**6. Conclusions**

SLNs are the most studied lipid-based drug delivery systems, which can deliver drugs and nutrients for various routes of administration due to their biocompatibility, low toxicity, high loading capacity, slow-release rate, and high stability.

The physicochemical properties and stability of lipid nanoparticles depend on the composition of the lipid nanoparticle formulation. The lipid nature of these support systems is one of the key features that has attracted the interest of many researchers. Based on the organization of lipids and drugs in the particles, many structural models of SLNs have been described.

Lipid nanocarriers such as SLNs offer much more flexibility in drug loading, modulation of release, and improved performance in the production of final dosage forms such as creams, tablets, capsules, and injectables. The effort to develop alternative routes and treat other diseases with these systems must continue to expand their applications. Penetration through the gastrointestinal tract and BBB may be a new trend, and combining two therapeutically active agents in a single nanosystem is another consideration for future development.

In conclusion, solid lipid nanoparticles are a promising drug delivery system due to the non-toxicity aspect and a variety of drug-carrying capacity, along with the advantages of drug delivery through all routes of administration.
