Table 1.

A brief summary of several NDDSs.

NDDS	Size	Advantage	Disadvantage
Liposomes	25–1000 nm	It can encapsulate both water-soluble drugs and lipid-soluble drugs; it can be modified; enhance drug targeting; prolong drug action time and improve drug stability; help overcome multidrug resistance; reduce adverse drug reactions etc.	It is unstable and easy to be hydrolyzed; it is prone to auto-oxidation, resulting in reduced membrane fluidity, drug seepage, and toxicity after aggregation and precipitation.
Polymeric micelles	10–100 nm	First, Polymeric micelles have lower critical micelle concentration, larger compatibilization space, stable structure, and can encapsulate drugs by chemical, physical, and electrostatic methods according to the different properties of the hydrophobic segment of the polymer; secondly, the drug is encapsulated by nanoparticles, which avoids the allergic reaction of natural drugs and does not require pretreatment. Third, the dosage of Active Pharmaceutical Ingredient required can be greatly increased through the supplementation of nanomicelles.	The stability of polymer micelles will be greatly weakened after entering the human body, resulting in premature release of drugs and loss of targeting effect. At present, there are many means to increase the stability of micelles, including cross-linking the hydrophobic core, adding conjugated targeting molecules at the end of the segment, etc. However, as the design of micelles becomes more and more complex, the evaluation of its performance is also difficult. Correspondingly, it becomes difficult, time-consuming and labor-intensive, which is not conducive to the clinical application of polymer micelles.
Nanogels	<200 nm	First, they are small in size and easy to be phagocytosed by cells; second, they can easily penetrate various protective membranes in the human body, such as the meninges, so that drugs can be administered to the brain; third, the drug-carrying efficiency is high.	Its preparation requires the participation of organic solvent.
Nanoemulsion	<200 nm	It can make the oil phase and the water phase together; increase the solubility of the drug, improve the bioavailability of the drug, and avoid the first-pass effect of the liver.	Its preparation cost is relatively high. Most of the nanoemulsion processes are prepared by the emulsification of a high-speed emulsifier. The investment in equipment and the technological requirements for the emulsification process are relatively high. In addition, nanoemulsion is a liquid preparations less stable than solid preparations. The shelf life of nanoemulsion drugs is usually 6 to 18 months, while that of solid preparations is 2 to 3 years. Many liquid preparations of traditional Chinese medicine cannot use nanoemulsion technology.
Nanoparticles	<100 nm	It can probe into the cell wall of the pathogenic microbes and even have the capacity to intrude into cellular pathways. Nanoparticles themselves are capable of destroying unwanted foreign particles or toxic cells, which enter into our bodies. Nanoparticles can combine with specific drugs and deliver to target specific cells with lesser side effects. Nanoparticles showed higher internalization uptake, accumulation and retention time of drug improving antibacterial activity drug decreasing an-timicrobial resistance and also inhibit biofilm formation	Both naturally derived nanoparticles and synthetic nanoparticles are toxic, which also hinders the progress of clinical applications.