Table 3.

Methods for obtaining niosomes.

Type of Method	Description of the Method	Ref.
Thin-Film Hydration (TFH) Method	Initially, the TFH technique was used to synthesize liposomes, but over time, it was also used to obtain niosomes. In this method, surfactants and cholesterol are homogeneously dissolved in an organic solvent such as chloroform or a mixture of solvents. The solvent is completely evaporated using a rotary vacuum evaporator, resulting in a thin film on the inner surface of the flask. The resulting film is rehydrated using either water alone or phosphate-buffered saline (PBS), which usually contains the encapsulation drug. Once the rehydration is complete, MLV niosomes of various diameters are formed.	[33,55]
Solvent Injection (SI) Method	The SI technique involves dissolving the surfactant and cholesterol with diethyl ether or ethanol. The homogeneous solution is placed in a syringe pump and introduced dropwise through a needle into an aqueous solution at a constant temperature (which is higher than the boiling point of the organic solvent). The residual solvent is removed by evaporation in a vacuum rotary evaporator. This process leads to monolayer vesicular niosomes of various sizes.	[33]
Reverse Phase Evaporation (REV) Method	The REV method was first presented by Szoka and Papahadjopoulos [26] in 1978 as a technique to obtain LUV-type niosomes. It involves the preparation of two phases, organic and aqueous. The organic phase usually consists of a mixture of ether and chloroform, containing Span 60, cholesterol, and stearoylamine to form the membrane. The aqueous phase consists of water or PBS in which the drug is dissolved. The organic phase is mixed with the aqueous phase, and then the whole mixture is vigorously shaken or subjected to ultrasound to obtain the emulsion. The next step of the process is to evaporate the organic phase using a constant temperature vacuum evaporator, resulting in LUV-type niosomes.	[26,33]
The Bubble Method	Niosomes are obtained without the use of organic solvents. Surfactants, additives (e.g., cholesterol), and the buffer (pH 7.4) are added into a three-neck round-bottom flask. The flask is placed in a water bath to control the temperature. The dispersion of surfactants and additives occurs at 70 °C. To obtain a homogeneous dispersion, a high-speed homogenizer is first used, stirred for 15–30 s, and then bubbled with a 70 °C nitrogen gas. Nitrogen gas is passed through a sample of homogenized surfactants resulting in the formation of large unilamellar vesicles.	[56,57,58]
Freeze and Thaw Method	It is an improved and much simpler method of niosome preparation derived from the TFH technique. MLV-type niosome suspension prepared by the TFH method is frozen in liquid nitrogen and then thawed several times in a short time using a water bath.	[59]
Dehydration–Rehydration Vesicles (DRV) Method	It was first described by Kirby and Gregoriadis [34]. SUV-type niosomes prepared by the TFH technique are used to form MLVs. Small monolayer vesicles (SUVs) are separated by centrifugation, and then SUV-type niosomes containing the drug are added to the aqueous phase. The resulting suspension was lyophilized overnight. After the dried product was rehydrated, multilamellared niosomes formed.	[33]
Supercritical Carbon Dioxide Fluid (scCO2) Method	It is a new method to obtain niosomes, and it was first presented by Manosroi et al. [60]. Surfactant, cholesterol, PBS with glucose and ethanol are placed in a glass cell of a constant volume and two windows. CO2 is then introduced into the cell while maintaining a pressure of 200 bar and a temperature of 60 °C. Niosomes are obtained after 30 min of stirring all ingredients on a magnetic stirrer and then lowering the pressure. With this method, LUV-type niosomes with sizes ranging from 100 to 440 nm can be obtained. The greatest advantage of this method is the one-step process, which does not require the use of toxic, flammable, and volatile organic solvents.	[33,60]
Heating Method (HM)	The technique has been recently developed and is used to obtain nanocarriers, including niosomes. The method involves the addition of surfactants, cholesterol, and active ingredients to an aqueous phase (such as PBS). The solution is prepared by stirring and heating the aqueous phase, and then a 3% w/v (weight/volume) polyol such as glycerol is added to the resulting solution. The main advantage of the method is that there is no need for toxic and volatile organic solvents.	[33]