Advancements in drug delivery: The role of solid lipid nanoparticles and nanostructured lipid carriers

Lipid-based nanocarriers have emerged as a promising strategy to overcome major challenges associated with conventional drug delivery, including poor solubility, limited bioavailability, instability, and off-target toxicity. Among these systems, solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) represent two important solid-matrix platforms that combine biocompatible lipid materials with nanoscale dimensions to enhance therapeutic performance. SLNs, composed of a single solid lipid core, offer controlled drug release and good physical stability but are often limited by high crystallinity, low drug-loading capacity, and drug expulsion during storage. NLCs were developed as a second-generation improvement by incorporating liquid lipids into the solid matrix, resulting in a less ordered, defect-rich structure that enhances drug accommodation, reduces expulsion, and provides more sustained release profiles. This review highlights the structural and mechanistic differences between SLNs and NLCs, their encapsulation and release behaviors, comparative advantages, and applications across oncology, neurology, anti-infective therapy, and inflammation. Safety, toxicity, and regulatory considerations are also discussed, along with future research directions focusing on surface engineering, theranostics, and quality-by-design approaches to facilitate clinical translation.