxicity, regulatory aspects, and their applications in oral, parenteral, ocular, pulmonary, nose-to-brain, tumor targeting, and transdermal drug delivery have been dealt in detail. Patents granted on the NLCs have also been enlisted.