9.6.3.2　Nanostructured lipid carriers（NLCs）

NLCs are considered as the second generation of the lipid nanoparticles.NLCs have been developed so that the drawbacks associated with SLNs can be overcome.Based on SLNs，NLCs replace solid oil with a mixture of solid oil and liquid oil，which makes them have a more irregular defect structure，thus generating more space to accommodate more active substances，effectively improving its coating rate and the stability of active substances in the long-term storage process.Compared with SLNs，NLCs are more convenient for the coating of active ingredients because of its incomplete crystallization and amorphous state.At present，there are three main structures of NLCs coating active ingredients：amorphous type，imperfect type and multiple type.

Compared to SLNs，NLCs show higher drug-loading capacity for entrapped bioactive compound because of the distorted structure which helps in creating more space.Other limitations of SLNs（e.g.，reduced particle concentration and expulsion of drug during storage）are solved by manipulating the formulation of NLCs.They are formulated by biodegradable and physiological lipids that show very low toxicity.NLCs have modulated drug delivery profile by a biphasic drug release pattern.In this case，the drug is released initially with a burst release，followed by a sustained release at a constant rate.They possess numerous advantageous features，including increased skin hydration due to occlusive properties，and the small size ensures close contact to the stratum corneum leading to the increased amount of drug penetration into the skin.There are stable drug incorporation during storage and enhanced UV protection system with reduced side effects.Using NLCs loaded sunscreen can greatly improve the sunscreen effect of the system，reduce its irritation to the skin，reduce the dosage of chemical sunscreen，and improve the compatibility and stability of the sunscreen system.(https://www.daowen.com)