Table 4.

The characteristics of the siRNA inhalation delivery systems.

Delivery Systems	Characteristics
	Advantages	Disadvantages
Liposome	Improving siRNA stability, promoting endocytic uptake and transfection efficiency Facilitating siRNA endosomal escape	Prone to causing an inflammatory response Potentially cytotoxic
Solid lipid nanoparticle	High transfection rate Low cytotoxicity Prolonging in vivo half-lives of drugs	Low drug loading efficiency Poor stability
Nanostructured lipid carrier	Good bioavailability and biocompatibility Slow-controlled release capability High drug loading efficiency	Cytotoxic effects Irritating and sensitizing effects of surfactants
Nanoemulsion	Non-toxic and non-irritating Improving the stability and bioavailability of the drugs	Expensive preparation process Less selectivity of applicable excipients Instability during storage
Polymeric micelle	High structural stability and drug loading capacity Less immune response than liposomes Functional modification	Complex polymer synthesis Ineffective drug incorporation techniques
Polymer nanocapsule	Good biocompatibility Avoiding siRNA degradation and sudden release Functional modification	A certain toxic effect
Nanosphere	Biodegradable Sustained release Increasing the ability to penetrate the airway mucus layer	Low transfection efficiency of PLGA NPs Poor cell permeability of chitosan
Dendrimer	Multiple branch points Nano size Water solubility Biocompatibility Monodispersity High drug loading capacity	Dose-dependent cytotoxicity
Pulmonary surfactant	Increasing the solubility of insoluble drugs Enhancing drug stability Optimizing drug delivery efficiency	/