solid lipid nanoparticle

A solid lipid nanoparticle, or SLN, is like a microscopic droplet of fat that has been frozen solid. It starts as an emulsion of melted lipid in water, stabilised by a surfactant; when it cools, the lipid hardens into a solid core with the drug trapped inside. Imagine a tiny ball of butter holding a drug, rather than the liquid oil droplet used in an ordinary emulsion.

Because the core is solid rather than liquid, the trapped drug moves more slowly, which gives more controlled, sustained release and better protection of sensitive molecules. SLNs use lipids the body already handles well, can often be made without organic solvents, and are relatively easy to scale up — practical advantages over some other nanocarriers.

Their main weakness comes from crystallisation. As the solid lipid rearranges into a more ordered crystal form during storage, the well-ordered lattice has little room for drug, so the medicine can be squeezed out and the particles may gel or grow. A later design called the nanostructured lipid carrier deliberately blends solid and liquid lipids to create a less perfect, more drug-friendly core that loads more drug and expels less of it.