Solid lipid nanoparticles in drug delivery: bridging tradition and innovation

Solid Lipid Nanoparticles (SLNPs), introduced in the early 1990s, have emerged as a promising class of lipid-based nanocarriers for drug delivery. These nanoparticles, typically 10–1000 nm in size, consist of a solid lipid core stabilized by surfactants and are solid at both room and body temperatures. Their biocompatibility, biodegradability, ability to encapsulate labile or poorly soluble drugs, and the ability to provide controlled and targeted release make them highly attractive compared to traditional systems, such as liposomes and polymeric nanoparticles. Despite their advantages, first-generation SLNPs faced challenges such as low drug loading and drug expulsion during storage due to lipid crystallization. This led to the development of second-generation Nanostructured Lipid Carriers (NLCs), which incorporate a mixture of solid and liquid lipids, resulting in a disordered matrix that enhances drug loading and stability. Another innovative type, Lipid Drug Conjugates (LDCs), involves covalent bonding between the drug and lipid, further improving stability and drug retention. SLNPs can also be categorized based on size, which influences their pharmacokinetics and suitability for specific delivery routes. Overall, SLNPs and their advanced derivatives aim to bridge the gap between lipid emulsions and polymeric carriers, offering a robust platform for safe, effective, and scalable drug delivery across multiple administration routes.