Optimization of nanostructured lipid carriers: understanding the types, designs, and parameters in the process of formulations

Lipid-based nanoparticles for drug delivery have been employed in the development of nanomedicine for various applications. One such versatile nanoparticle type is nanostructured lipid carriers (NLCs) that include multiple combinations of lipids and drugs for diverse routes of administrations. Optimization of NLCs to achieve ideal particle size distribution, dispersion in the aqueous environment, long-term stability, drug protection ability, and targeting features is necessary for designing improved drug formulations. However, very few studies have attempted to discuss explicitly the sequential requirements for optimization. Besides, several compositional variables can confound the design of an NLC drug formulation, making it essential for critical evaluation of factors that affect the NLC's physicochemical properties. Therefore, this review intends to discuss the multi-step process taken during optimization and highlight the components, methods, statistical designs, trends observed between the variables, and modifications of NLCs for targeted delivery, with the objectives of improving efficiency and increasing success rates in drug delivery studies.