9.6.3.1　Solid lipid NPs（SLNs）

SLNs are the first lipid NPs developed from substituting the liquid lipid（oil）of an oil/water nanoemulsion with physiologically，well tolerated and biodegradable melt-emulsified lipids which are solid at room and body temperature.They consist of a hydrophilic shell and a hydrophobic core which allows the encapsulation of hydrophobic compounds.Their mean particle size ranges from 40 nm to 1000 nm.

SLNs have UV resistant properties and act as physical sunscreens on their own.SLNs as carrier for 3，4，5-trimethoxybenzoylchitin and vitamin E sunscreen are developed to enhance UV protection.However，they have some drawbacks：①little stable，since they are prone to drug expulsion phenomena during storage or usage because of the complexity of the physical state of the lipid，and to the simultaneous presence of alternative colloidal structures；②insufficient drug loading due to the limited solubility of drugs in the solid lipid matrix；③not suitable for oil-based formulations as they will dissolve.(https://www.daowen.com)