Nanoparticles are a kind of nanomaterials with high dispersion characteristics. It can pass through the hair follicle or stratum corneum, thereby improving the transdermal absorption of the drug and the sustained release of the drug, and can protect the drug from degradation. Solid lipid nanoparticles (SLN) is a new type of nano-drug carrier developed in the 1990s. It uses natural or synthetic lipid materials (such as lecithin, triglycerides, etc.) as a carrier to wrap and adsorb drugs on A solid colloidal particle drug delivery system formed in the lipid core. A certain proportion of liquid oil or mixed lipids is used to replace the solid lipids in the solid lipid nanoparticles to form a new type of solid lipid nanoparticles, which are called nanostructured lipid carriers (NLC). SLN and NLC not only have the advantages of high physical stability of polymer nanoparticles and slow drug leakage, but also the advantages of liposomes and emulsions with low toxicity, strong transdermal ability, and large-scale production. Therefore, they have broad application prospects as transdermal delivery carriers. Among them, solid lipid nanoparticles have the following characteristics as a transdermal drug delivery system. Encapsulation Effect Improves Skin Permeability Solid lipid nanoparticles have better skin adhesion and increase with decreasing particle size. When the nanoparticles adhere to the surface of the skin, the accumulated particles prevent the evaporation of water on the surface of the skin. Nanoparticles fuse and deform with each other to form a film on the skin surface to produce an encapsulation effect. Solid lipid nanoparticles with low melting point lipids, high crystallinity and small particle size can produce the maximum encapsulation effect. The encapsulation effect reduces the loss of moisture on the skin surface, increases hydration, and promotes the transdermal absorption of drugs. Solid lipid nanoparticles can increase skin hydration by 31%. Skin hydration has nothing to do with lipid types, no matter whether single lipid (SLN) or mixed lipid (NLC) is used, hydration can be enhanced. Enhance Drug Stability The unstable drug is wrapped inside the nanoparticle to isolate air and oxygen, which is conducive to the stability of the drug. The solid lipid nanoparticles significantly improved the stability of coenzyme Q10, and did not degrade after being stored at 40°C for 360 days. Solid lipid nanoparticles significantly enhance the chemical stability of the encapsulated vitamin A, and the degree of stability is closely related to the type of material and surfactant. Good Formulation Stability As an excellent carrier for transdermal drug delivery, liposomes have been widely used in the fields of pharmaceutical preparations and cosmetics, but poor physical stability has always been a major problem that plagued liposome preparations. Solid lipid nanoparticles and nanostructured lipid carriers maintain the state of solid particles during storage, which largely guarantees the physical stability of the preparation. In the solid lipid nanoparticle aqueous dispersion, the lipid content and nanoparticle concentration are low, the particles are easy to move freely, and the particles are prone to collision and aggregation. In nanostructured lipid carriers with relatively high lipid content, the particle concentration is very high, resulting in the formation of a “pearl” chain-like network structure between most particles, reducing the chance of collision and aggregation, and improving stability. Skin Targeting Certain topical preparations, such as tretinoin, corticosteroids, podophyllotoxin and other drugs, have serious side effects or skin irritation, and should reduce systemic absorption, while enhancing local skin absorption and reducing irritation. In 1997, Hoffman et al. used liposomes to target drugs to skin hair follicles for the first time, and the concept of skin targeting appeared, that is, to promote the penetration and absorption of drugs in the skin or epidermal layer, while reducing the transdermal absorption of drugs. SIN and NIC are excellent carriers for obtaining drug skin targeting. The absorption of prednika ester SLN in the human skin layer is 30% higher than that of ordinary creams. The increase in its penetration capacity may be due to the smaller particle size of SLN and stronger interaction with the skin. The slow and controlled release of SLN is the main factor that reduces the transdermal absorption of drugs. The SLN has skin targeting ability only when the carrier is good for the drug. However, when the drug is distributed or adsorbed on the surface of the nanoparticle, it is difficult for the SLN to promote the local skin absorption of the drug. Due to the presence of some liquid lipids in NLC, the drug may be released faster when transdermal, and has a certain transdermal ability, and its skin targeting effect is significantly lower than that of SLN.

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